A harmless little riddle

I have never seen an airplane standing still take off.

There is a speed for every airplane known as Vy which is the airspeed which the wings create lift enough to take off. This number is different for every aircraft.

So to answer your question, the plane must have an airspeed of Vy in order to take off.

Im no physicist, but I fly almost every day.

You guys are looking at the problem the wrong way. The answer has already been said, but people are still arguing. Unlike cars, the wheels of planes are not powered. When they're on the ground, they're either being towed, or the engines are giving the trhust. This means that the wheels can spin freely. Therefore, if the plane's thrust is 150 mph, the treadmill is goping 150mph, the relative speed is 300 mph so the wheels are turning incredibly quickly, it will slow down a bit due to friction, but essentially the speed will still be around 150 relative to the ground.

it WILL take off.

The plane will not take off, a big portion of why a plane is able to fly is not due to the engines but to the lift developed by air passing under the wings. If the plane is on a treadmill going at the same rate of speed as the wheels on the aircraft, the air under the wings is therefor not accelerating and therefor not producing the lift necessary for the plane to take of, the engines just keep the plane moving forward, the wings provide the life necessary for flight. If it was on a treadmill it would be like having a plane with engines but no wings, because on the treadmill the wings dont provide any lift. For every action there is an equal and opposite reaction, which is what the engines provide by moving air at a high rate of speed giving the plane thrust but on a treadmill there will be no lift so the plane WILL NOT FLY!!!

I agree with the above poster, since the riddle CLEARLY states that the treadmill is coated with a special NO LIFT substance that will prevent the plane from taking off. HURR HURR

Sreiously, did you read a single post besides the first one?

Your point is well made. I can't figure why people think the 150 mph speeds should be added to make 300 MPH. The belt of the treadmill and the wheels of the plane are going in opposite directions. While the engine would normally be propelling the plane forward creating air movement around the wings which makes the lift, the treadmill negates the forward movement.Of course the plane will not fly. It would be neat if they could, we wouldn't need airstrips for take offs, just large belts that would spin with the wheels and the plane would take right off. People are dreaming if they think this is possible.

How many times does it need to be clearly demonstrated that the plane will be moving forward, and that moving forward creates "air passing under the wings" (over, for lift, actually), and that this will generate lift and allow the plane to take off?

Try it out yourself with any free-wheeled object. Take your roller blades to a treadmill, and apply constant forward force to them up the treadmill belt. You will easily overcome the treadmill and move the rollerblades off the front.

1) The plane must move forward to take off

2) The plane has propulsion capable of moving it forward

3) No force great enough opposes this propulsion

It will take off.

And also, it will not magically take-off by spinning the wheels. This is not an argument for the use of conveyor-belt take-off methods.

It must travel a certain distance until it reaches a speed that provides enough lift. It will either hop off the treadmill and continue to accelerate and lift, or it will reamin on the long treadmill until lift.

Your roller blades will over come the treadmill if they are moving faster than the belt. If the wheels are moving at the same speed you don't move forward.

Take your roller blades to a treadmill, and apply constant forward force to them up the treadmill belt. You will easily overcome the treadmill and move the rollerblades off the front.

I didn't say that. By your logic, turn the engines on and have the wheels spin on the belt on the plane should fly, right

But your second paragraph argues our point. Yes the plane must travel forward.

And also, it will not magically take-off by spinning the wheels. This is not an argument for the use of conveyor-belt take-off methods.

It must travel a certain distance until it reaches a speed that provides enough lift. It will either hop off the treadmill and continue to accelerate and lift, or it will reamin on the long treadmill until lift.[/quote]

After reading most of this thread, and seeing supposed aerospace experts and physics teachers argue, in the face of overwhelming logic and evidence to the contrary, that this plane won't take off, I wonder which of the following statements is true:

1. We have been witness to a virtuoso trolling performance. It takes a talented writer and a good understanding of the question in order to counter the correct arguments without appearing to be too ignorant and without revealing oneself as a troll.

2. We have been witness to a sad demonstration that makes it more apparent how such a large proportion of one of the wealthiest and highly-educated populations in the history of the world can still believe in nonsense like creationism, or that the sun orbits the earth.

Your post is on the money. Interesting.

I'm guessing the second point is realty. Didn't our president state that Intelligent design should be taught along with the science of evolution?

Do you think presidents of the other technologically advanced countries would say that?

I have no physics education beside some common sense.

If I stood on a tred mill wearing a pair of roller skates the amount of energy needed for me to keep from being thrown off is just a little more then the amount needed to push me forward,assumming a flat treadmill.So the wheels are dissapating alot of the treadmills energy using the spinning motion.Now if I also had a rocket motor strapped to my back that had way more energy than what it took for me to hold on and let the wheels spin I would go rocketing forward.IOW the plane takes off but needs a bit more than normal amount of thrust to do so.

Charlie

Charlie,

What you are failing to realize is that if you had a rocket pack to help push you foward, the treadmill would speed up to help hold you in place. The force generated by the treadmill is equal to whatever force or forces you have to push you foward. Thus, negating all force and providing no motion.

Has anyone mentioned the term aerodynamics. Without air flow, lift cannot occur. Velocity relative to the ground is irrelevant. Look at it this way, if a hurricane comes through town with 200mph winds, a plane could lift off and "fly" though technically, it would not change horizontal positions on the earth. Kind of defeats the purpose, doesn't it?

If he's on skates the force to move him forward is the same if the treadmill is going 1 mph or 100 mph. Think about it.

If you're standing behind the treadmill pushing on his back you won't need to exert more force to hold him still as the speed of the treadmill increases.

Jack, Jack, Jack

Congratulations. I can see the blurb on the main page: 'Jack Frost' is troller of the year for 2005 with a strong push durng the final eligable days. With a brilliant act of innocent ignorance he kept dozens of posters perplexed, constantly replying and trying to sqeeze water out of a rock.

You are my hero Jack Frost

Granted, I haven't read every single post, but with all of the supposed "aerospace experts" weighing in on the topic, why hasn't a single person mentioned the three most basic words in all of engineering... three words, that when applied properly, would reduce all this meaningless jibberish to just that...

FREE BODY DIAGRAM!

Draw a free body diagram of the f***ing plane. The "backward" motion of the treadmill produces a slight backward force on the plane due to ROLLING RESISTANCE (not friction) of the tire/treadmill interface as well as a small backward force due to bearing friction between the wheels and axles. That's the only force that the treadmill imposes on the plane. Peiod. Now, draw the THOUSANDS OF POUNDS OF THRUST (another word that I haven't seen yet) in the OPPOSITE direction, and it will be clear that, most definately, the plane will generate plenty of force to move and no doubt, take off.

I defy any of you jackasses to draw a free body diagram and contradict me.

Stupid motherf***ers.

A vote for "No" with some input from my aerospace engineer dad. I'm also in the industry but as a tech writer (i.e. no real knowledge). Here's my experiment...

Take an average Hot Wheels car. I like the ones made of shiny gold best. Put it on a regular treadmill at the gym. Turn the treadmill on. What happens? The car flys off the back.

Go retrieve the car. I'll wait. Got it? Good. Now place it on the treadmill and have a friend turn on the treadmill again. The car again head backwards on the treadmill thanks to our good friend Mr. Friction. However, this time something I like to call "The Hand of God" (your hand) steps in and holds the car in place. The car is now stationary on the treadmill. You are exerting a force on the car, albeit a very, very (nearly undetectable) small one as the car is very, very tiny.

Now exert a bit more force (without increasing the treadmill's speed)...the car moves forward on the treadmill. If your friend increases the speed of the treadmill, at some point forward progress will again halt when the speed on the car produced by the force (your hand/arm/stregth) equals the speed of the treadmill.

Now lets head outside where John Travolta has kindly donated his jumbo jet and an extra large mile and a half long treadmill (just to be safe) for this experiment. We start the same way, but firing up the treadmill with an unpowered plane. Wham the plane flys back and off into the distance.

It's gone, but thankfully we have another ready to use. We fire up the treadmill and the plane again drifts back. But then we use the plane's own "Hand of God" (the big jet engines) to match the speed of the plane to the speed of the treadmill. Again, like your hand holding the car in place the plane's engines (much bigger hands for a much bigger objects) keep the plane from moving. The engines are roaring, but because no air is moving over or under the plane's wings, everyone's grounded.

Also think about it this way:

You're driving a plane down a runway at a constant 50mph. The second half of the runway is a treadmill spinning at a contant 50mph. What happens when the plane reaches the treadmill? I think it will stop and would invite other points of view.

This topic has completely ruined my day and my run. My girlfriend hates me because all I've been talking about is finding a surplus 747 and 2000 treadmills.

I just thought of another way of explaining it to you non-engineering majors.

If a plane is in the air, and you're hanging off the landing gear with a power drill spinning the wheels in the direction opposite of it's flight, is the plane going to fall out of the sky?

And yes, the relative TANGENTIAL velocity is 300 MPH (at the tire/treadmill interface) if the plane is moving 150 MPH (relative to the ground) in one direction and the treadmill is spinning at 150 MPH in the opposite direction.