The greatest question in the history of human kind.

[rotor_av8]

Re: The greatest question in the history of human kind.

I watched the video. The plane moved foreward of course because the wheels are only slowed by the friction of the bearings and that isn't much. What a lame myth. They should have had the plane stay in one location relative to the ground. THEN the only air moving over the wings would be the prop wash.

I actually think myth busters misunderstood this myth. "Like a treadmill" implies that the aircraft does not move relative to the ground. When you run on a treadmill you don't move foreward.

Did anyone see the videos I posted? I thought those were a TON more interesting.

 

[mudmagnet63]

Re: The greatest question in the history of human kind.

I actually think myth busters misunderstood this myth. "Like a treadmill" implies that the aircraft does not move relative to the ground. When you run on a treadmill you don't move foreward..

Thats because your legs are the mode of movement and are in contact with the treadmill, same as a cars wheels Prop, Prop Prop

 

[SgtMaj]

Re: The greatest question in the history of human kind.

I think that is pretty much the cruix of the misunderstandings... but if you read the airplane on a treadmill thread, it does explain that the plane is not held stationary.

I think that if the word treadmill was replaced with "moving runway"... more people would get it.

 

[mudmagnet63]

Re: The greatest question in the history of human kind.

Ah confucious say man who stand on stool high on pot

 

[Bass Man Bruce]

Re: The greatest question in the history of human kind.

Did anyone see the videos I posted? I thought those were a TON more interesting.

Yes I did and yes they were.

btw I think the treadmill works great in the myth as so many people are unable to separate the wheels from the prop vis a vis propulsion.

 

[QC]

Re: The greatest question in the history of human kind.

Agree ^^^^^^ this is the 2nd thread that proves that!

 

[mike176]

Re: The greatest question in the history of human kind.

I would have belived it if the tredmill/runway was moving just was fast as the air moving under the wing of the plane and the plane lifted off without any forward motion. Think about it, if it really worked don't you think the navy would have done this on aircraft carriers a long time ago? Sometimes i think "mythbuster science" is somewhat fuzzy.

 

[puddle jumper]

Re: The greatest question in the history of human kind.

I thought this thread was gonna answer "What do women really want?"

It's kinda like Jeopardy, "and the answer is, The greatest question in the history of human kind."

"What do women really want?"

I dont know but i just bought my wife a new fishing rod/reel combo. I think its going to work just fine for me.

 

[JustJason]

Re: The greatest question in the history of human kind.

if there is minimal to no breeze.... can you fly a kite without running???

It's a sham... there is no way a plane can take off on a treadmill type machine.

It all comes down to airspeed over/under the wing.

It's the speed of the air that matters... not the speed of the rollers/wheels.

Lets say you take a plane... and with its current configuration (amout of lift by design.. and HP) When it's actually flying its only going to go so fast. A plane has its own WOT... and that's it.
So if a plane takes throttles up on a treadmill. and if there is no breeze (headwind) It will slowly out accelerate relative to the treadmill. It will keep on doing so unless the length of the treadmill is indefinite. Eventually (if the treadmill is long enough) The max HP of the plane will only let it pull the plane so hard.
Now if that plane is at WOT, and the treadmill is at a matching speed 1 of 2 things can happen.
1. you can slow down the treadmill, and keep plane prop rpm constant... which would mean the plane would accelerate against the treadmill (and also the air) and if it has enough... it will take off... it would probably take miles of treadmill or 1 thousand pounds of thrust in a 500LB plane to do so.
or..
2. You speed up the treadmill to the point that the plane can not keep up... again this would take miles of treadmill because the loss through friction on the wheels isn't a huge number. But eventually the friction will matter, and the plane will slowly slide back untill it falls off the treadmill.

 

[SgtMaj]

Re: The greatest question in the history of human kind.

2. You speed up the treadmill to the point that the plane can not keep up... again this would take miles of treadmill because the loss through friction on the wheels isn't a huge number. But eventually the friction will matter, and the plane will slowly slide back untill it falls off the treadmill.

The only way to do that, would be to speed up the treadmill to near light speed. There is simply not enough friction in the wheel bearings to successfully keep the plane stationary unless they are travelling between tens and hundreds of thousands of miles per hour.

 

[SgtMaj]

Re: The greatest question in the history of human kind.

Going back to the name of the myth... if they actually put the plane on a treadmill, it wouldn't fly, because the treadmill would act like wheel chaulks... this should instead be called airplane on a conveyor belt... since treadmills aren't much bigger than the wheels themselves, but conveyor belts can be as big as you want.

Just my .02 cents worth. I think if you asked the same people who didn't think it would fly if they thought it would take off on a conveyor belt... half of them would say yeah. The other half would still not get that the engine doesn't run the wheels.

 

[JustJason]

Re: The greatest question in the history of human kind.

The only way to do that, would be to speed up the treadmill to near light speed.

no not light speed.... it would be the same speed as the WOT speed of the plane

 

[Caveman Charlie]

Re: The greatest question in the history of human kind.

I would have belived it if the tredmill/runway was moving just was fast as the air moving under the wing of the plane and the plane lifted off without any forward motion. Think about it, if it really worked don't you think the navy would have done this on aircraft carriers a long time ago? Sometimes i think "mythbuster science" is somewhat fuzzy.

How would this help the navy? As was proved on the show the plane still will, and has to, move forward .Then it takes off.

 

[SgtMaj]

Re: The greatest question in the history of human kind.

no not light speed.... it would be the same speed as the WOT speed of the plane

Another victim of not being able to seperate wheels from engines...

If you run the conveyor at the WOT speed of a plane, the wheels just spin twice as fast as the WOT speed of the plane, because they are not linked in any way to the throttle. The engine of the plane acts like a winch... you can move the conveyor under the plane just as fast as you want, and the plane will still move forward at the same speed that the winch is pulling.

Think of it this way, what's the fastest plane ever built... mach 11 or something like that? Run the conveyor at mach 11 with the plane chained to a winch that's not moving? What happens? The wheels spin at mach 11... now start cranking the winch, what happens? The wheels spin at mach 11 plus the speed of the winch and the plane moves forward and air begins to move over the airfoils (wings) which begins to create lift. Now lets say you run the winch at 500mph (well beyond the liftoff speed of any aircraft)... what happens? The same thing, except now the plane is moving forward fast enough that the air passing over the wings is enough for it to take off. That's exactly what's happening here because the propellor acts like a winch. It doesn't matter how fast the wheels are moving, because the propellor will pull the plane forward through the air at the same speed as it would if the wheels wern't moving at all.

Another way to think of it is this...

If a plane is flying over a conveyor belt at an altitude of 100 ft... does it matter how fast the conveyor is moving? Nope... does it matter how fast the planes wheels are spinning? Nope. The only thing that matters is the airspeed of the plane, which is achieved the same way in the air as it is durring takeoff... the prop is pulling the plane forward through the air.

So now imagine that plane flying at 100ft. is at WOT and has an airspeed of 100mph (just for the sake of easy math)... now assume that the wheels are spinning at a speed that matches the speed of the conveyor moving under it, and let's say the conveyor is moving at twice the speed of the plane at WOT... The plane is still flying the same because it doesn't matter how fast the wheels spin... so now if the pilot descends until the wheels touch the conveyor, has anything changed? Is it any different than if the plane was flying above the conveyor? Not at all.

So the aircraft takes off, unless you move the conveyor so fast that the ever so slight friction of the wheels is enough to overcome forward thrust... but that requires the conveyor to move much faster than we have the capability to move anything... think of it this way, airplanes on skids still takeoff, even though the skids excerpt thousands of times the amount of friction that wheels do... so to to move the conveyor at a speed high enough to slow a wheeled aircraft, you would have to move the conveyor at thousands of times the speed that you would have to move it to keep an aircraft on skids from taking off... and since aircraft on skids already have proven they can move over land at more than 100mph... you'd have to move the conveyor at thousands of times 100mph to have the same effect on a wheeled aircraft, as a non-moving runway has on an aircraft on skids. You're already past the speed of light, and you haven't even put enough friction into the picture to prevent it from taking off.

And that's why the plane will always take off.

 

[i386]

Re: The greatest question in the history of human kind.

Here's another way to look at it.

Put on a pair of roller skates and get on the treadmill. There's a pair of handrails running parallel to the treadmill on each side of you. Hang onto those. Now start the treadmill. As long as you hang on you do not move backward. Now, to move forward you just pull with your hands. It will not require much more effort to pull yourself forward on a moving treadmill than a stationary treadmill. As you increase the speed of the treadmill you will find it doesn't require any extra effort from you to continue moving forward.

Ok let's loose the handrails. Now let's tie a rope to a fixed object in front of you. Start the treadmill and hang on. As you increase the speed of the treadmill, it does not require that much more effort from you to hang on to the rope. (Neither does water skiing). Now start pulling the rope toward yourself. You move forward on the treadmill.

It should become clear that as long as your method of propulsion applies force to a fixed object, it's not necessary to overcome the treadmill as your wheels just spin freely.

 

[Nos4r2]

Re: The greatest question in the history of human kind.

AAAAAAAAARGH!!!!!!!!

It FLIES.

For the treadmil/conveyer to make the plane stay stationary the treadmill would have to be moving at MANY times the speed of the plane-and THATS NOT THE IN THE PARAMETERS!

Mudmagnet... Confuzus say, many dumb people make hard work of contemplating wrong question.

 

[lakelivin]

Re: The greatest question in the history of human kind.

Here's another way to look at it.

Put on a pair of roller skates and get on the treadmill. There's a pair of handrails running parallel to the treadmill on each side of you. Hang onto those. Now start the treadmill. As long as you hang on you do not move backward. Now, to move forward you just pull with your hands. It will not require much more effort to pull yourself forward on a moving treadmill than a stationary treadmill. As you increase the speed of the treadmill you will find it doesn't require any extra effort from you to continue moving forward.

Ok let's loose the handrails. Now let's tie a rope to a fixed object in front of you. Start the treadmill and hang on. As you increase the speed of the treadmill, it does not require that much more effort from you to hang on to the rope. (Neither does water skiing). Now start pulling the rope toward yourself. You move forward on the treadmill.

It should become clear that as long as your method of propulsion applies force to a fixed object, it's not necessary to overcome the treadmill as your wheels just spin freely.

Congratulations i386, you not only clearly explained the answer, you also clearly illustrated the original hypothesis, which seemed to be as big a source of confusion as anything else!