Mythbusters will finally test...

[photon]

Originally Posted by kdoir345

Because the plane shouldnt move until the propeller generates enough of a force to counter what the belt is doing to the plane. Say what you will about the wheels not driving the plane, but there is still going to be an element of friction there that the wheels cant over come completly

There will be an element of friction yeah, but it's orders of magnitude lower than the thrust of an airplane.

Assuming the belt moves backwards at the same speed the plane moves forward, then it only has to overcome twice as much friction as it would have to if it was taking off from the runway.

[BlackArcher101]

Originally Posted by kdoir345

But what im saying is that will the belt not play any role in this whatsoever.

Would it not be like a racecar in a wind tunnel. They set those cars on belts and run them as if they were running full speed but they still have to generate the wind from a fan to get the realistic areodynamic info from the car. Does the forward motion of the plane not do anything, because if it is still does that not mean that there is no air speed?

Not sure what the wind tunnel speed test on a car has in relation to this. The difference is that the car is not trying to move, it's actually fixed. It's true that the fan is to create wind for aerodynamics testing. The conveyor belt they run on is only to get real world results since a rotating tire drastically changes the way the air flows around the car. A couple pounds of extra drag or miscalculation can cost a car the race by a fraction of a second.

Yes, the belt will play a role in this, as does the forward motion of the plane. The belt will move the aircraft backwards, but once positive thrust is attained, the backwards speed will start decreasing until the plane is at a stand still relative to the air, but the wheels will be moving at conveyor speed. After that, the thrust will starting to move the plane forward (simply continuing it's positive acceleration), with the wheel speed increasing and the airspeed as well. The plane, after a longer than usual distance due to friction will take off.

[kdoir345]

Originally Posted by BlackArcher101

Not sure what the wind tunnel speed test on a car has in relation to this. The difference is that the car is not trying to move, it's actually fixed. It's true that the fan is to create wind for aerodynamics testing. The conveyor belt they run on is only to get real world results since a rotating tire drastically changes the way the air flows around the car. A couple pounds of extra drag or miscalculation can cost a car the race by a fraction of a second.

Yes, the belt will play a role in this, as does the forward motion of the plane. The belt will move the aircraft backwards, but once positive thrust is attained, the backwards speed will start decreasing until the plane is at a stand still relative to the air, but the wheels will be moving at conveyor speed. After that, the thrust will starting to move the plane forward (simply continuing it's positive acceleration), with the wheel speed increasing and the airspeed as well. The plane, after a longer than usual distance due to friction will take off.

meh, i think im still gonna go with the plane NOT being able to lift off, I just dont see it working, but Ive been wring before so who knows.

I still think it all depends on how fast the belt is moving back against the plane, the thrust still has to overcome that no matter what no? Is it not the plane acutaly moving FORWARD that creates the air speed?

[The Fonz]

I don't know if this works, but I tried thinking of it this way.

Think of a boat, just a regular boat you'd go skiing behind. If you attached wheels to the bottom side of it, and these wheels were running on a conveyor which was traveling in the opposite direction the boat was traveling, would the boat be able to move? Yes, because no matter how fast those wheels are going in the reverse direction, the water remains still, and boats use a propeller to push the water. So the boat would move. Back to the plane, it doesn't matter how fast those wheels are moving in the reverse direction, because the air remains still, therefore the propeller would still be able to pull the plain forward until it reached a great enough air speed to lift off.

I could be so far off base here...but whatever...I tried.

[burn_baby_burn]

If this truly was possible? The US Air Force would allready be doing it.

[You Need a Thneed]

The answer is extremely simple:

If the myth assumes the plane remains stationary, then it will not take off.

However, if the myth assumes that the plane is free to move and use its jet/propeller engines, it will take off without any more difficulty then if it was on a normal runway - The wheel speed will just be higher.

Period.

I voted "Confirmed" assuming that the myth was assuming the second option.

[ken0042]

Originally Posted by burn_baby_burn

If this truly was possible? The US Air Force would allready be doing it.

You are thinking Aircraft Carriers, aren't you? That was my thoughts too.

Actually I think that's Navy, but that isn't really important.

[burn_baby_burn]

Originally Posted by ken0042

You are thinking Aircraft Carriers, aren't you? That was my thoughts too.

Actually I think that's Navy, but that isn't really important.

Air craft carriers or any other place that does not afford the space for a proper run way.

[You Need a Thneed]

The added friction on the wheels is easily overcome by the motors. A plane trying to take off on water, or a plane trying to take off on a grass runway would have as much friction as tires on pavement going twice as fast as normal.

[Barnes]

Actually, the more I had to think about this i have realized it is possible. It would not reduce the take off distance though.

[octothorp]

Originally Posted by Barnes

Actually, the more I had to think about this i have realized it is possible. It would not reduce the take off distance though.

Yeah, that's what I'm thinking, too. The same math that dictates it's possible to take off on a treadmill also dictates that there's nothing to be gained by doing so: it doesn't increase the thrust or lift.

Now, if you replaced the treadmill with a high-powered wind generator, you could in theory generate much more lift than on a conventional runway and shorten the lift distance.

[photon]

Originally Posted by Barnes

It would not reduce the take off distance though.

Of course not, it'll increase it by a small amount. The takeoff distance is determined by how quickly the plane can accelerate to the speed necessary to generate enough lift to counteract gravity.

The belt moving will generate a (small) force counteracting the thrust of the plane, extending the takeoff distance (assuming all other things are equal).

[photon]

Originally Posted by octothorp

Now, if you replaced the treadmill with a high-powered wind generator, you could in theory generate much more lift than on a conventional runway and shorten the lift distance.

Heh, until they left the influence of the big fan.

Though I wonder if you could do it in such a way that the plane could transition..

[Hack&Lube]

LOL, conveyer belt = no air moving under the plane's wings = no lift = no fly

Mythbusters is getting pretty stupid sometimes, most of these things are pretty obvious. The Superspecial was very disappointing - waterskiiing behind a cruise ship? How is that even a myth?

[Bill Bumface]

Originally Posted by Hack&Lube

LOL, conveyer belt = no air moving under the plane's wings = no lift = no fly

Mythbusters is getting pretty stupid sometimes, most of these things are pretty obvious. The Superspecial was very disappointing - waterskiiing behind a cruise ship? How is that even a myth?

I'm always amazed that people are fooled by this. It is very obvious, but in the other direction. It's totally obvious the plane will take off. Jets/propellors act on the air, not on the ground. The conveyor belt has nothing to do with the air, so accelleration will be the same* and take off distance will be the same*.

*Assuming friction in the wheel bearings is negligible, which it is darn close to.

[photon]

Originally Posted by Hack&Lube

LOL, conveyer belt = no air moving under the plane's wings = no lift = no fly

Yeah but when you turn on the engines, forward thrust = plane moving = air moving over plane's wings = lift = fly

[burn_baby_burn]

Originally Posted by photon

Yeah but when you turn on the engines, forward thrust = plane moving = air moving over plane's wings = lift = fly

How big of treadmill are we talking about?

[photon]

Originally Posted by burn_baby_burn

How big of treadmill are we talking about?

As big as you want it to be.

[Ducay]

Guys, the plane takes off.

Just because the ground is moving below the wheels has no impact on the plane itself, it just makes the wheels spin faster. Doesn't matter if its a jet plane or a prop, it'll take off.
But the theory behind it is that there is virtually no significant friction with the wheels. So bascially that implies that if the airplane was off and just sitting on its gear and the treadmill was on, it would stay in one place as the wheels spun.

[burn_baby_burn]

I was assuming that the plane would be stationary on the treadmill similar to a person running on a treadmill. How would air move over the wings?