Can a Airplane take off from a treadmill moving the same speed?
Debate Rounds (4)
I accept your challenge for debate.
As there were not many specifics given as to the conditions of the hypothetical, I assume that the only condition is that a treadmill has a speed equal to the plane such that when running, the plane does not move forward in space relative to the treadmill. No other restrictions as to the make or operation of the plane have been dictated beyond the assumed use of jet or propellor powered thrust and airfoil wings.
I look forward to this debate and wis my opponent good luck.
My main argument is that if the plane is stationary relative to the ground, and going, say 1200 mph relative to the treadmill, provided that there is little or no wind, then there will be no airflow over the wing, providing no lift.
I agree that your initial conditions did specify a jet, not a propeller based aircraft. On a side note, I like that your example is a Jet Blue jet for the New York Jets. Way to hammer home the point.
Bold text added for those skimming over this debate who don't want to read the whole thing.
When looking at airplanes, there are four main forces to look at for a basic perspective.
Thrust- From the jets themselves, pushing forward
Drag- From air resistance, pulling backward
Gravity- A function of the weight of the plane, pulling down, and
Lift- Pushing up from various forces.
What I need is to get more lift than gravity to achieve a takeoff.
Now luckily, this debate is hypothetical, and I don't need EVERY plane to take off from a treadmill, just any. There is no need to worry about practicality or realism for fuel or price economy. So I'll make my own plane, and stick a space rocket strength jet engine on it. As long as the jet propulsion is forward, and lift is still coming from the airfoil wing, it's still a jet plane.
Clearly I would have enough thrust to carry me upwards now, since a space rocket can do that, even without a wing, and once I'm in the air and no longer restricted by the treadmill, I can get enough speed to maintain flight from the wings. However, a plane starts its takeoff from paralell to the ground, and since the thrust only goes forward, I wont get off the ground. So from here my problem is to generate enough lift from the wing to get me up just high enough to change the plane's angle to the ground. If I do that, the rocket strength jets will do the rest.
One way to get lift is from drag. Since the wings can adjust themselves to some extent, all that needs to be done is to adjust the wings so that incoming air hits the wing at an angle, and the drag will put an upward force on the plane. A strong enough current of incoming air will give enough of that force to raise or tip the plane, achieving my goal. My opponent argues that since the plane isn't moving forward in space, it isn't moving into the air fast enough to generate that force.
Then whether the plane is moving forward and hitting stagnant air or the plane is still and wind is hitting the plane, from the rest frame of the plane, that is to say, from the perspective of someone sitting in the plane for whom the plane doesn't move with respect to them, either way the apparent velocity of the air is the same. So for the purposes of generating lift, moving forward or remaining still in the face of wind both produce the same effect. This can be seen in the case of a kite, which remains tethered in place, yet still produces lift from the drag of incoming air. I could simply say then, that yes, an airplane CAN take off from a treadmill moving the same speed, IF that airplane was in a typhoon. Since the treadmill is keeping the plane in place, it is effectively a tether for the plane in the face of wind, so it should be lifted by the same principles as a kite. Problem solved, position maintaned.
But for the sake of being thorough, let's say that there wasn't a typhoon. This isn't necessary, since the debate conditions allow for wind, but let's see what would happen.
The treadmill is moving at an equal speed to that which the plane would be going. We are assuming this experiment doesn't take place in a vaccum, because a plane can't fly in a vaccum anyway. Therefore, we have particles of air just above the treadmill's surface. As the treadmill runs, it would encounter a minor degree of friction from the air, as particles of gas drifting around would bump into the treadmill. When this happens, the surface of the treadmill would impart some of its momentum onto the air particles, pulling it in the direction the treadmill is moving. The motor of the treadmill would push the momentum of the treadmill back up to keep it even in speed with the plane, so the motor in effect is pumping energy into this system through the treadmill to the air.
Now if I am understanding Bernoulli's Principle correctly, and for the record I'm not a fluid dynamics engineer, so thats a big if, then the air moving due to the friction will have a reduced pressure with respect to the rest of the air above it. The high pressure air will be drawn into the lower pressure space, and subsequently be knocked forward by the fast moving air particles, gaining momentum in the direction of the treadmill's motion.
As the wind generated from the friction moves forward, it will want to expand because of its increased kinetic energy, but since it cannot move down because the ground is obstructing it, it will move upwards. Hence, there will be a flow of air moving in the opposite direction of the plane and slightly upward due to the treadmills speed. If we increase the speed of the treadmill, more wind will get blown into the plane. Luckily, as I mentioned, I can make whatever kind of plane I want, and the treadmill has to match its speed. So let's put some ridiculously powerful jets on my imaginary plane. The result is ridiculously powerful resulting wind from the treadmill into the plane, which creates drag, tips my plane upwards, and allows for takeoff. Problem once again solved.
NASA SON. WHAT NOW.
Also, do you concede that not all aircraft can lift off in these circumstances?
I concede that if the treadmill is going fast enough, then it will produce a air current.
Also, I would like to keep this jet plane in reasonable boundaries. If I was on your side, I could claim that my plane powered by rainbow-pooping nyan cats propel this plane at billions of mph, obviously providing enough lift.
The fastest air breathing official jet plane is the SR-71 Blackbird, which can travel up to ,530 km/h (2,193 mph). Although I suspect that this is in the air, and not on the runway, I will give this to you to try and prove that this speed is sufficient enough to create enough lift to lift the nose of the SR-71 Blackbird, thus taking off.
I have no idea on how to do those types of calculations, but I think you would have to do them to prove your point.
Thank you for your prudent response.
I agree, we are talking about jet planes. What I had said in my argument was a "rocket strength" jet on my hypothetical plane. I realize this was perhaps misleading, but to clarify, I intended on saying a jet plane with a more powerful engine, using a comparison to a rocket simply as reference. I did not literally mean to strap a rocket to my plane, and did not even necessarily mean exactly the strength of a rocket, only that it would be significantly more powerful that industrial standard plane jets.
I do concede that not all aircraft can take off from your treadmill scenario. However, all I need to prove is that AN airplane CAN take off a treadmill moving the same speed. It shouldn't matter if EVERY case works, I need only one example to say that yes, that is true.
Since I already noted a case where that could happen, namely when appropriate wind conditions are provided from the environment(a condition which was never precluded from discussion in the original proposal), I shouldn't need to go any further. However, you go on to say that I can't use my hypothetical plane at all, which I take issue with. You are limiting me to your SR-71, which may be the fastest plane currently available, but it is not the fastest plane that mankind can build. I am not proposing that magic poptart cats are pooping out of a plane. However, if you doubt me, I will try to provide evidence for my claim that a faster jet could be built.
A jet plane gets its speed from thrust from the jet, and the thrust comes from the force that the jet can output. We can see from this webpage that 1. Maximum speed is dependent on thrust vs momentum drag, so increasing the power of my jet will increase my max speed, and 2. the thrust itself is based on the difference between airspeed and jet speed and the difference between air pressure and jet pressure, along with a few other values that are invariant for a given jet. Since the pressure in the jet dictates how much force the air is shot out at and therefore the jet speed, we can comfortably say that the pressure inside the jet engine vs outside is the major factor for jet strength, being roughly proportional to output. By the ideal gas law, PV = nRT, where P is pressure and T is temperature, we should also be able to say that Temperature is proportional to jet strength.
Now traditional jet fuel burns at temperatures up to 2000 degrees Celsius. However, we can make a lot more heat than that. The highest temperature that mankind can generate and sustain is probably that of extremely hot plasma used in magnetic confinement experiments. Scientists use magnetic fields to suspend plasma in space and inductive heating to bring it up to temperatures rivaling that of some stars. The ITER experiment I just referenced can get 150 million degrees Celsius without melting its container thanks to magnetic confinement. Thats a factor of 7500, so using this technology, despite its expense, a jet engine could be developed that is 7500 X stronger than current jets.
Now air resistance is proportional to the square of velocity, so a plane won't go 7500 X as fast, I admit, however, the square root of 7500 is still over 85 X the speed. That means I should still be able to go 186405 mph if I match the Blackbird's design. Even if I allow for some loss for needing to ruggedize my plane I would think I could still consider 150000 mph possible, which is ridiculously fast, that's over Mach 200.
The treadmill would then have to reach mach 200 as well. With that insane velocity, it would have an incredibly high momentum, M*V, and upon collision with an air particle, that means a large amount will transfer to the air(Collisions distribute momentum based on mass so it should get the same percentage of that momentum from the treadmill regardless of if you are going 50000 mph or 2 mph).
Now I don't know the exact calculations needed to prove this would be enough, but I did find this. The well known powerhouse of commercial jets, the Boeing 747, has a maximum crosswind takeoff of 35 knots, which turns out to be about 40 miles per hour. Past that, it isn't safe for a plane to try to take off. That would mean, I expect, that at 40 mile an hour winds you get significant enough force to jostle even a massive jet like the 747. And recall from my last round that a jostle is really all I need. Just the slightest lift would give me the upward component on my thrust I need to get my jet off the ground and no longer restricted by the treadmill. So if my speed is increasing by an estimated 85 X and the distribution of momentum should be consistent regardless of speed, then the resultant wind from a Blackbird going on the treadmill needs only be .47 mph(40/85) for a magnetic confinement jet to get the necessary 40 mile an hour winds to achieve takeoff. 1 mile in 2 hours is very slow, and would be completely reasonable to assume that a treadmill running with a linear velocity of 2000+ mph would generate. Therefore, I believe we can assume that a jet can takeoff under the conditions I've outlined.
Since you've refused to accept my last argument before, I will provide 1 more just in case, even though I've already given 2 that I believe are adequate and that you have not as of yet refuted. Even if a treadmill is moving at the same speed as the airplane on top of it, that should not necessarily stop the plane from moving forward. This WOULD be the case if a car were being considered, as a car moves by driving its wheels, which create force through friction with the ground. Thus it's forward motion is directly relative to the ground, and if a car was driving at 60 mph, it would be moving that fast with respect to the ground.
An airplane, on the other hand, does not drive itself through its wheels. The wheels exist only to allow the plane to move forward at all. Instead the force which creates motion comes from the jet thrust on the outside air. So if a plane is trying to move at a speed of 60 mph, it would do so with respect to the AIR around it, not the ground below it. So the plane would move forward even on a treadmill moving backwards. Consequently, this means that the wheels of the airplane need to spin twice as fast, as fast as they would need to to carry the plane 120 mph on steady ground. Because the plane isn't deriving its motion FROM the wheels though, this is irrelevant. The wheels speed is a result of the plane's speed, not the other way around. There would be some friction, which would slow the plane to a degree, but it would not keep it in place. Therefore any plane, even a standard model like the SR-71 Blackbird, should be able to move forward on such a treadmill, and therefore achieve lift from drag and take off normally.
I have submitted to you now 3 potential arguments, 1. Liftoff during intense wind 2. Liftoff due to increased speed 3. Liftoff by standard means. I leave it to you to provde your counterarguments and whatever additional arguments you wish.
Sources for last Round that I forgot:
1 votes has been placed for this debate.
Vote Placed by Geogeer 2 years ago
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Reasons for voting decision: Con conceded the debate, however pro won not with the "superplanes" or even the takeoff due to head wind. He wins for recognizing that the thrust of the plane comes from velocity relative to the air. Thus the low friction delivered by the wheels should enable the plane to take off.
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