Propeller Effects on an Aircraft : th-cam.com/video/WnJxrHmtT_c/w-d-xo.html The Only Video Needed to Understand Airplane Propellers : th-cam.com/video/hvboi6w1Z9A/w-d-xo.html Does This Common Argument Disprove This Lift Creation Theory? : th-cam.com/video/kMdJMbggD90/w-d-xo.html
Most impressive. Thank you for the detailed presentation. I worked as an Aerospace Engineer for over 31 years and never have seen all these issues presented so concisely in one presentation.
Fantastic explanation. Most people get three bladed props because "they look cool". I just put a new 2 blade prop on my TR182 because it is just flat out faster with the 2 blade prop. If you maintain the prop as well as you should, the 2 blade will be every bit as smooth as the 3 blade prop as well. Just an aside, in the old days, model airplanes used to use one bladed props with a counterweight as they were even more efficient.
Years ago my father purchased an airboat from a NASA engineer. It had a 6 cylinder Corvair engine. My father and I were both engineers and my father was a WW II B25 bomber pilot. The airboat would do 40+ mph at 4000 rpm. We wondered if the boat had the correct prop. We looked up the engine specs, 140 hp at 4200 rpm and measured the prop diameter. We calculated the speed of sound at sea level, about 1100 ft/sec. We calculated the prop tip speed, just under the speed of sound. We concluded the NASA engineer had selected a good prop for the boat. It would require a major engine and prop change to get the boat to go 50 mph. The flat bottom John boat was not built for the job. After a few years, a weld cracked on the front of the boat from the pounding of the water. Conclusion, the engine and prop were very noisy and care was needed leaving and returning to shore not to disturb others.
@@bidenisasnake9932 Boats also have a hull speed and maximum engine power, which we had exceeded. They are also worthless in choppy water that rips the welds apart. Don’t overload with ice and beer and throw back the large hammerhead sharks. But they are a lot of fun flying on glass smooth water at 40+mph in 6” deep water that no other boat can go. To go where no man has gone before.
The Corsair and P47 originally had 3 bladed narrow blade props. It was said that going to the 4 bladed "paddle prop" was like adding 1,000 hp in a climb! One pilot in Britan said that his P47 was faster and would tangle well with spitfires untill they pulled up and climbed they always did this to him in mock dogfights until his plane got the 4 blade paddle prop and water injection, at which point he pulled up with them and passed them blowing their minds!
P-47 always had four blade props unlike the Corsair. But, later versions had more power and got paddle blade propellers increasing their performance in the climb.
@@vascoribeiro69 I always wondered about the German propellers being smaller diameter and much larger chord that allied aircraft. (The propellers of the FW 190 and Me 264, for example)
@@331SVTCobra yes, they had a lower aspect ratio. I don't know the reasons or trade offs. I think they stuck with three blade propellers for some reason (productivity?) and, with increasing engine power, they just augmented the blade area. We can discuss blade drag, but they were very well designed, being elliptical, thus reducing induced drag.
Great video. Thank you. I owned a Comanche 250. I replaced the Hartzell 2 blade with a McCauley 3 blade. A friend replaced his original 2 blade Hartzel with a compact hub Hartzell 2 blade at considerably more expense. He claimed his would be faster than mine so I challenged him to a comparison. So at 4500 ft, we both fire walled the throttle and prop controls. I walked away from him by several knots. Haha, faster and several thousand dollars cheaper. As a side note, my takeoff roll was considerably shorter and the engine/prop combo much smoother but my power off glide suffered considerably due to the extra drag. All in all, the 3 blade was a great improvement.
Thanks for this video getting out there. I can't remember how many times I've tried to explain things like this. I think people get something in their head and they just don't like someone bringing math and facts to replace it with new or better information. Often, I start off by stating that almost everything in this world is not 1:1 then try to correct them with nonlinear thought.
Great Presentation, glad you mentioned the F4U Corsair, would like to know how when the Corsair got a more powerful engine they went to a 4 bladed prop. Also I would like to know why the C46 Commando went from a 4 bladed prop to a 3 bladed prop. My Dad worked 4 bladed prop C46's in the Philippines but most pictures show C46's with 3 bladed props.
I love the fact that in WWII the planes got too powerful engines and they were not able to use all the power so the 3 and 4 bladed props were born. You lose efficiency gain speed.
When the tip of the rotating propeller reaches more than the speed of sound, it creates shockwave. The molecules of the air compacted in the shockwave. The adjacent propeller have not enough air molecule to grab to create thrust.
I think a big factor in the choice of a long prop on the P-47 is the fact that it needed high efficiency at high altitude. Otto Koppen who designed the Helio Courier wanted a long as possible prop for the H-391B, it used a 101inch two blade propeller and GO-435 Lycoming. In the prototype Helio they used a 11 foot prop behind a 145 hp engine, three point landing and take off was required. One design factor not often talked about is twist, if you want efficiency, the correct amount of twist is required for the intended speed.
12:30 in theory, it sounds like you could get even lower scrubbing drag AND some nice bonus lift if you could find a way to stick 2 massive propellers at the wingtips. Obviously, structural concerns say otherwise for most cases...
There are some interesting bespoke air frames that have been modified for speed(what else!) that demonstrate all your points perfectly. I don't think cost was mentioned which is a major factor at the design stage for most aircraft, as with any other machinery. Great video.
I liked your video. A very Basic and simple theory of props. Your next video should be on a steped up props. Pull vs Push, prop wash, Hi speed props, F-1 racing props, Twin rotating props, Reverse rotating props and then less Do some Hi speed turboprops.
I think Corsair with its absurdly large propeller best shows the point why a large propeller can work togheter with high speeds. Corsair was one of the best planes in WW2. Its combat ability was superior and enormous, but it had one major drawback and that was that it was difficult to landing such an aircraft. And the plane was despite its design as a naval plane and its great air combat performance kicked off the aircraft carriers and became a land based plane instead.
There's a reason most (not all!) fans, be it ceiling, standing, computers, laptops... have an odd number of blades. I'm pretty sure that jitter on opposing blades can introduce resonance across the pair, and increase noise as a result. So there's an odd number so that you don't have opposing blades resonating and making noise if the balance isn't great. I would imagine on an aircraft, where you could pay more attention to the balance, it wouldn't matter too much, but it might still be a factor.
Short Propellers are used in Air Racing Appliacations where Rate of Climb and High Altitude Performance don't matter. In Air Racing with fixed Pitch Props you want to fly with a coarse Pitch Propeller that doesn't have a lot of RPM change through the Speed Range of the Aircraft.
Yeeees! Since the equation of drag is the same as lift, the faster propeller slipstream not only increases drag as a function of V^2, but also lift. In the context of the video however, that faster propeller slipstream of the smaller diameter, faster spinning propeller is more concentrated over the fuselage that creates very little lift, and misses most of the wings, flaps and slats. A slower spinning, larger diameter propellers slipstream is slower, but spread out over a wider area, and will go over a larger portion of the airplanes wings, flaps and slats. So there is no real increase in lift by going for a faster spinning, slower diameter prop. On STOL one would want the largest possible diameter prop spinning right up to the max tip speed of mach 0.8, even closer to 0.9, to make use of this increased lift from the propeller slipstream.
Another fantastic video about something I woner about all the time! The only question I have is what about short thick props? Can not this move larger volumes of air at lower RPM? (:
Thanks. It difficult to move a similar amount of air with smaller diameter props, even with thicker blades turning faster. There is much efficiency in length, if you consider that a roughly 40% increase in blade length doubles propeller area (when spinning).
Back in the 60s & 70s I was messing about with control line model aeroplanes. I have 2 glow-plug engines of the same make & capacity, but different performance characteristics. A standard Taipan 2.5 cc engine commonly used for stunt models and a 2.5 cc gold head racing engine with a 1/4 wave tuned rear exhaust tuned pipe, commonly used for speed & racing models. These engines had different performance characteristics. The 1st one was for larger slower thicker (high lift) wing aircraft designed to pull very tight maneuvers at lower speeds It would. The racing engine was for smaller slimmer winged aircraft designed to fly as fast as possible in level flight. The stunt engine would commonly carry a prop 8" dia x 4 " pitch and would rev to something like 18000 rpm, while the racing engine would carry a 7" dia x 6" pitch prop and would rev out to something approaching 30000 rpm. Now, my memory of the rpm values is not exact. The figures stated are very approximate. However, the point is to indicate how performance parameters are so profoundly interrelated with each other. You can't change one aspect of a design without affecting other aspects and optimal prop choice dia, pitch, blade number & width etc. So you can't make generalized statements. Design choices influence each other & influence the out come, or you can put it this way, the desired performance outcome & considerations of practicality & economics influence the design choices in a complex & integrated way. L = 1/2 . p . V^2 . S . Cl D = 1/2 . p . V^2 . S . Cd M = 1/2 . p . V^2 . S . MAC . CMo But this simple synopsis hides a vast wealth of complexity.
My grandfather was a crop duster and he flew an Ayer’s Thrush Commander with a 600 hp radial that had a 2-blade prop. Talk about loud. We would always hear him for miles.
I would like to see some discussion of matching the propellor to the engine. Obviously a larger propellor would potentially provide more thrust but it would also demand more torque from the engine than a small one. Too large a propellor would slow down the rotational speed. Engines initially produce more power with increasing RPM ( revolutions per minute). But this increase is not completely linear. andit higher speed the torque output from the engine levels out and an unloaded engine will end up with some RPM at a top speed giving zero useful torque. More powerful engines like that in the p-47 had a reduction gearing that drove the propellor RPM at a fraction of the engine crankshaft PRM. Small aeroplanes commonly have a direct drive at crankshaft RPM. to save cost and complexity. They could obviously do well with a reduction gear that could permit a larger prop. Also on the ground with zero airspeed ( and no wind) any engine/propellor set up would achieve a certain max RPM . Then in flight with some free stream speed the prop /engine combination will rev up a bit. The prop proportion and size must be selected to let the engine run at its maximum power. A reduction gear helps this
What to make of counter rotating propellers like some late Spitfires and the Tupolev Bear bomber? Supposed to be very efficient but also very noisy. And then there is the CFM Rise "open rotor" engine being developed for jet liners with its variable rotating and static blades. Presumably it must be more efficient than standard turbo props, faster (and equally quiet or quieter), otherwise they wouldn't bother.
Maybe I'm not thinking about this clearly, but it seems to me that a prop works by essentially making a circle (spinning 360 degrees), so I am wondering if the more blades you have on a prop, would make it more efficient? (if physical size, and weight were not a consideration). I would think that a 3 bladed prop (so each blade only having to move 120 degrees) would be more efficient and offer better performance than a 2 bladed prop (each blade having to mode 180 degrees) that is the same weight, and diameter. Am I not thinking about this clearly, or is there some logic to my though process?
On my electric-powered RC models, I want the diameter-to-pitch ratio (D:P) to be between 1.5:1 and 1.75:1. The highest I’ll use is 2:1. Longer blades take more energy to turn and that shortens the flight time.
Turning the prop FASTER takes more power. The longer prop can turn much slower for the same thrust. Thereby being more efficient. That's why the video, and any aerodynamics textbook, will tell you a longer prop is more efficient. Because they can turn much slower for the same thrust.
@@senseisecurityschool9337 In the past week, I replaced a 12x4 prop (3:1 D:P ratio) with a 10x5 prop (2:1 D:P ratio). The airplane flies faster, the motor draws less current, the battery lasts longer, and the plane is more fun to fly. The 10x5 prop pushes a smaller column of air (less thrust), but it pushes that column of air faster (higher pitch speed). The airplane is faster, but doesn’t climb quite as well, which is fine with me. I don’t have fly at full throttle now to keep the plane from mushing around. I don’t care that it won’t go straight up out of sight.
@@txkflier The area of a circle is Pi*rSQUARED. the 10" prop is 25" * Pi, the 12" prop is 36" * Pi. A 12" prop is 50% LARGER than a 10" prop. You put on a much SMALLER prop and found it's a better fit for the motor you have. So what you just told us is that 12" is too large of a prop for the RPM / KV of your motor. It would be more efficient to run a 12" 4.5 with a lower KV.
That isn't how a radial engine exhaust tone sounds. They make a low-pitch rumbling/gargling sound, not a high pitch "screaming" noise like in the clip in the video. When the T6 is in cruise, and the propeller pitch is set coarser, i.e. slowing down the propeller speed and thus the tip speed, it doesn't make that sound anymore.
This is for the consideration of aircraft designers only. Your existing airworthy aircraft's propeller is limited by the type certificate data sheet, so you DON'T get to experiment with propellers on an aircraft with a type cert.
You can experiment as you like as long as there is an STC for each prop you fit. Take a look the STC's for the Cessna 172 for example, you have 2 and 3 blade options, of various blade lengths. Depending on the engine and model of Cessna 172, you can fit certain Hartzell, McCauly, MT prop, Sensenich and possibly more. That's certified aircraft. On most experimental there are virtually no propeller legal restrictions.
@@LetsGoAviate You are exactly right with an exception. If you place the aircraft in experimental for a short time while experimenting you can do whatever you wish. Then bring it back to normal with a certificated prop installed. But I bet you knew that too! I have done this many times with different engines and such doing research for mods.
Why would one use a shorter three bladed prop on an engine that can only provide adequate power for a longer two bladed one? Would a 2 bladed one not be more efficient? A reason would seem to be too high RPM, but your example states 2600 RPM, That's (usually) not too high is it?
Larger props are more efficient than smaller faster ones not because of propeller wake. They are overall more efficient in any case, that's why helicopters have huge propellers and why modern big propeller high-bypass jet engines are much more efficient than old low-bypass ones
Maybe you can help me! Why is it so taboo to manipulate the flaps just before landings. As a former Alaska 135 pilot. The first of two thing I was told to learn. Was to get comfortable pulling the flaps before you touched the runway. Cessna 207's and grand Caravan had the same kind of flaps. Wherever you moved the indicator, the flaps will move to match it. You're not going all fall out of the sky because you're right in the middle of ground effect. Your stall speed is way low. I'm not trying to argue about this. This is what I did for four years. I just want to know why it's such a big deal.
One thing I didn't hear is that a single bladed prop is most efficient as it runs in less disturbed air, as a two blade is more efficient than a three blade again because the blades run in less disturbed air or blade wake and so on. Could you comment on this issue.
Single blade is more efficient, but not because of less disturbed air. The propeller pushes the wake backwards, so by the time the 2nd or 3rd blade gets to that point, it hits new undisturbed air. So perhaps a myth that I will cover in the next one. Blades has efficiency losses, noise, bending etc, so less blades is more efficient. But this is fairly minor compared to the fact that more blades have more power absorbtion potential. Someone said it's thrust that pushes the plane, not efficiency, and 1 blade has very limited power absorbtion or thrust, regardless of higher efficiency.
@@LetsGoAviate Hey its exactly what I said, the single blade runs in less disturbed air, or cleaner air. The plane moves forward, so it runs is less disturbed air.
Yes 3 blades propellers (if all other parameters are the same) generate similar noise at similar RPM as 2 blades propellers, but to fly the plane we need a given amount of thrust, not RPM and 3 blades propellers give the same thrust at lower RPM therefore they *are* less noisy. If the engine isn't able to produce that thrust at lower RPM, that is an engine and/or transmission problem, not a propeller problem, therefore taking it into account when compering propellers to each other is unfair. You missed the biggest factor why large propellers better for high speed. The plane goes foward by pushing air backward, it gets the same foward momentum as backward momentum the air gets (Newton's III.). The thing that is decided basically by the diameter of the propeller is whether we want to achieve that momentum by pushing less air with more speed, or more air with less speed. For easy understand lets say for e.g. 1 unit air with 2 unit speed or 2 unit air with 1 unit speed. Both will give the same forward momentum to the plane, but as kinetic energy is 1/2*m*v^2, in the first case the air get 1/2*1*2^2=2 unit energy while in the second case it will get 1/2*2*1^2=1 unit energy, so pushing more air with less speed gives less energy to the air while give the same amount of thrust to the airplane. All this energy is coming from the airplane's engine and if you want to go fast, its better to use your fuel to give energy to the plane, not to the air (it is true for all speed, but when the power is a limiting factor, its more crucial).
If there is nothing behind the prop (no part of the fuselage) then there is no slipstream drag that the fuselage goes through. The disadvantage of pushers is when the air gets to the propeller it has already been disturbed by the fuselage, wings etc and that reduces prop efficiency.
one thing I must disagree with you on is the statement that you made. "The air on the front of the propeller travels faster than the air on the rear" But just as in a wing, the air on top moves at the same speed as the bottom, causing the air molecules on the top of the wing to stretch or thin out and meeting at the root, causing a lower pressure on the top, giving lift. The same principle goes for propellers. Except for one thing, the pitch adds thrust also.
The air going over the top of a positive lift creating wing or propeller blade does go faster that air going below. It's fact, not an opinion. Here's a wind tunnel video showing air over the top going faster th-cam.com/video/e0l31p6RIaY/w-d-xo.htmlsi=Bw03vecloDjXmRVE
- NB, a higher cambered blade needn't be thicker - of course with combustion it is expedient to make blades substantial to offset vibration fatigue.. With electric propulsion is is simple to lighten the blades using a thin cambered blade. NB - lower RPM prop doesn't mean slower slipstream - also not to forget the prop wash is spiraling - not straight, cheers. - The pitch reduction quip - if anyone proposes that - means they don't understand thrust at all... (Shorter blade, higher pitch, lower camber, more blades - absorbs more power - with faster airspeed setpoint, and results in a longer takeoff roll. (that balance with static thrust and critical angle of attack at low airspeed...) Aart from aerobatic concerns - more blades are only useful once maximum geometric diameter is reached (for the installation size) and power remains to be absorbed - somewhere in the desired flight regimes.
All good points. However regarding the speed of a slower spinning propeller's slipstream, are you referring to the blade tips specifically? The mean speed if the slipstream will be slower, it has to be with the law of conservation of energy followed by newtons 3rd law. I'm making some assumptions here of course, one of which is that a spinning long prop and short prop have the same blade tip speed (thus the shorter one having a higher rpm) and all else being equal, they will move an almost identical amount of air per second past a point just aft of the propeller. If the larger diameter (slower spinning) prop then move more air as a result of it's bigger spin area, the slipstream must to be slower.
Civil Aircrafts: 2 or 3 is enough: Normal Piston engined planes: 3-4 is good. Griffon Spitfires: Five. Kyushu J7W1 Shinden: SIX Late Griffon Seafire: 6, but 3 of them rotates the other way! Germans: 3. Take it or leave it. He-117 and Ju-288C: 4! we have 2 engines for one propeller so we get an extra blade, yay! Also some German plane: What's a propeller? some British Plane: See, exactly what I'm asking....
Hmm...🤔 A couple of things come to mind regarding the significance of a propeller's slipstream [blowing back over the fuselage]: 1) - Taking a well-known example: the Gee Bee Racer, with its huge, prop-obscuring fuselage and slipstream-swallowing engine cowling. That flew satisfactorily (albeit with notable quirks). 2) - If prop-wash/slipstream is important in terms of drag, why don't more propeller-driven planes use a 'pusher' configuration? I've built and flown several radio-controlled aircraft with these design points, and experimented with numerous combinations of engine, propeller, fuselage size, and so on. Back in the '90s I built a series of planes which had a blunt-nosed cylindrical fuselage 10" in diameter. The engines were enclosed by a 10" diameter aluminium cowl and mounted on a solid firewall 3" behind the prop, which in iteration 1 was 2-bladed and had a diameter of 12"; in iteration 2 it was 3-bladed and 10" in diameter; and in version 3 the prop had 4 blades and was 8" across. In version 3 there was no slipstream blowing back over the fuselage and wing roots. All three planes flew normally. I didn't think to take any sound-level [dB] measurements, though. My slipstream experiments were neither scientific nor systematic. Those with pusher propellers were also just random planes of various types - high-wing, low-wing and delta. My only [unscientific] observation was that pusher props/engines seemed to make more noise than those in a tractor layout. Flying characteristics weren't noticeably different, so just how important IS propeller slipstream where efficiency is concerned? Are pusher-planes unpopular because of the basic problem of getting them off (and back onto) the ground without hitting the propeller? Please note: I appreciate that there is a world of difference between a 1.5- or 2-metre span model and a full-sized aircraft (Reynolds numbers, etc), but even so, I'd be interested to know why such things don't seem to make any difference to a plane's flying abilities. (Not too technical, please; I'm not a mathematician or an engineer.)
In world war II the Germans developed the Dornier Pfeil fighter plane with both a puller and a pusher propeller. One drawback was that for the pilot conventional bailing out was impossible without being chewed up by the rear propeller, necessitating the use of an early ejection seat. The Convair B36 post war nuclear bomber had wing-mounted "pusher" propellers. Because the engines were mounted the wrong way round to normal it was prone to cooling and carburettor icing problems.
The propellers of pusher config planes don't get clean undisturbed air, the air having passed over the fuselage and wings before reaching the propeller, which reduces prop efficiency/thrust. So that is the "equalizer" and is one reason why pusher isn't necessarily better than tractor.
I dont know ...but the weight of 3 propeller= 12 propeller may be more fascinating and practical. As material king Carbon fibre have been around for a decade..
It had 3 blades on early versions actually. As they made the engine more powerful on later versions, they could increase propeller power absorbtion by making the blade chord wider, or by adding another blade. Adding another blade was more efficient. As it already had the longest possible blades for the prop rpm, it couldn't be made any longer.
More blades have more drag. So a single blade would be most efficient. But noisy. More blades are quiet and transmite more power. With limited power 2 blades are faster but with more power multi blades are faster
Single blade is more efficient, but has very limited power absorbtion. The blade can only be made a limited length before tip speeds become and issue. And if making the chord wider to add power absorbtion, it loses efficiency, and there would be a crossover point where it would be more efficient to add a second blade, than making the single blade chord wider. And same 2 vs 3 blade, 3 vs 4 blade etc.
I'm sorry but there is no such thing as the air goes faster over tge curve of the wing/ propeller, that's a myth that had been disproven. The air does not change speed, it changes in air density. Sorry to add another myth to your list of myths. Faster airspeed is old theory.
For discussion: The “faster” idea is supported by the observation that supersonic shock waves form on wing tops and other fuselage parts at airspeeds approaching but not equal to Mach 1. It was found that this phenomenon could be delayed by sweeping the wings back, enabling higher airspeed before encountering Mach 1 on the wing, vertical and horizontal stabilizers.
It does change speed, but not even enough to account for half of all pressure differences. Curvature does matter, but only because it imparts downward momentum onto the airflow from leading edge to trailing edge. The reason wings are shaped the way they are is because: 1. They must have thickness for structural strength. Or you can go with external bracing. Your choice. 2. A teardrop shape allows for streamlined enclosure of the wing's internal structure. The rounded leading edge allows flow attachment at a wider range of angles of attack than a pointed edge. The sharp trailing edge allows clean flow separation from the wing. 3. Camber (curvature) of the wing helps you to force the air downwards, even at 0 angle of attack, creating the majority of your lift. Of course, symmetrical airfoils do exist. They just need positive angle of attack to function. Even cambered wings require angle of attack on 99% of all cases. (However, if you can produce enough lift to fly at 0 or even negative angles of attack, your wings are oversized for the job).
Air going faster over the top of the blade/ wing is fact, proven time and time again. Here is wintunnel footage that shows it th-cam.com/video/e0l31p6RIaY/w-d-xo.htmlsi=eOy2ziBk24RGux9H
I lo e your videos with your face talking and the simple photos and videos you have however please refrain from using the "meme" or "funny" short video clips in between. They're npt funny and generally ruin the flow of the video. A better form of humor would be an actual funny and clever one coming from you yourself rather thsn these short clips.
what you are saying is the airflow must be slowed, I'm guessing that is so combustion occurs before the air leaves, but I was referring to the turbine blade tip speeds.
Fun facts 1. The Wright Brothers' real innovation was realizing a propellor blade was a wing turning in a circle. They were the only ones getting full efficiency from the engine. 2. An early misconception was that multi bladed props would aerodynamically interfere with each other.
That's not entirely a misconception, because drag exists. In a world with no drag and spherical cows, where the aircraft is not accelerating, they wouldn't interfere.
It's not much of a thought stretch in the modern world to think that if you invert a ramp and drag it forwards by the tip fast enough it'll levitate. The simplest wing is literally just an upside-down ramp that's having forward thrust applied to it in such an angle that it ramps itself up in the airflow. The electric fan was invented just over 20 years before the first flight, so the basics of propellers were already known, at least. The biggest challenge was getting an engine with a sufficient power-to-weight ratio, as early engines were rather weak.
The Wright Brothers had other innovations too. They were the first to use a wind tunnel to test airfoil designs. They developed the first system to control their airplane in all 3 axes.
Ehm, not interfere? Okay, not many pilots do a tail slide. That means, flying up vertically, until the plane comes to a fool stop and.... starts falling down, tail first. At that moment of hanging still, you bet the prop blades get into each others wash. But again, this is aerobatics. And a dangerous one too, you can break the rudder. Do not try this at home. This is TH-cam, it's loaded with crash video's.
The worlds fastest propeller driven aircraft is the Tu-95 Bear strategic cruise missile carrier. It has two sets of four blades because it has 15,000hp engines to absorb the enormous thrust. The blades are long and thin. You mention drag and thrust with single engined aircraft, but what about twin engined aircraft like the Mosquito with two engines in pods on the wing with less drag than if they blew air over the fuselage?
Yeah a twin should have less propeller slipstream drag, but more free stream/total drag due to the fuselage + two nacelles hosting the engines, where the single has just the fuselage and nose combined that hosts the engine. Thus I don't think a twin has a much drag advantage, but I've not done the math to confirm this.
25 years ago, I did a lot of Test flying of Piper Lance's with Lycoming IO-540 300 horsepower. With all sorts of different speed mods. The 2 bladed propellers consistently had shorter Take off runs and higher top speeds. 3 bladed propellers were always smoother. I always get a laugh when I read or see Propeller companies selling 3 bladed propellers With all sorts of faults claims. Great video!
But the most important part is having "constant speed" propellers for high speed, so the blade angle always remains at the optimal angle regardless of airspeed, and enough torque (and thus power) to overcome the ever-increasing drag in addition to the trust-vector (the "lever-arm") of the blades shortening up fast as the blade angles moves past 50° angle. The fastest mass produced prop (sustained high speed) is the old Tu-95 "bear", nearly cruising at the same speed as your typical domestic jet. But it does infact have huge diameter propellers (nearly 6m / 20ft) and fairly skinny blades, but they are also contra-rotating in addition to being constant speed. Contra-rotating is also what gives it a bit of an "edge" as the main job of the rear-most propeller of the contra-rotating pair, is to recupe and straighten the induced swirl of the main propeller, and ad a bit more velocity to the core stream as to narrowing the cone of the slipstream, conserving even more of the imparted thrust.
I have long wondered how much extra drag is created by having the fuselage within the propeller slipstream... Almost like it would be better to have the propeller(s) mounted out on the wings... 😉
Propeller Effects on an Aircraft : th-cam.com/video/WnJxrHmtT_c/w-d-xo.html
The Only Video Needed to Understand Airplane Propellers : th-cam.com/video/hvboi6w1Z9A/w-d-xo.html
Does This Common Argument Disprove This Lift Creation Theory? : th-cam.com/video/kMdJMbggD90/w-d-xo.html
Now do court nozzles!
Most impressive. Thank you for the detailed presentation. I worked as an Aerospace Engineer for over 31 years and never have seen all these issues presented so concisely in one presentation.
I build and fly Quadcopters. This is a topic than none of the Drone related channels cover. So thank you most of my propeller questions are answered.
Fantastic explanation. Most people get three bladed props because "they look cool". I just put a new 2 blade prop on my TR182 because it is just flat out faster with the 2 blade prop. If you maintain the prop as well as you should, the 2 blade will be every bit as smooth as the 3 blade prop as well. Just an aside, in the old days, model airplanes used to use one bladed props with a counterweight as they were even more efficient.
There’s a few J3 cubs still out there with one bladed props too! Performs noticeably better than a two blade
You'd think the thrust imbalance would cause issues on a one-bladed prop... =/
If you buy a Cirrus SR-22, you can order a 4 bladed prop as an option (standard is 3 blades). It's a $22,000 option, but it looks great!
Phenomenal video, I've never seen anyone discuss propellers so well!
You actually explain this stuff so well!!!
Excellent explanation!
Years ago my father purchased an airboat from a NASA engineer. It had a 6 cylinder Corvair engine. My father and I were both engineers and my father was a WW II B25 bomber pilot. The airboat would do 40+ mph at 4000 rpm. We wondered if the boat had the correct prop. We looked up the engine specs, 140 hp at 4200 rpm and measured the prop diameter. We calculated the speed of sound at sea level, about 1100 ft/sec. We calculated the prop tip speed, just under the speed of sound. We concluded the NASA engineer had selected a good prop for the boat. It would require a major engine and prop change to get the boat to go 50 mph. The flat bottom John boat was not built for the job. After a few years, a weld cracked on the front of the boat from the pounding of the water.
Conclusion, the engine and prop were very noisy and care was needed leaving and returning to shore not to disturb others.
Silly Wabbit, Jon Boats are for Fishing not flying. But Mini air propped Jons make good canal boats.
@@bidenisasnake9932 Boats also have a hull speed and maximum engine power, which we had exceeded. They are also worthless in choppy water that rips the welds apart. Don’t overload with ice and beer and throw back the large hammerhead sharks. But they are a lot of fun flying on glass smooth water at 40+mph in 6” deep water that no other boat can go. To go where no man has gone before.
A video that clearly explains propellers, well done ! 😀
The Corsair and P47 originally had 3 bladed narrow blade props. It was said that going to the 4 bladed "paddle prop" was like adding 1,000 hp in a climb! One pilot in Britan said that his P47 was faster and would tangle well with spitfires untill they pulled up and climbed they always did this to him in mock dogfights until his plane got the 4 blade paddle prop and water injection, at which point he pulled up with them and passed them blowing their minds!
P-47 always had four blade props unlike the Corsair. But, later versions had more power and got paddle blade propellers increasing their performance in the climb.
@@vascoribeiro69 thank you for that comment.
Did you read Juggernaut, by Robert Johnson?
@@vascoribeiro69 I always wondered about the German propellers being smaller diameter and much larger chord that allied aircraft. (The propellers of the FW 190 and Me 264, for example)
@@331SVTCobra yes, they had a lower aspect ratio. I don't know the reasons or trade offs. I think they stuck with three blade propellers for some reason (productivity?) and, with increasing engine power, they just augmented the blade area. We can discuss blade drag, but they were very well designed, being elliptical, thus reducing induced drag.
Great video. Thank you. I owned a Comanche 250. I replaced the Hartzell 2 blade with a McCauley 3 blade. A friend replaced his original 2 blade Hartzel with a compact hub Hartzell 2 blade at considerably more expense. He claimed his would be faster than mine so I challenged him to a comparison. So at 4500 ft, we both fire walled the throttle and prop controls. I walked away from him by several knots. Haha, faster and several thousand dollars cheaper. As a side note, my takeoff roll was considerably shorter and the engine/prop combo much smoother but my power off glide suffered considerably due to the extra drag. All in all, the 3 blade was a great improvement.
Nicely done. Most people really don't understand propellers.
Thanks for this video getting out there. I can't remember how many times I've tried to explain things like this. I think people get something in their head and they just don't like someone bringing math and facts to replace it with new or better information. Often, I start off by stating that almost everything in this world is not 1:1 then try to correct them with nonlinear thought.
I like this video. VERY informative.
EXCELLENT presentation ! Thank you, sir !
Very well made
well explained
Easy way to remember 3 for show 2 for go!
Excellent video, new subscriber 👍
Great Presentation, glad you mentioned the F4U Corsair, would like to know how when the Corsair got a more powerful engine they went to a 4 bladed prop. Also I would like to know why the C46 Commando went from a 4 bladed prop to a 3 bladed prop. My Dad worked 4 bladed prop C46's in the Philippines but most pictures show C46's with 3 bladed props.
I love the fact that in WWII the planes got too powerful engines and they were not able to use all the power so the 3 and 4 bladed props were born. You lose efficiency gain speed.
When the tip of the rotating propeller reaches more than the speed of sound, it creates shockwave. The molecules of the air compacted in the shockwave. The adjacent propeller have not enough air molecule to grab to create thrust.
Thankyou!! So interesting!
I think a big factor in the choice of a long prop on the P-47 is the fact that it needed high efficiency at high altitude. Otto Koppen who designed the Helio Courier wanted a long as possible prop for the H-391B, it used a 101inch two blade propeller and GO-435 Lycoming. In the prototype Helio they used a 11 foot prop behind a 145 hp engine, three point landing and take off was required. One design factor not often talked about is twist, if you want efficiency, the correct amount of twist is required for the intended speed.
12:30 in theory, it sounds like you could get even lower scrubbing drag AND some nice bonus lift if you could find a way to stick 2 massive propellers at the wingtips. Obviously, structural concerns say otherwise for most cases...
There are some interesting bespoke air frames that have been modified for speed(what else!) that demonstrate all your points perfectly. I don't think cost was mentioned which is a major factor at the design stage for most aircraft, as with any other machinery. Great video.
I liked your video. A very Basic and simple theory of props. Your next video should be on a steped up props. Pull vs Push, prop wash, Hi speed props, F-1 racing props, Twin rotating props, Reverse rotating props and then less Do some Hi speed turboprops.
I think Corsair with its absurdly large propeller best shows the point why a large propeller can work togheter with high speeds.
Corsair was one of the best planes in WW2. Its combat ability was superior and enormous, but it had one major drawback and that was that it was difficult to landing such an aircraft. And the plane was despite its design as a naval plane and its great air combat performance kicked off the aircraft carriers and became a land based plane instead.
Super nice video! ☺️👍👍 Thank you 🐈🐾🐾
This is very information dense and requires further study! Thanks for the informative lecture.
There's a reason most (not all!) fans, be it ceiling, standing, computers, laptops... have an odd number of blades. I'm pretty sure that jitter on opposing blades can introduce resonance across the pair, and increase noise as a result. So there's an odd number so that you don't have opposing blades resonating and making noise if the balance isn't great. I would imagine on an aircraft, where you could pay more attention to the balance, it wouldn't matter too much, but it might still be a factor.
Nice video. Suprised you only have 10k subs. Thoughts you had like 100k before I looked
Brilliant. Thanks for sharing.
Short Propellers are used in Air Racing Appliacations where Rate of Climb and High Altitude Performance don't matter. In Air Racing with fixed Pitch Props you want to fly with a coarse Pitch Propeller that doesn't have a lot of RPM change through the Speed Range of the Aircraft.
For STOL though, it should also be appreciated that the prop stream accelerated flow is enhancing to high lift devices; slats and flaps.
Yeeees! Since the equation of drag is the same as lift, the faster propeller slipstream not only increases drag as a function of V^2, but also lift. In the context of the video however, that faster propeller slipstream of the smaller diameter, faster spinning propeller is more concentrated over the fuselage that creates very little lift, and misses most of the wings, flaps and slats. A slower spinning, larger diameter propellers slipstream is slower, but spread out over a wider area, and will go over a larger portion of the airplanes wings, flaps and slats. So there is no real increase in lift by going for a faster spinning, slower diameter prop. On STOL one would want the largest possible diameter prop spinning right up to the max tip speed of mach 0.8, even closer to 0.9, to make use of this increased lift from the propeller slipstream.
Very interesting video. Thank you !
1:05 the cat has awakened
Oddly fascinating - thank you
Another fantastic video about something I woner about all the time! The only question I have is what about short thick props? Can not this move larger volumes of air at lower RPM? (:
Thanks. It difficult to move a similar amount of air with smaller diameter props, even with thicker blades turning faster. There is much efficiency in length, if you consider that a roughly 40% increase in blade length doubles propeller area (when spinning).
Great information. Thank you.
Back in the 60s & 70s I was messing about with control line model aeroplanes. I have 2 glow-plug engines of the same make & capacity, but different performance characteristics. A standard Taipan 2.5 cc engine commonly used for stunt models and a 2.5 cc gold head racing engine with a 1/4 wave tuned rear exhaust tuned pipe, commonly used for speed & racing models. These engines had different performance characteristics. The 1st one was for larger slower thicker (high lift) wing aircraft designed to pull very tight maneuvers at lower speeds It would. The racing engine was for smaller slimmer winged aircraft designed to fly as fast as possible in level flight. The stunt engine would commonly carry a prop 8" dia x 4 " pitch and would rev to something like 18000 rpm, while the racing engine would carry a 7" dia x 6" pitch prop and would rev out to something approaching 30000 rpm.
Now, my memory of the rpm values is not exact. The figures stated are very approximate. However, the point is to indicate how performance parameters are so profoundly interrelated with each other. You can't change one aspect of a design without affecting other aspects and optimal prop choice dia, pitch, blade number & width etc. So you can't make generalized statements. Design choices influence each other & influence the out come, or you can put it this way, the desired performance outcome & considerations of practicality & economics influence the design choices in a complex & integrated way.
L = 1/2 . p . V^2 . S . Cl
D = 1/2 . p . V^2 . S . Cd
M = 1/2 . p . V^2 . S . MAC . CMo
But this simple synopsis hides a vast wealth of complexity.
Great video!
My grandfather was a crop duster and he flew an Ayer’s Thrush Commander with a 600 hp radial that had a 2-blade prop. Talk about loud. We would always hear him for miles.
Would a 3 bladed prop not actually make MORE (in stead of the same amount of) noise as a 2 bladed one (given everything else is the same)?
Good Work!
Any comment about things as Coanda Propulsors, Variable Pitch propellers, and Ducted Fans?
I would like to see some discussion of matching the propellor to the engine. Obviously a larger propellor would potentially provide more thrust but it would also demand more torque from the engine than a small one. Too large a propellor would slow down the rotational speed. Engines initially produce more power with increasing RPM ( revolutions per minute). But this increase is not completely linear. andit higher speed the torque output from the engine levels out and an unloaded engine will end up with some RPM at a top speed giving zero useful torque. More powerful engines like that in the p-47 had a reduction gearing that drove the propellor RPM at a fraction of the engine crankshaft PRM. Small aeroplanes commonly have a direct drive at crankshaft RPM. to save cost and complexity. They could obviously do well with a reduction gear that could permit a larger prop.
Also on the ground with zero airspeed ( and no wind) any engine/propellor set up would achieve a certain max RPM . Then in flight with some free stream speed the prop /engine combination will rev up a bit. The prop proportion and size must be selected to let the engine run at its maximum power. A reduction gear helps this
I have an e-prop 3 blade on my Zenith 701. Prior prop was a 3-blade scimitar- shaped ga prop by Luga. Eprop is superior.
What to make of counter rotating propellers like some late Spitfires and the Tupolev Bear bomber? Supposed to be very efficient but also very noisy. And then there is the CFM Rise "open rotor" engine being developed for jet liners with its variable rotating and static blades. Presumably it must be more efficient than standard turbo props, faster (and equally quiet or quieter), otherwise they wouldn't bother.
Engine shaft HP/torque is a big factor in what prop you can use, You need the torque to spin the prop to optimal RPM
Maybe I'm not thinking about this clearly, but it seems to me that a prop works by essentially making a circle (spinning 360 degrees), so I am wondering if the more blades you have on a prop, would make it more efficient? (if physical size, and weight were not a consideration). I would think that a 3 bladed prop (so each blade only having to move 120 degrees) would be more efficient and offer better performance than a 2 bladed prop (each blade having to mode 180 degrees) that is the same weight, and diameter. Am I not thinking about this clearly, or is there some logic to my though process?
On my electric-powered RC models, I want the diameter-to-pitch ratio (D:P) to be between 1.5:1 and 1.75:1. The highest I’ll use is 2:1. Longer blades take more energy to turn and that shortens the flight time.
Turning the prop FASTER takes more power. The longer prop can turn much slower for the same thrust. Thereby being more efficient.
That's why the video, and any aerodynamics textbook, will tell you a longer prop is more efficient. Because they can turn much slower for the same thrust.
@@senseisecurityschool9337 In the past week, I replaced a 12x4 prop (3:1 D:P ratio) with a 10x5 prop (2:1 D:P ratio). The airplane flies faster, the motor draws less current, the battery lasts longer, and the plane is more fun to fly. The 10x5 prop pushes a smaller column of air (less thrust), but it pushes that column of air faster (higher pitch speed). The airplane is faster, but doesn’t climb quite as well, which is fine with me. I don’t have fly at full throttle now to keep the plane from mushing around. I don’t care that it won’t go straight up out of sight.
@@txkflier
The area of a circle is Pi*rSQUARED.
the 10" prop is 25" * Pi, the 12" prop is 36" * Pi.
A 12" prop is 50% LARGER than a 10" prop. You put on a much SMALLER prop and found it's a better fit for the motor you have.
So what you just told us is that 12" is too large of a prop for the RPM / KV of your motor.
It would be more efficient to run a 12" 4.5 with a lower KV.
@@senseisecurityschool9337I didn’t want to change the motor or the battery pack I was using. Now go away..
How do you know that on an AT-6 Texan, that sound doesn't primarily come from the exhaust pipes?
That isn't how a radial engine exhaust tone sounds. They make a low-pitch rumbling/gargling sound, not a high pitch "screaming" noise like in the clip in the video. When the T6 is in cruise, and the propeller pitch is set coarser, i.e. slowing down the propeller speed and thus the tip speed, it doesn't make that sound anymore.
Now mix in Air Boats and/ Submerged. It'll Make your head spin, Clock wise or Counter clock wise I don't know..
This is for the consideration of aircraft designers only. Your existing airworthy aircraft's propeller is limited by the type certificate data sheet, so you DON'T get to experiment with propellers on an aircraft with a type cert.
You can experiment as you like as long as there is an STC for each prop you fit. Take a look the STC's for the Cessna 172 for example, you have 2 and 3 blade options, of various blade lengths. Depending on the engine and model of Cessna 172, you can fit certain Hartzell, McCauly, MT prop, Sensenich and possibly more. That's certified aircraft. On most experimental there are virtually no propeller legal restrictions.
@@LetsGoAviate
You are exactly right with an exception. If you place the aircraft in experimental for a short time while experimenting you can do whatever you wish. Then bring it back to normal with a certificated prop installed. But I bet you knew that too! I have done this many times with different engines and such doing research for mods.
Why would one use a shorter three bladed prop on an engine that can only provide adequate power for a longer two bladed one? Would a 2 bladed one not be more efficient?
A reason would seem to be too high RPM, but your example states 2600 RPM, That's (usually) not too high is it?
Hi, do you have any cast off aviation related items for sell please?
Ibrahim from Cameroon.
@8.16. If Thrust = Drag then why not leave the entire propulsion system in the hanger and fly a glider.
TLDR: it comes down to the formulae of kinetic energy (m*v^2) and impulse (m*v), and edge conditions (such as engine limitations and speed of sound)
Larger props are more efficient than smaller faster ones not because of propeller wake. They are overall more efficient in any case, that's why helicopters have huge propellers and why modern big propeller high-bypass jet engines are much more efficient than old low-bypass ones
Maybe you can help me! Why is it so taboo to manipulate the flaps just before landings. As a former Alaska 135 pilot. The first of two thing I was told to learn. Was to get comfortable pulling the flaps before you touched the runway. Cessna 207's and grand Caravan had the same kind of flaps. Wherever you moved the indicator, the flaps will move to match it.
You're not going all fall out of the sky because you're right in the middle of ground effect. Your stall speed is way low. I'm not trying to argue about this. This is what I did for four years. I just want to know why it's such a big deal.
At 3:44 the 3 bladed propeller would make more noise as there would be 3 sources of noise, but it would also be creating more trust,
More blades are always quieter. Two blades make a racket.
One thing I didn't hear is that a single bladed prop is most efficient as it runs in less disturbed air, as a two blade is more efficient than a three blade again because the blades run in less disturbed air or blade wake and so on. Could you comment on this issue.
Single blade is more efficient, but not because of less disturbed air. The propeller pushes the wake backwards, so by the time the 2nd or 3rd blade gets to that point, it hits new undisturbed air. So perhaps a myth that I will cover in the next one.
Blades has efficiency losses, noise, bending etc, so less blades is more efficient. But this is fairly minor compared to the fact that more blades have more power absorbtion potential. Someone said it's thrust that pushes the plane, not efficiency, and 1 blade has very limited power absorbtion or thrust, regardless of higher efficiency.
@@LetsGoAviate Hey its exactly what I said, the single blade runs in less disturbed air, or cleaner air. The plane moves forward, so it runs is less disturbed air.
Thus, two engine planes where the airstream only flows over the wing makes sense.
I would love for him to expand this conversation to climb rats, high altitude flight and turbo normalized engines.
slight under Cambridge has some benefits.
Yes 3 blades propellers (if all other parameters are the same) generate similar noise at similar RPM as 2 blades propellers, but to fly the plane we need a given amount of thrust, not RPM and 3 blades propellers give the same thrust at lower RPM therefore they *are* less noisy. If the engine isn't able to produce that thrust at lower RPM, that is an engine and/or transmission problem, not a propeller problem, therefore taking it into account when compering propellers to each other is unfair.
You missed the biggest factor why large propellers better for high speed. The plane goes foward by pushing air backward, it gets the same foward momentum as backward momentum the air gets (Newton's III.). The thing that is decided basically by the diameter of the propeller is whether we want to achieve that momentum by pushing less air with more speed, or more air with less speed. For easy understand lets say for e.g. 1 unit air with 2 unit speed or 2 unit air with 1 unit speed. Both will give the same forward momentum to the plane, but as kinetic energy is 1/2*m*v^2, in the first case the air get 1/2*1*2^2=2 unit energy while in the second case it will get 1/2*2*1^2=1 unit energy, so pushing more air with less speed gives less energy to the air while give the same amount of thrust to the airplane. All this energy is coming from the airplane's engine and if you want to go fast, its better to use your fuel to give energy to the plane, not to the air (it is true for all speed, but when the power is a limiting factor, its more crucial).
How a pusher configuration changes propeller slip stream drag?
Is that the source of some advantage for pushers?
If there is nothing behind the prop (no part of the fuselage) then there is no slipstream drag that the fuselage goes through. The disadvantage of pushers is when the air gets to the propeller it has already been disturbed by the fuselage, wings etc and that reduces prop efficiency.
The zero blade propeller is still the best. Glider gang!
one thing I must disagree with you on is the statement that you made. "The air on the front of the propeller travels faster than the air on the rear" But just as in a wing, the air on top moves at the same speed as the bottom, causing the air molecules on the top of the wing to stretch or thin out and meeting at the root, causing a lower pressure on the top, giving lift. The same principle goes for propellers. Except for one thing, the pitch adds thrust also.
The air going over the top of a positive lift creating wing or propeller blade does go faster that air going below. It's fact, not an opinion. Here's a wind tunnel video showing air over the top going faster
th-cam.com/video/e0l31p6RIaY/w-d-xo.htmlsi=Bw03vecloDjXmRVE
- NB, a higher cambered blade needn't be thicker - of course with combustion it is expedient to make blades substantial to offset vibration fatigue.. With electric propulsion is is simple to lighten the blades using a thin cambered blade.
NB - lower RPM prop doesn't mean slower slipstream - also not to forget the prop wash is spiraling - not straight, cheers.
- The pitch reduction quip - if anyone proposes that - means they don't understand thrust at all...
(Shorter blade, higher pitch, lower camber, more blades - absorbs more power - with faster airspeed setpoint, and results in a longer takeoff roll. (that balance with static thrust and critical angle of attack at low airspeed...)
Aart from aerobatic concerns - more blades are only useful once maximum geometric diameter is reached (for the installation size) and power remains to be absorbed - somewhere in the desired flight regimes.
All good points. However regarding the speed of a slower spinning propeller's slipstream, are you referring to the blade tips specifically? The mean speed if the slipstream will be slower, it has to be with the law of conservation of energy followed by newtons 3rd law. I'm making some assumptions here of course, one of which is that a spinning long prop and short prop have the same blade tip speed (thus the shorter one having a higher rpm) and all else being equal, they will move an almost identical amount of air per second past a point just aft of the propeller. If the larger diameter (slower spinning) prop then move more air as a result of it's bigger spin area, the slipstream must to be slower.
Civil Aircrafts: 2 or 3 is enough:
Normal Piston engined planes: 3-4 is good.
Griffon Spitfires: Five.
Kyushu J7W1 Shinden: SIX
Late Griffon Seafire: 6, but 3 of them rotates the other way!
Germans: 3. Take it or leave it.
He-117 and Ju-288C: 4! we have 2 engines for one propeller so we get an extra blade, yay!
Also some German plane: What's a propeller?
some British Plane: See, exactly what I'm asking....
Hmm...🤔 A couple of things come to mind regarding the significance of a propeller's slipstream [blowing back over the fuselage]:
1) - Taking a well-known example: the Gee Bee Racer, with its huge, prop-obscuring fuselage and slipstream-swallowing engine cowling. That flew satisfactorily (albeit with notable quirks).
2) - If prop-wash/slipstream is important in terms of drag, why don't more propeller-driven planes use a 'pusher' configuration?
I've built and flown several radio-controlled aircraft with these design points, and experimented with numerous combinations of engine, propeller, fuselage size, and so on.
Back in the '90s I built a series of planes which had a blunt-nosed cylindrical fuselage 10" in diameter. The engines were enclosed by a 10" diameter aluminium cowl and mounted on a solid firewall 3" behind the prop, which in iteration 1 was 2-bladed and had a diameter of 12"; in iteration 2 it was 3-bladed and 10" in diameter; and in version 3 the prop had 4 blades and was 8" across.
In version 3 there was no slipstream blowing back over the fuselage and wing roots. All three planes flew normally. I didn't think to take any sound-level [dB] measurements, though.
My slipstream experiments were neither scientific nor systematic. Those with pusher propellers were also just random planes of various types - high-wing, low-wing and delta. My only [unscientific] observation was that pusher props/engines seemed to make more noise than those in a tractor layout.
Flying characteristics weren't noticeably different, so just how important IS propeller slipstream where efficiency is concerned?
Are pusher-planes unpopular because of the basic problem of getting them off (and back onto) the ground without hitting the propeller?
Please note: I appreciate that there is a world of difference between a 1.5- or 2-metre span model and a full-sized aircraft (Reynolds numbers, etc), but even so, I'd be interested to know why such things don't seem to make any difference to a plane's flying abilities. (Not too technical, please; I'm not a mathematician or an engineer.)
In world war II the Germans developed the Dornier Pfeil fighter plane with both a puller and a pusher propeller. One drawback was that for the pilot conventional bailing out was impossible without being chewed up by the rear propeller, necessitating the use of an early ejection seat. The Convair B36 post war nuclear bomber had wing-mounted "pusher" propellers. Because the engines were mounted the wrong way round to normal it was prone to cooling and carburettor icing problems.
The propellers of pusher config planes don't get clean undisturbed air, the air having passed over the fuselage and wings before reaching the propeller, which reduces prop efficiency/thrust. So that is the "equalizer" and is one reason why pusher isn't necessarily better than tractor.
I dont know ...but the weight of 3 propeller= 12 propeller may be more fascinating and practical. As material king Carbon fibre have been around for a decade..
there is a mathematical formula that you can convert 2blade prop to 3blade prop
proper
Well, it's pretty simple , the more blade the more drag but the limit is the diameter
woooo i love this accent, where from?
So why did the F4U have 4 blades - wasn’t it the fastest prop fighter
It had 3 blades on early versions actually. As they made the engine more powerful on later versions, they could increase propeller power absorbtion by making the blade chord wider, or by adding another blade. Adding another blade was more efficient. As it already had the longest possible blades for the prop rpm, it couldn't be made any longer.
All the 3 blades i come across are noisy.
all the airplanes I come across are noisy
THE BOY DOESN'T HAVE TO HAVE THE EXACT SAME SHAPE OVER ITS ENTIRE LENGTH
DAVID ADAM GRENIS
More blades have more drag. So a single blade would be most efficient. But noisy. More blades are quiet and transmite more power. With limited power 2 blades are faster but with more power multi blades are faster
Single blade is more efficient, but has very limited power absorbtion. The blade can only be made a limited length before tip speeds become and issue. And if making the chord wider to add power absorbtion, it loses efficiency, and there would be a crossover point where it would be more efficient to add a second blade, than making the single blade chord wider. And same 2 vs 3 blade, 3 vs 4 blade etc.
Clear as mud. Sorry.
Surprised you didn't mention that one bladed props are the most efficient since you were diving into theory.
My FPV 5inch drones are faster with a 3 blade prop. 😅
I have to try and keep my speed down cause of my length, because cause it makes your mom... I mean the air to go supersonic and become too noisy...
The four propellers better
ขอบคุณมากครับกับสาระดีน่าติดตาม❤❤❤
What is that accent?😊
Afrikaans
@@hencojoubert1563 what a complex accent
I'm sorry but there is no such thing as the air goes faster over tge curve of the wing/ propeller, that's a myth that had been disproven. The air does not change speed, it changes in air density. Sorry to add another myth to your list of myths. Faster airspeed is old theory.
For discussion: The “faster” idea is supported by the observation that supersonic shock waves form on wing tops and other fuselage parts at airspeeds approaching but not equal to Mach 1. It was found that this phenomenon could be delayed by sweeping the wings back, enabling higher airspeed before encountering Mach 1 on the wing, vertical and horizontal stabilizers.
The equal transit time concept is thought because it is simple. The concept fails for inverted flight.
If it changes density, it changes speed. There are plenty of videos showing an airmail working.
It does change speed, but not even enough to account for half of all pressure differences. Curvature does matter, but only because it imparts downward momentum onto the airflow from leading edge to trailing edge.
The reason wings are shaped the way they are is because:
1. They must have thickness for structural strength. Or you can go with external bracing. Your choice.
2. A teardrop shape allows for streamlined enclosure of the wing's internal structure. The rounded leading edge allows flow attachment at a wider range of angles of attack than a pointed edge. The sharp trailing edge allows clean flow separation from the wing.
3. Camber (curvature) of the wing helps you to force the air downwards, even at 0 angle of attack, creating the majority of your lift. Of course, symmetrical airfoils do exist. They just need positive angle of attack to function. Even cambered wings require angle of attack on 99% of all cases. (However, if you can produce enough lift to fly at 0 or even negative angles of attack, your wings are oversized for the job).
Air going faster over the top of the blade/ wing is fact, proven time and time again. Here is wintunnel footage that shows it
th-cam.com/video/e0l31p6RIaY/w-d-xo.htmlsi=eOy2ziBk24RGux9H
I lo e your videos with your face talking and the simple photos and videos you have however please refrain from using the "meme" or "funny" short video clips in between. They're npt funny and generally ruin the flow of the video. A better form of humor would be an actual funny and clever one coming from you yourself rather thsn these short clips.
Why don't turbines have a sound speed limit?
The problems with noise & efficiency are less of a problem in a turbine because the shroud has control of the airflow
They have, the air getting in the compressor must be subsonic. That is why supersonic AC have variable intakes.
what you are saying is the airflow must be slowed, I'm guessing that is so combustion occurs before the air leaves, but I was referring to the turbine blade tip speeds.
@@Iowa599 yes they may go over Mach 1. But also with the increase in pressure and temperature the speed of sound goes higher.
Fun facts 1. The Wright Brothers' real innovation was realizing a propellor blade was a wing turning in a circle. They were the only ones getting full efficiency from the engine. 2. An early misconception was that multi bladed props would aerodynamically interfere with each other.
☝️
That's not entirely a misconception, because drag exists. In a world with no drag and spherical cows, where the aircraft is not accelerating, they wouldn't interfere.
It's not much of a thought stretch in the modern world to think that if you invert a ramp and drag it forwards by the tip fast enough it'll levitate. The simplest wing is literally just an upside-down ramp that's having forward thrust applied to it in such an angle that it ramps itself up in the airflow. The electric fan was invented just over 20 years before the first flight, so the basics of propellers were already known, at least. The biggest challenge was getting an engine with a sufficient power-to-weight ratio, as early engines were rather weak.
The Wright Brothers had other innovations too. They were the first to use a wind tunnel to test airfoil designs. They developed the first system to control their airplane in all 3 axes.
Ehm, not interfere? Okay, not many pilots do a tail slide. That means, flying up vertically, until the plane comes to a fool stop and.... starts falling down, tail first. At that moment of hanging still, you bet the prop blades get into each others wash.
But again, this is aerobatics. And a dangerous one too, you can break the rudder. Do not try this at home. This is TH-cam, it's loaded with crash video's.
The worlds fastest propeller driven aircraft is the Tu-95 Bear strategic cruise missile carrier. It has two sets of four blades because it has 15,000hp engines to absorb the enormous thrust. The blades are long and thin. You mention drag and thrust with single engined aircraft, but what about twin engined aircraft like the Mosquito with two engines in pods on the wing with less drag than if they blew air over the fuselage?
Yeah a twin should have less propeller slipstream drag, but more free stream/total drag due to the fuselage + two nacelles hosting the engines, where the single has just the fuselage and nose combined that hosts the engine. Thus I don't think a twin has a much drag advantage, but I've not done the math to confirm this.
The TU95 props were so loud, it rattled your teeth when flying close to it. I don't know how the aircrew managed.
@@bryankirk Lots and lots of vodka.
Its props are moving higher than speed of sound!
@@petrvalkoun4539No. This is a popular misconception.
Genius, well explained. So glad you didn’t mix it up on this tutorial with the additional engineering of variable pitch pitch props
or scimitar prop tips, or Q-tips
P-47 Thunderbolt should have been named Airbeast, because it was a monster.
25 years ago, I did a lot of Test flying of Piper Lance's with Lycoming IO-540 300 horsepower. With all sorts of different speed mods. The 2 bladed propellers consistently had shorter Take off runs and higher top speeds. 3 bladed propellers were always smoother. I always get a laugh when I read or see Propeller companies selling 3 bladed propellers With all sorts of faults claims. Great video!
But the most important part is having "constant speed" propellers for high speed, so the blade angle always remains at the optimal angle regardless of airspeed, and enough torque (and thus power) to overcome the ever-increasing drag in addition to the trust-vector (the "lever-arm") of the blades shortening up fast as the blade angles moves past 50° angle.
The fastest mass produced prop (sustained high speed) is the old Tu-95 "bear", nearly cruising at the same speed as your typical domestic jet. But it does infact have huge diameter propellers (nearly 6m / 20ft) and fairly skinny blades, but they are also contra-rotating in addition to being constant speed. Contra-rotating is also what gives it a bit of an "edge" as the main job of the rear-most propeller of the contra-rotating pair, is to recupe and straighten the induced swirl of the main propeller, and ad a bit more velocity to the core stream as to narrowing the cone of the slipstream, conserving even more of the imparted thrust.
What a terrific video. Reinforces that aero engineers are smart! Thanks.
I have long wondered how much extra drag is created by having the fuselage within the propeller slipstream... Almost like it would be better to have the propeller(s) mounted out on the wings... 😉
While I didn't believe in these myths, it was still immensely educational and easy to understand so I really appreciate it and will be subscribing.