Will this plane take off?

[crazy 8's]

This has turned into a huge debate on a non-r/c board that i came across on. here is the scenario. Think about it.

"Let's say you have a single engine airplane sitting on a runway that is 3000 feet long, and through some great engineering the runway is actually a giant treadmill. It's engineered so that when the plane starts to move forward the runway moves in the opposite direction at exactly the same speed., i.e. as the airplane's wheels pick up speed the runway matches it.
Will the plane get airborne?"

 

[SublimeRevo]

I am going to go with no. Basically the plane is stationary. Planes do not fly by having their wheels spinning. It would have to be moving though the air to create the pressure differences on the wings known as lift.

 

[joneser4u]

I'm gonna ask why? and what he^^^^ said is true.

 

[HeartBreak]

Mythbusters are rumored to be taking this one on coming up.

 

[Lessen]

SublimeRevo is correct. Whether or not the plane moves relative to the ground beneath it is not the significant factor. If the plane is not moving in relation to the air around it then there is no air flow over/under the wings, therefor there is no lift. The plane stays grounded.

 

[bentover]

Wowzers, I got a headache now.

 

[crazy 8's]

Where i saw this question theres some speculation that it will fly. Here is just one response. See if it makes any since to you.

Think of it this way.

If you're on a treadmill thats off, you're doing 0mph. Correct?


Now if the treadmill is doing 10 mph, and you're holding where you're at you're still doing 0 right?

Now, if you're doing 10mp, and the treadmill is doing 10mph, what does that mean? That you're moving forward. Your wheels are doing 20, because you have your 10mph, and the treadmills 10 mph.

If you have the ability to increase your speed, without having to push against the tread mill, you will continue to accelerate, and move forward, until the airplane reaches lift off.


you're thinking about this like a car, which would sit in once place, and show 10mph while still having a speed of 0 mph. This, is because the car has to push against the treadmill to go faster.

An airplane pushes against air, not the ground. The wheels are just there to give the airplane a method of movement, with less friction than the belly of the plane.

 

[Rolex]

YOU are burning the calories to produce the energy to move at 10 MPH on the treadmill. Do you feel the wind blowing in your face? No....neither will the plane.

If the plane needs to reach 20 miles per hour to lift off, the only way it could do so from a stationary position is if a wind generator was blowing at it with the WIND at 20 MPH. At that point, the airfoil would generate lift.

The myth will be BUSTED. Not even plausible, and never to be confirmed.

It was pre-empted the other night, but they're about to see how much a truck weighs with X pounds of canaries inside when they are all in flight. I caught a discussion on that one over 15 years ago, and I'm still wondering.
My guess is there won't be a cargo weight anymore, just the barren truck weight.

 

[Lessen]

Think of it this way.

If you're on a treadmill thats off, you're doing 0mph. Correct?

correct

Now if the treadmill is doing 10 mph, and you're holding where you're at you're still doing 0 right?

This comment may be confusing because it's not very clear. If you're standing still on the treadmill then you are traveling 10mph backwards. If you're "holding where you're at" relative to the ground then yes, you're essentially doing 0 even though you're simulating a speed of 10mph.

Now, if you're doing 10mp, and the treadmill is doing 10mph, what does that mean? That you're moving forward.

No, you are not moving forward. If the treadmill is doing 10mph and you are jogging on the treadmill at 10mph relative to the treadmill, you are not making any forward movement relative to the ground.

Your wheels are doing 20, because you have your 10mph, and the treadmills 10 mph.

No.
If the treadmill is running in it's standard direction then you are not moving relative to the ground.
If the treadmill is running in it's generalized opposite direction (forward) then and only then are you traveling at 20mph relative to the ground.

If you have the ability to increase your speed, without having to push against the tread mill, you will continue to accelerate, and move forward, until the airplane reaches lift off.

Yes. However, this is NOT the scenerio that was originally given.

The bottom line is that if a treadmill is running backwards (like treadmills are supposed to) then the speed of the person, car, plane or dog needs to be traveling at a speed greater than the treadmill in order to make any forward movement. It doesn't matter if the source of the planes movement is at the wheels/ground or propeller/air. The lift is created when enough speed is met. this needs to be true speed, not simulated speed. If a takeoff speed is 150mph and a treadmill is moving at 150mph (backwards, like they do) then the plane needs to reach a simulated speed of 300mph (relative to the treadmill)in order to travel at a true 150mph (relative to the earth) and lift off.

My guess is there won't be a cargo weight anymore, just the barren truck weight.

yep.. I guess that myth is plausible...

A Rolex DOES get smarter with age. Whoda thunk it?

 

[Greyryder]

This sounds bizarre to me. It will make it more difficult for the plane to take off, due to the increased rolling resistance. As was stated in a previous post, airplanes push against the air, not the ground, so it would still be able to to take off. This just means that the wheels have to roll faster, which means more resistance. It'd probaly be similar to taking off with a tail wind.

 

[Rolex]

A Rolex DOES get smarter with age. Whoda thunk it?

LMAO! We learn from our 'lessens'.

Now, back to the treadmill and the airplane.
Look at it this way...The plane (R/C of course) need 20 MPH forward speed to achieve lift off.
So, the treadmill is moving at 20, and the plane is putting out enough power to stay even.
Simply put, IT CAN NOT lift off. Think about it. What would happen if it could? Would it stay in the air without any forward movement, or would it suddenly surge forward trying to reach 20? If, through some never seen error in physics it was able to lift off the treadmill, what would happen to it when it was in the air above the treadmill doing ZERO miles per hour?
Never happen. There is NO LIFT on a stationary plane without creating lift on the wing. THAT's what makes them fly.
If you thing for an instant that the theory would work, we would no longer need long decks and catapults on carriers.

Again, BUSTED.

 

[Lessen]

I can't believe this is creating this much headache. This really isn't that complicated.

I keep reading the same thing about a plane pushing through air, not across ground. You have to keep in mind the basics here. With any given aircraft there is a certain speed that it MUST attain to create enough lift for it to take off. If you don't get the speed, you don't get the lift. That's it.

Yes, I understand that a plane attains speed by pushing air. I'm getting the feeling that some folks seem to think that because the energy is being transferred in the air instead of at the ground, that if the ground (treadmill) is moving it won't affect the energy ouput of the propellers and therefore the plane will lift off.

What some are failing to realize is that there is a transfer of energy. The energy being displayed at the props in the air is transferred to a rolling energy at the wheels... this is how the plane moves forward. Now take the wheels off. I don't care how fast the props spin... that plane ain't flyin because there is too much resistance for the plane to reach enough speed to lift off. Those props could spin fast enough to allow an already airborn plane to do 250 mph but without those wheels it will never be able to transfer the energy into enough forward motion to lift.

 

[Rolex]

Pretty much my point in my previous post. If it could take off on a treadmill (but it CAN NOT), what happens next?
It's now in the air at ZERO miles per hour? Can't happen.

 

[rcnut143]

The physics behind it.

But I agree with what the poilt says at the end of this trailer. "If I match my speed to exactly the speed of the conveyer belt and theres no air over the wings I should just sit there like a brick."

 

[Lessen]

Pretty much my point in my previous post. If it could take off on a treadmill (but it CAN NOT), what happens next?
It's now in the air at ZERO miles per hour? Can't happen.

Well, I wouldn't say that it is impossible for a plan to take off on treadmill. But certainly not with the circumstances stipulated in the first post.

http://www.youtube.com/watch?v=-EopVDgSPAk

The physics behind it.
http://www.youtube.com/watch?v=siYQU99VaAM


But I agree with what the poilt says at the end of this trailer. "If I match my speed to exactly the speed of the conveyer belt and theres no air over the wings I should just sit there like a brick."
http://www.youtube.com/watch?v=KSBFQOfas60

Good links here. First of all, Kudos to dad for doing a terrific science experiment with his son. :thumbup::thumbup:

The 2nd clip pretty much puts it all on the table.

The force of the thrust would need to be greater than the sum of all forces working against it... and that's just for it to see forward movement. In order for it to take off it, it still needs to reach that exact speed needed to create lift.

So theoretically it IS possible for a plane to take off on a treadmill (This seems to be the point being made in the first video). It just needs to have enough thrust to overcome the extra negative forces + the thrust necessary to reach lift off speed.

If you put an F-15 on a treadmill doing 20mph it's still going to be able to take off. If it only puts out enough thrust to equate to 20mph then it's just gonna "sit and spin".

 

[Rolex]

Well, I wouldn't say that it is impossible for a plan to take off on treadmill.

I would, unless it's a Tilt-wing Rotorcraft, such as the Osprey, able to generate forward speed as well as it's own lift.

In order for it to take off it, it still needs to reach that exact speed needed to create lift.

We're back to the same point....it can NOT be done. If you need 20MPH to take off, and the treadmill is moving at 20 MPH, and to create lift in this situation you need to reach 40 MPH, it totally negates the treadmill, and, again, proves that you need the proper forward speed to create lift on the airfoil.
Understand that the 40 MPH is NOT ground speed, but 20 MPH is energy wasted to overcome the treadmill. The other 20 MPH is forward motion as it relates to the ground, even though it's 40 MPH as it relates to the treadmill.
Again, no forward motion, no lift. Busted.

 

[bentover]

Why don't we all just chill and get our asses on a tread mill!?!?!?!?

 

[djdoug99]

I don't understand how this is even debatable. In order to create lift you need air moving over and under the wings.

 

[Rolex]

I don't understand how this is even debatable. In order to create lift you need air moving over and under the wings.

Thanks, that's the point I've been making all along.

 

[djdoug99]

I know sorry, just had to get my .02 in. I think if everyone knew the basics of flight physics, they would all agree that this would not work.