PLANE on a CONVEYOR BELT! Will it TAKE-OFF? Explained by CAPTAIN JOE
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Dear friends and followers, welcome back to my channel!
I’m sure you have seen this question/riddle before!
Imagine a 747 is sitting on a conveyor belt, as wide and long as a runway. The conveyor belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?
Watch the video to learn more!
Thank you very much for your time! I hope you enjoy this video!
Wishing you all the best!
Your "Captain" Joe
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Next Riddle: How will the plane land on the Conveyor belt
Ask a Navy Aviator
It think it just like landing in a moving ship/aircraft carrier
I don't think so. It would bounce too much.
That kinda ez I guess if it going opposite
Hmm
3:01
Captain Joe: rocket science, math, aviation
Me: oooo yellow black
*insert Wiz Khalifa - Black And Yellow here
It’s the wind going over the wings that causes lift, irrespective of the wheel speed.
I think this guy is wrong.
There would be No wind over the wings, If the conveyor belt moved at the exact same speed as the wheels.
The plane Has to move forward, in relation to the ground, to get lift. As long as the plane is On it’s wheels, the conveyor belt would negate its forward motion.
If not, why do planes even need runways? Could just build a large dynamometer, and planes could take off without moving forward.
@@stevehackett2678 it's more the case that a plane will act as if the conveyor isn't there. when you drive a car the engine moves the wheels along the road. when you fly a plane it move the air through the jet or propeller. you have to imagine that the air is the planes' road and the mode of propulsion is the wheels equivalent .If say instead of wheels a plane had skis and a flat icy surface, it'd move forward and eventually take off as normal.
@@stevehackett2678 The plane is not "fixed" to the wheels due to the bearings. The wheels are not the driving force. No matter how fast you spin the wheels, the engines will still see the air as standing still and thus create thrust. If you have thrust, you have forward motion. It's a plane, not a car...
@@stevehackett2678 You’ve basically just restated the problem. But the conveyer belt moving backwards (and the wheels spinning backwards) has no effect on the plane’s forward motion, as the forward thrust is provided by the engines and not by the wheels.
@@stevehackett2678 The plane does NOT have to move forward in relation to the ground in order to get lift, it has to move forward in relation to the AIR. So regardless of what it's wheels are doing it will still move forwards and gain lift - just as it normally would. It will travel the same distance forwards, and it will rotate at the same point it normally would. The ONLY difference is it's wheels would be spinning faster than they usually would, that is all.
Please never be the captain on my flight. The plane does not need ground speed to take off. It’s needs airspeed to takeoff. If there was tail wind that kept the same speed as the plane, it could not take off. However, ground speed is irrelevant.
@@Joshcodes808 it’s saying there is no motion at all. From the frame of reference of a person standing to the side of this setup, all the motion seen would be the conveyor rolling and the test vehicle wheels rolling in perfect sync.
Technically, you don’t even need a conveyor. You could have the test vehicle on a dynamometer type of cylinder to simplify the visualization. The same principle would apply. As the force is applied to the vehicle, we know how wheeled vehicles roll across the surface and if the (absurd powered dyno) surface is set to the same speed, the test vehicle will indeed remain motionless except for the futile rotation of the wheels as the dyno keeps pace.
It’s hard to set-up and pretty impractical all the way around, but that’s what the math and physics describe.
Joe, I’m pretty sure the wheels in scenario 1 would spin up exponentially and presumably explode but don’t think it would have a significant effect on airspeed any more than scenario 2.
Correct!
Exactly
Scenario 1 is an impossible (and absurd) theoretical/mathematical scenario; v(ground) needs to be >0 to create airspeed, but for that to happen v(wheels)>v(belt) which the text says is impossible (they're alway the same)... both conveyor and wheels will reach infinite speed in t=0 (infinite acceleration) and break the equations.
@@nloko I agree! Scenario 1 cannot be performed in real world (infinite is not an option in real world), so has no meaning.
@@paolodalbono Agreed, but assuming the answer to the riddle is meant to be "Yes." or "No." rather than "Exploding infinity tires." - and keeping in the spirit of the problem - even if you adjust the conveyor belt to something reasonable, you still have what the Mythbusters already did in small and full scale. Even if you say the conveyor belt gets to accelerate twice as fast and to twice the take-off speed, right to just before the tires fail - which is presumably double the parameters of what this riddle is asking, the plane still takes off pretty effortlessly.
“ the only 747 that can do that is the captain’s joe 747“
I liked that part 🤣
You’ve become a good commercialiser
Thrust
Not before you touch up with Manscaped!
@@kingkenny97 haha
thrust
Only if it's VTOL, lol
@Buddy Austin The wheel bearings prevent the conveyor from imparting backwards force on the plane, but the engines still accelerate the plane forward.
The riddle is that you can't in reality make a treadmill that matches the speed of an airplane wheels. The wheels don't propel the plane, they just respond to the relative motion of the plane with the ground. Which means if you move the ground (i.e. treadmill), the plane or it's wheels don't know the difference. The plane will just move forward through the air not caring what the wheels or ground are doing.
My thoughts exactly.
The wheels are not what's propelling the plane forward. They are just free-wheeling.
As the plane picks up speed, the wheels would spin faster than the plane's forward movement would indicate, but other than that they would not in any way influence the plane's acceleration.
Maybe a few tires would blow because they are spinning much faster than their designed limits, but it would not prevent the plane from taking off.
A easier to think about situation that is equivalent is placing a trailer on the same treadmill and pulling it off with a car in front. It moves (or the tires explode if the treadmill can go that fast). Now replace the trailer with a glider being pulled with a cable. It starts moving and takes off. And finally an airplane being pulled (or pushed) by it's prop or jets. In all those cases, the thing being moved is being moved by a force applied not though the wheels, so they are basically the same, so the airplane will move as well.
@@robertwatson818 The engines push the plane forward through the air (regardless of what the wheels are doing). The wheels on a plane are simply free-spinning bearings to allow the plane to "roll" on the ground, they have nothing to do with propulsion.
@@robertwatson818 but there will be because the airplane WILL move forward. The THRUST propelling the aircraft forward does not care that the conveyor is moving backwards. The wheels are free spinning. Make the conveyor move as fast as you want, the wheels will simply spin faster until the bearings or tires explode. The plane WILL move forward because the force propelling it will be exerted on the AIR, not transmitted through the tires to the roadway as will a car. Only if the combined friction of the free-spinning wheels overcomes the force of thrust would the aircraft not move forward and again, at that point you would have blown up your landing gear.
Wheels are not free spinning, they have friction, if the plane is not already flying, the friction will create drag, that's where the first part leads to (however you won't have infinite friction since the pressure downward is constant, is that enough to prevent the plane from take off we simply don't know, because the threadmill would overheat before it can reach that)
That’s one big conveyer belt.
It's made from my belt cause of my lockdown belly.
@@techmantra4521
😂😜 funny stuff kiddo !!
The earth is one big conveyer belt ;-)
@@brantwedel 🤯
It did take off BUT if you watch it closely the plane started moving forward before it rotated
Alternate title: Can plane on conveyor belt destroy landing gear of the plane?
Alternate ALTERNATE title: can you find a conveyor belt big enough to fit a plane?
Yes, it can.
Who cares. We're talking about a 747 on a treadmill. Just imagine the wheels can take the forces.
Yes. The bearings in the landing gear will break their rolling elements if the wheels spin too fast. The centrifugal effect causes the rolling elements to load the contact force between the outer race and the rolling elements, and when that contact force exceeds the limiting strength of the materials, the rolling elements and outer race will rupture.
The 747 can only take off if the airflow over the wings is sufficient to provide enough lift.
So the 747 must move forward at takeoff airspeed, regardless of the surface being a runway or a conveyor belt.
Because the plane gets enough AIR-speed to take-off. The jet engines propel the AIR to move forward just like jet fighters.
👍@stmounts
You have put your finger on the pulse when you state that relative movement of air over wing surfaces causes lift.
The conveyor belt and engines are not the elements which generate lift. Only the foreward motion of plane (with the help of the engines, etc) generates a pressure differential on 'curved' surfaces to create lift.
How else does
a glider stay aloft ?
And Why do aircraft carriers use catapults to get off the deck?
@@yjk2202its so enough air to pass through the wings to generate lift.
@@waddup2336 Your understanding of how lift works vs thrust is not even close to how it actually works, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
I think this question was thought up to highlight the difference between how a car is propelled down the runway and how an airplane is propelled down the runway. As such it is a thought problem and would work better (less confusion) if it was explicitly idealized. My suggestion is to include in the problem statement something like "consider the wheels themselves to have no friction in their bearings, no rotational inertia, no rolling friction, and no residual drag in the brakes when they are released." (visualize them to be something like a bicycle's spoked wheels with zero mass, and no brakes at all." LOL (also utterly indestructible). The question seems to me to be, then, "how can this conveyer belt runway PULL on this idealized airplane?" My answer is "it can't" - run the conveyor belt as fast as you want, all that will happen is the wheels will spin. The inertia of the airplane (tendency to resist changes in velocity) will keep it sitting there, until the throttles are advanced. With 4 big engines attached firmly to the body of the airplane it would accelerate down the runway with no trouble at all and take off when its airspeed reached the value to start rotation. However, if the wheels are given mass, and the conveyor belt runway is given access to unlimited energy and power, then pulling on the bottom of the wheels will actually transmit some force onto the body of the airplane (as well as give the tire rotational kinetic energy) and with infinite energy and power the conveyor belt would win.
for fair experiment lets take force of the conveyor equal for the force of plane engine. In that case plane take off easily always
Even if the wheels have only just enough friction from the ground to prevent slipping, the energy it takes to rotate them is coming from the engines. You can't just disregard the wheels because they are stealing all the energy you need to move the whole aircraft forward.
it is immaterial how the vehicle is propelled. The only thing that matters is that the vehicle only moves while it is on the ground by rolling. If it rolls, they you know the rolling speed and as such you can set the magical, hypothetical, and impractical conveyor to the same exact speed and with the same exact rate of change.
People are trying to complicate the simplicity of the thought problem. The thought problem is trying to show that you can't get a plane flying if you don't have airflow over the wings to create lift.
You can either do a deep dive four force analysis while it's on the ground and measure the force, the drag, the weight effect on the rolling, etc.
or you can take at face value the basic introduction to physics stuff where the velocity of the vehicle minus the velocity of the conveyor gives you a net zero in motion.
@@MrDefreese My point is unless the speed of the conveyor belt can affect a longitudinal FORCE on the airplane wheel axles, there is NOTHING to keep the airplane from accelerating down the runway as the mighty (777-300ER) engines each apply 115 THOUSAND pounds of force! When the throttles are advanced, without brakes, the airplane accelerates down the runway until it is time to rotate and climb out., at which time it flys off. During acceleration on the runway when this idealized conveyer belt is going like a bat out of hell, it has NO GRIP on the airplane.
By the way, something like this was tried on MythBusters using a long tarp pulled backwards and a Cessna going forwards,.
The Cessna took off just fine.
@@monteevans7985 that's not quite right all around. The force applied by the aircraft only results in either rolling speed on the wheel set or scrubbing across the surface. If you have one speed, the (magical, absurd) conveyor is explicitly described as matching that speed (with some equally absurd force).
What you have is not just an aircraft floating above the surface with a horizontal force due to its engines. You are dealing with a system that includes the interaction of the wheel set while it's on the ground. You could just as easily use a cog gear set since we are hopefully assuming that the craft is not going to scrub across the surface in this exercise, but will only be constrained to rolling.
If you have those meshed gears rotating at the same rate, guess what, there is no net motion. That's what we have.
Now, people frequently cite Mythbusters, but they didn't do their experiment properly. You can see that they gunned the truck and gunned the aircraft with not consideration for the rate of change between the two. That's not a proper way to do that experiment.
A little known factoid is that they did a preliminary test with a little RC car on a treadmill. In that instance, they revved the RC motor and then set the treadmill speed to exactly match the RC car speed. That's what the thought project is telling you.
Where MythBusters went wrong with that preliminary experiment is that they kept the treadmill at a single, static speed while they varied the speed of the RC car. That's not what the thought project explicitly describes.
No matter how complex people want to make it or how big a force people want to apply, all that matters is that the rolling speed of the wheel set is expressly described as being matched exactly by the conveyor. We don't have any flexility in trying to change that parameter for this though project.
What it's trying to show, again, is that force alone does not result in lift if there is no airflow over the aircraft.
You can do a variation of this same though project in a non-controversial way. Take a landing gear set off the aircraft and place it on the conveyor. Give it a shove and you get a certain velocity - call it V1. Guess what speed the conveyor instantly attains. Also V1.
Now place the wheel set back onto the aircraft and add whatever force you want so it goes from V1 to V2. The conveyor also matches not only the speed of V2, but the rate of change from V1 to V2.
Mathematically, you get the same result taking the derivative of speed to get acceleration or the integral of speed differential to get position. Change in speed is 0; change in acceleration is 0; position is unchanged.
With cars, this conveyer belt would be called a dynamometer. :)
I love when you say it in German 5:44
Because he's German...
@@jimday666 what's with the "..." ?
@@treeinafield5022 *sigh*. He's German
Oh come on man, just when some of us were able to put this train wreck out of our memory you go and dredge it back up again. Have you no conscience?
This whole video is just so damn stupid.
@@pequalsnpsquared2852 nah, just a case of very unrealistic things coming together
Which Train Wreck?
@@eliass.4743 This whole “plane on a treadmill” thing dates back to the early 2000’s and was one of the first viral internet events. It spawned many a virulent argument that totally consumed message boards at the time.
@@unclerojelio6320 Wow, people are dumb.
The wheels on a car aren't driven by the engine either. The engine creates spinning that turns something else that turns something else that eventually turns the wheels. The same thing happens with airplane thrust. The thrust creates a force that pushes on one thing, etc down the line to the wheels.
If jet engines are pushing left, the conveyer pushing right, the wheels are just bearings and play no affect.
Ever heard of friction? As soon as you try to move forward the conveyor counters it so you would never move
@@jrunsvold7150 Right, friction is the key. I'm really frustrated that neither those arguments nor those counter arguments is taking friction into account, which is the only way to make things clear. But to cancel the thrust of the engine, we need the same amount of friction, which I don't know if is actually possible (something tells me this is not going to happen in real life. I would still call this theoretically possible though.)
@@jrunsvold7150 ever seen a travelator at an airport? Think you could push a trolley along it in the opposite direction? Of course you could. It just needs enough power.
@@Xiaotian_Guan problem is the plane has wheels, and in an ideal situation (which is fair to assume since we have a conveyor belt the size of a big ol plane) the wheels are frictionless so the movement of the wheels exerts no force on the plane itself, it just spins the wheels. The wheels can't exert a force on the plane, so therefore it doesn't hold it back at all
Nothing can be frictionless. Otherwise nothing would exist at all
Myth busters did a great live demo with an actual airplane (ultra light) but still fun to see
And it did take off in case anyone is still wondering.
@@ricksharpe6895 There's a short 2min clip of that myth here on yt. It should answer your question.
Yes I saw the Mythbusters ep showing a plane taking off on a conveyor belt.
Yes, however... he explains this in the second half of the video. The belt they used was meant to match the ground speed of the plane. And ... given the technology... they could not match the wheel speed *instantly and exactly.* The problem is more.with semantics than anything.
@@gitbse Yeah, but in that case the answer to the riddle should be that such theoretical conveyor belt would instantly generate friction on the wheels equal to thrust. Only that would prevent the plane from moving. It's a pretty pointless riddle.
The answer is in airflow over the wings, wich generates LIFT. Flying has NOTHING to do with wheels.
Actually it’s the airflow under the wings - Newton’s 2nd law. That’s what gives it lift.
@@ntsecrets agreed, but in any normal GA plane, how Mitch does it account?
Something that’s not clear is where the lift is coming from, are the engines sending air under the wings or are they pushing the plane forward which makes air rush over them to create lift?
@@ntsecrets I heard otherwise.
@@ntsecrets Not really. Most lift comes from the negative pressure over the wing. Bernoulli's theorem applies, not Newton's Second Law.
The way I understand this, is that if the conveyor is matching the groundspeed, the wheels basically double in speed.
If the propeller makes the plane begin to move, the conveyor will start as well. So if the plane crawls along slowly at 5km/h, the wheels will do the same 5km, which is matched by the conveyor. But because the wheels spin freely, and the plane is still able to move forward at 5km/h the wheels add on that extra ground speed, and will spin at 10km/h.
So matching the groundspeed will simply double the speed of the wheel spin.
The test could be done by putting a small model of a plane, attach it to something stationary, then turn the power to full. If you release it, it wouldn't automatically shoot up into the air. It would still need to reach takeoff speed to do it.
The conveyor isn't matching the ground speed, it's matching the wheel speed. If it is matching the wheel speed then ground speed is always 0 and the plane cannot ever take off
@@ClikcerProductions Wrong. The wheels can not hold back the plane if the engines are pushing it forwards. Oh, and the wheels are stuck to the plane, right? So they too move forwards relative to the ground. That movement determines how fast the belt is going backwards.
@@paldyvik7915 A force can be applied through free spinning wheels, this is something extremely obvious if you just hold a toy car on a running treadmill, you need to apply a force to keep it in place, if you remove that force the car is pushed backwards through it's free spinning wheels, the same thing can be done with the plane. If you think the plane moves forwards you are either allowing the wheels to slip (which is just super boring) or you do not understand very basic geometry, the only good argument for the plane being able to take off is that the treadmill would reach speeds high enough to produce winds fast enough to reach take off velocity while in place on the conveyor
@@ClikcerProductions I'm not stating that there is NO increased force from the conveyor belt moving the opposite direction. What many people don't realize is that these are WHEELS. Wheels are touching the surface below, and normally not slipping much (assuming friction exists). This contact point is however not what determines the speed of the wheel. The speed is measured at the CENTRE of the wheel, which may be moving relatively freely forwards and backwards, disregarding how fast the surface below is moving or not.
The wheels are stuck to the plane, and when the engines start pushing the plane forwards, the wheels of course follow. as soon as the plane reaches 1 knot towards the left, the belt has responded and moves at 1 knot to the right. That causes the wheels to ROTATE at an RPM corresponding to 2 knots, but they are MOVING at a speed of 1 knot. The same continues as the plane accelerates and MOVES to the left, and at the moment take off speed has been reached, the belt is going to the right, also at "take off speed".
Any argument have seen that the plane will stay stationary are false. Mostly, people assume that the extra rotation induced by the belt are able to magically cancel the push from the engine.
Now figure this:
1. Imagine you are in your car, driving at 100 km/h. You probably realize that your wheels are moving at the same speed, right? If not, hand in your license.
2. Imagine a toy car, pointing to the left, with a red string attched to the front. Now pull that string to the left at a constant speed. Do you see the car moving?
3. Imagine the car is standing on a green paper sheet. Pull at that green paper sheet below the car, towards the right and at the same speed as the red string, but in the opposite direction. (You may want to practice with empty hands first, to build confidence in yourself as a researcher.)
4. Repeat step 3, while carefully observing whether or not the car is moving to the left. Repeat one or more iterations until the shock settles. Also observe the rotation of the wheels compared to in step 2. (Hint: The car IS actually moving to the left!)
5. The car is the 747. Pulling on the red string represents the push from the jet engines. Pulling on the green sheet represents the conveyor belt responding to the movement of the plane and its wheels. (Remember step 1?)
The fact that the belt moving to the right does not prevent the plane from moving to the left at the exact same speed, as stated in the riddle, proves that the plane will be able to accelerate and its wings gain lift.
Riddle solved: Take off OK!
@@paldyvik7915 The speed of the wheels is not the speed of the center of the wheels, that makes it a completely pointless thought experiment, if you want to interpret it that way you can, but that interpretation is so impressively lacking in any level of nuance or intrigue that I would expect a more interesting intellectual conversation from a 5 year old. The wheel speed is very clearly meant to refer to the speed of the surface of the wheel relative to it's center of rotation, I want to be very clear here that YOU are choosing to interpret the though experiment in a way which makes it pathetically dull. Please only reply if you have any interest in discussing the thought experiment the video is actually covering
Yes it can. Speed of the wheel have nothing to do with airplane speed relative to the ground.
But it doesn't matter . What matters is the TAS. And if the aircraft has a GS of 0 it means that there is no wind flow over the wing for them to be effective . So a plane on a conveyor belt would be the same as if it applied full throttle and applIed the brakes it just won't take off .
@@mojojojo3852 the engines and only the engines provide the forward thrust, even it was a plane on ski's, on floats, on 'wheels on a conveyor belt', it doesn't matter as long as it does not prevent the aircraft from moving (=attaching it to chains or putting large concrete blocks in front of the wheels - normal chocks won't do the job). If the conveyor belt was moving forward with the same speed, the wheels would not rotate and the aircraft would take of as normal. With the belt running backwards, the wheels will spin twice a fast (only marginally increasing wheel/axle friction) but the aircraft will 'thunder' along the runway thrusted forward by the engines. Maybe the tires will deflate because rotational speed is well above it's max. rating of somewhere around 220+ knots (but that is a different discussion).
@@DIBOYOU not really comparable with ski's or floats. If you stop the engines, the plane will go backwards due to friction belt/tire, because the plane has a weight that pushes down on the belt. So a part of thrust will be consumed just to make the plane still compared to ground. You will never be able to reach take off speed, because you'll always have this conveyor speed to compensate.
What you say works if the plane weight is equal to zero.
@@pik2005 Not true, there is an accident investigation of a DC8 (I think) which had it's wheels frozen and on the slippery runway the aircraft started it's take off movement almost as normal. but given the enormous friction, it failed to take off. In this conveyor example, the wheels will only have minimal increase of friction in it's axles. The take off roll and speed will increase slightly, but as long as the axles don't seize completely due to overspeed, the aircraft will get airborne. If the conveyor belt turns in the other direction, the take off run will be marginally shorter, but the airplane won't lift of like a helicopter even with it's wheel not rotating at all. So yes it is comparable with ski's, floats, etc. all have different gradients of friction, but absolutely far less than the (jet) engine thrust
Lol what about the wind that gives the lift? How high do you fly off the treadmill in the gym?
If I'm on a treadmill on roller skates holding a rope my wheels will match the speed exactly, but if i pull on the rope I move forward. The engines are pulling the plane forward, the belt will not stop the plane from moving forward, the plane always takes off
you're assuming the treadmill's speed is always the same. the riddle's premise is that as you pull on the rope, the speed of the treadmill will also increase
@@jbt816but that won’t change anything, if the treadmill is going 20mph and you pull yourself forward at 1mph and some increases the speed of the treadmill at the same time you will still pull yourself forward at 1mph. The speed of the wheels and treadmill is completely irrelevant.
@@jagheterbananyou will pull your torso forward, but the conveyor adapts to the increased wheel speed and still results in the ‘wheel axle’ remaining static. That’s the whole point of the unintuitive example of the conveyor speed matching rolling speed.
You would essentially tip over forward.
@@MrDefreese The wheels are attached to the roller skates with bearings essentially disconnecting them from you so no you wouldn’t tip over you would just increase the speed by which the wheels are turning. This of course brakes the premise that the wheels and treadmill are supposed to be going at the same speed, the only way to keep that premise is to not move i.e. not pull the rope.
If you translate that to the airplane it would mean you can’t increase the thrust, so yeah an airplane that you’re not applying thrust to won’t takeoff but it’s not really because the conveyor belt is stopping you.
@@jagheterbanan the wheels and treadmill moving at the same speed means the position of the wheel never changes. The force applied by pulling the rope does mean that part of the body moves. We could do fun body deformation experiments with that - rigid body, flexibility at the waist, etc.
The issue is the interpretation of 'matching'. The sane interpretation is that 'matching' happens no matter what speed the wheels go, because 'matching' is a functional result of the mechanical contact between the wheels and the conveyor belt. In other words 'matching' means 'synchronizing to' not 'going as fast as'. But, since the rule demands compliance from the conveyor belt, not from the wheels, the interpretation doesn't even matter. If the conveyor belt runs afoul of physics, that is its problem, not the airplane's problem or the wheels' problem, thus the plane will happily ignore the logic explosions consuming the treadmill and take off regardless.
In both situations, the plane doesn't take off. Instead of a conveyor belt, think treadmill instead. The thrust applied moves the plane forward on its wheels, but the "ground" - in this case, the treadmill - speeds up instantly to match with exact backward movement the same forward movement the plane is trying to achieve. This means since it's effectively stationary, there's no airflow over the wings, regardless of if the propulsion is from the wheels or the turbofans.
Of course it can take off! The speed of the wheels' rotation has nothing to do with the plane getting into the air -- that only counts when trying to stop at the end of the flight.
The engines are producing thrust which pushes the plane forward, and as long as no brakes are applied, the air moving over the wings as the plane moves forward will begin to generate lift, and once the speed hits V2, you can rotate and start flying, regardless of whet the conveyor is doing under your wheels!
exacly
(After watching) Well, okay, if you want to set up a scenario that requires breaking the laws of physics..... :D
@@Ayelmar It doesn't really break the laws of physics. If the conveyer matched the forward momentum perfectly it would stay still and have zero ground speed and therefor no air moving over the wings to generate lift. Considering IRL conveyers dont move much air even at high speed and the problem itself does not state that the conveyer is also moving the air you have to assume it isnt. IF there was a statement stating that the conveyer does move the air above it then yes the plane would take off. That would be no different then a conveyer pulling a plane through at take off speed.
@@zazuch Ah, but as noted, you're not driving your wheels against the ground or conveyor below you to move forward in a plane. If it's prop-driven, you're pulling/pushing the aircraft forward against the air surrounding you, not the surface below you, and if it's a jet, you're pulling in air to burn the jet fuel and generating thrust to push the plane forward via Newton's Third Law of Motion ("for every action, there is an equal and opposite reaction").
The "breaking the laws of physics" part comes in because, as Joe stated tbe problem, the conveyor and the wheels would quickly reach infinite speed, breaking the speed of light! But, because the thrust of the engine(s) acts independently on the mass of the aircraft, it will still move forward regardless of what the belt is doing underneath, though the air turbulence generated by the transonic shock waves thrown off by the belt might make the takeoff a *tiny* bit difficult! ;D
@@zazuchit breaks the laws of physics because the wheels will match the belt speed + plane acceleration. You can't have a sum feeding off itself without getting infinite, which is impossible.
Forgive an old fool but how exactly does the conveyor belt matching the speed of the wheels cancel out the thrust of the engines? This is the bit I really struggle with, the wheels play no part in propelling the aircraft forward. Air is sucked in, forced out and the conveyor's speed doesn't alter the thrust produced.
He’s wrong on the first case. It would still take off. He’s thinking of it like a car.
@@ChrisFranklin.2260 hes not. If the conveyor belt was able to completely match the speed of the wheels, it would have no forward motion in reference to the air it is trying to use to take off. This is completely impossible in real scenarios due to a number of factors, but the baseline assumptions of the first example would mean that the plane would not be able to make forward progress and move through the air which it needs to take off
@@Professor-fc7vc I'm still not convinced. His arguments for the first case did not seem well fleshed out to me. There's still nothing to cancel out the hundreds of thousands of pounds of thrust on the body of the aircraft. Doesn't matter what the wheels are doing, or what the speed controller for the belt is basing its output on.
@@ChrisFranklin.2260 thrust just makes a mass go from one speed to another speed. That’s it.
We know a (hypothetical and absurd) conveyor can reach any speed possible so it’s just recognizing that such a device can put the total system in equilibrium. No net speed at the wheel axis.
It would work. Think about it, airplane engines produce thrust. They don’t drive the wheels on the landing gear as well.
Nope. The plane would explode.
How will the wings generate any lift? They won't, so the plane can't fly.
@@chesterwang3070 I cant believe people still this would work..
@@Dan007UT sure it can work...if the fan you set in front of it is big enough😂
@@Schumicomeback2010 haha true! or if its in a hurricane
What about BushPlanes? They don’t need runway at all and still can take off. Wheels don’t power plane. Engines do.
Bush planes definitely need sufficient airflow over the lifting elements and they take advantage of strong headwinds wherever possible. They still have to roll on the ground (and capitalize on clever design) in order to minimize takeoff speed and distance.
The pilot who flew the plane on Mythbusters also thought he would not take off.
Mythbusters’ experiment didn’t match the speed of the wheels, which is the biggest misconception with this riddle. Their experiment was flawed.
@@cshoffie6593 it's the problem with the interpretation of the question. Captain Joe already explained both interpretations in this video. Mythbusters simply followed the 2nd scenario, while most people think the 1st.
Planes without wheels take off, as do VTOL aircraft, as can a aircraft with sufficient headwind without moving forward - a good pilot knows that takeoff and flying has nothing to do with ground speed
@@davidioanhedges I understand that, but the riddle isn’t about VTOL aircraft or a headwind sufficient for lift. It’s a hypothetical scenario of the wheels being cancelled out by the conveyor belt. Wheels obviously affect the movement of the aircraft while on the ground. If you have your brakes on, it’s going to be very difficult if not impossible for the aircraft to move to generate lift. So, considering you’re not in a VTOL aircraft and you have zero headwind, and if the wheel speed is being matched by a conveyor belt in the opposite direction, without delay, the aircraft cannot move.
The confusion about this is a result of people adding variables to the riddle that shouldn’t be there.
@@cshoffie6593 Yes, but the brakes *aren't* on when the airplane is trying to take off. Given the lack of brakes, the only affect the wheels have on the plane's horizontal movement is a slight friction effect. So, yes, the conveyor belt will *slightly* slow the plane, but not enough to keep the plane from taking off.
With this logic on the conveyor belt, it doesn't mean anything as you could ramp the conveyor up to 10x the speed of the plane in the opposite direction and yet the plane would still move forwards
@@lukeheasman350the conveyor only moves the exact distance the vehicle moves. Not more, not less, not faster, not slower. The wheel axis never moves.
@@MrDefreese the wheels dont have anything to do with plane moving forward with thrust
@@user-xu9bq2lf6p yes they do while it’s on the ground. In fact, all thrust does is take the body from one speed to another speed (less any losses).
@@MrDefreese the wheels just spin and thrust moves it forward
@@user-xu9bq2lf6p yeah, that’s an inadequate understanding of wheel motion. In your mind, do wheels scrub on the surface or do they roll on the surface. Either option give you the speed at which the test vehicle moves which is exactly the speed the surface moves…therefore you get 1-1=0.
The real question to answer here is "how does the airplane stay flying once the wheels are off the ground?" Once you know the answer to that, its easy to work the problem out.
The plane is pulled forward by the engines. Once you reach a high enough ground speed, the plane lifts off. Independent of underground and wheel speed. Although the wheels would in this case explode.
The real question is something you'll never understand, because you couldn't read it in the first place.
Simple thermodynamics, my friend. :) All mechanical systems boil down to energy in = energy out. In this case: thrust = friction. At infinite speed, the friction of the wheels will remove infinite energy from the mechanical system. Also, the conveyor is defined as matching the speed of the wheels. Any forward movement of the airplane with respect to the ground violates this definition.
@@c182SkylaneRG incorrect, if your going to try to pull that crap then you failed. Under no point in the question did it state the rotational speed of the wheels. Therefore the only logical assumption is that it is match the forward motion of the wheel itself. Your trying to selectively add things into the question. If I asked you the speed of a tire that broke lose from a moving vehicle noone would give you its rotational speed.
This is a common issue with technically educated people and commonly worded questions. You destroy the spirit of the question by adding in stuff not present into the question. I mean why would you add in that if the pilot would apply a little bit of steering then you'd have wheels moving at different RPMs and the belt would therefore enter into a paradoxical state where it would need to be moving at multiple speeds at the same time.
Basically this is equivalent to the mathematician that argued 2+2=5 could be true because it theoretically could be 2a+2b=5c or maybe some other hidden or non presenting variables or perhaps a variant numerical system.
@@nicolivoldkif9096 The term "wheel speed", lacking any other description, means the speed of the wheels across the ground, which is taken at the hub/axle. In this scenario, that would be the speed of the wheels relative to the conveyor belt. Their rotational speed is translated to a linear speed based on their diameter, which can only be in reference to the surface they're rolling on (the conveyor).
Any good pilot starts on the center line of the runway, and stays on the center line of the runway. No self-respecting pilot takes off cock-eyed with respect to the runway centerline. Be realistic. :D
Think of it another way... Replace thrust with a rope. If the rope is reeled in, it doesn't matter how fast the wheels or conveyor are moving, the plane WILL move forward because the mode of locomotion is disconnected from the wheels.
There is no rope. All energy of the thrust is converted to belt speed
@@Coren999 Hilarious mate. The thrust is on the plane and cares not one jot about what the wheels are doing. You didn't even watch Captain Joe at a guess (not that he's right, I address his error in a comment here).
The thrust causes the tires to move faster than the conveyor belt
@@donaldfegley6127 Nonsense. If you set a constraint on a system that constraint is not broken. The thrust propels the plane forwards. It cares not one jot WTF is happening at the wheels as long as, and this is a limiting issue is considered, any drag they exert that works against the thrust.
You have not watched the video clearly nor read my explanatory comment in which I explain how Captain Joe errs, because if you had, you would have a full assessment already of the issue of what happens to the speed of the wheels and conveyor. But the thrust cares not one hour about that unless it causes drag, and propels the plane forwards.
@@BerndWechner So explain this to me then, if the plane moves the throttles forward and the wheels start to move from the ground speed of the plane starting to move, but then the conveyor then perfectly matches the speed of those tires for ground speed, so no the plane in no longer moving forward or backwards, how to the planes wings which have to have airspeed flowing around them to produce lift, produce lift if the plane is not moving at all on the ground so no lift is being produced by the wings? When the engines produce the thrust to get the plane moving on the ground to speed the plane up so the air around the plane is producing lift on the wings, the ground speed is then completely stopped by this conveyor that now puts the planes ground speed to 0 which then means there is no airspeed being produced for the wings to create lift. Just because the engines of a plane done care what happens on the ground does not mean that the wings can produce the lift from having no airspeed to then convert to lift as the plane that is on the ground has to have forwards movement to create the airspeed required for the wings to get the lift needed, but if the forward movement is 0 because the conveyor is now keeping the plane still, which makes the airspeed 0 over the wings, which means 0 lift is now being produced to have the plane take off.
Every time this does its rounds. It turns into a battle between pilots and engineers
I hope pilots and engineers are on the same side. I am an engineer and I say it will take off in all cases.
@@jphilb then you are not a good engineer
@@joshualengers7743 Put a rocket on the conveyor belt. Bet it will move.
@@joshualengers7743 lift comes from the air passing over the wings. Why do you think the belt should be able to hold back the plane?
@@joshualengers7743 The wheels are free-wheeling. The plane is effectively on roller skates. If I put you on roller skates and push you forward at 5mph on a conveyor belt, you still move at 5mph but the wheels on your skates move faster than they would normally.
A video on a start up from cold and dark would be super interesting
Another way to think about the problem is to ask, "Can a sea plane take off from a river going upstream?" The obvious answer is yes. The plane doesn't care much about the water speed, only the airspeed.
The difference is the river has constant speed while the belt speed is dynamic - it matches the wheel speed. You will not be able to take off from the river IF the river speed matches you forward speed - you will be stationary compared to a tree on the river bank. If the river moves downwards with a speed of e.g. 200 mph - that does not apply to the air at the surface of that river.
@@bakkks The belt could be going twice the speed, it wouldn't matter.
Yes, if the movement of the wheels is initiated by thrust, then the plane would take off. The thrust is not related to the wheels. The jet engine is not pushing against the ground. The travel distance before rotation airspeed/Vr would be similar to a normal takeoff. In this scenario the tires would be turning faster but the plane would still be moving forward through the air opposite of the thrust, thus generating lift. The wheels only contribution during takeoff is to mitigate friction between the aircraft and ground. They do not propel the aircraft during takeoff. Maybe this will help: if I hold a non powered toy car on a treadmill with my hand while the treadmill is running I can still make the car move forwards and backwards even if the treadmill were to instantly speed up/slow down as I moved the car forwards/backwards. In this case I am the jet engine and the wheels aren’t the source of power.
See, it's the qualifier of the conveyor belt exactly matching the speed of the tires with no delay. For this to be true, to take your car example, if I tried pushing the car forward, I would see (and probably hear) the tires and treadmill speed up proportional to how hard I push, but the car would never move forward - that would require the tires to move faster than the conveyor belt. It would be like an invisible, equal, and opposite force, pushing against me. I could even pull on the car until the treadmill and tires are at rest, I could pull even more and make them rotate the other way, but the car would never actually move. To actually move its position relative to the treadmill would be to break the requirements of the scenario with regard to the treadmill.
It's not possible, but given the premise of the conveyor, the rest of physics would need to accommodate it. The aircraft will never produce enough thrust, regardless of means, to gain any relative airspeed (or true, or ground, or any motion period for that matter), for it would break the rule of the conveyor. The only way I see a possible takeoff is with headwind equal to or greater than rotational airspeed, or if the engines produced enough of a vertical thrust component to separate the aircraft from the conveyor, or if a hypothetical aircraft is constructed in such a way that the exhaust airflow is sufficient and positioned in a way to impart effectiveness on the control surfaces/wings, which sounds really goofy to me but maybe somebody can tell me if that's even possible or not.
@@dogboy0912 "It would be like an invisible, EQUAL (emphasis mine), and opposite force ,pushing against me". What force? Why equal? In the toy car example, the wheels would have to overcome a marginal amount of friction as they turn around the axel and where they make contact with the treadmill. Are you suggesting that I could not push the car forward as a treadmill was speeding up, even if instantly? Other than the weight of the car (not even the full weight because of the wheels) and a small amount of friction, what force would I have to overcome? Let's say I push the car forward with 50 pounds of force from my arm which I could easily do. What force is going to push back against me at 50 pounds?
I've heard and seen numerous versions of this question and then also seen a Mythbusters episode on it. How it's asked and how the illustration is presented makes all of the difference in my view. The way it's posed here and was demonstrated on Mythbusters, where the "conveyor belt" is/was a length that at least matched the minimum takeoff distance of the plane, sure the plane can take off. But I've seen this illustrated with a 747-400 sitting on a conveyor belt that was barely the length of the plane. A plane that requires 10,400 feet of runway to take off normally is not taking off while on anything that's barely the length of its body be it a runway or a conveyor belt. If it moved forward at all it would be past that surface within a few seconds of the brakes being let up. The tires and what they're doing or not doing make no difference as I see it for that reason.
@@dogboy0912 "The aircraft will never produce enough thrust, regardless of means, to gain any relative airspeed (or true, or ground, or any motion period for that matter), for it would break the rule of the conveyor."
The engines provide forward thrust. What, in your thinking, prevents the plane from accelerating? If you push the car on the treadmill, what force prevents the car from moving?
The constraint that the wheel and conveyor speeds must match prevents all forward motion. It doesn't matter if the wheels push or not. Any forward motion will rotate the wheels and the wheels and conveyor must be perfectly locked together. No forward motion = no lift from the wings = never takes off. It's not possible to do this in a real-world scenario because there will always be imperfections that enable forward motion.
Mythbusters is wrong. I have a video on the subject that explains in depth. Actually, I have two, because the response to the first one was so full of people not understanding that any forward motion violates the core constraint.
What happens if the plane is on skids on a normal runway. That actually matches the scenario perfectly, since the skid could be considered a wheel that's not in motion, and the runway an inactive treadmill. The plane is still going to take off because the plane's engine is operating on the air, not the ground.
However, the only way I can envision the wheels and conveyor moving at the same speed but opposite direction is if the plane is held stationary relative to the ground as the conveyor moves, assuming perfect transfer of energy from the conveyor to the wheels. Even THEN the plane could still lift off if there's sufficient headwind, as then the plane would be moving relative to the air. This is why you try not to park planes, particularly light ones, in the direction of the prevailing winds.
That's swell Jody. Videos, awesome.
Let's hash this out. Genuine PhD physicist here by the way. Okay, GEO physicist, but hey, I do grasp the most elementary ideas of Newtonian physics.
I'll start with the opening argument which uses a Boeing 747 as an example.
How can the power of four massive turbofan engines who's thrust can roughly be converted to a total of 120000-160000 bhp depending on engine variety, be absorbed by the free spinning wheels? They can't, they are not mechanically linked to said huge turbofan engines. They are mounted on bearings which mechanically disconnect them from the plane and engines.
Now your rebuttal and counter argument.
@@AB-80X "Genuine PhD physicist here by the way. Okay, GEO physicist" - _Appeal to authority logical fallacy_
"How can the power of four massive turbofan engines...be absorbed by the free spinning wheels?" - _They aren't. The question doesn't say that._
"They can't, they are not mechanically linked to said huge turbofan engines. They are mounted on bearings which mechanically disconnect them from the plane and engines." - _The question imposes a constraint. The engines are irrelevant because they have nothing to do with the constraint. The wheels must not rotate faster than the conveyor belt regardless of being "free-spinning" or "unpowered" or "not mechanically linked" and if there is any forward movement, the wheels are implicitly rotating faster than the belt, so unless you propose the only workaround which is "the plane drags the locked wheels along the completely stopped conveyor belt," the plane cannot take off...not because the plane's engines can't overpower everything holding it back, but because the constraint requires that they don't do that._
You can spin the wheels as fast as you want in any direction you want. The thrust isn't coming from the wheels. I don't know why this is such a difficult riddle.
It is not. It looks like about a third of the comments agree that the plane will take of in both cases
And that’s the first problem, the second, it wont take off because of the lack of air flowing over the wings.
@@joshualengers7743 Think of it this way, if you put a model car onto a treadmill and you hold it there with your hand you can move it forwards or backwards regardless of how fast the treadmill is going. In this scenario your hand is the air moved by the engines, they will push the aircraft forward regardless of how fast the treadmill is running backwards.
it's a riddle where you have to read exactly what the question is.
the question is the same as can a stationary aircraft take of when it is stationary?
the belt in combination with the engines nullify the other to a 0 point. the engines can put out as much energy backwards (pushing the plain forwards) but the belt is in this case going as fast at the same time going the opposite way with 0,0 time delay.
the resulting action in this case means that only the wheels are spinning and noting else.
in real life you can't have that. even with a delay of 0,0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.0000.00001 there is enough delay that motion has been made. might it be the belt moving a fraction faster back from the 0 point or the plain moving forward again from the 0 point motion has been made.
@@jphilb it's sad only a third of the comments are right.
Wheel speed matters not one bit. Ever wonder why you’d want to put your small prop plane inside if there’s a windstorm?
Joe, it is the wind over the wings. If the that determines lift...wheels have nothing to do with flying. I think your 2nd answer is nonsense.
Was just going to say this. I was a little disappointed in his erroneous answer
I agree.
Sorry. Joe is right and you are wrong. But his diagram is not clear and so I can see the confusion. In the first example the conveyor is matching the engine thrust, so the aircraft will always be stationary and because - as you say - it is airflow that counts, the plane will not take off.
But! In the second example the conveyor does not match the aircraft power. It is set to a fixed speed. So once the engine is pushing harder than the conveyor, the aircraft will start to accelerate along the conveyor, gaining airflow and taking off. Joe’s diagram is silly because it shows a short conveyor. The real conveyor would need to be as long as the real runway!
But the real point is that a car puts power down through the wheels. To move faster than a conveyor you have to first push the engine to match its speed, and then push it even harder. But an aircraft doesn’t put its power through the wheels. So once you have matched the conveyor speed, you would just accelerate normally, with normal engine power.
ie if a car’s top speed were 200mph, and you put it in a conveyor going 100mph in the opposite direction, the car would be able to go no faster than 100mph compared to the ground. But if an aircraft’s top speed were 200mph, it would be able to reach that. The conveyor is backwards momentum but it can be overcome.
Anyone who disagrees with this video is empirically, factually, wrong.
Unless a physical experiment takes place "Empirical", cannot be rightm
@@jimhignett6993to do it perfectly correct, one would have to have a mechanism to measure the instantaneous speed on the wheel at any given parameter, pump that figure into a controller on the conveyor to exactly match that speed and the rate of change.
It’s possible, but the experiments that have been done skip over the ‘exactly matches’ stipulation.
The experiments on display on TH-cam or elsewhere try to sharpshoot one particular speed to reach equilibrium, then they crank up the speed of the test vehicle without changing the corresponding speed of the conveyor.
An engineering controls class could do it properly.
Isn't it amazing to know that no one anywhere in the world has finished watching this video at this time?
Well, Joe has 👀
The editor has
The speed of the conveyor will always match the speed of the plane (in the opposite direction) if the conveyor is meant to exactly match the speed of the wheels. He tries to draw a distinction between the hypotheticals “conveyor belt matching the wheel speed” and “conveyor belt matching plane speed” when there is none. As long as the wheels aren’t sliding for some reason (friction/ breaks), they’ll be in contact with the conveyor which means they’d be matching its speed. So, saying the conveyor belt matching the wheel speed is the same as saying it’s matching the plane’s speed. Think about it as the top of the wheels moving it the direction plane is moving (at that speed) and the bottom, in the direction the conveyor is moving (at the conveyors speed). Those speeds added together equal the rotation speed of the wheels. So the conveyor matching the speed of the wheels spinning would mean it’s also matching the speed of the plane. This is how circles works. The only good point here is the mention of the max wheel speed. If the wheels couldn’t spin fast enough (they’d only have to spin twice as fast as they would on a static runway since the runway in this case is moving backwards at the same speed the wheels and plane are moving forward) then yes, that friction would prevent the plane from gaining enough speed to provide lift (air flowing over the wings fast enough).
Yes it will move forward and take off! But only due to thrust from the engines... The conveyor belt's velocity is completely irrelevant, since the wheels are not powered!
How does thrust from the engine allow a plane to take off??? It doesn’t. You need airflow under the wings to create lift.
@@tracruz Yes it does.Thrust from the engine push the plane forward, gaining velocity thus airspeed
@@stevenfpv2345 But the plane isn't moving forward at all... The power of the engine is irrelevant, it's not a helicopter
@@moebekdache3756 Yes it is. How does an airplane is supposed to fly once in the air? Once the wheels aren't touching the ground anymore? Engines push the plane forward, regardless what happens to the wheels
@@stevenfpv2345 So are you saying, that if 2 forklifts lifted the plane either side by the wing, let engine hit full power, then back the forklifts away, the plane will then go?? Correct me if I'm mistaken
I am pretty sure third law of Newton is at play here, eg, the engines push air backwards so the plane must move forward. The speed and direction of the conveyor belt is moot.
But perhaps the riddle might indicate the the engines of the plane are not at full trust if you read the riddle in some way?? . At least I would expect full trust in the riddle, wouldn’t you not?
Or is perhaps the riddle not complete?
The bottom line is that the wheels are irrelevant, as the plane isn't driven
by the wheels.
That's the logical error that people make.
Mythbusters tested it irl. The plane will take off
@@bibaso12 if the plane takes off then the wheel speed is not matching the conveyor belt speed so you are talking about a different problem than the one in the original question.
Engines provide a force of thrust which is matched by the rolling friction and air friction of rotating wheels. If a plane move forward you are no longer satisfying the conditions in the question - the wheel and conveyor speeds are not matching.
@@tomaz2007 Which is why that isn't the spirit of the myth, is a deterministically dumb way to argue it because it presents a rule that violates physics to achieve a desired outcome, and is thus about as meaningful as arguing whether or not my imaginary superhero can beat your imaginary supervillain.
The original intent of the question was "Can a plane can takeoff on a treadmill going equally as fast in the opposite direction." Mythbusters effectively demonstrated the concept which was bounded within reality.
Plane is stationary relative to ground under the treadmill:
Plane Vground = 0mph Vtreadmill = 0mph Vwheel = 0mph
Plane starts throttling the engine:
Plane Vground = 1mph Vtreadmill = -1mph Vwheel = 2mph
Plane is now barreling down the runway about to takeoff:
Plane Vground = 100mph Vtreadmill = -100mph Vwheel = 200mph
i like how u explain everything super clearly
There is nothing I enjoy more than pilots that don't know how airplanes work. If the plane isn't moving forward then the wheel speed is 0. Treadmill speed is zero. What is countering the thrust of the engine. The wheels only rotate if the plane moves forward.
IKR? When the 747 starts moving at 1 kts from the engine thrust, the conveyor moves backwards at 1 kts, so the wheels are spinning 2 kts. So 80 kts forward speed from the engine, 80 kts backward from belt, wheels spinning at 160 kts. At 160 kts from the engines forward, the 747 can rotate to take off. The belt is going backwards at 160 kts and the wheels are spinning at 320 kts. The wheels don't drive the 747 forward, the engines do, which even this pilot messed up.
Wheel speed does not matter unless rolling resistance is greater than thrust of engines so it should take off.
The speed of the vehicle is only due to rolling. The explicit constraint of this exercise is that rolling speed is exactly neutralized by the magical adaptive nature of the conveyor.
That’s why he gave the follow-up example if the conveyor had a steady speed which could be overcome by an acceleration (thrust or increase automobile speed).
He explained it correctly.
@@MrDefreese That's my prediction not a counter, also if rolling resistance is greater than the thrust the wheels don't turn, the conveyor would thus be still and plane goes nowhere. Its like trying to take off with the park brake on.
@@MrDefreesethe speed of the vehicle is not due to rolling of wheels. The thrust of engines is pushing the plane forward. How would the belt create a counterforce to that if wheels are rolling freely?
@@psychosis7325 not correct. The wheels just roll along on the surface. The wheels don’t seize in place. He shows this in his first animation of the scenario.
@@Jashtvorak the vehicle only moves forward by rolling on the surface. You are given the express condition that the surface is moving at the same speed as the wheel which is exactly the vehicle speed. They are one and the same. For extra thought projects, we could resolve the force involved for such a conveyor. It is obviously impractical and out of the bounds of normal engineering design.
Straps CRJ 200 behind a really big fan
Me: “guys I made an expensive kite”
You could use wind turbines, when they're not blowing aircraft into the air they can carry on their normal function of generating power.
Or why not use a catapult? That would be brilliant for short take-offs from ships, then catch them with a very strong elastic band when they land. Once the plane has stopped, the elastic band will pull it back to the start of the runway ready for the next takeoff.
@@rogerbarton497 better yet remove engines from the aircraft entirely for short haul flights and just use big gliders and glorified slingshots.
If you’re an adrenaline junkies we can just put you in a padded ball and launch you up to 60 miles away into a net, and hope the wind doesn’t change enough to cause you to...miss
@@grantkendrick277 It's strange how the simplest ideas are the best. I'm sure we could engage the services of top snooker and billiards players to solve the problem about getting the balls in the correct net.
Of course it can it doesn’t use wheels to provide power
Exactly
That does not matter a damn bit!
If the belt matches the speed of the wheels then all forward thrust of the plane is being used to not be sent backwards!
@@thedausthed even if the wheels and the belt are made of sand paper, there’s only so much friction going on between the axels of the wheels and the landing legs which can easily be overpowered by the engines
@@thedausthed The belt can transmit a lot of spin to the wheels. But the wheels cannot transmit very much backward force to the airplane, because of their bearings. There will indeed be a slight backwards force due to internal friction, but regardless of the wheel speed the engines will have more than enough power to move the plane forward. If spinning wheels caused huge backwards forces, we also wouldn't be able to coast on roller skates without quickly coming to a stop.
Bro . The plane would fly in both scenarios ( the fact that the wheels will accelerate to infinity along with the conveyor belt doesn't matter )
It's a thought experiment . I mean we don't have a conveyor belt the size of a runway , nor do we have super advance sensors that can match the plane instantaneously.
▓▒░ I paused this video and thought about it
for -an hou- a few minutes.
If the conveyor belt is moving in the *opposite*
direction at the same speed as the wheels are,
this means that the aircraft isn't moving toward
the wind.
In other words, it's standing still.
It would be a miracle
if it does take-off.
`
Today is Saturday,
the sixty-fifth day of the year
two thousand and twenty-one. ░▒▓
`
How does a float plane take off against a current? Does the water direction pushing backwards stop you from taking off? The answer is no. Your ability to take off is only governed by the your airspeed. The plane pushes on the air not the water.
If the ground is moving, it is possible of course for the plane to move even if the wheels aren’t spinning or are even spinning backwards. The plane can push against the air directly, so it makes no difference which way the wheels are spinning. The only reason the wheels spin is the difference in speed between the axle and the ground beneath them, the freely spinning whee has no significant effect on the speed of the axle or the ground beneath it.
I mean it really is basic mechanics. Velocity in one direction with an equal and opposition direction in the other. You're net velocity would be zero. You can't achieve lift if you have no forward momentum.
Your "mechanics" are not basic, they're non-existent.
the interaction between the belt and the airplane wheels is the key here. If the belt moving back literally and effectively moves the airplane back and thus nullify the engine going forward, then lift off is pretty much impossible for a 747. But, if the belt moving backwards just makes the wheels spin faster, then sure, the plane will move forward and eventually fly. That is the key.
Hey Joe, at 2:45 you say the plane has to move forward relative to the ground....but isn't it the plane moving through the air that creates lift?
@@maafg4435 that shouldn't matter, imagine the jets are 2 guys at either side of the plane pushing the wings while not standing on the treadmill. it'll move forward because the treadmill has no effect on the speed these guys push.
No one said the engines were on. Also, substitute skis for wheels, is there any difference?
The simple answer is there needs to be enough airflow across the wings to create lift.
I still think that this explanation is wrong.
The plane will move throught the air. The wheels just spin at both speeds (air + conveyor belt) and the will move until is plane airspeed and lift
@@fredericosilvadias4218 I the vehicle is on the ground. It has to roll.
Joe I feel that the answer in the first scenario is absolutely YES the plane would take off! If the plane was a car using its wheels to propel it forward and the conveyer belt could match it no matter what, then it would stand still.
An airplane of course uses air to propel itself forward so those wheels would probably be spinning many times their normal rate when the plane is fast enough to fly.
Yeah, I'm not sure is this video is a troll. It makes no sense. It's like the idea of superman using his strength to hold a helicopter down without grabing something on the ground. Strength does not matter, only weight. If the thrust is greater than his weight, he will get lifted.
Actually there is no answer at all because the scenario doesn’t work. If you apply thrust then the plane must move forward but it can’t due to the logic of the problem’s wording.
@@debateme9204 Of course, if we consider that Superman can apparently accelerate in flight to near (or even exceed) the speed of light, there's is apparently some force that is allowing for that (no, no, no! I am *not* going to pursue idea of "jet propulsion" using flatus...). Telekenisis perhaps? Anyway by whatever mechanism that allows for that, he should be able to keep a helicopter from taking off (i.e. he simply uses this force to "push down" to counteract the lift of the rotor).
@@nuk1964 that's my point though. Superman strength is irrelevant in this scenario. He would need to fly otherwise he would just be pulled up into the air. In other words if you take away Superman's ability to fly his super strength would do him no good in this scenario unless he found something on the ground to Anchor himself with.
@@debateme9204 And I was simply pointing out that Superman has abilities aside from super-strength -- i.e. ability to not only fly, but accelerate in flight -- that could be used explain how he could keep a helicopter from taking off.
No, there won’t be any lift.
yup the exact answer (I hope) as there wont be any airflow which should create lift.....technically if you push the plane strong enough it could take of without any engines (just confirm that for me Captain Joe)
Easiest answer ever... the wind needs to hit the aileron at a certain speed, and if the plane is literally standing still, it won't do that. That's literally no different than a plane sitting at the gate, will it just take off like a helicopter? No, it won't.
I think it wil be able to take of of the conver belt is fast enouf. There will be enouf air going over the wings
@@ottodepotto5956 No, it's the opposite. If the conveyer belt is moving at the same speed as the plane's wheels, then the plane is essentially stationary with no wind hitting the wings and ailerons, therefore it won't produce and lift as the plane's real ground speed is 0.
@@thecomedypilot5894 plane is NOT stationary though! It doesn't matter how fast the wheels are moving underneath - if the plane is pushing against air then it'll move forward no matter what!
Planes don't use wheels for power, so it's completely different from a car!
I think the flaw might be thinking that the wind speed equals the conveyor belt speed. At full thrust the wind speed moving over the wings would be greater than the tire rotation speed. This is how you can lift off into an extreme headwind with very little forward ground speed. Right?
Creating lift by moving the wheels, Genius.
Magnus effect
Making comments without listening to the video, Genius.
@@grummhd3020 Plane would spin around wheel axis, since magnus effect is exponential.
Even if the conveyor could match the wheel speed instantaneously, it won't produce additional drag. The jet thrust would still push the plane forward and it will take off just fine.
True. It doesnt mater if the wheels are going 10000 miles per hour backwards.... the plane will move forward...
yeah he got this completely wrong. lol. guess that's why he's a pilot and not a physicist. though honestly it doesn't take even that much know-how to realize that a plane is propelled forward by the jet engines and/or propellers moving it through the air - the wheels provide absolutely zero propulsion and are completely irrelevant to the plane's forward momentum.
But the wheels are acting on the conveyor belt using with the gravity of the plane. If the plane wanted to move forward, the wheels would have to drag against the ground, similar to a plane trying to take off with no wheels.
@@joedagg4495 you're doing an impressive amount of mental gymnastics to defend your nonsensical point. no, the plane's wheels don't have to drag against the ground, because the wheels on a plane work like wheels on a wagon - they're not self-propelled. the plane is propelling itself via the jets or the propeller pulling it through the air - EVEN when it's sitting on the ground - the same way is if you are pulling a wagon from its handle, the wheels follow the handle - the wheels themselves have zero role in pushing the wagon forward. you pulling it by the handle is doing that - the same as a plane's jets or propeller are going to pull it forward regardless of whatever the wheels are doing. in the case of the conveyor belt scenario, the wheels are just going to spin against the conveyor belt faster as the plane moves forward at the exact same speed because the wheels aren't offering either resistance nor propulsion - the plane's jet engines or propeller are doing that, and they're not competing with the conveyor belt - they're competing with the air they're pulling through them that's moving the plane forward. the wheels are just like the wheels on a wagon - they'll spin as fast or as slowly as the jets pulling the plane forward require them to, on a conveyor belt or not. something the mythbusters demonstrated quite definitively when they tested this myth. the wheels on a plane ARE NOT moving the plane. the jets pulling it through the air are. so unless you can figure out a way for the air the plane is using to pull itself forward to also move in the opposite direction of the propeller or jet engine's thrust (the opposite direction of the conveyor belt, by the way) at an equal force to the jet engines or the propeller, you're not gonna stop any plane from taking off, conveyor belt or not. the wheels play no role in propulsion - full stop - and are just going to spin faster as the plane moves forward and offer zero resistance otherwise, just like the wheels on a wagon would if you set a wagon on a conveyor belt and stood next to the conveyor to pull the wagon forward with its handle in the air. the wagon would still move forward, even though the wheels would be spinning faster to compensate for the treadmill. same thing with the plane. you're just not making any sense.
@@adesignersperspective wow you totally don't understand the question do you? I understand the wheels don't generate the force. The issue is whatever Horizontal speed the jets produces, the conveyor belt will match going the opposite direction and since the wheels of the plane act to create zero friction between the plane and the ground, the wheels would literally have to slide against the ground if the plane were to accelerate. Kind of like attaching a horizontal jetpack to your torso, if your legs can't move fast enough they will literally start dragging on the ground.
Ever heard of gravity? You can't just throw friction out the window dude.
Yes because it doesn't matter what the wheels do on an airplane, airplanes rely on airspeed not groundspeed.
No because there is no windspeed. There is groundspeed but the windspeed is none. I don’t know why you said yes because you understand the concept but I assume you already watched the video.
@@AndreasRSD Nope, there's nothing the conveyor belt can do to stop the plane moving forwards, all it will do is cause the wheels to be rotating faster than they normally would at the point it takes off.
I watched the vid, and I also watched the mythbusters vid, where they actually tested it with a real plane, and it took off with no problem.
@@AndreasRSD He's playing on the wording of proposition. If there is a strong enough wind that goes on the opposite direction that has enough force to generate lift and the engines can use it push enough thrust, so Yes it can. There are bush planes that can take off with as little 3 feet of ground because of the strong wind in the wildeness. Though the conveyor belt runway is useless and didn't contribute anything to the take-off. As Captain Joe pointed out, the question is tricky.
Yes groundspeed no wheel speed.
@@LeoH3L1 They used a small bush plane for that experiment, not a 747. Even a empty 747 will require a certain forward speed or a certain airspeed to generate lift.
If the 747 cannot generate enough forward thrust to counteract the trend mill and cannot move forward, it will not take off.
I love how people cite myth busters as some sort of gospel. Adam sucks. Long live Jamie.
*fails to use logic from scenario 2 on scenario 1* The plane can still take off in scenario 1 as long as the shrapnel from the exploding wheels doesn't break anything.
Plane takes off in both scenarios. Conveyor belt has no effect apart from the wheels friction, but as the wheels spin freely, the aircraft engines would push the plane to proper airspeed and let it take off.
That's what he explained accurately.
@@Maniacguy2777 no, he said the first scenario was impossible, it is not.
@@fyrtiotva he said if both in equal speed the conveyor belt and the plane in equal speed is possible to take-off
not necessarily, the interaction between the belt and the airplane wheels is the key here. If the belt moving back literally and effectively moves the airplane back and thus nullify the engine going forward, then lift off is pretty much impossible for a 747. But, if the belt moving backwards just makes the wheels spin faster, then sure, the plane will move forward and eventually fly. That is the key.
Imagine a toy plane on a treadmill and a hand which acts like the plane engines pushing the plane forward. Would it get enough air speed or any at all for takeoff?
This guy gets it. Perfect explanation. Definitely no significant hurdle for the omnipotent hand (engines)
Mythbusters did this one, starting with small model planes, and working their way up to an actual piloted small plane: th-cam.com/video/YORCk1BN7QY/w-d-xo.html
If your hand reaches take off speed, the plane WILL in fact take off
@@debateme9204 I mean, if you don't move forwards, you cant make lift
@@toasterhavingabath6980 If your hand is moving at take off speed....that means you are moving the plane forward.
the wheels and treadmill are a red herring in this scenario, it doesn't affect the thrust produced by the engines which determine the airflow and thus lift. That is why Air Speed is important in flight, and not ground speed
You are just wrong. No one is saying the conveyor belt affects the thrust produced, but the basic geometric fact at the centre of this issue is that if the contact patch of the wheel is moving backwards at exactly the wheel speed then the net velocity of the wheel MUST be 0, literally just google "velocities on a wheel". You'll see that in every single case where the bottom of the wheel is moving backwards at the wheel speed that the centre of rotation has a velocity of 0. 0 velocity means no air speed beyond that of the wind, and wind isn't gonna make a 747 take off
@@ClikcerProductions good thing the velocity of the wheel has nothing to do with the forward velocity of the aircraft. The plane would take off.
@@ClikcerProductions starting by “you are just wrong” and then being wrong is a whole new level.
@@szilveszterszalai230 if the wheel speed and treadmill speed ate identical literally by definition the plane can't be moving forward, if the plane is going forward then wheel speed is exceeding treadmill speed and you've completely ignored the question, set up your own different question, and claimed the correct answer to the original question is wrong 🤦♂️ that is the level of stupidity you are at, someone said 2+2=4 and your answer was "nO oNe PlUs OnE iS tWo"
You completely misunderstand, the wheels definitely do matter. If they didn't then breaks wouldn't work to slow the aircraft down. With the runway spinning faster and faster to match the speed of the wheels and with no slipping the aircraft isn't going anywhere.
The actual answer and the key to the problem (in first version from the video), which everyone is missing, is: wheels will start skidding (so we achieve forward movement relative to the treadmill and airplane can take off) when the trust exceedes the friction
There is no real reason for skidding. The whole point of the wheels is for this to be an exercise in rolling wheel behavior.
@@MrDefreese I don't understand what you mean. 2nd Newton's law is as real reason as possible. Wheels will be spinning with the belt matching their rotation speed (teoretically with speed tending to infinity), but the aircraft will start moving forward when thrust > friction, so tires will start skidding on the belt. It's a similiar scenario to a car braking with locked wheels. I know wheels would be spinning in our problem, but the key is the difference in speeds: car's actual speed is bigger than the speed that would correspond to wheel rotation rate. And that's the case in the discussed problem - even if aircratf wheels' rotation speed is not zero, unlike in the car example.
there is no need for any sliding / friction worries, The only reason the wheels would slide/scrub across the ground is if the bearings are busted and rolling is not the way the wheels would perform.
Of course, a meme like this automatically assumes things like perfectly rolling wheels, perfect contact with the patch on the conveyor, instantaneous speed response of this magical conveyor, deformation of the tires is not a factor, etc.
Simplifying it to the bare elements, we are dealing with just a vehicle rolling on a conveyor that has the exact matching rolling speed so that the vehicle never advances or 'retreats' no matter what thrust is applied, so there is no airflow involved and thus no lift generated by the airflow over the wings.
The trick as mentioned is that the conveyor instantly matches the wheel speed exactly - you need instant response controls and power to run this hypothetical conveyor, but that's the question posed to us. It's what we would see in a physics textbook and nothing remotely resembling a real world situation.
@@Siatkowkarzadzi
@@MrDefreese Well, I assume that we stick to basic physics and that assumptions in the description are constants (if it says that the belt matches wheels speed, then the belt is just capable of it and the wheels will just sustain any speed). Friction is a constant too, because it's the only relevant/significant interaction between the two main objects - belt and aircraft. Without friction the belt has nothing to do with aircraft's movement.
I disagree about "textbook" part - in some simple scenario we would consider a car (driven by wheels) as you said, but here we have an aircraft powered by jet engines producing thrust - it's completely different scenario, more complex one - deliberately. So the key to the problem is understanding that not only the lack of relative movement (if we exclude skidding) cannot be neglected, but the thrust force cannot be neglected as well. Physics exercises are often just about basic forces (like friction contradicting some opposite force) or speeds. So my solution satisfies both the laws of physics (in terms of forces) and main assumptions of the problem (matching rotation speeds).
We may disagree about assumptions and what parts of reality to consider, but my view on the problem and solution to it is logically/physically valid. In fact, your simplified version (and the explanation in video) just assumes the friction to be infinite, not in any way non-existent.
Trust Will nevére exceeds friction.Thats the point. They Will be Always equal.
Your wrong of course. The thrust is in the air not on the wheels. The wheels are irrelevant to forward momentum.
But without wheel plane is not going to move.
I think this depends on the friction between the wheels and the conveyor belt. If the belt was low friction, you can put the park brake on, so the conveyor belt does not move and just take of as if you had skis.
You are 100% correct. When the plane starts to move, the conveyor belt has to move the same speed as wheels, but moving the belt spins the wheels faster. So if there is any friction involving the wheels, the belt and wheels will speed at infinite speed almost instantaneously. The only way to spin them at the same speed is to have the energy from the thrust of the engine be matched by the frictional energy lost by the wheels on the belt. So unless the wheels skid as you say, the given conditions are impossible. Same speed needs to be defined better.
Not how that works at all, and not the point of the question
@@Ryan50c actually, it's a brilliant, out of the box, solution to the problem. The belt doesn't move because the wheels are locked. The engine thrust then pushes the plane forward, belt and all. The only potential drawback is if you say the belt will only move under its own power and opposite the direction of the aircraft. But the principle is pretty hoopy thinking.
Im confused why you said the correct answer is "no" at first... You land at the correct conclusion in the second part of the video. It doesnt matter how fast the conveyor belt is moving, the plane moves forward through the air, pushed by the engines (not the wheels). So the only correct answer is 'yes' even if the conveyor matches the wheel speed exactly
You are obviously correct about scenario 2, however I’m not convinced about scenario 1. How can the plane be stationary on the conveyor belt? If the plane’s jet engines are spinning, it is pushing a lot of air behind it. Where is all that energy going? How does your explanation for scenario 1 fit with Newton’s third law?
I realize I’m way late here, but any absolute forward speed from the aircraft necessitates infinite speed in the wheels and conveyor belt, which would presumably explode the world.
Example: say the plane has nearly reached takeoff speed, at 150 mph. This means the wheels are going at least 150, right? But that means the conveyor belt is going 150 rearward, which means the wheels are actually going 300, which means the belt is going 300, which means the wheels are actually going 450, which means the belt is going 450, which means the wheels are going 600… ad infinitum.
Well it does. Adam Savage just recently explained it in one of his tested vids
Glad someone is paying attention.
The time-lapse at 5:50 is really cool. I didn't know the body of the plane rises as it increases speed on the takeoff roll, I thought the body stayed at the same ride height until the pilot rotated.
The wings are designed to create lift even at zero angle of attack. Not enough to make the plane lift off at reasonable speeds, but enough to reduce the load on the suspension. Just like a racing car gets progressively pushed to the ground with increasing speeds due to aerodynamic downforce.
It depends on the pilot's settings of the control surfaces. These can be set to hold a plane onto the runway past the point it had sufficient lift, or caused to lift the plane prior to when it could sustain flight (terrible idea), or to balance the forces such that the plane will itself lift at V1 or some other desired speed.
There isn’t enough friction in the wheel bearings to overcome the thrust and thus stop the plane from moving. It also won’t reach infinite speed. The plane will take off with the wheels spinning 2x takeoff speed. Once that happens the conveyor wheel speed escalation stops since there isn’t enough friction between the wheel and the conveyor.
yes there is, because the magical theoretical question designs it to be exactly that -- the wheels move faster and faster (without failing, cuz they're magic) until the rolling resistance produces sufficient friction and energy dissipation until it equals to the engine output energy
If you're saying that their isn't sufficient fiction you're reading that "the conveyor belt is designed to exactly match the speed of the wheels" and just saying "nah" in response. This isn't a physical scenario, it's a thought experiment, and the simple fact is if you say the plane moves forward you have completely ignored it
@@ClikcerProductions even in this scenario the plane will move forward. It must do so for the wheels to turn at all. So for whatever length of time it is, no matter how short (say 0.0000001 seconds) the plane must move. That means it is faster than the conveyor. When the conveyor instantly matches that speed, it only adds to the wheels speed, playing a never ending game of catch up. Additionally, the engine thrust will continue to add to the gap between the conveyor and the wheel speeds up again, ultimately reaching take off velocity.
@@beauxguss6321 If the plane ever moves forward you have ignored the thought experiment entirely, it's that simple, I'm not going to argue because that is literally just a basic fact of the extremely simple Geometry of the problem
@@ClikcerProductions if the plane doesn't move forward you have ignored the physics involved.
Let's take this off of the runway and put it in the gym. Get on the same speed matching treadmill wearing roller skates. You can't move forward by skating, since the treadmill will match the speed of your wheels. But if you reach out and pull yourself forward using the frame of the treadmill (or a friend on the ground pushes you forward) no amount of speed matching will stop you from moving forward.
This is because there is a force outside of the relationship between the wheels and treadmill that is providing the momentum. When the treadmill tries to match, it merely adds that extra speed to the free spinning wheels. It's the same for the plane.
Me before video: "The engine or prop will pull the plane through the air. What the wheels are doing is irrelevant. Yes, the plane will take off without any difficulty."
Vehicle behavior is because it is rolling. People who say it will take off either act like it is already flying or that it just floats on its bearings. The relationship between vehicle speed and the rotation of the wheels is fundamental
@@MrDefreese So the Captain is right. The debate isn't actually about the mechanics involved but rather the interpretation of the scenario by the person evaluating the question. If you re-word the question (but preserve the intention) to "an aircraft sits on a giant conveyor belt whose entire purpose is to maintain the aircraft's position as it attempts to take off", all of a sudden the outcome is far more obvious.
@@jeff6555there are physical and math issues which provide some confusion. Then there are interpretation issues which might contribute to dispute. ‘Opposite direction’ and ‘exactly match’ might lead people to envision different parameters,
The Captain has a good graphic that too many people are ignoring because ideology takes over.
Your 2nd example kills your first.
The wheels move freely. And we use jet engines to get speed. We only use the gear to keep the fuselage from scraping on the ground during taxi.
3:28 No, the wheels/conveyor would not reach infinite velocity. It would reach equilibrium where the max engine power would equal the power required to overcome rotational drag of the wheels. Granted, they would be spinning mighty fast, but not infinitely fast.
exactly! LISA IN THIS HOUSE WE OBEY THE LAWS OF THERMODYNAMICS!
Dose it say if te engines are up and running at take off power?
Im sorry i didnt watch the video its not a complete scenario.
True. But since we are accounting for these sorts of externalities, my response is that the belt, tires, bearings, etc would catastrophically fail long before the engines are maxed out by drag.
If the plane is moving forward in scenario one, it means the wheels are moving faster than the conveyor belt. This violates the premise of the question so it’s impossible. It’s a silly hypothetical and scenario 2 is way better. But people often misstate the riddle as scenario 1 and then get mad when people insist takeoff is impossible.
Yes but a little slower unless the tires explode due to centrifugal force. There will be slightly more friction in the wheel hubs as the wheels will be spinning twice as fast. There would also be some energy loss from inertia due to having the tires rotation brought up to double the speed.
Centrifugal force isnt a real force. soooo...
@@codyj9983 Soooo that doesn't stop wheels from ripping themselves to pieces if they are spun up too fast.
@@sigmaoctantis_nz but that won't happen...? Why does anyone think a tire could spin so fast that it rips itself apart? The plane will take off before that even comes close to happening.... Understand that a propeller plane flies because the propeller pushes air past the wings to cause lift and so the plane can be stationary (by putting it on a conveyor belt) so long as a propeller is blowing air over the wings the plane will take off. This does not work with a jet engine. And literally has NOTHING to do with the wheels. Drive a plane forward at 100mph with a conveyor belt going the opposite way at 100mph so the plane doesn't move it will still take off because it's the propeller that is pushing the air past the wings, not the speed at which the plane is moving forward. It's the propeller!!!!
This is terrible because it completely fails to take into account the physics of how airplanes actually take off and the physics of rolling friction. Airplanes do not push on the ground to speed up, they push on the air, so having the ground move underneath it would not prevent the airplane from gaining forward velocity. Then comes rolling friction. Rolling friction is a constant, so no matter how quickly the conveyor belt is moving the resistance force will be the same as if the ground were normal. The only way the airplane would be unable to take off would be if the conveyor belt were moving so quickly the landing gear melted causing the fuselage to scrape against the ground.
yes, because:
- Newtons Third Law: the force produced by the engines accellerates the plane, not the wheels
- the wheels can spin at any speed, independently from the belt (if wheel friction is not simplified it'll get a more complicated, but the friction force is ways smaller than the thrust force)
hence the speed of the plane relative to the belt doesn't matter (as long as friction force
this is the only good answer out here
Love your videos Joe but in this instance you're wrong. The plane would take off no matter how you interpret it. The speed of the wheels and belt are irrelevant. If the belt exactly matched or even went faster than the wheels then the plane would still move forwards.
yeah, i think the best way to look at it is that the air is ropes being feed into a winch (jets). the plane is gonna move forwards because the jets aren't spinning the wheels they're dragging the the plane forward irrespective of the ground to wheel relation.
“The airplane has to move forward relative to the ground”. Do you think that you had a headwind equal to Vr you couldn’t take off? That ground speed, rather than TAS or IAS is what governs flight dynamics? Really? If the engine is generating thrust, Newton tells us the plane moves forward. If not, where is the equal and opposite reaction? All the conveyor belt is doing is spinning the wheels up at double speed. I am confounded that this experiment has been done and it was proven the plane takes off, but some people ignore experimental evidence because it conflicts with their (faulty) understanding.
Discaimer: I understand in practice (speed of belt = ground speed of plane, or any other higher reasonable speed the wheels can handle) the plane would take off no problems since the engines of a plane are not dependent on the wheel speed.
The main issue in this ridle is as you wrote: "All the conveyor belt is doing is spinning the wheels up at double speed." Since the ridle says that belt matches the speed of the wheeels exactly it is now mooving at double speed also. So the wheels are moving at triple speed now. Belt matches and wheels are at 4x speed. Belt matches and so on. This has only 2 solutions:
Wheel Speed = 0 - plane not moving so it does not take of.
Wheel Speed = infinity - Wheels explode, plane on fire due to friction, black hole forms when speed reaches speed of light, either way plane propably not taking off...
The riddle as witten just messes with math a little. From physics we know speedOFwheels = speedOFbelt + airplanegroundspeed. But since the ridle says speedOFbelt = speedOFwheels that is only possible if airplanegroundspeed = 0.
I'm with you! I'm embarrassed to admit that I, incorrectly, thought the plane wouldn't be able to takeoff when the Mythbusters conducted their test. I'm a lifelong aviation enthusiast and huge fan of Capt. Joe but disappointed that he got this wrong.
Capten sorry but your plane will lift off in any case. Matching or even double the speed of the belt backwards it (if the weels can hold the spin) you will take off! If your consider is about if the weels can hold on the frictions ect it is another riddle
A question on this is where is all of the thrust going?
As I disagree with this conclusion.
I would counter that the plane would move fwd with the wheels spinning at twice the speed of the aircraft. So the "match the speed of the wheels" is maintained
The wheel speed is entirely disconnected (assuming minimal resistance in the wheels) from the aircrafts speed and air flow.
If it where a car on a conveyor belt, a boat in a flowing river or indeed a plane in flight against a head wind.
It would absolutely be stationary but an aircraft with free spooling wheels in still air it can take off.
Yes, during 150knots head winds
2:43 It has to move forward relative to the air, not the ground.
My problem with the riddle is that it's not _quite_ defined well enough. Specifically, what _exactly_ does "designed to move at precisely the speed of the wheels in the opposite direction" mean?
I see two main, and somewhat ambiguous, interpretations:
1. If it means that the conveyor's velocity is always equal and opposite to the average velocity of the wheels, i.e. the velocity of the central hub (which is the same as the velocity of the plane itself), then yes, it can probably take off. This would effectively simply double the radial velocity of the wheels, and as long as that is something that's within the tolerances of the tires and hubs to not explode and overheat, respectively (which I suspect it is, since a no-flaps landing in a tailwind could come pretty close to that ground speed), then there should be no problem taking off, since the plane doesn't rely on ground friction for its thrust and acceleration. Yes, there'd be a little more friction from the hubs and rolling resistance of the tires, due to the increased apparent wheel speed, but compared to the power of a passenger jet's engines, my head-napkin math says that should be negligible.
2. If it means that the conveyor's absolute velocity relative to an inertial observer is equal and opposite to the tangential velocity of the tires as they spin, then... probably not, but it still might be possible. This definition is recursive, so the wheels' speed and the conveyor's speed, which are each defined by each other, would create a positive feedback loop that would exponentially ramp the speed up toward infinity. Of course, you could never actually build an infinitely fast conveyor belt, so it would depend on whether the conveyor can go fast enough to over-speed the wheel assemblies before the plane has enough lift to take off.
Edit: Cool, that's pretty much exactly the conclusion you came to.
If you ever _do_ find yourself taking off on a conveyor belt in either scenario, I recommend the most extreme possible short-take-off setup... brakes on full as long as possible until engines spool up as fully as possible, for starters. I might even consider starting in a clean configuration for the initial acceleration, then dump flaps/slats approximately one cycle time before rotation speed (the earliest rotation speed possible given the load parameters, with engines running at absolute max power). Could you even spool up most of the way with reverse thrust selected, so that the reversers would be closing just as thrust passed maybe the 60% mark, and finish the transition just as the thrust pushed the mechanical limits of the hydraulics?
In any case, since you'd be doing so in real reality instead of spherical cow thought experiment land, I think you could put your faith in the safety factor the engineers of the tires and wheels designed into them, over the bizarre possibility of an infinite-velocity, infinite-acceleration conveyor belt. That is, assuming the take-off is super-important, like to escape the massive volcano island on the verge of erupting that the supervillain who built the conveyor belt anti-takeoff system triggered, or something. If it's just, like, to go to another city for business, I'd just ...
Actually, scratch that. If you ever find yourself facing a conveyor runway, just take off on the longest taxiway instead.
you are not going to believe this, but for the first time in a long time, I just used the phrase, "outside the box thinking" to describe another take. Then I read your comment and you used it. Crazy coincidences like that are what life was made for.
Anyway. I think the whole thing comes down to the external force of the engine thrust acting on what is considered to be a closed system.
The conveyor moves at the speed of the wheels, right? Well, in order for the wheel to turn in the first place, there must be forward movement. The engines will inch the aircraft forward just a bit, and the wheels will begin to roll. Nothing the conveyor can do, even magically can reverse that first movement. It then becomes a game of cat and mouse with the conveyor instantly (but with some imperceptible delay) matching the speed of the wheels. This acceleration will also be added to the speed of the wheels. All the while, the external thrust will continue to add to the gap between the speeds until the plane reaches takeoff speed.
As for the whole breakdowns thing. Why does nobody consider the treadmill to be breakable? Everybody wants to talk about the wheels failing, but not a multi KM long treadmill with a motor, a belt system and tens of thousands of rollers with their own bearings that could heat up under all this stress.
If I not mistaken, the Mythbusters has done this experiment. not sure what season/episode...
Can't tell you the season but here's the final result: th-cam.com/video/YORCk1BN7QY/w-d-xo.html
Yup, Mythbusters tackled it. The aircraft they used was just slightly smaller than a 747 (IIRC it was something loosely derived from a Piper Cub).
Same principles apply. Aircraft thrust is applied directly to the atmosphere (either via a propeller [or multiple propellers] or a jet engine [or multiple jet engines, or high bypass turbofans]). The wheels have no function really other than that of the rear wheels on a front wheel drive car - basically they prevent scraping the belly on the pavement (and provide a little help with braking and steering).
Inflate a party balloon 🎈, but don't tie its nozzle, just hold it pinched closed between your fingers, then get on a treadmill, then release the balloon while walking, jogging, or even running on the treadmill. Same basic principle...
@@frederickevans4113 Nope that is completely wrong its very very different , in the myth busters one the had airflow over the control surfaces from the propeller and the fact that they allowed forward movement the conveyor belt did not do its job , mythbusters is great entertainment but that aircraft got airborne due to airflow over the wings creating lift.
@@myflight448 The plane in this question would also move forward, generate airflow, and take off from lift. Everyone agrees that the plane needs to move forward to take off. *If* a conveyor belt actually could keep the airplane stationary, the it wouldn’t take off. But a conveyor belt cannot keep an airplane stationary. If I get on a treadmill wearing roller skates, I can move myself forward or backward with the handrails regardless of which way the treadmill is moving.
Mythbusters addressed the original form of the question which was can it take off from a moving conveyor belt. The answer is yes because an airplane's engine doesn't care about the wheels. This form of the question with a conveyor belt matching the speed of the wheels is different in that the belt speed changes meaning no matter how much thrust the engine produces it can never move forward because the conveyor belt adapts to that level of power rather than maintaining a constant speed.
It's a different scenario with a different outcome and much more difficult to test. I think Grant Imahara (RIP) could have designed a system to create such a conveyor belt -- he was the most technically savvy of the bunch.
Its always a good day when Captain Joe uploads
No airspeed = no takeoff.
Edit: I realized later that I was wrong and understood the problem with a skateboard on a treadmill.
The planes propulsion is through the jet engine, the wheels are free spinning and will only affect the plane if the brakes are activated.
The conveyor belt’s speed only affects the wheels, which are free-spinning.The jet engines push the plane forward through the air.Therefore, the plane will still move forward, generate airflow over the wings, and take off.So, even on a treadmill, the plane will take off because the engines move the plane forward relative to the air, not just relative to the treadmill.
@@sbosboniso7036but then if the plane does move forward then that means the wheels are spinning faster than the treadmill. It specifically says, treadmill matches wheel speed.... cancelling out the possibility of being able to roll forward
@@sebsshenanigans The wheels have NOTHING to do with the force moving the plane forward.
@@calebfuller4713 but if the plane moves forward on the belt... then the wheels are spinning faster than the belt aren't they? Which it specifically states that they spin at exactly the same speed
@@sebsshenanigans Yet the plane must move forward, in accordance with Newton's 3rd law. The force of the engine thrust MUST act to push the plane forward. Any other result breaks basic physics. That plane IS moving forward, regardless of what is going on with the wheels.
So if you take that interpretation - a belt that always and instantly increases in speed to match the wheel, you end up with the engineering impossibility of a conveyor belt that MUST spin at potentially infinite speeds.
OMG. This guy is wrong. Oh its a jet which cant send air over the wings If it were a prop plane it WOULD take off because it sends air over the wings and creates lift. Even if the plane is not moving forward relative to the ground. Because its a jet the plane needs to be moving forward to create the airspeed over the wings to cause lift.
The plane could take off, if the tires dont explode. you Accelerate by pushing air the ground didnt matter..
if the plane isn't moving air isn't flowing over the wings and no lift will be generated
indeed, the forward motion of the airplane is provided by the engines only, as long as the wheels don't provide enormous friction (which is not the case on the conveyor belt) the aircraft will have enough forward motion (=lift) to take off
@@DIBOYOU well isn't the idea of this conveyor belt that it in some magical way cancels out the forward motion of the airplane while keeping the wheels spinning? if it is just a regular conveyor belt then i get your point, the wheels would just spin a lot faster than they normally would and the plane gets the forward motion relative to the air around it it needs to lift off.
@@kristian4559 No, it doesn't say that the conveyor stops the forward motion, only that it spins -exactly- the speed of the tires in the opposite direction. That this would cause the plane not to move is a fallacy, one most people fall into because we're used to vehicles which are driven by exerting force against a road.
A plane can take off without wheels, so I think they are pretty irrelevant if they are on a conveyor or not.
🤣I am curious about your statement...how will a plane take off without wheels plz elaborate!
@@AtharvaSathaye Seaplane
the plane can take off but the wheels would probably explode from the rpm. The wheels aren't pushing the plane forward the engines on the wings are
The wheels would explode prior to moving a single centimeter forward, since the belt is matching the speed exactly. Afterwards, the plane would slam into the belt, sending lots of sparks and fire everywhere, and I don't think it will be taking off.
Did you even watched the video bro? doesn't matter how it moves forward, IF it moves forward it means that the wheels somehow are moving faster than the belt, therefore violating the rule of matching speeds, not even mentioning(as it is already mentioned in the video), the wheels have a speed limit, and if they blow, good luck trying to drift your way through the runway with a fricking 747
The problem here is people can differentiate between the wheel ground speed and the aircraft’s airspeed being independent of each other .
If you turn scenario 1 around. Start at the end of the runway and move the aircraft backwards with the conveyor. With no thrust it moves backwards. But in order to remain stationary it only needs to produce enough thrust to compensate for the friction in the wheel bearings. Thus in either Scenario this is the only backwards force acting on the aircraft.
The only way it won’t take off is if the conveyor is moving so fast that the bearing friction matches the thrust which is absurd.
In both cases the aircraft takes off with its wheels spinning faster.
The conveyor is essentially adaptive to wheel speed. He explains it in not so great fashion because it’s a subtle difference. In his second example, he provides the explanation of a conveyor with a constant speed which would of course allow takeoff.
A conveyor that always exactly matches (rolling) speed, there is no velocity change.
@@MrDefreese Scenario 1 - aircraft will not move ONLY as long as thrust force is less or equal to the friction between the wheels and the belt. If thrust will exceed the friction, the aircraft will start moving (tires will start slipping/skidding on the belt)
@@Siatkowkarzadzi correct. Implicit in this example is that the wheels roll (freely) and excludes add-on items like busted bearings, absurd headwinds, etc. boiling it down, this is a basic cart and wheel physics problem where we are given unity for linear speed of the conveyor and the rotational speed of the wheels.
@@MrDefreeseonly if the wheels eventually fail. But if we’re assuming the conveyor is magic and can sustain infinite speeds, and we assume the wheels can sustain infinite speeds, they neutralise and the thrust still pushes the plane forward.
Maybe this is covered better later in the video, but ground speed doesn’t matter at all when it comes to flight. What matters is the air moving over the wings
True, but the problem here is that people focus on the wheels and extrapolate from cars. However, airplanes use propellers/turbines/etc. to push themselves off the surrounding air, with the wheels not being powered at all.
@@germansnowman you're rigth. Planes don't need to have wheels to take off. So they're not part of the equation
1:00 Take-off shouldn't be a problem: Planes gain speed by generating thrust with the engines mounted to their wings. Are there even any motors rotating the wheels? I don't think so. 🤔
No motors in aircraft wheels (except some experiments with 'electric taxiing') that are assisting the take-off. Only the engines are providing the forward thrust, which is totally not connected to any conveyor belt type of runway (it will only impact the rotational speed of the wheels, not the airplanes forward movement)
It will be a problem. If the belt and the plain are moving in the exact same speed in the opposite direction.
the plain needs a forward motion in order to get the air under it's wings. If the belt is moving at the same time the same speed the other way. the plain in total would have a movement of 0, (zero) it is motionless only the. in this case the positive force and the negative force cancel the other.
however real life dictates that this is impossible ether the aircraft is reacting to the belt or the belt is reacting to the aircraft. even a delay of 0,0000000000000000000000000001 would mean that motion has been made.
@@sirBrouwer it's not speed it forces.
ok, there are a few questions hidden in this thought experiment, and all are a problem of the relative motion of three objects, the air, the ground, and the plane:
1. will a plane take off if it is held in place by a conveyor belt keeping it from moving forward by exerting enough force on the wheels that the wheels exert enough force on the plane to prevent forward movement?
if the plane can move the air past itself fast enough, it will take off. if the plane can't do that, it won't take off.
if the air moves enough, the position of the plane relative to the ground doesn't matter. the plane can take off without moving forward, as the air moves fast enough to lift the plane
2. will a plane take off on a conveyor belt designed to keep the airplane in the same position relative to the air?
if the air and plane aren't moving relative to each other, it doesn't matter how fast the plane moves relative to the ground, it won't take off.
To the one person reading this: you’re a legend and adorable, stay safe