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DPChallenge Forums >> General Discussion >> Plane and a Treadmill
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Showing posts 226 - 250 of 286, (reverse)
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 12/06/2006 08:39:27 PM · #226
Originally posted by MrEd:
Originally posted by SamDoe1:
How about we discuss time travel next? :-P

Anything except religion......

Added: I can't wait for someone to actually try this.


Time travel makes my brain hurt...
12/06/2006 08:43:29 PM · #227
I heartily agree that I could be incorrect, and look forward to someone testing this one day.

Thanks for the brain-workout... now where's that bible LOL. Scratch that - the beer sounds better right about now!
 12/06/2006 09:34:49 PM · #228
Originally posted by rossbilly:

The engine creates a force in one direction, the treadmill (and the aircraft's wheels) absorb that force in the OPPOSITE direction. The wheel spins around the bearings, and forward motion is ZERO.


Yes, if the treadmill balanced the force, you would be correct.

However the question implicitly says that that is not true.

The treadmill accelerates to match the speed of the plane. It does not accelerate to create an equal and opposite force. (Which would require a vastly higher acceleration)
 12/06/2006 10:21:09 PM · #229
I admit my first instinct was to say No, but I say Yes. Without the breaks engaged the wheels move indepently of the plain's body. It does say "huge treadmill runway" so it's probably just as long as a regular runway , enough for the plain to gain enough speed for liftoff.

Quote "The treadmill has a clever design and always matches the speed of the plane" seems this line is just to added to confuse reader.
 12/07/2006 02:18:18 AM · #230
Originally posted by SamDoe1:
How about we discuss time travel next? :-P


Correct me if I'm wrong (like I have to worry about that) but...

If the plane moves forward on the treadmill due to the force of the engine on the air behind it then wouldn't the wheels be traveling at a slightly faster pace than the treadmill? If so and this mythical treadmill instantly matches the speed of the plane then wouldn't the wheels and the treadmill ultimately speed up to infinitely? And because this is all would happen instantaneously wouldn't that create like a super nova or a black hole or something? Or as soon as the wheels accelerated faster than the speed of light they would be traveling into the future... oh great, well I guess we know how the world ends. STOP THAT TREADMILL!!!
 12/07/2006 02:25:51 AM · #231
I'm thinkin'..............who gives a rats ass whether it flies, sits or crashes and burns up 300 acres of some guys corn.
 12/07/2006 02:40:20 AM · #232
Originally posted by Megatherian:
Originally posted by SamDoe1:
How about we discuss time travel next? :-P


Correct me if I'm wrong (like I have to worry about that) but...

If the plane moves forward on the treadmill due to the force of the engine on the air behind it then wouldn't the wheels be traveling at a slightly faster pace than the treadmill?

Wheelspeed would always be 2X the actual speed.
 12/07/2006 05:18:11 PM · #233
bump
The comments by NTSB Chairman Mark Rosenker came 10 1/2 months after the government panel recommended a more conservative method to figure out how much landing room is needed and two days before the anniversary of the accident that killed an Indiana child in a car struck by the airplane.

While the Federal Aviation Administration has recommended that airlines make the change, which entails not assuming thrust reversers will stop a plane on slippery runways, a new rule requiring the change has not yet been adopted.

12/07/2006 05:41:46 PM · #234
Originally posted by legalbeagle:
It is amazing that the tyre can cope with the stresses generated by accelerating from 0 to 600mph while bearing hundreds of tonnes of force in the instant of touchdown.


Just a quick side note. The struts and tires are indeed quite impressive. However, even 747s land waayyy below 600mph. More like 125 mph.

Where's B74A when you need him? I believe he flies 747s for a cargo airline.

Now, private pilots like me fly stuff that goes a lot slower. Planes I typically fly take off and land at around 60mph. They can't even get up to 125mph except in a dive. :)

Even at only 60mph, though, one technique that's taught is to keep only the balls of your feet on the bottom of the rudder pedals on final approach because the brakes are activated at the top. No fun landing with locked brakes!

Oh, as to the question at hand, I'm finally convinced the plane will go forward with wheels spinning twice as fast.

Message edited by author 2006-12-07 17:42:44.
 12/07/2006 05:54:49 PM · #235
This is the first time i've seen this thread, and its over my head. All I can add is why dont you just cantact Mythbusters and get them to give it a shot ;)
 12/07/2006 05:56:49 PM · #236
Originally posted by boysetsfire:
This is the first time i've seen this thread, and its over my head. All I can add is why dont you just cantact Mythbusters and get them to give it a shot ;)


Cuz its not a myth just a logic problem. But if you want a good laugh go to the myth busters site and read the forum posting of this topic. Too funny.

:-D

Message edited by author 2006-12-07 17:57:38.
 12/07/2006 06:25:08 PM · #237
Originally posted by thegrandwazoo:
Originally posted by boysetsfire:
This is the first time i've seen this thread, and its over my head. All I can add is why dont you just cantact Mythbusters and get them to give it a shot ;)


Cuz its not a myth just a logic problem. But if you want a good laugh go to the myth busters site and read the forum posting of this topic. Too funny.

:-D

Logic question or myth....they might decide to do it anyway. Maybe with a RC plane and treadmill.
 12/07/2006 06:32:57 PM · #238
Originally posted by MrEd:
Logic question or myth....they might decide to do it anyway. Maybe with a RC plane and treadmill.


That would be interesting to see, I thought they talked about it on a show once though...although I'm not entirely sure.
 12/07/2006 07:25:49 PM · #239
NOT WORK SAFE. LANGUAGE
All I have to say, this question has caused a lot of headache's. Check this guy out as he tries to explain. Will it take off?
12/07/2006 07:54:47 PM · #240
I don't think I've seen this thought experiment, so let me try it.

Imagine the plane sitting on its belly on nice, smooth, wet ice. No wheels here, just a big fat plate of metal. But essentially no friction between the ice and the plane.

Now start sliding the ice backward past the plane. Doesn't matter how fast. 1 mph, 1 million mph. Whatever. No friction, so the plane just sits there.

Now someone sits in the back of the plane and blows backward. What happens to the plane? It scoots forward a bit. The ice is still whizzing by with no friction, but even a tiny puff of air will move it forward.

Now assume a smidge of friction between the ice and the plane, and the plane does feel a little tug backward. But even a small engine could easily overcome it. Now add a real, full-blown engine, and the plane not only scoots forward, it zooms forward, eventually taking off. The ice is still whizzing past at however fast you want to make it go.

The ice has little or no effect on the plane, just as the wheels have little or no effect on the plane.

If you don't buy that, then answer this: what will you see happen? Let's assume the plane doesn't move relative to the ground under the treadmill, which seems to be the main argument against it taking off. Then the treadmill doesn't move, because the treadmill exactly matches the plane's speed. Then you have a plane sitting on wheels with full thrust but not moving anywhere.

Message edited by author 2006-12-07 20:29:36.
 12/07/2006 08:39:23 PM · #241
Originally posted by legalbeagle:
.....However, I have always been impressed with the technology that goes into aircraft wheels, ever since they placed a 747 undercarriage strut in the entrance hall to the science museum in London. It is amazing that the tyre can cope with the stresses generated by accelerating from 0 to 600mph while bearing hundreds of tonnes of force in the instant of touchdown.


Seriously they are amazing - I saw footage of the 1st 747 doing a full power emergency stop to failure (full thrust and full lock) and it blew all sorts of stuff off the bottom of the plane - fire, smoke, rubber the whole deal. The comparative footage of the 747-400 doing the same test (after the break smoke clears) sees this screaming plane at full tilt sitting stationary with bright white CF discs inside the wheels.
 12/07/2006 08:54:31 PM · #242
Originally posted by robs:
Originally posted by legalbeagle:
.....However, I have always been impressed with the technology that goes into aircraft wheels, ever since they placed a 747 undercarriage strut in the entrance hall to the science museum in London. It is amazing that the tyre can cope with the stresses generated by accelerating from 0 to 600mph while bearing hundreds of tonnes of force in the instant of touchdown.


Seriously they are amazing - I saw footage of the 1st 747 doing a full power emergency stop to failure (full thrust and full lock) and it blew all sorts of stuff off the bottom of the plane - fire, smoke, rubber the whole deal. The comparative footage of the 747-400 doing the same test (after the break smoke clears) sees this screaming plane at full tilt sitting stationary with bright white CF discs inside the wheels.


The brakes are designed for a specific number of landings.

They can do an emergency stop once.
 12/07/2006 09:00:51 PM · #243
Originally posted by Spazmo99:
[quote=robs] [quote=legalbeagle]...It is amazing that the tyre can cope with the stresses generated by accelerating from 0 to 600mph while bearing hundreds of tonnes of force in the instant of touchdown.


For reference, the landing speed of a 747 is around 160mph.
 12/07/2006 09:49:01 PM · #244
Someone used the analogy of a guy walking the opposite direction on a moving sidewalk. Thats all fine and dandy and yes he will stay in place if he is walking on the treadmill, BUT if you stick a set of roller blades on him and throw him a rope, even if you have that sidewalk cranked up to 100mph he will be able to pull him self forward with little trouble as the only thing that the sidewalk is affecting is the rotational speed of the wheels and not the poor bugger standing on them :)

Same thing with the plane except rather than the plane being pulled by rope, now its being pushed by the engines which are in NO way connected to the wheels...

-dave
 12/07/2006 10:08:02 PM · #245
Originally posted by dknourek:
Someone used the analogy of a guy walking the opposite direction on a moving sidewalk. Thats all fine and dandy and yes he will stay in place if he is walking on the treadmill, BUT if you stick a set of roller blades on him and throw him a rope, even if you have that sidewalk cranked up to 100mph he will be able to pull him self forward with little trouble as the only thing that the sidewalk is affecting is the rotational speed of the wheels and not the poor bugger standing on them :)

Same thing with the plane except rather than the plane being pulled by rope, now its being pushed by the engines which are in NO way connected to the wheels...

-dave


That is a great way of looking at it, I'm sure you convinced a few more of the people with the no take-off vote.
 12/07/2006 10:13:30 PM · #246
Originally posted by kirbic:
Originally posted by Spazmo99:
[quote=robs] [quote=legalbeagle]...It is amazing that the tyre can cope with the stresses generated by accelerating from 0 to 600mph while bearing hundreds of tonnes of force in the instant of touchdown.


For reference, the landing speed of a 747 is around 160mph.


You are correct, but I didn't say it was 600 mph.
 12/07/2006 10:31:24 PM · #247
I can't believe I've missed this thread through so many pages :-) I've never seen so many people getting so far off track on anything, I don't think. I haven't read every single post (I got bogged down in giggling) but of COURSE the plane can take off. If my takeoff speed is 60 mph (about right for a small plane) then when I am traveling through the air at 60 mph the treadmill would be running backwards at 60 mph and the wheels would be "spinning at 120 mph", but the plane is still moving forward at 60 mph and it will lift off. The wheels are irrelevant, they just exist to provide a (relatively) friction-free connection to the ground until lift takes over and separates me from the ground.

Right?

R.
 12/07/2006 10:43:20 PM · #248
Originally posted by Southern Gentleman:
No! because what make a jet/plane airborne is the wind going over the the wing making an updraft under the wing giving it lift. That's why most take offs are into the wind and landings with the wind.


WHAT EVER YOU DO, DONT LAND A PLANE! hahaha

Im a pilot, and both takeoff and landings are done INTO the wind. Why is that.

Lets say rotation speed is 60 knots.

The headwind is 20 knots.

The Indicated airspeed would be 60 knots, but the groundspeed is 40 knots.

So, you would get off the runway earlier, and also you would land with a slower groundspeed.
 12/07/2006 10:45:23 PM · #249
Originally posted by legalbeagle:
An interesting problem:

A plane equipped with fixed horizontal engines and wheel landing gear is placed on a huge treadmill runway. The treadmill has a clever design and always matches the speed of the plane, but runs in the opposite direction. Will the plane take off and fly or not?

Any takers?


And no, the plane will not fly, Since you need airflow to gain lift.
 12/07/2006 10:46:41 PM · #250
Originally posted by Magnus_i:
And no, the plane will not fly, Since you need airflow to gain lift.


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