Nope, you missed again. In the original problem the treadmill IS self powered and DOES match the speed of the plane exaclty. But it doesn't matter. The plane wheels are not powering the treadmill. The treadmill is transmitting force to the wheels which in effect absorb that power and do not transfer it to the airframe so the motion of the treadmill does not slow the airframe in any way. It just spinns the wheels which are along for the ride on the airframe. The engines push the airframe to take off speed while the wheels spin and the plane takes off. Did you happen to catch the video of the fan on the skateboard?

 

You still don't get it. If you were relying on the friction of the wheels turning to power the treadmill the you WOULD NOT take off. But since you are not relying on friction at the wheels(because the engines push the PLANE, not the ground) the plane WILL take off. It would accelerate straight down the conveyor just as it would a normal runway, or frozen lake, or grass strip. You are still thinking of an aircraft in the same context as a car. Where the wheels do the pushing. Imagine this scenario. You disconnect the driveshaft of your truck. You route all of your engine's power thru the tranny to a gearbox that drives a big propeller in the bed. And just like a fanboat, or an airboat this big prop pushes your truck around. No power going to the wheels. Now imagine driving that truck on a solid sheet of glare ice. You would be able to take off from a stop exactly the same as you would on dry concrete. Why? Because the wheels are not being driven, the chassis of the truck is being pushed from behind. Now imagine this truck on a conveyor. Just like the glare ice,this propeller driven Ford does not care what is going on underneath it. It's being pushed up a backwards spinning conveyor just as easily as dry pavement because it's power is not being transferred thru it's wheels.

 

You're not relying on the friction of the wheels to power anything. There is no power going to the wheels of the plane, they are totally passive. All they do is just sit there and spin. If the tread mill is going 60 mph, the wheels of the plane will be turning at least that fast. What makes the wheels of a plane spin? The movement of the body of the plane. The body of the plane is moved by the engines pushing against air. The plane starts moving and hits 1 mph, the treadmill will move backward at 1 mph, and the plane's wheels will be moving 2 mph.

And traxxis, I commented on you vector diagram. Very good.

 

Holy cow - 10 pages to debate this?

Oh, you guys, where are the plane's engines? Powering the planes wheels like a truck? No, of course not. They're up on the wings or in the hull pushing directly on the air. They couldn't care less what the plane's wheels are doing. You can spin the plane's wheels backwards at 400mph if you want, and the engines will continue to happily push against the air around them, blissfully ignorant of the wheels or any treadmill.

This isn't even a physics question - just a common sense question.

 

OH, my head really hurts!!

How about this?

If the air is like a rope and one end tied fast, the engines are like you with your hands pulling on the rope, the same as the engines pulling the air, you do have roller skates on and are standing on a conveyor. You are going to move forward for sure! he roller skates are useless in keeping you stationery, just spinning like heck! They are added in this cause some guy wants to play with your head and not the the obvious!

So it's get even time! Not sure if I'll drop 50 lbs of steel on him or 50lbs of feathers on him! Doesn't really matter as they both weigh the same!

I WILL NEVER BOARD A PLANE THAT IS SPOTTED ON A CONVEYOR!! THIS IS WHAT I LEARNED!

 

It really is this simple:

The plane would not lift off the ground in the scenario (treadmill) described.

Unless it happend to be sitting in a windtunnel or in a hurricane with steady 180 mph winds blowing directly from the front.

It is simple vector addition - 8th grade math.

 

You added the vectors wrong.

 

Yeah, big time. It most definitely would take off. Period. There is no maybe or what if. No headwind needed. The plane creates it's own headwind by travelling at 180 miles per hour.

 

I can't believe we're still discussing this.

 

LMAO, 10 pages and every page had wrong answers on it! The wheels have nothing to do with if it's going to take off. It will fly.

 

10 pages is nothing. Last time I was on the mythbusters page it was at 54 pages.

 

Let me try to help you. Take a perfect wheel on a perfect, frictionless bearing. That wheel and bearing is on a shaft suspended from a rope and touching a moving treadmill. There is no slippage between the belt and the wheel, all force of the belt is transferred to the wheel. The force vector of the belt is trasferred to the wheel and is transformed from a linear vector to a rotational vector. Assuming perfect conditions, the wheel will simply rotate, the axle will not move back and forth on the string due to the force vector applied by the belt on the wheel.

In the original problem, nothing is said about the wheels or bearings so we can assume they are perfect and do not contribute to this problem. The force of the belt goes only to the wheels on the plane where it is transformed into rotational energy. None of that force is transmitted to the axle and hence the rest of the plane. Therefore the force vector of the belt is cancelled by the rotation of the wheels and the only force vector left is the thrust of the engines. The plane flies. Like you said, simple 8th grade math.

 

This isn't the board you're referring to is it? This one is a physics board, and they're at page 129 in their debate.

 

nope...

I just browse through the other board and all I can say is "Incredible!"

 

Thanks for the offer, but I'll return the favor (offering to help)

It won't fly.

If it WOULD take off under the circumstances desribed, then there have been HUGE blunders made over the years. Those large, heavy drag inducing appendages on aircraft known as "wings" are, in fact, NOT NEEDED.

Lift is generated by THRUST, not Bernouli's principle.

NOT!!

There is no lift (no vector perpendicular to the force of gravity) - there is no flight.



As I think about this now, I do NOT believe that anybody really believes the plane would fly.

I DO believe folks post acting like they believe it just to hassle guys like me and keep an amusing thread going.

And some folks will reply to this post saying they absolutely DO believe the plane would fly, all the while laughing, knowing full well it would never leave the ground.
Also knowing guys will continue to repsond to try and convince them it really would NOT fly.



That's what I think.