Time to solve it once and for all...

[Majik]

We had a discussion on it. Every forum on the Internet that really wants to call its self a forum has probably had a discussion on it. Now the mythbusters are going to get in on the action.

Airplane Hour
(Weds., December 12 at 9 PM ET/PT)
Adam and Jamie find out if either of them can safely land a Boeing 747-400 on a runway in varying weather conditions. Meanwhile, Kari, Tory and Grant risk life and limb to investigate skydiving myths regularly featured in Hollywood action films. Is it possible to catch up with someone in freefall if that person jumps out a plane before you do? Can you really hold a conversation during freefall? And would you survive if you opened your parachute only a few feet off the ground? Finally, Adam and Jamie carefully navigate their way through a myth that has baffled everyone from web bloggers to pilots. If a plane is traveling at takeoff speed on a conveyor belt, and the belt is matching that speed in the opposite direction, can the plane take off? Extensive small-scale testing with a super treadmill and a nearly uncontrollable model airplane don't completely resolve the myth, so our flight cadets supersize the myth with help from a willing pilot and his Ultralight flying machine.

http://community.discovery.com/eve/f...5321919039/p/1

[synaptik]

thats funny you know i just finished reading the old plane on a treadmill forum on here ... not 5 min before you posted this

[Radio-Active]

First off, whether or not its on a treadmill, the plane is still going to move forward. The wheels may be turning twice as fast, but the plane will still move forward.

I have been in a Cesna 120 where the wind oposing the plane was moving faster than the airplane itself. The plane was climbing and the road below was moving forward in front of the plane.

[synaptik]

.. but ... if the plane physically does not move then airflow is not going to change ... so it wont lift ...in your cesna you already had wind below your wings ...


and an old post lives again .....

[MadMonkey]

.. but ... if the plane physically does not move then airflow is not going to change ... so it wont lift ...in your cesna you already had wind below your wings ...


and an old post lives again .....

An airplane on a conveyor belt is still going to move because the wheels are freewheeling, they aren't what is driving the aircraft.

The question is usually impossible anyway, because it's worded wrong. If you want the conveyor to match the wheel speed, it's impossible because it turns into a feedback loop; as long as the plane is accelerating, the conveyor will accelerate until it and the wheels are spinning at a million mph and it STILL won't have an effect.

If the conveyor matches the aircraft speed, it still won't have an effect on the freewheeling wheels.

In the end, the only effect that the conveyor will have on the plane is friction/drag from the wheel bearings, that's all.

[synaptik]

there are variables not listed in the question

but not actually moving forward ... in theory would not be pushing more airflow beneath the wings therefore not creating lift :p

mind you i am by far no expert ...

but it seems kinda like putting your car on the dyno ... yes your wheels turn fast but ... no extra air pushs against the front of your car .. hence the reason some places but a fan down by the intake when they test it

[Majik]

there are variables not listed in the question

but not actually moving forward ... in theory would not be pushing more airflow beneath the wings therefore not creating lift :p

mind you i am by far no expert ...

but it seems kinda like putting your car on the dyno ... yes your wheels turn fast but ... no extra air pushs against the front of your car .. hence the reason some places but a fan down by the intake when they test it

But you are forgetting the wheels on the car are what drive it. So on a dyno it wont go anywhere. Strap a jet engine or even propeller to the car and put it in neutral. It will go right off of the dyno.

[synaptik]

will be interesting to see what the mythbusters get out of their tests

[Majik]

Here, this kid gets it. Linkie

[synaptik]

Here, this kid gets it. Linkie

blocked by the office firewall

[Jesse]

The plane will move forward and fly because air is generated by the propeller and thus flows over the wings & create lift.

[synaptik]

but it wont actually move forward ... it will stay stationary since the ground beneath it is moving in the opposite direction, you could stand next to it the whole time

[Rogue]

The plane will move forward and fly because air is generated by the propeller and thus flows over the wings & create lift.

A Piper Cherokee will not "fly" until 55mph airspeed.
Assuming your on 35, and wind 35 at 40mph, rotation will be at 15mph groundspeed.
That is why a Cub/Champ/T-craft can actually fly backward.
Wind greater than airspeed.
A prop can not create enough "air" to get a plane off the ground, a rotor can.
The ground has nothing to do with flying.

If you want proof, come grab a chair and watch.......bring beer!

[Dave04]

You guys are making my head hurt... but here's my

I think we all agree that the plane will fly (i.e. lift off the ground) if there is enough air flow over the wings. So the real question here is, when the pilot runs up the engines will the plane move forward or will it stay in place.

Consider this picture... a plane on a treadmill with a rope attached to the front.



I think we all agree that in this case, the plane will move forward (we can keep arguing whether the wheels roll later). But I think we can all agree the plane will move forward. Due to the fact that the engines are producing similar thrust, the plane should move forward and eventually get enough airflow over the wings to cause it lift.

OK... flame on... I'm done...

[HudsonHawk]

yup that pretty much sums it up.

[black roadster]

It all depends on the power of the airplane's motor to overcome the power of the treadmill's motor. If they were completely balanced, I could see the plane attaining a stationary balance.

If the treadmill was more powerful than the plane at full thrust, the plane would move backward.

If the plane was slightly more powerful it would advance on the treadmill but may not attain enough airspeed to create enough lift for flight.

If the plane can produce enough power to counteract the reward propulsion of the tread mill, it will gain enough airspeed to create lift.

Now the myth says the speed of the airplane's forward movement is the same as the treadmill's reward movement. To me this suggests the first scenario. A perfect balance thus the plane stays stationary which prevents enough air movement to create lift.

Think of it this way. A runner can sustain a speed of lets say 10mph. If you set the treadmill to 10mph, the runner would be able to counter the motion of the treadmill but would not gain any forward motion, thus no wind. (outside of general wind movement).

[Titus]

It all depends on the power of the airplane's motor to overcome the power of the treadmill's motor. If they were completely balanced, I could see the plane attaining a stationary balance.

If the treadmill was more powerful than the plane at full thrust, the plane would move backward.

If the plane was slightly more powerful it would advance on the treadmill but may not attain enough airspeed to create enough lift for flight.

If the plane can produce enough power to counteract the reward propulsion of the tread mill, it will gain enough airspeed to create lift.

Now the myth says the speed of the airplane's forward movement is the same as the treadmill's reward movement. To me this suggests the first scenario. A perfect balance thus the plane stays stationary which prevents enough air movement to create lift.

Think of it this way. A runner can sustain a speed of lets say 10mph. If you set the treadmill to 10mph, the runner would be able to counter the motion of the treadmill but would not gain any forward motion, thus no wind. (outside of general wind movement).

Problem is, the runner and the plane are nothing alike. The runner is applying a force to the treadmill, and the treadmill is counteracting that force. With the plane, the plane is applying it's force to the air. The treadmill is applying virtually no counterforce to the plane's fuselage, as it all is being wasted on the bearings of the free spinning wheels.

[MadMonkey]

The plane will move forward and fly because air is generated by the propeller and thus flows over the wings & create lift.

Uh uh.

but it wont actually move forward ... it will stay stationary since the ground beneath it is moving in the opposite direction, you could stand next to it the whole time

Like I said (why do I ALWAYS get into these arguments), the only effect that the treadmill will have on the plane is spinning the wheels. Ifthe treadmill starts first, yes, the plane will move backwards due to friction in the wheel bearings But as soon as the plane produces enough thrust to overcome that friction, it will begin moving forward (and that will be at a very, very low throttle setting). I'd say be quiet and quit while you're ahead

A Piper Cherokee will not "fly" until 55mph airspeed.
Assuming your on 35, and wind 35 at 40mph, rotation will be at 15mph groundspeed.
That is why a Cub/Champ/T-craft can actually fly backward.
Wind greater than airspeed.
A prop can not create enough "air" to get a plane off the ground, a rotor can.
The ground has nothing to do with flying.

If you want proof, come grab a chair and watch.......bring beer!

He knows what he's talking about ^^

Except there's even more planes that can fly backwards

And as for props not creating enough airflow to get a plane off the ground, I also call

It all depends on the power of the airplane's motor to overcome the power of the treadmill's motor. If they were completely balanced, I could see the plane attaining a stationary balance.

If the treadmill was more powerful than the plane at full thrust, the plane would move backward.

If the plane was slightly more powerful it would advance on the treadmill but may not attain enough airspeed to create enough lift for flight.

If the plane can produce enough power to counteract the reward propulsion of the tread mill, it will gain enough airspeed to create lift.

Now the myth says the speed of the airplane's forward movement is the same as the treadmill's reward movement. To me this suggests the first scenario. A perfect balance thus the plane stays stationary which prevents enough air movement to create lift.

Think of it this way. A runner can sustain a speed of lets say 10mph. If you set the treadmill to 10mph, the runner would be able to counter the motion of the treadmill but would not gain any forward motion, thus no wind. (outside of general wind movement).

Man... I always took you for being a pretty intelligent guy (no idea why though ).

A runner is powered by his legs, which are running on the treadmill. In other words, the legs are the driving force which is propelling him along. So just like a car, if either is going 10mph against a treadmill which is going in the opposite direction at 10mph, they'll stay stationary.

On the flip side, an airplane has (for the sake of simplicity) a PROPELLER which is the driving force. The wheels have no effect whatsoever, except friction as I mentioned earlier. Assuming the bearings, tires, etc are capable of handling infinite RPM without destroying themselves, and assuming the treadmill is trying to match the speed of the plane, the plane will still move forward. However, it turns into a feedback loop, as the wheels accelerate, the treadmill attempts to match, which causes the wheels to accelerate, etc.

The plane will fly, assuming the treadmill is long enough.

I thought the same as you until I really sat down and did some serious brain work.

[Majik]

Now the myth says the speed of the airplane's forward movement is the same as the treadmill's reward movement. To me this suggests the first scenario. A perfect balance thus the plane stays stationary which prevents enough air movement to create lift.

You are getting velocity and force mixed together. Yes the treadmill is running at the same velocity of the airplane. It is also creating a very small force against the airplane. This is the force of friction in the tires and the bearings in the hubs. The engines are creating a forward force. I would guess that you can imagine the force of the engines is much greater than the force of the friction. So much greater that in most problems the friction would simply be ignored because it is so much smaller than the force of the engines. Now you can see that the forces are unbalanced. And if the forces are unbalanced acceleration will occur.

[blackzx3_13]

I'm waiting for Iain's answer. . . .