It can't.

there is no wind beneath its wings.

Lift isn't generated by an aircraft from underneath it's wings...it's generated from the downforce of wind flowing OVER it's wings... :)

No

Um...Yes... :)

lies

Actually it's created by "lowering the pressure" of the wind above the wing. Thus the shape of the airfoil with a longer surface above the wing than below.........

The lesser the pressure, the easier to create lift.

That's a theory...and thus, we now have the greatest internet debate in the history of the OMB, back up and running over here... :)

Im pretty sure lift has to be an UPforce.

And the plane takes off, airspeed determines lift not ground speed

this has already been debunked on mythbusters. can't be done. move along now. 678hnn77

I have a friend in the Aviation program studying to be a pilot. I'm going to have a talk with him and get his input

Actually, Lift may be an UPforce...but it's generated by a the DOWNforce of pressure and air, created from air flowing over the wing....that's the Downforce i'm referring to...Lift isn't a downforce...it's created by one... :huh:

It can't be done onthe levelof mythbusters. They did a show about could a whirlpool in the ocean suck a boat down. They did it in a tank, with a toy boat. All the time science and earth science find things that are not what they think. When Mythbusters can get a real good plain and a longe enough and fast enough treamill set up to create something more realistic, then thy can bust it.

I think it's safe to say that both the air traveling over and under both might have something to do with it, but with a plane on a treadmill, there is not much force created by air moving over the entire wing.

Actually, that episode of mythbusters proved that it could be done...the original premise they were trying to prove was "A Plane canNOT take off from a surface moving backwards" and they proved that it could...that's why it says "Busted"... 8DRTV75

I didn't see that episode :(

It aired back at the end of Jan or beginning of Feb. It's been called episode 97, but I thought it actually aired as their 100th...whichever...I can't keep up with all their episodes. Some are great...others not so. I think you can find portions of it on You Tube... 8DRTV75

Reread Doc post about Bernolli principle. Wind speed increases over the top half of the wing. Because of this increased velocity pressure is lowered above the wing resulting in lift. The only downforces are gravity and drag.

Problem is, that's 1 piece of the whole equation...forces have to act in opposition to one another for planes to takeoff. You can't have "lift" without downforce...there's more the idea of airlift than just the Bernolli principle. There's also Newton's Third Law of Motion. The force and pressure of the air being pushed down, bounces off the ground, and generates the "Upforce" that you're referring to...this upforce is Lift...but Lift requires a downforce... :)

Here you go:

http://www.youtube.com/watch?v=YORCk1BN7QY

If lift is generated by these forces bouncing off the ground, what happens at 10,000 ft?


FYI, there is a ground effect lift which acts in conjunction with standard lift at takeoff. But it dissipates above a dozen feet.

AT 10K feet, it's no longer about lift...it's then about air worthiness...and who slew of other physics formulas and equations.. :blink:

Somebody is yanking my chain.

I always loved this discussion, maybe it's my past as an airplane manufacturer.
Think of it as a hamster in a wheel, in theory he could go somewhere, were it not that the wheel being round and connected to a base. If the airplane is not in motion thus creating friction with the wind there is no lift. If the plane is not propelled forward (hence the treadmill\conveyor) no friction is being created, therefore the propeller alone cannot create lift.

Lord, please let me never fly in one of those planes.

The question does not say the plane cannot be in motion, it merely states the plane is taxi-ing? on a treadmill.

And that's why I love and hate this particular debate Rob...because it's all theoretical...I doubt we'll ever have a proven conclusion to it. If we had an infinite supply of resources than we could construct the and perform the experiment, and factor in every single variable. Until then though, the discussion/debate will rage on...but there are some days where this kind of "deep thinking" makes my skull ache...on those days, I'm praise Odin for Maker's Mark... g6wvuymh87

I was a damn good welder and I always passed the FAA inspections, when I wasn't token. Ever flown in a STOL?
I stray, to taxi, is to be in motion from one location to another, being in a forward motion creates the friction which is needed for lift and cannot be the case if it were on a conveyor.

What prevents forward motion on the conveyor?

In the hypothetical sense of the experiment, as thrust was increased which would naturally cause the plane to accelerate, likewise the conveyor system speed would increase causing the plane to remain in a fixed location.

Like Ton mentioned; it would require an "infinite supply of resources than we could construct the and perform the experiment, and factor in every single variable".

On the other hand, something else comes to mind I was told many many years ago when I first became interested in flying and got involved in Model Aeronautics.

Horsepower is a key ingredient in modern flight. With enough horsepower you can fly a brick. Of course that was referring to "propeller driven" engines. In today's world, horsepower would equate to thrust developed by jet engines.

Regardless the principal is the same.

With enough thrust, there's no need to have a forward motion, but rather apply power and "snatch" the plane off the ground, with control surfaces taking affect after it's airborne.

Why is there still debate over this? Mythbusters already proved that a plane CAN take off on a conveyor belt.

I want to pull my hair out every time I see this because it's so simple yet many people can't grasp the concept.

If you place a car going 100 mph on a treadmill going in reverse at the same speed, its ground speed will be zero.

However, if you place an airplane on the same treadmill going 100 mph, it will go forward at 100 mph no matter how fast the treadmill is going in the opposite direction.

The reason for this is simple. A car derives its forward motion from the friction of the spinning tires against the road surface. An aircraft derives it's motion from a propeller or jet engine acting against the air. If the aircraft were on a treadmill, its wheels would spin at a faster rate but the aircraft would go forward no matter how fast the treadmill goes.

Sounds logical doesn't it?

However, in your own example, the plane must move forward.

The forward motion is created by the thrust or prop, and "airspeed" is reached by gaining ground speed on the wheels. A "given" amount of air has to pass over the wing to create lift.

For comparison use the Cessna 150-152. Basic flight specs.

runway length requirement - 1500 feet - (750 feet with 10-15 kt. headwind)
take off speed - 70-80 MPH (65 kts avg)
landing approach speed with flaps - 60-70 MPH (52-60 knots)
stall speed without exceeding the critical angle of attack (stall angle of attack) - 48-55 MPH (42-48 knots)

IN order for a Cessena 150-152 to become airborne, a wind speed of 70 MPH (65 knots min.) must be traveling over the wing.

BUT, if the conveyor is moving at the same speed as the plane, and conveyor speed increases as thrust increases, isn't the plane just spinning it's wheels like the car?

NO.

The plane will ALWAYS move forward no matter how fast the treadmill is going. The reason is because an airplane is not driven forward by torque from its wheels.

If a treadmill could be matched with the thrust of the aircraft, it's wheels would spin twice as fast as normal, but the airspeed would NOT change.

Actually, I think the wheels would have to spin several hundred times as fast as normal to keep the plane on the ground.

The forces pushing the plane forward - the thrust from the engines, would have to be equalled by the forces pushing the plane backward - the frictional forces of the tires againt the conveyor belt and the internal friction of the wheel bearings.

For those small frictional forces to equal the thrust of even a small prop plane would requred the wheels to spin at speeds that would tear the tires apart and burn the wheel bearings up in a second.

Of course I discounted the comparatively minute effects of friction. My point is that while the speed of the wheel rotation would be faster, the forward speed would not change (but for the effects of friction).

Correct!

I think it's funny how many people try to argue it can't take off because it's not moving forward, they somehow miss that the plane moves forward as normal on the treadmill and that the wheels move twice as fast as the plane...

This debate is over though, Mythbusters took off in a REAL plane on a treadmill. Surprise it works! eheh

The answe is..YES

Here ya go.

What a waste of billions of taxdollars... <_<

Nope :)