Thread: Airplane on a treadmill

I already have.

Originally Posted by ramblingboy42

I already have.

Are you are referring to post #4?
It does not address that issue at all.
That post shows that you have just accepted at face value the comment about the treadmill matching the speed of the plane.
The point is that it can't match the speed of the plane no matter how hard it tries.
You have assumed it will match the speed of the plane when in fact that is impossible.
All you have done is state the obvious point that the plane won't fly if it doesn't move.
Explain why it won't move.

Consider a stationary plane with frictionless wheel bearings on a stationary conveyor.

If the plane's engine is not going and the plane's wheel bearing are frictionless then when the conveyor is started the planes wheels will spin but the plane will remain stationary.

It does not matter how fast the conveyor runs or which direction it runs, the plane will remain stationary because there is no force acting on the plane to move it. No force from the movement of the conveyor or the spin of the wheels can be transmitted through the frictionless wheel bearings to the plane. The wheels just spin as the conveyor moves.

Newton says - a body will remain at rest unless acted on by a force. There is no force from the conveyor acting on the plane.

Once the plane's engine is started the propeller generates a force. The plane now moves forward under the influence of that force. The direction of movement or speed of the conveyor is still having no influence over the plane because no force from the conveyor can be transmitted through the frictionless wheel bearing.

In the real world the wheel bearings are not frictionless but they are minimal friction so the the force transmitted to the plane caused by spinning wheels from the movement of the conveyor is also minimal. That minimal force is easily overcome by the thrust of the propeller allowing the plane to move forward almost as easily as if it was on stationary ground. So it will take off if the conveyor is long enough to approximate the length of a conventional runway.

Nothing about the movement of the conveyor has a great influence over the movement of the plane at any time. Provided the wheels spin freely then in practical terms it is not possible to drive the conveyor fast enough to impart a force through the spinning wheels on the plane that is equal but opposite to the force generated by the propeller and so bring it to a standstill preventing it from taking off.

Not withstanding all of the above, it is money that makes a plane fly. That's what my flying instructor told me after I explained the high pressure low pressure thing over the wings. "Try not paying your instruction fees & see how far you fly" he told me.

Originally Posted by Milton477

Not withstanding all of the above, it is money that makes a plane fly. That's what my flying instructor told me after I explained the high pressure low pressure thing over the wings. "Try not paying your instruction fees & see how far you fly" he told me.

Truth right there.

Want to go faster, further, higher, heavier? That'll cost more it's an exponential curve too. Twice as fast = four times the money

Originally Posted by Milton477

Not withstanding all of the above, it is money that makes a plane fly. That's what my flying instructor told me after I explained the high pressure low pressure thing over the wings. "Try not paying your instruction fees & see how far you fly" he told me.

And the propellor is a fan to keep the pilot cool. Want proof? See how much they start to sweat if it stops mid flight.

This is an hillarious thread.

Unless the aircraft has physical forward airspeed, yes - airspeed, it will not fly. The only exception is in a wind tunnel or a catapault launch. A model aeroplane really isn't a good example, as most of them have a huge power to weight ratio. When I say that, I mean the thrust of the propeller can just about lift the plane off purely on its own.

As others have alluded to, you would need a conveyor with the physical length of whatever runway is required. Doesn't matter whether it's running or not. The aircraft only recognises airspeed-not groundspeed.

I used to fly Dash-8's (Canadian STOL aeroplane). The quickest I got one airborne was in a headwind of about 45 knots (remember I said the aeroplane only recognises airspeed?) So when I lined up for takeoff, the airspeed indicator was reading 45knots. V1/rotate is around 95knots, so I only needed to accelerate another 60 knots. That took about 200m. In no wind, it would've been around 500m or so.

Had we been on a conveyor, it would still need to be 200m long in order to get sufficient AIRSPEED to fly. (And have a 45 kt wind blowing).

The B737 I fly now needs about 150kt to get airborne. Put it on a conveyor running at 150kt, and the aircraft will still need a 1200-1500m long conveyor to get up to 150kt airspeed. Problem is the tyres are only rated at around 200 mph, so theoretically you would need to run from the back to the front of the conveyor in order to get the 150kt forward airspeed, which would have the wheels turning at 300kt. Can't be done.

200 metres isn't short by Canadian standards.

Have you seen these?

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