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

[Edge540]

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.

No movement.

 

[ImbracableCrunk]

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!!

It seems to me that there are three camps:

1. The This is a joke camp.

2. The It'll eventually accelerate because I know more about physics than you camp.

3. The This question clearly states the plane remains in the same spot (ignoring wheels and friction and z-ratings) camp.

Why does this question make me think of dihydrogen monoxide?

 

[PCL_128]

Yes..One:

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

The airplane does move forward. The treadmill can't counteract the thrust provided by the prop/jet. Simple.

 

[ImbracableCrunk]

The airplane does move forward.

Hmmm. The question clearly states that the airplane stays in the same relative position. How do you respond to that given?

 

[PCL_128]

Hmmm. The question clearly states that the airplane stays in the same relative position. How do you respond to that given?

The question is written incorrectly. Quite simply, it's impossible for the treadmill to hold the airplane in the same relative position. The airplane will move forward despite the opposite direction of the treadmill.

 

[ImbracableCrunk]

Ahhhhhhhh. The fourth camp:

The I know what question was really asking camp, even though it clearly states something else camp.

 

[belchfire]

Ahhhhhhhh. The fourth camp:

The I know what question was really asking camp, even though it clearly states something else camp.

Na, now there's a fifth camp...the camp that says the question was posed by someone that was educated beyond their native intellectual capacity...that knew little about the limitations of treadmills and even less about aircraft!

What, the Cylons are building giant fracking treadmills now instead of more Cylons???

The chemtrails are falling the chemtrails are falling!

 

[Edge540]

Ahhhhhhhh. The fourth camp:

The I know what question was really asking camp, even though it clearly states something else camp.

:beer:

 

[runwayjockey]

You guys have way too much time on your hands!

 

[runwayjockey]

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.

The original question assumes the aircraft does not move, It states "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.

An aircraft with no relative wind will not fly! This question clearly states the aircraft has no relative wind.

 

[Edge540]

How about this one. You take off in a tail wind, as you increase forward speed the tail wind also increases to match your forward speed, Aircraft 10 KIAS, Tail wind 10 Knots, seconds later aircraft 20 KIAS, Tail wind 20 Knots, several more seconds later Aircraft 100 knots, Tail wind 100 knots. Would the aircraft take off?

I think you might have written the question wrong. KIAS is indicated airspeed, and if you have indicated airspeed you have relative wind flowing into the pitot tube and therefore across the wings. With indicated airspeed you generate lift, with enough of that stuff you will fly.

 

[runwayjockey]

I think you might have written the question wrong. KIAS is indicated airspeed, and if you have indicated airspeed you have relative wind flowing into the pitot tube and therefore across the wings. With indicated airspeed you generate lift, with enough of that stuff you will fly.

Should have been ground speed not KIAS, you posted it before I could finish the edit.

 

[Edge540]

Should have been ground speed not KIAS, you posted it before I could make the correction.

Yeah, I figured as much. In your new scenario the plane would not fly. The tires would blow up and you would come to a grinding halt. All without ever getting a single knot IAS out of the deal.

 

[aussieflyboy]

The difinitive answer is NO, no takeoff!!!!

Here's why...

The question clearly stated that the relative position is maintained constant. This is the key thing!!! The people who think that it'll take off and are using the rationale that the airplane will move forward based on the fact that the airplane will be propelled despite the treadmill. That's what would happen in reality, but it's not what was specified in the question.
The question specifically stated that the airplane MAINTAINED ITS RELATIVE POSITION!!!

This scenario is best simulated by a float plane trying to take off against a raging current. If the float plane was doing 50 knots of speed through the water but the current was also 50 knots then the float plane would have zero knots of relative motion, therefore the wings of the stationary airplane would not be moving too, thereby producing zero lift.

To all you guys saying people like FEDEX were stupid, you're the dumb ones, there's no way that the airplane would get airborne, NO WAY AT ALL, given that the question specifically said that there was no relative motion.

Dopey mofo's

 

[aussieflyboy]

I'm sucked in because I starting to have a hard time telling who believes what. . .

Just because someone asks a question, it doesn't mean the question itself is valid. The question has two mutually exclusive states.

If you begin to move and the plane goes faster, you could takeoff.

However, if you are in the same relative position and maintaining the aircraft's relative position, you will not fly.

Bingo!!!!!!!!!
I'm glad someone else understands what the F**K's going on here...
The question is flawed. As stated, it wouldn't fly, but if the plane started moving, it would.

Anyone who thinks that if the plane stayed in the same position on the treadmill and would still lift off is a complete dumbass and slipped through the cracks to get his pilot's license and/or college degree!!!!! (and there are alot who believe that based on the posts on here)

 

[Flyingdutchman]

Its amazing how much idots out here think it would fly... down right scary.

Please turn in your CPL/ATP

No relative wind = no lift !!!!!!

 

[Flyingdutchman]

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.

Are you for real ?

 

[unreal]

Woosh!

 

[Edge540]

Woosh!

Not the same scenario.

You guys think we have too much time on our hands? Think about the guy who made that graphic.

 

[Flyingdutchman]

Woosh!

1) You need to get laid

2) The original question assumes the aircraft does not move, It states "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.