I haven't had a helo in an elevator, but I can say that the helo doesn't move with the flight deck when the ship goes up and down. We wish it did, though...

Oh no.... think of the possibilities for argument:

1) We could build proximity sensors into the helicopter that sensed the approach of the floor or ceiling and change the helicopter's altitude (relative to the ground) to a constant relationship within the upper and lower hard decks of the elevator. <img src="/forums/images/graemlins/wink.gif" alt="" />

2) We could posit that because the helicopter was operating in an enclosed space, the rotors would blow all of the air toward the floor and the air would bounce off the floor, slip by the rotor tips and go to the ceiling of the elevator, leaving the bottom of the helicopter in a vacuum and the rotors no longer able to support the helicopter... so it would obviously fall to the elevator floor in a vacuum... and of course, the extra air above the rotors would be compressed and exert downward pressure on the helicopter, which would accelerate the drop. But if we could make the elevator rise fast enough before the fall of the helicopter reached terminal velocity of 32' per second squared, the pressurized air would fall back to the floor and the helicopter would be able to gain enough lift to stay off the floor. <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" /> Or maybe we'd just need some air pumps and valves to move the air around the elevator so the helicopter wouldn't have to worry about all that aerodynamic stuff. <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" />

3) We could accelerate the elevator faster than the air could move and the position of the helicopter would not be able to overcome the friction of the air...... <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" /> <img src="/forums/images/graemlins/wink.gif" alt="" />

Frank
<img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/ignore.gif" alt="" />

(sigh) Well, it only took about 60 posts for me to change my mind and see the light. lol

I'll stand down - This is exactly how I was coming at it. Although I am still not convinced it would need to accelerate to infinity in this case. If this opposite force is applied at the instant from static rest neither the plane nor treadmill will barely move. You could think of it as happening in pulses. Cancelled out before it starts.

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Ya know...I'm thinking here about rescinding my acknowledgement. He is only talking about speed of the wheel - and that was never my understanding and the basis from my argument which I clearly state. Of course it would take off then. I'm talking speed of say, the nose of the plane in relation to the fixed ground (Ground Speed)

Yes....thinking this through...

[color:"blue"] I STAND BY MY ORIGINAL CLAIMS!!!!!!!!!!!! [/color] And I will even go so far as to repeat that neither (in a perfect environment) - will barely move

Why? Because in my case of it being in relation to True Ground Speed - That number is "a" in the formula. It will not move - ever.

<img src="/forums/images/graemlins/butwiggle.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" />

I just asked a Navy Pilot with a Masters in Aerospace Engineering. He is going to e-mail me a reply <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/patriot.gif" alt="" />

Heck, even a dunce like me was able to figure that one out right away.
I'm losing respect at "treadmill speed" for some of you. <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/smile.gif" alt="" /> <img src="/forums/images/graemlins/pfft.gif" alt="" /> <img src="/forums/images/graemlins/smile.gif" alt="" /> <img src="/forums/images/graemlins/lol.gif" alt="" /> <img src="/forums/images/graemlins/butwiggle.gif" alt="" />

Let me ask you YES people my riddle again because it is the spirit of the original riddle. Depending on your answer will determine one of two things...

If a glider going 100MPH GS touches down on a treadmill going 100MPH GS in the opposite direction - does it stop instantly?

If you answer yes it will stop - then it is semantics and we are interpreting the original riddle differently. If you say no you are not understanding the concept.

Remember the original riddle does not concern itself with thrust. Only speed of plane. So the glider is completely appropriate and I think helps visualize the concept a little better

It would depend on ground speed. If it had lift from a headwind and was flying forward very slowly (ground speed say 1-2mph), maybe friction could grab it. Otherwise, only if it dives in vertically - At 100mph (ground speed), momentum will cause it to lose traction with the treadmill and skip for a distance until momentum is scrubbed off. The frictional force is the same thing that the treadmill lacks on a plane with wheels. At 100 mph ground speed, if you managed to create enough friction to capture the glider fuselage, momentum would probably rip off the wings. For proof, look at the historical pictures of the WWII gliders in Europe.

In the case of the airplane on the treadmill, the treadmill can't build or counteract momentum of the airplane, because the tangential force applied in a horizontal direction to the wheels cannot be transferred efficiently.... because (unlike the glider), the wheels spin. If from a dead stop, the plane's wheel bearings were completely frictionless, I doubt there would even be much inertial movement of the plane with the engine off if you spun the treadmill at 500mph - because to overcome the resistance of the air surrounding the plane, it would require more power transfer than the treadmill was able to provide. However, once the plane's engine is on, the plane CAN build momentum and speed, since it has a prop or turbine that can bite and move air to create thrust.

Have you ever seen an "on-car" dynamic tire balancer work - you know the one where you jack up the car at the corner and the machine spins the wheel up to 50 mph? Have you ever seen a car thrown off the jack from wheel spin generated by the machine?

Frank

Well I THINK we are debating semantics Frank <img src="/forums/images/graemlins/lol.gif" alt="" />

In reference to your fathers idea in WW2 I understand where you are coming from...but throw that aside - there are lots of technological technicalities that will make this only hypothetical...

We will have to imagine that our glider touches down and its ground speed is calculated to a horizontal approach - so it matches or Airplane Takes Off model.

Picture the glider with gear wheels - and the treadmill with matching gear tread. When the planes touches they mesh perfectly.

It doesnt matter what speed it comes in - wheel bearings frictionless, perfect contact i.e. no skip or slip of the wheel - it will stop do you concur?

Now here is the problem I am having with everyone.



Any speed relative to the ground is matched by the treadmill speed relative to the plane to infinity. I think you all are picturing this treadmill as having a point of maximum speed - but it does not. And it doesnt need it.

Momentum is mass times velocity correct?

So the plane 100 lbs.

Velocity of the plane matches velocity of treadmill. They cancel out. Zero.

100x0 is zero - no momentum.

No momentum means no forward motion.

THEY DO NOT CANCEL OUT! AIR speed of the plane increases as the WHEELSPEED of the plane increases X2 The plane cares NOTHING about the treadmill moving backwards ever at any point in this problem. Begining, end, middle... nowhere does it matter. Treadmill speed, OR direction is irrelevant to the plane taking off. It could be matching the planes speed, and DOUBLING it in direction that the plane is going, and it woudl not HELP the plane take off just like it will not HINDER the plane from taking off while going in reverse.


Phil. The treadmill cannot FORCE the plane in ANY direction no matter what.

IF we go by the riddle, the treadmill will move in the opposite direction at the speed of the plane except in reverse, and YOU SAY that this will cancel the foward movement of the plane out relative to a set point in space.

THE TREADMILL in all of its infinity CANNOT UNDER ANY CIRCUMSTANCE HOLD THE PLANE BACK, AND KEEP IT STATIONARY. Tell me why it can,(I WANT YOU TO EXPLAIN TO ME WHY the treadmill will hold the plane back.. I want to know "your" FORCES involved in the treadmill NEGATING the planes foward movement) and you will prove this in your favor.