Plane on a Treadmill

[ISUAlum2002]

Re: CyBookie - Plane on a Treadmill

Our understanding (many posts about this on an automotive messageboard that I frequent) is that the original question involves the treadmill moving backwards at the same speed that the plane is moving forward. ACTUAL FORWARD MOVEMENT, NOT WHEEL SPEED.

For example....if the plane is moving forward at 20 mph (AIR SPEED, NOT WHEEL SPEED), then the treadmill is moving backward at 20 mph, and the wheel speed is 40 mph. So, if a particular plane's takeoff speed is 80 mph, then the wheels are moving at 160 mph while the treadmill is going backwards at 80 mph.

Inifinity speed of the treadmill is not an option. In this scenario, thrust from a jet engine or propeller will EASILY overcome the friction of the wheel bearings.

 

[cmoneyr]

Re: CyBookie - Plane on a Treadmill

Put a SMALL jet engine (i.e. a model plane one) on the back of someone who is on rollerblades on a treadmill. Will the person move forward on a treadmill given that the treadmill can go, say 40 MPH?

That's what's up for debate here. The answer is "it depends". With enough friction and little enough thrust, the answer is no, he won't go anywhere. Obviously you can strap enough thrust onto someone to overcome the limits of the treadmill and the friction it's capable of generating through the wheels, but that's not necessarily the point of the test.

The plane will probably be producing a lot of thrust, not little thrust. Sure you could have the plane produce 10% of the thrust it's capable, but that's not really fair to the myth.

 

[brownie]

Re: CyBookie - Plane on a Treadmill

It seems to me an airplane is different than other modes of transport because of its wings, which create lift due to air movement across them. If there is no air movement - which there won't be - there is no chance of flight. You can try the same experiment with a tank. It can't fly regardless of "ground speed" because there is no lift. Thrust by the engines is doing nothing unless there is forward motion. Or the airplane is a Harrier - type with vertical lift due to downward thrust.
But that's just me. I could be wrong!

 

[jumbopackage]

Re: CyBookie - Plane on a Treadmill

Our understanding (many posts about this on an automotive messageboard that I frequent) is that the original question involves the treadmill moving backwards at the same speed that the plane is moving forward. ACTUAL FORWARD MOVEMENT, NOT WHEEL SPEED.

For example....if the plane is moving forward at 20 mph (AIR SPEED, NOT WHEEL SPEED), then the treadmill is moving backward at 20 mph, and the wheel speed is 40 mph. So, if a particular plane's takeoff speed is 80 mph, then the wheels are moving at 160 mph while the treadmill is going backwards at 80 mph.

Inifinity speed of the treadmill is not an option. In this scenario, thrust from a jet engine or propeller will EASILY overcome the friction of the wheel bearings.

If that is the point of the test, it's a stupid test, because obviously the plane will take off, just with a higher wheel speed. If the question is "what is the amount of thrust needed to overcome a treadmill capable of going x MPH", there's an answer to that, and anything below that level of thrust will result in the aircraft not moving forward, and never being able to take off. If the treadmill is capable of infinite speed, the answer is there is never enough thrust, given that you have bearings that aren't truly frictionless. If you have truly frictionless bearings, the answer is, it doesn't matter how fast the wheels are spinning, the plane will take off.

 

[twittkop]

Re: CyBookie - Plane on a Treadmill

It seems to me an airplane is different than other modes of transport because of its wings, which create lift due to air movement across them. If there is no air movement - which there won't be - there is no chance of flight. You can try the same experiment with a tank. It can't fly regardless of "ground speed" because there is no lift. Thrust by the engines is doing nothing unless there is forward motion. Or the airplane is a Harrier - type with vertical lift due to downward thrust.
But that's just me. I could be wrong!

The thrust is what causes the forward motion on a plane though. There isn't somebody on the runway that pushes the plane to get it moving initially.

 

[jumbopackage]

Re: CyBookie - Plane on a Treadmill

The plane will probably be producing a lot of thrust, not little thrust. Sure you could have the plane produce 10% of the thrust it's capable, but that's not really fair to the myth.

Sure it is. you can put engines that are, say, just barely powerful enough to get the aircraft airborne on the aircraft, and put it on the treadmill. It proves the point that the aircraft will not be able to take off if the wheels are producing enough friction to counter the thrust of the aircraft, which normally would have been enough to get it airborne.

Of course you can design an aircraft that can exceed the limitations of the treadmill, but that's not really fair to the myth either, is it? You're just overpowering your treadmill.

 

[Wesley]

Re: CyBookie - Plane on a Treadmill

What would a Hawkeye Political Science Major say and do this question?
'I think I will watch the show to see what happens."

 

[jbhtexas]

Re: CyBookie - Plane on a Treadmill

The engines develop thrust by changning the velocity of the air from engine inlet to engine outlet. If the engines are running, they will develop thrust. If the engines are developing thrust, what ever is opposing the motion of the plane, which in this case is normal air resistance + the resistance between the tires and the treadmill + the wheel bearing resistance, has to equally oppose the thrust developed by the engines, or the plane is going to start accelerating forward.

The question is whether the rolling friction forces developed between the tires and the treadmill and in the wheel bearings will be sufficient to counteract the thrust of the engines. If those friction forces aren't sufficiently strong (and I don't think they will be), and the plane has a long enough runway, the plane will eventually accelerate to the speed required to develop takeoff lift.

Regarding the interaction between the tires and the runway, it is a relative velocity issue. In the case of the plane on a runway, the plane moves at xxx mph forward and the runway moves at 0 mph, and the wheels rotate accordingly. In the case of a plane on a treadmill, the plane will be traveling at xxx mph forward and the treadmill will be moving at yyy mph in the opposite direction, so the wheels will just spin faster than they would if the plane was on a runway.

If the wheels start spinning too fast, the tires will eventually fail because they will not be able to absorb (dissipate is probably a better term) all the energy developed by the friction between the tires and the treadmill, or the wheel bearing assemblies will fail because they will not be able to absorb all the energy developed by the friction in the rotating bearing assembly.

The treadmill will not be able to achieve infinite speed, so the wheels on the plane will be spinning at whatever rotational velocity is required for a plane moving forward at xxx mph and the treadmill traveling backwards at yyy mph.

 

[brownie]

Re: CyBookie - Plane on a Treadmill

The thrust is what causes the forward motion on a plane though. There isn't somebody on the runway that pushes the plane to get it moving initially.

Agreed but the whole point of a treadmill is that it is stationary. There is no forward movement. Unless you're moving the treadmill, carrying the plane, down a runway. Which defeats the whole purpose. My point was, there is no lift, so forward thrust is not an issue.

 

[JRCampy]

Re: CyBookie - Plane on a Treadmill

Humans run using their legs. Planes do not move using their wheels as propulsion.

In your example, strap a jet engine on the back of the human running on the treadmill. Will the human move forward? The answer is yes. So the plane WILL take off.

I've only read the first page of this thread and its already ridiculous to see how many people believe the plane moves forward based on power from its wheels.

But a human doesn't run faster than the treadmill, otherwise they should just go outside and run, because they'll need a pretty long treadmill if they don't.

Obviously you're going to create air movement if your groundspeed is greater than that of the treadmill, so yes I would agree that the plane has a chance to take off if it's thrust is great enough to overcome the friction of the ground and the speed of the treadmill... but that's not the point.

 

[ISUAlum2002]

Re: CyBookie - Plane on a Treadmill

Obviously you're going to create air movement if your groundspeed is greater than that of the treadmill, so yes I would agree that the plane has a chance to take off if it's thrust is great enough to overcome the friction of the ground and the speed of the treadmill... but that's not the point.

:wideeyed::wideeyed: That's EXACTLY the point. :wideeyed::wideeyed:

 

[chadm]

Re: CyBookie - Plane on a Treadmill

The question I need answered. How big is this treadmill, and does the test allow the plane to move forward on the treadmill.

 

[ISUAlum2002]

Re: CyBookie - Plane on a Treadmill

The question I need answered. How big is this treadmill, and does the test allow the plane to move forward on the treadmill.

Its not about allowing the plane to move forward on the treadmill, because it WILL move forward due to the thrust it generates.

Obviously if the plane is forced to stay stationary due to some outside force other than the treadmill it will not take off as the treadmill is not moving air.

 

[jumbopackage]

Re: CyBookie - Plane on a Treadmill

It could also be this airplane:

This is the BA609, a tilt rotor plane, which is produced by Bell Augusta Aerospace. This was initially a project by the military, but they gave up on it because they kept crashing it.

Actually, you're probably referring to the V-22 Osprey, which is very much alive in the military. V-22 Osprey - Wikipedia, the free encyclopedia . The BA609 is being produced as an entirely different airframe, much smaller, and aimed at corporate/commercial applications. Bell also was the prime for the V-22, which has indeed had some issues.

 

[aeroclone08]

Re: CyBookie - Plane on a Treadmill

Forget about the wheels for a moment since they're only there to prevent the underbelly of the plane from being destroyed on takeoff/landing. Imagine the plane hovering stationary a few feet above the treadmill (like someone just photoshopped the wheels out). Now increase the thrust of the engines and start the treadmill as well. What is there to keep the aircraft from moving forward (and creating a pressure differential on the wings)? Nothing, the aircraft will move forward and eventually lift off.

Now if we put the wheels back in the picture they act the same way- they only keep the body of the aircraft off the ground. The will spin freely (up to infinity velocity if you want), but there is no force there to counter the forward thrust of the engines (whose thrust is NOT transferred through the wheels.)

 

[twittkop]

Re: CyBookie - Plane on a Treadmill

The question I need answered. How big is this treadmill, and does the test allow the plane to move forward on the treadmill.

I hope they make the "treadmill" longer than the takeoff distance the plane requires when the "treadmill" is stationary. I think it is going to take more power/distance for the plane to takeoff when the "treadmill" is in motion to overcome the friction of the wheel bearings.

 

[jbhtexas]

Re: CyBookie - Plane on a Treadmill

Now if we put the wheels back in the picture they act the same way- they only keep the body of the aircraft off the ground. The will spin freely (up to infinity velocity if you want), but there is no force there to counter the forward thrust of the engines (whose thrust is NOT transferred through the wheels.)

Yes, there are forces there. There are friction forces between the wheels and the ground, and friction forces in the wheel bearing assemblies. Both these forces oppose the forward motion of the plane. But those forces are normally small relative to the thrust of the engine.

If you don't believe that, go drive your car a few miles, let it coast to a stop (no braking energy), and then go put your hand close to the wheels.

 

[twittkop]

Re: CyBookie - Plane on a Treadmill

Actually, you're probably referring to the V-22 Osprey, which is very much alive in the military. V-22 Osprey - Wikipedia, the free encyclopedia . The BA609 is being produced as an entirely different airframe, much smaller, and aimed at corporate/commercial applications. Bell also was the prime for the V-22, which has indeed had some issues.

I had no idea this program was still alive in the military. I heard at work that it was abandoned, but apparently what I heard was incorrect. The only reason I knew about the BA609 was because I wrote a small amount of code for the AFD on the BA609.

 

[jumbopackage]

Re: CyBookie - Plane on a Treadmill

Forget about the wheels for a moment since they're only there to prevent the underbelly of the plane from being destroyed on takeoff/landing. Imagine the plane hovering stationary a few feet above the treadmill (like someone just photoshopped the wheels out). Now increase the thrust of the engines and start the treadmill as well. What is there to keep the aircraft from moving forward (and creating a pressure differential on the wings)? Nothing, the aircraft will move forward and eventually lift off.

Now if we put the wheels back in the picture they act the same way- they only keep the body of the aircraft off the ground. The will spin freely (up to infinity velocity if you want), but there is no force there to counter the forward thrust of the engines (whose thrust is NOT transferred through the wheels.)

Granted, however, in application, the wheels DO have a certain amount of rolling friction, that increases as the ground speed of the plane does (as long as it's in contact with the ground).

I think there are two questions, really, here. There is the "theory" question, and the "practical" question.

In THEORY, if you could engineer a treadmill that went fast enough, you could keep a plane from taking off by increasing the speed to a certain point, given that the wheels wouldn't explode, and the bearings wouldn't seize up. You would have to build a wheel system capable of absorbing the amount of energy output from the engines.

In PRACTICE, any reasonably powerful aircraft would be able to overcome the amount of friction that it's possible to generate through it's wheels, and would probably take off.

 

[jumbopackage]

Re: CyBookie - Plane on a Treadmill

I had no idea this program was still alive in the military. I heard at work that it was abandoned, but apparently what I heard was incorrect. The only reason I knew about the BA609 was because I wrote a small amount of code for the AFD on the BA609.

Yeah, I know for sure that the Air Force has some down at Hurlburt Field. I don't know where the Marines are keeping theirs. The AF SOF guys have been using them for a while. It's still a pretty contentious airframe, but it's being delivered anyway. After they dumped that sort of money into it, it's unlikely they will just zero it out before they spend a ton more on it. Even despite the military's suggestions (witness the B-1 and SR-71).