Caporegime
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Re-build the pyramids.
What Myth would you want to see busted?
- Thread starter Linkex
- Start date
With regards to the plane on a conveyor belt, I'd also like to point out a story from an old WW2 pilot i knew, sometime after the war he was flying a light aircraft into a small airfield. Now the landing speed of this aeroplane was about 70knots, and the wind speed was about 70mph. He had to perform a rather tricky manoever and actually landed the plane vertically like a harrier, once on the ground with engine still running and the airspeed indicator still reading 70mph he had to get some ground crew to come and hold the wings of the pane down and chock up the wheels so he could turn the engine off.
Basically if you put a plane on a treadmill that was at the same speed as take off then it would fall off the end very quickly, if you increased the speed of the treadmill with the speed of the engines then the plane would stay on the treadmill. If wouldn't take off though because the plane would only be going fast enough to stay stationary with the air and it is the movement of air over the wings that creates lift. Helicopter becomes a little more tricky because of the tail rotor.
Basically if you put a plane on a treadmill that was at the same speed as take off then it would fall off the end very quickly, if you increased the speed of the treadmill with the speed of the engines then the plane would stay on the treadmill. If wouldn't take off though because the plane would only be going fast enough to stay stationary with the air and it is the movement of air over the wings that creates lift. Helicopter becomes a little more tricky because of the tail rotor.
After thinking about it (before you posted the video) I'll concede the plane on the belt thing, but that is because it is using the air as it motive medium and tire friction as it's negative medium, hence they don't cancel and as you say the rotation spins twice as fast.
Not sure that it applies to the helicopter though as both rotators are using the same medium friction to a surface, ie turntable spins helicopter due to surface friction, helicopter spins blade due to surface friction.
Not sure that it applies to the helicopter though as both rotators are using the same medium friction to a surface, ie turntable spins helicopter due to surface friction, helicopter spins blade due to surface friction.
Soldato
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*facedesk*
conveyor belt movement != air movement
mythbusters have proved this one with a full size plane. it is a fact that a plane on a conveyor belt will take off no matter how fast the conveyor belt is going
That doesn't even make sense. The resistance is always there due to gear and bearing friction. The reason I can't push a heli rotor around by hand isn't because "it has to compress the air" it's because it is attached to large hunks of metal which are attached to even larger hunks of metal being held in place by large chunks of metal.
If it was an infinite conveyor belt though and the plane had to start from zero it wouldn't take off because the wheels are still attached so it would never get forward momentum.
Jesus wept....
I can't believe people are still struggling with this. I don't know whether to
or 
This would only be true if the spin speed of the wheels was limited to the speed of the experiment.
Think about it, the plane is travelling at 700mph backwards, or whatever Vmax is in a 747, no way is it ever going to take off!
Soldato
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yes it would take off. the sum total of the effect of a conveyor belt on a plane is making its wheels spin backwards. while this will have a very tiny effect on the planes speed it will not stop it from taking off because a plane powers itself with a giant prop/jet engine blowing air backwards which, by newtons laws, makes it go forwards
mythbusters have proved this with a full sized plane and conveyer belt.
back to the helicopter on the turntable:
helicopter spins anticlockwise at 100RPM
engine has max speed of 100RPM in other direction
engine cannot rotate relative to the helicopter, so the engine itself is rotating at 100RPM anticlockwise, or -100RPM clockwise
engine gets to max speed of 100RPM
blades go at -100RPM + 100RPM = 0RPM
how you think that an engine that is rotating has no effect in the internals boggles my mind.
That's not the resistance I'm talking abut, when an engine is off you have a massive amount of resistance which isn't there when it's running,
And lol.
Les go to car.can you push a car with clutch in. Yes you can despite being joined to massive lump of metal. Now pop it in gear. And try pushing it, you won't budge it. Due to the resistance in the engine. You now have to provide not only the nervy to move the crankshafts and pistons, but to also compress the air in the cylinders..
No the Ground is moving the wheels 700 mph.
The forward thrust (Air thrust) is also still moving the vehicle forward at 700 MPH
So your wheels spin at 1400 MPH but you still have your relative movment forward using air thrust.
This IMO differs from the helicopter problem as plane wheels are free spinning and have no direct force to turn them the same cannot be said for a helicopter rotor
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This is what i think, but then until literally about 5 minutes ago i thought a plane couldn't take off from a treadmill.
What happens to the tail rotor?
Somebody really needs to draw a picture i think.
My mind has literally just melted a little bit. Can't believe i got to this age not knowing we should install treadmills at airports.