Rocket Propulsion Basics
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- เผยแพร่เมื่อ 25 พ.ค. 2024
- This video provides some basic insights on how rocket motors work. The video addresses subjects such as combustion, internal pressure, rocket nozzle theory, and thrust curves. It also includes a test of a model rocket igniter and a static firing of a C6-5 model rocket motor. This video is intended for high school students (or higher) with a basic background in physics.
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you don't deserve 1.64k
you deserve 1.64 million
@J D Why do you care
This is the best basic explanation of how a rocket motor works that I have seen on youtube.
This is the issue I have with TH-cam’s algorithm. This video is great and should have WAY more exposure.
Only 8 views? Excellent presentation
There has been some discussion about internal pressure imbalances and how they produce thrust. Here are a couple of quotes that support the content in this video. "Thrust is the force that propels the rocket forward... Physically speaking it is the result of the pressure which is exerted on the wall of the combustion chamber ." (Rocket and Space Technology Training Couse). "The size of the arrows indicates the relative magnitude of the pressure forces. The axial thrust can be determined by integrating all of the pressures acting on the areas that can be projected on the plane normal to the nozzle axis. The radially outward acting forces are appreciable but do not contribute to the axial thrust, because the rocket is axially symmetrical." (Rocket Propulsion Elements - An Introduction to the Engineering of Rockets - George Sutton).
@TR-Labs What? I am sorry, but you do not know what you are talking about. No it will not. Notice you have no time component mentioned. Acceleration is a function of force applied for an amount of time. If the area of pressure imbalance multiplies out to a force that is greater than the weight and air resistance, then the Rocket accelerates.... that is it.
In ideal rocket (that somehow never changes mass through burning fuel) let's say that it weighs 1,000,000 kg, so it obviously needs at least enough force to overcome its own weight.
Let's say we want it to accelerate at 50 m/s^2. This means that with the acceleration of the rocket's gravity(weight) being overcome and then an extra 50 m/s^2 that we need a total force of 59,800,000 Newtons. That is 13,443,574 lbs. A mid-high performance rocket engine should have about 2000 psi in the engine. That would make the nozzle throat need to be about 7ft 8in in diameter.
If you do this math that takes an extremely long distance, but in reality, the Rocket is losing mass as it is combusting the fuel for acceleration. Something like more than 85% of a rocket's mass is fuel if that gives you some perspective. Completely ignoring that we still get a 1,000,000 kg rocket only needing a nozzle throat less than 8ft wide producing 2000psi inside the combustion chamber. Numbers outside of that are completely possible too as it is merely a function of total time there is thrust. 2000psi with a certain nozzle throat and burn time takes a certain amount of time to accelerate to 17,000mph and then many other combinations of throat size/time could be calculated.
There is nothing close to 8,000,000psi ever needed for the rockets we see today. My lord nothing even close.
I fell in love with your style of teaching
this is like the best video i've ever seen
Amazing video! Thank you sir!!!
Excellent breakdown with right amount of details!
You deserve many more subscribers and viewers! Your videos are awesome and well produced. Thank you!
Respect from India...
Bro just saved my aerospace EOC grade. Thank you. 🙏
8:54 Thrust Curve!
Concept well explained!
Thank you for these videos!❤
amazing content
Excellent!
Great video,thank you
Thank you!
Very easy to understand
Beautiful!
Great video, I've been searching for an answer to a question about where thrust acts on a rocket. You've gotten me much closer to the answer. My question is, how are all of those forces transferred to the rest of the rocket? If a rocket can produce millions of lbs of thrust, why doesn't the nozzle crumple and crush under all of that force? Nozzles look like an extremely delicate component that's extremely thin walled. Even if a nozzle is being cooled, its still operating at extremely high temperatures enough to make the nozzle glow white hot. I can take a hammer and deform red hot metal. Why do the forces not immediately destroy the rocket? Are those forces acting all the way back through tons of delicate components the combustion plate, pumps, turbines all the way to the back of the extremely thin walled pressure chambers? Why don't those components break under millions of lbs of thrust??
For a liquid engine, the thrust loads are transferred to the rocket body via struts. The struts must be very strong and thus the proper metal and design must be used. The problem is complicated when the nozzle must be gimbaled to provide guidance. It all comes down to engineering... Most of the forces are in compression which helps out a lot. As for the heat, again its good engineering and proper material selection. Some nozzles are cooled by flowing cold fuel through small channels in the nozzle skin (regenerative cooling). Some nozzles use ablative which chars and flakes off during the burn (like a space capsule heat shield). Some engines us radiative cooling and materials like Niobium Alloy, which are very strong and can handle a lot of heat. As for the forces, it comes down to engineering once again. In some nozzles you may notice "hoops" which provide circumferential strength which supports the nozzle skin.
Ah ha! This was a great video! I now understand why the nozzle is used. Seeing the pressure being split up into its components at the nozzle makes sense, it is so that you can get some more forward-facing pressure for better thrust? If there was no nozzle, all the gas would escape perpendicular?
man you deserve so much more than this
Hi. I am looking for a calculation which I can use to determine the size of the combustion chamber. I am using Methalox as a fuel for the rocket.
I love "Rocket" science 😍 ❤️
Thanks master
thanks!
So it’s not the expulsion of mass exiting the nozzle (action-reaction) as much as it is the pressure acting on the front of the motor?
In the divergent section of the nozzle, the pressure continues to decrease in comparison to the throat, and because the flow is supersonic, the velocity increases. If the flow remained subsonic, the increase in cross-sectional area would lead to a decrease in velocity according to the Bernoulli principle.
When you say that the thrust is calculated either from the pressure thrust or the momentum thrust, I’m not that sure… I read in ‘Rocket Propulsion Element 9th Edition’ from Georges P. Sutton that the overall thrust will be F = dm/dt * v(ejection) + Dp * Area where Dp is the pressure difference between the atmospheric pressure and the pressure at nozzle exit. So I’d like someone to explain me what’s the real thrust or what I’ve understood wrong.
I think the point IS
You can calculate the thrust on a rocket by:
integrating the pressure on the inside of the nozzle over all of the surfaces.
OR
Calculating the mass flow out the back and determine the momentum, then using the Law of Conservation of Momentum.
Both methods give the same answer.
@@stuartgray5877 Yeah that’s true. Thanks for the precision!
Great video! Your video is only the second one I've seen on You Tube that gives the correct explanation of the generation of thrust in a rocket motor. Most of the other videos state that trust comes from Newton's third law of motion whereby the ACTION of the gas exiting the rocket CAUSES a REACTION force to be generated. But there is no notion of cause and effect in the third law. If two bodies are exerting forces on each other, the third law merely says that the forces are equal and opposite, but nothing about one force causing the other. Other videos use the law of conservation of momentum. Here again there is no notion of cause and effect in the law. The law is merely a bookkeeping of the total momentum of a system and is valid only if the Sum of the external forces acting on the system is Zero. At launch, the rocket is subject to external forces, namely gravity and aerodynamic forces. So, conservation of momentum isn't applicable until the rocket is out of the atmosphere and moving perpendicular to the earth's gravity.
- "But there is no notion of cause and effect in the third law"
That is false.
Apparently, you don't properly understand the three laws.
When one mass applies a force to another mass - BOTH masses must feel the force.
Imagine a test case where a person is trying to push a refrigerator across an ice rink.
Place a scale between the person and allow them to start pushing on the refrigerator.
Now you are an observer ON THE Refrigerator, and you can see the readout of the "force-scale".
The person begins pushing on the fridge attempting to accelerate it.
Now as the person begins PUSHING, he can see the scale and it reads 20 Newtons.
What does the person on the refrigerator read on the scale?
20 Newtons.
So, from the perspective of the person on the fridge: Is the person applying the force, or is the fridge applying the force?
BOTH are applying the same force on each other.
The scale does not ONLY read when the force pushes in one direction.
All forces occur IN PAIRS. It is impossible to have a single-ended force.
If the fridge did not PUSH BACK, then the fridge would accelerate away effortlessly, and the scale would never read any force.
But the fridge PUSHES BACK because it has INERTIA which is the resistance to being accelerated.
What is the ejection charge for? Also, your solid rocket motor only burned for 1.3 seconds. Does that mean it is its Isp?
The ejection charge blows the parachute (or streamer) out of the rocket. There is a smoke delay between burnout and ejection charge firing. The TOTAL IMPULSE is the area under the thrust curve and has the units of Pound*Sec (or Newton*Sec). The Specific Impulse (ISP) is the Total Impulse divided by the weight of the fuel.
@@labratscientific1127 thank you
8:11 - What would happen if the divergent module section was removed?
The gas flow will expand much too quickly and the engine will be inefficient. Also, there is a forward component of the pressure force acting inside the divergent section of the nozzle which contributes to the forward thrust. This element of the thrust will be eliminated if the divergent section is removed.
So according to that an F1 engine bell and injector plate sustain 750 TONS of force. Hard to believe all those welded together tubes could take that much force.
The Saturn V (or any object) will only accelerate (speed up or slow down) if an external force is applied to it (F=ma or a=F/m). To get the Saturn V to lift off, the thrust must be greater than its weight. The only things producing forces are the F1 rocket engines (neglecting drag at this point). This means a force is being transferred from the engine to the rocket structure. The only way a force can be generated in a rocket engine is gas pressure. This pressure has to react on a surface (F = (lb/in2) * in2 = lb) to create a force. Momentum of the exhaust gas is a means to calculate force and conservation of momentum can be used to estimate the speed of the rocket, but again, it is actually the pressure forces in the engines that push the rocket... It is hard to believe, but the engines are designed to carry the resulting loads.
@@labratscientific1127 So essentially, a rocket DOES push against something. It pushes against the mass/inertia of it's own exhaust gasses.
@@billshiff2060 Yes "Rocket Thrust" is just RECOIL from pushing on MASS.
@@labratscientific1127 So what's applying the external force?
@@papalegba6796 SO from WHERE does the force originate that accelerates the mass of the exhaust gas into the vacuum?
The pressure INSIDE THE NOZZLE.
The rocket NOZZLE applies a force to the mass of the exhaust gas accelerating it into the vacuum.
THAT is the answer you are scared to admit.
Because THEN (per Newtons THIRD LAW) you would HAVE TO ADMIT that there IS an "equal and opposite" force PUSHING BACK ON THE ROCKET.
Now be sure to hurl some juvenile insults instead of addressing my FACTS.
Ok so 500 milliamperes and under 9 volts. Why does a brand new fully charged standard alkaline battery direct to an igniter not light?
ok I am confident of building a rocket now.. anyone there wants to fund my attempt!
64 YEARS IN DEFENSE AND
COUNTING ! IN JESUS NAME . AMEN .
I am the 69th like
Nice
And how is it in a jet engine? The jet engines of fighter jets? Because they all say : “the jet engine ejects gases , hence Newton’s third law” but the jet engine doesn’t actively “push gases away”
A jet engine does eject high velocity gas out the back end. The compressor blades at the front of the engine feed high pressure air into the combustion chamber(s) where it is burned. The expanding gas increases the internal pressure causing the gas to flow out the back of the engine. The pressures acting inside the engine cause the action/reaction forces that push the aircraft forward and the exhaust gas backwards. There is a Mithbusters episode where they blow a bus over using the exhaust of a jet engine. This is evidence that gas is pushed out the back of the engine.
@@labratscientific1127Great explanation and great video, just subbed, thanks.
pressure is a scalar. so your sllly diagram is BS.
Yes, pressure is scalar... But I think you may have misinterpreted my "silly diagram" - which I assume is the one showing the arrows inside the motor. As stated in the video, I was talking about the "forces" inside the motor. The forces that are created by the pressure (lb/in2) acting on a surface (in2). Pressure x Area = Force... The forces act perpendicular to the surfaces thus do have a direction of action. And the frame of reference that I was using allows you to break the forces into x and y components - which was my assessment inside the motor's exit cone. Think of this - If I have a PVC pipe capped at one end and covered with a rubber membrane on the other, as pressure is added inside the pipe, the membrane is pushed outward. The only way the membrane can move is if there is a force acting on it (Newton's Laws). Since the membrane if moving along the axis of the pipe it indicates a force acting along the axes of the PVC pipe. That's one direction. If I make a big hole in the side of the pipe, cover it with a rubber membrane, then pressurize the pipe the membrane will push out towards the side. This indicates a pressure force pushing radially on the inside of the pipe (another direction). I believe this supports my "silly diagram"... But you are right - pressure is scalar... You can also go to any propulsion text book and see the same kind of explanation.
@@labratscientific1127 your silly diagram only showed pressure at one end of the combustion chamber. which means you are claiming pressure is not a scalar. also i'm pretty sure N1 refers to external force, but your silly diagram shows internal force. so it won''t be much use moving anything, will it?
@@papalegba6759 As I work through the diagram in the video I'm eliminating forces that are offset by equal and opposite forces. The "upward" forces on the casing wall are offset by the "downward" forces on the opposite side of the casing. So I eliminate them. Since they are all equal and opposite there is no net force causing the motor to move sideways. The same happens at the forward and aft ends. In the video you see me eliminate some of the left and right forces acting on the front and back of the motor. At the nozzle there is so surface for the pressure to push on so there is no pressure force. Lb/In2 x 0 in2 = 0 lb... So there is no force pushing to the right to offset the force pushing on the front of the motor to the left. As such, there is a net force towards the left. Again, I'm talking about the pressure force, not the pressure... As for Newton's Law, the force pushing on the front of the motor casing is an "external" force relative to the surface. So it will push the front of the motor towards the left. And since the front of the motor is attached to the rest of the motor and the rocket as well, everything will move. I have made these pressure calculations on an actual rocket motor and they produce accurate results...
@@labratscientific1127 so the combustion in an INTERNAL combustion engine counts as an EXTERNAL force? um - no. plus you're still treating pressure as non-scalar, whilst stating it is a scalar. that's quite enough of your topsy-turvy nonsense, muting you now.
@@labratscientific1127 Don't bother with Papa Legba. He literally thinks that RECOIL stops working in a vacuum.
He has even stated that C4 would NOT EXPLODE IN A VACUUM if that is any indication of how utterly stupid he is.
You CANNOT convince him to research the Law of Conservation of Momentum because he DOESNT think it applies to the MASS of the exhaust gas!
Watch THIS:
Papa Legba, Please answer the following BASIC PHYSICS QUESTIONS:
1 - When the exhaust gas leaves the rocket nozzle DOES IT GET ACCELERATED (does it CHANGE MOMENTUM)?
Yes or No?
2 - Does the Exhaust gas HAVE MASS?
Yes or No?
3 - Can MASS be accelerated WITHOUT A FORCE?
yes or NO?
now watch as he REFUSES to answer and just hurls juvenile insults instead.
this is because he KNOWS THAT ANSWERING TURHTFULLY - *PROVES HIM TO BE WRONG* .
maybe YOU should answer my questions to show him the correct answers?