Airplane Vs treadmill?

[ShnOmac]

Imagine a plane is sitting on a massive conveyor belt, as wide and as long as a runway. The conveyer belt is designed to exactly match the speed of the wheels, moving in the opposite direction. Can the plane take off?

Some people say no, because the plane will not move relative the the ground and air, and thus, very little air will flow over the wings. However, other people are convinced that since the wheels of a plane are free spinning, and not powered by the engines, and the engines provide thrust against the air, that somehow that makes a difference and air will flow over the wing.”

Do we have any physicists around here?

[CamaroSpike23]

oooooooooooooooooold

[CamaroSpike23]

if the wheels are unlocked and the plane remains stationary with the treadmill moving against it. the wheels will spin and the plane wont move.

now if you locked the wheels and reversed the direction of the treadmill to go in the same direction the plane was pointing and could move the plane at speed. then you could gain enough lift by moving the plane fast enough

[ShnOmac]

Lets say take off speed in said plane is 150 knots. If the plane is going south to north with enough throttle to power it at 150 knots and the direction of travel of the tread mill is going north to south at 150 knots will they plane take off?

[tjbusa]

But if the brakes were set and the belt forward spun the jets IAS to 150 or so, sure

[tjbusa]

Originally Posted by shnomac77

Lets say stall speed in said plane is 150 knots. If the plane is going south to north with enough throttle to power it at 150 knots and the direction of travel of the tread mill is going north to south at 150 knots will they plane take off?

With flaps set, and the conveyor belt gave you even more airspeed, yes... but then youd crash because the throttle settings are still set at a stall speed.

[ShnOmac]

Opps that was supposed to say takeoff not stall.... fixed

[Number 3]

Mythbusters..................check it.

[Jamie Mac]

Air moves over the curved surface of the top of the wing at the same speed as it does the flatter bottom of the wing. However the air over the top has a greater distance to travel and a vacuum is created above the wing which provides the lift. If the plane is stationary due to the movement of the treadmill then the air is not flowing over the flight surface and no lift will be provided. Shut the engines off put on the brakes and provide enough air flow and the plane would lift off but of course you would be going backward. As the plane picked up speed the airflow over the wings would decrease and lift would be lost.

[Mr. Wyndham]

The trick is in the phrase "relative to the wheels". This is almost impossible. The Plane might as well not have any wheels, because they do NOT propel the vehicle. Once the propeller starts spinning, and the plane reaches it's takeoff speed, it's gone!

[RS/SS]

Very old, this was "Busted" on Mythbusters back in January 2008. Plane took off, end of story.

[nova]

I'm not a physicist but I do so happen to be an aerospace engineer so maybe I can provide a little insight. Specifically, the particular area in which I work is aircraft performance, including takeoff and landing performance.

Here's the short answer.

Yes it can takeoff. There's nothing to debate about it.

Here's the long answer.

The wheels of an airplane have negligible impact on the acceleration of the vehicle. If they are free wheeling, they will essentially have zero impact. When analytically determining takeoff distance, we typically neglect rolling resistance in our first approximations.

If the brakes and the thus the wheels are locked, that would be a big impact and can prevent you from taking off.

Airplanes are not like cars where the force to move the vehicle forward, comes from the force the wheels exert upon the ground. In an airplane, the force comes from a couple of different sources depending upon the configuration.

A. The prop on a propeller aircraft, is basically a wing swinging through the air. It creates a lift force vector pointing forward which drags the aircraft along with it.

B. Jet aircraft use a combination of pressure forces on the internal components and "newton's law" action/reaction forces to push the aircraft.

Hope that provides a little clarity about why the treadmill and wheels don't actually do anything...

[nova]

Originally Posted by Jamie Mac

Air moves over the curved surface of the top of the wing at the same speed as it does the flatter bottom of the wing. However the air over the top has a greater distance to travel and a vacuum is created above the wing which provides the lift.

Completely untrue. I can point you to dozens if not hundreds of airfoil sections that have a symmetrical profile.

The fluid over the upper surface moves faster than that on the bottom surface. Bernoulli's law being what it is, that results in a lower pressure on top vs bottom creating lift.

Said speed differential is dependent upon the angle of attack of the airfoil section and not the geometry of the airfoil profile.

The speed differential is caused by certain viscous fluid forces that are not even close to being completely understood. When I was an undergrad, there were PhD candidates in our program doing their dissertation research on "How airfoils produce lift" if that tells you anything...