Mythbusters, Plane on a treadmill..

[Amish RakeFight]

Well if you are running on a treadmill you dont get any wind resistance, so wouldnt that be the same for the plane?

Does your airplane have feet or wheels that drive it?

It is not the same as running on a treadmill where forward motion (provided by the runner's legs) is countered by the conveyor. The planes wheels do not advance the airframe. That is the job of a jet or prop. A jet will push the plane forward, regardless of the wheel movement. A tractor prop will pull the airplane forward just the same, irregardless of reverse movement under the wheels.

The plane will indeed fly. This shouldn't be so conceptually challenging as it appears to some individuals.

Think of a seaplane taking off into a strong current moving in the opposite direction. It will still lift off.

 

[COOPERVANE]

I used to be in the
"It will never fly and if you think so you are a moron"
crowd. Until I thought of a good analogy.

YOU are on a treadmill on roller skates. You have a rope tied around your waist. The other end is held by 5 strong men.

When they pull on the rope you move forward right? How fast must this treadmill move in order to keep you stationary?

It CANT because the "thrust" is being provided by the rope, not the wheels. You WILL move forward and wind WILL blow in your face.

The propeller is the rope that pulls the plane.

 

[siucavflight]

Bump.

 

[Amish RakeFight]

Bump.

you're so evil!

 

[go!ng for broke]

how many people think the tarp will suck up into the prop? When does this air??

 

[Captzaahlie]

Does your airplane have feet or wheels that drive it?

It is not the same as running on a treadmill where forward motion (provided by the runner's legs) is countered by the conveyor. The planes wheels do not advance the airframe. That is the job of a jet or prop. A jet will push the plane forward, regardless of the wheel movement. A tractor prop will pull the airplane forward just the same, irregardless of reverse movement under the wheels.

The plane will indeed fly. This shouldn't be so conceptually challenging as it appears to some individuals.

Think of a seaplane taking off into a strong current moving in the opposite direction. It will still lift off.

The seaplane analogy was the best explanation that I can think of....well done!

 

[Alltheway]

So if I sit at the end of the runway and apply full full power with the brakes on (not moving) I will make the cessna fly ?

 

[Say Again Over]

Alltheway, the point is you can't compensate the forward movement of the airplane by increasing the speed of the treadmill, just won't happen. Consider a rope tied to a grocery cart, the cart is on a treadmill, not you, you grab the end of the rope, now the tread mill starts running, do you have the strength to hold the rope at 30MPH, 60MPH, 250MPH, the answer is yes.

 

[Thedude]

Jeez....no airflow = no fly

 

[Singlecoil]

So if I sit at the end of the runway and apply full full power with the brakes on (not moving) I will make the cessna fly ?

The plane will fly if it is parked on a frozen lake and you are holding the brakes, which is another analogy for this treadmill business. Picture smooth glare ice with a layer of water on it. Perfectly slick, zero friction. In this case the tires aren't moving at all and the plane takes off. In the treadmill case, the tires are moving faster than normal, but the plane still takes off at the same airspeed as normal.
The point is, airplanes move by pushing air. How they interact with the ground (floats, skis, wheels) is secondary to the fact that thrust is produced by pushing air.

 

[Say Again Over]

Thedude, you are quite correct, unfortunately you will not stop airflow with a treadmill, jeez!

 

[SplitBar]

Think of a seaplane taking off into a strong current moving in the opposite direction. It will still lift off.

Not necessarily. Assume the water current was flowing at 100MPH. If the sea plane was taking off against the current it would have to attain a "waterspeed" of 101 mph just in order to get air flowing over the wings. The drag from the floats and the lack of power from the engine would never get the sea plane moving that fast thru the water. Add full power to the sea plane into a 100mph water current and the sea plane is going to do nothing but move backwards and never achieve any headwind airflow over the wings.

 

[COOPERVANE]

Not necessarily. Assume the water current was flowing at 100MPH. If the sea plane was taking off against the current it would have to attain a "waterspeed" of 101 mph just in order to get air flowing over the wings. The drag from the floats and the lack of power from the engine would never get the sea plane moving that fast thru the water. Add full power to the sea plane into a 100mph water current and the sea plane is going to do nothing but move backwards and never achieve any headwind airflow over the wings.

That is VERY accurate, the drag on a seaplane would never let it make any headway against a 100kt current, but the drag generated by the tiny tires of a conventional airplane would be 1,000 times less.

Try the roller skate on a treadmill analogy again.

 

[COOPERVANE]

Jeez....no airflow = no fly

I agree, but there WILL be airflow. Don't be so quick to judge without thinking it through. It is a little bit of a trick question. The question states that the treadmill will compensate for any forward speed of the aircraft. The trick is that it CANNOT do it.


The airplane WILL accelerate on the tradmill, thats the point. The tradmill CANT HOLD IT STATIONARY!!! It will try but it CANNOT DO IT

A little later when the light bulb illuminates, there will be some people who will then blame the wording of the original question for their lack of understanding.

 

[ackattacker]

I guess a lot of pilots failed high-school physics.

Reminds me of the time I was flying with another pilot (ATP even, multiple type ratings) and I suggested we alter course to avoid the thunderstorm at our 12 O'Clock and 30 miles. He said no need... the wind was blowing from our right and the storm would be blown away by the time we got there. I tried to explain about heading vs. course and same air mass and all that and ended up just giving up. Not worth arguing I guess.