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

[orangeskysurfer]

disregard

 

[orangeskysurfer]

The reason I like this riddle is because the first time it was posted, I could not believe ANYONE in their right mind would think it would fly. The whole relative wind thing.

I and several others argued till we were blue in the face.........And then it clicked......And I got it. I came slinking back to the computer and admitted that I was wrong. One by one some of the most well respected members saw the light and sheepishly agreed that it would fly.

It is a flawed question in that the plane WILL move forward eventually. The treadmill will TRY to keep up but it wont.

Coopervane - I thought you posted this as a joke!! Is this last post just darker sarcasm to add fuel to the fire?? Like just previously posted unless assumptions are made that you would eventually overpower the treadmill.. I dont see how youd fly..

If mythbusters did choose to take on such an idiotic myth.. It would most likely be way too expensive. seeing as they would need to use a jet aircraft.. any prop driven aircraft would not be able to maintain directional control as torque comes into play as you open the throttle.. torque would become much more pronounced than if actually on a takeoff roll.. With no wind flow over the rudder you would not be able to counter the left turning tendencies at even slow speeds.. Thus the only thing maintaining the centerline would be nose wheel steering.. Assuming the torque didnt steer you off the left side of the mill.. Friction on the nosewheel would increase very rapidly.. blowing the nosewheel and youd go tumbling off the rear of the treadmill..

If that last post WAS sarcasm.. right on!! ya got me to take a bite..

 

[hindsight2020]

JHC, I cannot believe this thread came back...which once again proves that it doesn't take an engineering degree to become a pilot, but that likewise it doesn't take full knowledge of why an airplane flies for somebody to take off and land without disclosing that fact ...SCARY!!!

Listen up. The only relevance a moving surface would have on the aircraft's ability to positively affect its relative motion is if the aircraft's thrust was enacted through the point of contact in question, the treadmill in this case. If it wasn't clear in PPL ground school, let me refresh the class: that cessna is NOT a car....repeat with me, IT'S NOT A CAR.

The thrust created by the engine, whether the propeller driven or jet persuasion alike, is translated through a different medium, not the ground, but the fluid we call air. Therefore, the only force the aircraft has to overcome on initial takeoff is the static friction force to make the tires begin to roll. As you can see the fact that the airplane is sitting on a moving or stationary platform is irrelevant to it. Taking into consideration the assumption that tire limit rotational speed is neglected, it doesn't matter how fast that treadmill is moving, all the airplanes sees is air beginning to rush through its wings once you push up that/those throttle(s).

To further illustrate the point of why force medium matters, clamp a rope to the front end of the aircraft to a post at the end of the treadmill, a stationary fix. Now, crank that treadmill into uber-ridiculous speed...what happens to the aircraft's relative motion with respect to the air? Nothing, the airplane sits there fat dumb and happy, 0 KIAS, with the tires spinning at the tire equivalent rpm for uber-ridiculous speed. Now what about the rope? hmm...yep, once again nothing. Furthermore, the tension force will STILL be nothing more than the friction force required to make the tires begin to roll from rest.

Now, push up the throttle, what happens? Holy crap a miracle! The rope slacks and the mighty cessna moves forward with respect to the air and the tires still on fire at uber-ridiculous speed-rpm+(rpm equivalent to X KIAS). But wait. Let's put skids on that son'b%tch, assume the treadmill is now an icy treadmill, and what happens? No way! It still moves relative to the air REGARDLESS of that moving treadmill at uber-ridiculous speed.

In a real world scenario, what would happen is that the takeoff roll would be increased by the initial head-start you gave the treadmill as it began moving the aircraft backwards with respect to the air as you sat there wondering to yourself if this experiment was going to work or not. A takeoff with an initial tailwind if you want to look at it in more familiar fashion. After brake release, throttles up, the wheels start rolling and you're moving forward w.r.t. the air son.

IF the aircraft had to overcome the speed of the treadmill by means of enacting its thrust by rotating the wheels, then the treadmill would be relevant. Look at it this way. Your bass boat is going up the river and the stream is wayyy too fast for that mercury, your buddies at both banks see you sitting there idling with respect to them, at max power, and throw you a rope, then pull you in. Are they able to pull you in in spite of the wicked fast stream? Sure. And that's a worse case scenario than the airplane on a treadmill, as the water will create higher parasite drag the faster the stream, which means billy bob needs to pull a little harder, whereas the aircraft tires will keep the friction force constant no matter the speed of the treadmill. So, if you can at least buy the "buddies pull you with positive relative motion in spite of the river speed" scenario then convince yourself that strapping an IO-360, with included propeller, to your head while you duct tape yourself to your bass boat is AN EQUIVALENT SYSTEM PROBLEM!!!!

If you cannot convince yourself of the latter, you need to go back to high school physics, for you will never understand why the airplane WILL attain flying airspeed regardless of a moving ground surface. F%ck, I need my g/f...and a drink.

 

[Edge540]

For those of you who say the airplane will fly...prove it.
For those of you who say the airplane will not fly...prove it.

Let me rephrase what you posted:

If you think it will fly..... you are a f*ing retard.

If you think it will not fly..... thank God someone out there has some sense.

How can you people honestly entertain this concept? Go bitch about something useful! This wheel speed must equal flight bs is ridiculous.

 

[PCL_128]

Let me rephrase what you posted:

If you think it will fly..... you are a f*ing retard.

If you think it will not fly..... thank God someone out there has some sense.

How can you people honestly entertain this concept? Go bitch about something useful! This wheel speed must equal flight bs is ridiculous.

Pretty soon this concept is going to click in your mind and you're going to realize just how much of an a$$ you made out of yourself. The plane will fly. It's just basic physics.

 

[Flysher]

Let me rephrase what you posted:

If you think it will fly..... you are a f*ing retard.

If you think it will not fly..... thank God someone out there has some sense.

How can you people honestly entertain this concept? Go bitch about something useful! This wheel speed must equal flight bs is ridiculous.

so you dont think the prop will pull the plane down the treadmill?

BTW im not a f*ing retard.

 

[Edge540]

so you dont think the prop will pull the plane down the treadmill?

BTW im not a f*ing retard.

All I'm saying is that without airflow moving over the wings at a sufficient rate to provide enough lift for flight, there will be no flight. A plane, stationary, on a treadmill will not fly....no matter how fast the wheels are spinning. Now if some how it can overcome the speed of the treadmill and gain some forward motion.... then I guess there is hope (if that's what you are asking).

 

[Herman Bloom]

I just took physics last year, and the professor put this exact question on the test. About 75% of the class answered that no, the airplane will not fly.

The rest of us got the question right.

It will fly, or so says a PhD physicist at George Mason University.

Any questions?

 

[Flyer1015]

All I'm saying is that without airflow moving over the wings at a sufficient rate to provide enough lift for flight, there will be no flight. A plane, stationary, on a treadmill will not fly....no matter how fast the wheels are spinning. Now if some how it can overcome the speed of the treadmill and gain some forward motion.... then I guess there is hope (if that's what you are asking).

That's the point, you're missing it.


The airplane DOES move forward DESPITE the treadmills opposite direction.

The wheels of the airplane will move forward, the treadmill goes opposite, but the friction force can only 'hold' the airplane for so much.

Soon, the airplane will move forward on the treadmill, burning rubber, smoking, and requiring tremendous power.


Theoretically, if the treadmill is long enough (several thousand feet long), and if you can get enough power, and if the tires are strong enough to take that kind of abuse, then the airplane will takeoff.


Note that the airplane is not stationary... it does move forward.



Theoretically, it can take off... realistically? No... tires will burst, and the plane will require much more power than trying to takeoff on a paved runway. So realistically, won't take off. Theoretically, it will.

 

[Edge540]

I just took physics last year, and the professor put this exact question on the test. About 75% of the class answered that no, the airplane will not fly.

The rest of us got the question right.

It will fly, or so says PhD physicist at George Mason University.

Any questions?

Yes..One:

If the airplane is not moving forward, where is the air coming from to provide lift? No relative wind = no lift

I always thought that catapults on aircraft carriers were worthless. They should just put a treadmill on it!!! What were they thinking?
uke: