Airplane Question that Drove Me NUTS!!! - Electroboom

[mfro]

However, if the conveyor belt can match the plane's speed, including engine thrust, then it's still not going to go anywhere, and no takeoff. The key difference being whether we are talking about the conveyor belt matching the planes wheels (and not taking engine thrust into account) or the conveyor belt matching the plane's speed, including engine thrust.

Umm, no. It's not about speed, it's about forces.

Forward forces accellerate, backward forces drag. Forward force = thrust, backward force = friction between belt and wheels and in the wheels themselves. Rolling friction forces are a lot less (nearly neglectable) in relation to thrust force (otherwise the plane wouldn't need brakes when landing).

[Darklord]

But nothing will happen without the Bernoulli effect. No flow over the wings, or insufficient flow, and no
matter how long the conveyor belt is, it's not going to take off.

[exxos]

Seems there is a whole site dedicated to this http://www.airplaneonatreadmill.com/. Too tired to read it right now.

I first was thinking the plane would not move but the engines are still be producing thrust and with every action has an equal and opposite reaction.. the engines are on the plane, so it would have to still move forward if the engines are pushing backwards. Wheels or conveyor belt is totally irrelevant.

The only thing which happens is the wheels would end up moving twice as fast as normal. Problem being the friction of the wheels would likely get too hot. Explode the tires and the super hot fragments hit the wing puncturing it and igniting the fuel causing the plane to explode. In which case, the answer is no, the plane will not take off :lol: :fire: :fire: :fire:

I asked ChatGPT :lol:

. Yes, an airplane can take off if it is on a treadmill that moves in the opposite direction to the wheels. This is because an airplane's propulsion system does not rely on the motion of its wheels to generate forward thrust. Instead, an airplane generates lift by using its wings to create a pressure differential between the upper and lower surfaces of the wing.

When an airplane is taking off, the thrust generated by its engines pushes it forward, causing air to flow over the wings, generating lift. The wheels of the airplane only serve to support the weight of the aircraft while it is on the ground and help it roll along the runway. Therefore, the motion of the treadmill will not affect the airplane's ability to generate lift and take off.

However, it is worth noting that the speed of the airplane relative to the air is what matters for takeoff, not its speed relative to the ground. So, even if the treadmill were moving at the same speed as the airplane in the opposite direction, the airplane could still take off as long as it is generating enough thrust to reach the necessary airspeed.

So I will go against the masses as usual and say yes the plane would still take off. :lol: :hide:

Unless you go with my mechanical failure hypothesis, in which case the answer is then no. The plane does not take off :lol:

[Darklord]

Just curious...

If said plane was actually setting on the runway, brakes locked full on and no movement allowed.

Engines engaged, taken up to FULL thrust. (assumption that this won't shake the plane to pieces
or cause damage).

No movement, brakes are still locked, strong enough to hold against full thrust. It won't take off, correct?

Then release the brakes all at once. Does the plane instantly leap into the sky...or does it still
require movement down the runway to gain enough forward motion to give sufficient lift for
the plane to take off?

Thanks.

[exxos]

Then release the brakes all at once. Does the plane instantly leap into the sky...or does it still
require movement down the runway to gain enough forward motion to give sufficient lift for
the plane to take off?

The plane needs the runway to build up speed in order to take off.

The action and reaction forces would be counteracted by the brakes. The action reaction would then be between the engines and wheels, which would be locked to the runway. The plane would not move assuming no mechanical failure and the wheels could provide enough friction to stop movement. But it's unlikely. It's why planes have thrust reversers to slow down on landing.

You need thurst and forward movement of sufficient speed to take off.

[Darklord]

I think so too. So if the conveyor belt was fast enough to keep up with the airplane's
speed with thrust on from the engines, how is it moving forward? No movement
forward, no lift, no taking off... Or so it seems to me.

I may just bail out of this thread - it's starting to make my head hurt. :lol:

[exxos]

It's the wheels I think which threw me. Because there is essentially a disconnect between the runway or belt and the plane itself because of the wheel bearings.

Look at it another way, if the runway is made out of magnets and the underside of the plane is also made out of magnets and arranged in such a way that the plane is floating above the runway on the magnetic field, now if the runway is stationary, or a conveyor belt which is moving forwards or backwards,it would be irrelevant because there is a disconnect between the runway and the plane itself.

There is no difference between the magnets or a wheel bearing other than the bearing will have a frictional resistance which would still be negligible for any significant effect.

So just "remove" the wheels from the equation altogether. Because regardless of what the plane or the runway is doing, they cannot affect each other because they are separated by a bearing. In this case the plane for all intents and purposes is just hovering above the runway. At this point you can remove the belt altogether as well. Once you basically remove the "BS" from it all, the only thing you are left with is the plane "sat" on the runway and when the engines fire, the plane will gain speed and takeoff as it would do normally anyway. Of course if you reintroduce the wheels and the belt the outcome is still exactly the same.

[Darklord]

I guess it's just me then, 'cause I can't wrap my head around this.

I keep thinking about a person on a treadmill (ala conveyor belt).

No matter how fast that person runs, IF the treadmill/conveyor belt
keeps up with them, they are *not* going to move forward.

Now strap wings on to that running person. They still won't fly,
no matter how fast they run, because they are not moving forward
and thus no movement = no lift = no flight.

Remember when I said I was going to drop out because this is making
my head hurt? Got a migraine now... :lol: :lol: :lol:

[tzok]

You don't get it... it is simple. You have fixed on the wheels, while they are completely irrelevant. Plane wheels roll free on the ground. The airplane is not powered by its wheels, it doesn't care about the ground speed, but only airspeed. Engine trust moves it forward, the conveyor belt moving backward would just add a little more wheel drag (braking force), but completely irrelevant. Engines push against air, not against the ground. So the plane would progress forward on the conveyor belt reaching the regular starting (air) speed, only its wheels would turn twice as fast as they normally would.

[exxos]

No matter how fast that person runs, IF the treadmill/conveyor belt
keeps up with them, they are *not* going to move forward.

Because that is a " direct drive of the wheels" like a car. So a person on a treadmill would be correct as you describe.

However this is not the same for a plane....

Now strap wings on to that running person. They still won't fly,
no matter how fast they run, because they are not moving forward
and thus no movement = no lift = no flight.

There is a physical disconnect between the plane and the runway via the wheel bearings. Simply adding wings will not work because you have omitted the jet engine part of the equation.

The jet engines push against the wings of the plane, a person running on a treadmill pushes against the ground/treadmill.

If you wanted a treadmill analogy, then imagine the person running on the treadmill which is covered in oil. Regardless of how fast the person runs, or how fast the treadmill goes. There is no direct connection exactly between the two because of the oil is separating the two forces.

If you forget the actual friction side of it all, the oil is separating the treadmill from the persons feet. Neither one can affect the other. So now if you strap a jet engine onto the back of the person he will just inherently be pushed forward. It is exactly the same with the plane.

The car analogy is different because if the car was going 100mph forward, and the conveyor belt was travelling 100mph backwards. Then the car would be perfectly stationary and would not move.

However, if you put the car in neutral, it is irrelevant how hard you step on the gas, it does not contribute to any motion. The conveyor belts speed would be irrelevant because the car is in neutral and does not affect anything other than the wheel speed. So then again if you strap a jet engine on the back of the car it would just inherently move forwards.

The bottom line of all this is, If the plane is travelling 100mph forwards on the runway, the wheels are turning at 100mph. Now if the runway/conveyor belt now goes 100mph backwards, the wheels are now turning at 200mph. The plane is pushed forward by the engines and would still be going at 100mph, and would still take off as it would ordinarily do in any other regular takeoff.