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RE: Airplane on a Treadmill - 1/31/2008 4:41:19 AM   
BMatthews



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Status: offline 		It sounds like it was proof that with real world limits on the "treadmill" as to velocity that it's not going to slow the plane down.


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RE: Airplane on a Treadmill - 1/31/2008 5:14:54 AM   
bentwings


 

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From: St.Paul, MN, USA
Status: offline 		I commented that they should have used a Dodge diesel truck to pull the tarp. It could have probably pulled it faster than the plane could fly. haha

At least we know the plane will fly after all.

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bentwings

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RE: Airplane on a Treadmill - 1/31/2008 5:21:34 AM   
mr_matt



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quote:

ORIGINAL: BMatthews

It sounds like it was proof that with real world limits on the "treadmill" as to velocity that it's not going to slow the plane down.



No Bruce, much easier than that.

They calculated the takeoff speed of the plane, and then ran the "treadmill" tarp in the opposite direction at that takeoff speed.

So the airplane just had to overcome the slight rolling resistance increase (at 20-25 mph I think). Ridiculously easy.

No attempt to have a high velocity conveyor produce any sort of significant rolling resistance at all.

In fact, the way they worded the question on the show, I am suprised there was any debate (or even question) at all to the outcome for the mythbusters staff. Seems like they would have tried harder to figure out the intracies of the original question, but they did not.



< Message edited by mr_matt -- 1/31/2008 5:22:14 AM >

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RE: Airplane on a Treadmill - 1/31/2008 7:42:32 AM   
BMatthews



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Status: offline 		Shows that they don't have the convoluted minds of our lot....

One of the posts in the old thread was mine where I realized that if there were no limits on the treadmill that it could move fast enough to accelerate the planes wheel's at a rate that would hold it back. But it would only be a little while before relativistic effects came into play....

I proved that it could happen for myself with a thread on a bobbin. If you hold the thread and drop the bobbin and then pull the thread up hard you can stop the fall of the bobbin and actually make it rise. But unless you can keep that acceleration going ( I couldn't, my arm was only so long) the bobbin (airplane wheels) falls but with more spin in it.


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RE: Airplane on a Treadmill - 1/31/2008 8:05:02 AM   
old git


 

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quote:

ORIGINAL: BMatthews

Shows that they don't have the convoluted minds of our lot....

One of the posts in the old thread was mine where I realized that if there were no limits on the treadmill that it could move fast enough to accelerate the planes wheel's at a rate that would hold it back. But it would only be a little while before relativistic effects came into play....

I proved that it could happen for myself with a thread on a bobbin. If you hold the thread and drop the bobbin and then pull the thread up hard you can stop the fall of the bobbin and actually make it rise. But unless you can keep that acceleration going ( I couldn't, my arm was only so long) the bobbin (airplane wheels) falls but with more spin in it.


That is just as I saw the Q and the A but I could not have explained it so succintly, congrat's.




old git - - - - aka John L.

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RE: Airplane on a Treadmill - 1/31/2008 1:59:45 PM   
P-51B



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quote:

ORIGINAL: proptop

I noticed near the end of the "Lead Balloon" episode, that on the dry erase board was a list...and "when pigs fly" (or words to that effect ) was on there...



Did their big lead balloon end up flying? I had to leave and missed the end of the show. Actually, I was really wondering if they could even get it constructed without tearing up the foil!

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RE: Airplane on a Treadmill - 1/31/2008 3:47:41 PM   
da Rock



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quote:

ORIGINAL: BMatthews

I proved that it could happen for myself with a thread on a bobbin.
If you hold the thread and drop the bobbin and then pull the thread up hard you can stop the fall of the bobbin and actually make it rise.
But unless you can keep that acceleration going ( I couldn't, my arm was only so long) the bobbin (airplane wheels) falls but with more spin in it.


But the bobbin continues to unroll. The bobbin analogy applies to the airplanes wheels, not the airplane. The wheels would roll just like the bobbin continues to unwind.

Until the drag in the wheel bearings burns them out, they're not going to hold back any but very low powered airplanes.

The original myth did not limit the airplane. And Mythbusters usually does not place limits that alter the concept.

But they used an airplane with limited power. And a simulated conveyor belt that came nowhere close to following the original myth, where the convey exactly matches the speed of the airplane.

Can an airplane take off with the axles encountering infinitely high rotational speeds? Yes.......
Some of today's fighters have restrictions on takeoff power. When too much is used, a couple of them take off.......... and leave the gear behind. Their bobbins don't unwind fast enough so the airplane tears the things off and leaves.

It has happened. It would have happened had the idiot fighter pilot who knew more about flying than the guys who wrote the proceedures been taking off from a treadmill. But it had better be a very fast treadmill or that jet would also leave it's gear behind.

Once the bearings freeze, the force resisting the airplane's acceleration gains a bit longer moment. It moves from being a wimpy force at the axles to whatever scrub resistance the tires can provide. And the jet fighters have already proven that a couple of tires' footprints don't stand a chance against a couple of good jet engines.


< Message edited by da Rock -- 1/31/2008 3:58:47 PM >

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RE: Airplane on a Treadmill - 1/31/2008 4:00:10 PM   
da Rock



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Status: offline 		Whatever a treadmill can do, the final battle will be between the airplane engine and the tires' traction.

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RE: Airplane on a Treadmill - 1/31/2008 4:29:40 PM   
mr_matt



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quote:

ORIGINAL: BMatthews

Shows that they don't have the convoluted minds of our lot....



Indeed......

I was talking to my wife about it, and I said that Mythbusters, to their credit, have to come up with an actual physical model of the concept they are addressing for each show.

To me, the original question was a pure thought experiment, not something anyone would go out and build. But I realize that 60% of people (which I have heard is about the ratio, 60/40) cannot grasp this problem as a thought experiment, but rather a physical construct.

If Einstein was this limited, I don't think he could have come up with a fraction of the ideas/theories/concepts he ended up so famous for. The technology needed to physically prove some of his theories took many years (after his death) to perfect. Same thing here.

What also suprised me was that Mythusters did INDEED try to identify the source of the massive disagreement on the issue. They convinced themselves it is the common misunderstanding that cars develop forward momentum by traction force with the ground and planes do not. They actually did a very nice job showing this with a model. Of course it has nothing to do with friction or angular momentum thought experiments, but it is OK for TV science I guess!!


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RE: Airplane on a Treadmill - 1/31/2008 5:37:57 PM   
Liberator


 

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Status: offline 		I thought it was hysterical that the pilot didn't get it. He was suprised? I guess they skip the part now about flight dynamics when you go get your Private Ticket.

Bottom line, If you took their same rig (full size) and were able to safely hook up an F-16 to pull the tarp, there is no amount of speed the tarp could go that the plane won't take off.

"You could plainly see that the plane was still rolling forward past the cones in the picture. It was just rolling faster than they was pulling the tarp.

The real deal would have been for the plane to lift off while it was sitting dead still in one place (while the tarp was moving) with the wheels turning an the engine turning at takeoff speed. "
Well of course it was moving, how can it not?

The plane will fly as long as the wheels are not impeded.

But it was fun to watch.

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RE: Airplane on a Treadmill - 1/31/2008 5:45:19 PM   
Tall Paul



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Status: offline 		The Mythbusters forum got 850 posts in 12 hours after the show.
Most of them outraged that the plane flew!
Oh shattered illusions, how painful are you to accept!

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RE: Airplane on a Treadmill - 1/31/2008 6:04:39 PM   
Liberator


 

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Status: offline 		LOL no kidding. And to all that still have doubts, the Easter Bunny isn't real either.

You heard it here first.

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RE: Airplane on a Treadmill - 1/31/2008 7:04:34 PM   
Tall Paul



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Status: offline 		From last night's episode....
http://www.youtube.com/watch?v=4VMkEb4Xzf4

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RE: Airplane on a Treadmill - 1/31/2008 7:10:51 PM   
bentwings


 

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From: St.Paul, MN, USA
Status: offline 		Don't ya just love it when you know you are right and are proven right to the nasayers.

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bentwings

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RE: Airplane on a Treadmill - 1/31/2008 9:11:45 PM   
fredsedno


 

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Status: offline 		Fellas,
What about prop wash accross the wings and lift generated by the air moving around& over the air foil? Woud this not reduce the weight on the wheels and reduce friction thus allowing the aircraft to hover and rotate?

obviously still not the sharpest tack in the box[but learning thanks to you guys]
fredsedno

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RE: Airplane on a Treadmill - 1/31/2008 11:33:35 PM   
da Rock



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quote:

ORIGINAL: fredsedno

Fellas,
What about prop wash accross the wings and lift generated by the air moving around& over the air foil? Woud this not reduce the weight on the wheels and reduce friction thus allowing the aircraft to hover and rotate?

obviously still not the sharpest tack in the box[but learning thanks to you guys]
fredsedno



It doesn't really need less weight on the wheels.
Or at least any airplane with adequate thrust to weight ratio wouldn't.
The friction on the wheels means nothing as resistance to the airplane moving forward until the wheel bearings freeze up.

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