Let's say you had a giant treadmill with an airplane on it

[orangeskysurfer]

yall gotta me kinda confused wid all this pilot mumbo jumbo.. but i got me a airboat back at the trayler with big block 350 chevy on da back. yall saying if i go fast enuff i could go up in the air? See i dont reckon i could do thiis cause when i put the throttle up so far past about where my nee is about.. the tork of my engine would make me go sidways and id be gettin all wet with the alligators. now if i put a hifallootin jet engine on dere i reckon i might not have that tork and id be goin reel reel fast. maybe then i could be kinda like yall pilot folk. ill run down to walmart tomorra and pick me up one of them treadmills and ill try it out.. see if i cant geterdun.. suzys always tellin me i shoudl have been a airline pilot cause they make the big bucks, but i was never one of them smart kinds

 

[Leroy Smith]

I thought I would dust off this old gem to kill the PIC thread.

Let's say you had a giant treadmill with an airplane on it.

As you add power and begin to move for the takoff roll, the treadmill speeds up and keeps the plane in the same relative position. As the plane goes faster, the treadmill speeds up, always maintaining the aircraft's relative position.

Would you ever be able to take off?

GO!!

Mr. Vane, you are my new Evil-Genius hero. "Scott Hall" is far more prolific, but this was just pure, unadultarated divine inspiration.

Bravo, Thank You, and may God have mercy on your soul!

 

[PCL_128]

If the airplane will fly, Midway airport wants to talk to you!

Get rid of that short-a$$ set of 30's era runways, and install a pair of threadmills!

Pos-and-hold...run 'em up...and launch!

It'd work, right?

No, because the runway length required for takeoff doesn't change. You'd need to have a treadmill that is just as long as the current runways.

 

[JimNtexas]

another way to look at is an airboat in a river. The thrust of the airboat is from an airplane propeller.

Aim the airboat up river and give her all she's got. If the river keeps accelerating downstream as you speed up going upstream. Will you move?

If the top end of the airboat is 100kts, and the river is flowing at 100 kts the other way, will you have moved past the dock you just left on the shoreline?

That analogy is incorrect. If you are in an airplane that lifts off at 100kts, and you point that airplane into a 100kt headwind then it will take off with a zero length ground roll.

Boats don't rise up off the water, unless they are flying boats.

The acceleration of our airplane with respect to the surface of the earth on the threadmill is given by:

A = F/M

where A is the acceleration in length/time squared, M is the mass of the airplane, and F is the net horizontal force on the airplane. The net horizontal force on the airplane is the thrust from the engines minus aerodynamic drag and rolling resistance.


To hold the airplane still with full thrust from the motors, some equal and opposite force must oppose the thrust of the motors.

 

[runwayjockey]

Since when did wheel speed equate to lift generated? The plane will not fly with no relative wind!

 

[Edge540]

Since when did wheel speed equate to lift generated? The plane will not fly with no relative wind!

Simply stated and 100% correct.

If you think the plane will fly, you are as smart as this guy:
http://www.metacafe.com/watch/315147/treadmill_vs_kid/




.....

 

[yournextFO]

It's all about friction in the wheel bearings....

 

[Blucher]

Come on now, everyone knows you just have BELIEVE you can fly! As long as you believe hard enough, you'll sore like an eagle!

-Blucher

 

[JimNtexas]

Since when did wheel speed equate to lift generated? The plane will not fly with no relative wind!

What force is acting to oppose the airplane's engine thrust and thereby hold the airplane stationary with respect to the earth?

 

[The_Russian]

If the aircraft remained in the same relative position, how could it take off?

 

[The_Russian]

What force is acting to oppose the airplane's engine thrust and thereby hold the airplane stationary with respect to the earth?

The treadmill moves at ANY speed nessecary to maintain the aircraft's relative position. If the speed required is equilivent to 300 knots to maintain the friction required to hold the aircraft's position, the the treadmill can do it.

 

[BigMotorToter]

I can't believe this aspect of this brain teaser hasn't been brought up yet.

What if the pilot of the plane on the giant treadmill is a Jetblue pilot, and he is in the back cleaning the cabin. Can he walk forward (counter to the treadmill speed) to the cockpit to push the throttles up so the engines can generate enough thrust to counter the wheel friction and take off?

Hee, Hee, Hee!

 

[Amish RakeFight]

I can't believe this aspect of this brain teaser hasn't been brought up yet.

What if the pilot of the plane on the giant treadmill is a Jetblue pilot, and he is in the back cleaning the cabin. Can he walk forward (counter to the treadmill speed) to the cockpit to push the throttles up so the engines can generate enough thrust to counter the wheel friction and take off?

Hee, Hee, Hee!

No, but the cabin will certainly be a lot cleaner before it takes off!

 

[30West]

That's pretty scary how many different answers there are posted to this question.
I think most have caught on to the satirical nature, but frighteningly some seem to be serious, though incorrect.

An FI classic!

 

[The_Russian]

Which one do you think is correct?