bentwings

I had to miss the 'event' as my son had a school even we had to go to.

So let's hear "the rest of the story" Preferably the long version.

The Toolman

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.

Ronnie

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.

bentwings

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.

mr_matt

My Feedback: (10)

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.

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.

old git

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.

P-51B

My Feedback: (5)

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!

da Rock

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.

da Rock

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

mr_matt

My Feedback: (10)

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!!

Liberator

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.

Tall Paul

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!

Liberator

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

You heard it here first.

Tall Paul

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

bentwings

Don't ya just love it when you know you are right and are proven right to the nasayers.

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

da Rock

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.

da Rock

You did notice that the airplane took off, right?

combatpigg

My Feedback: (3)

In the real world, the plane flys....but the plane either has to wheel hop or burn rubber to get airborne.
In theory, with perfect traction and a conveyor belt that can match the planes' forward thrust to perfection, the plane would have no way to make any ground speed.
My point is easy to see if you imagine the conveyor with a cogged belt and the plane with gears for tires. I only use this example to illustrate the point.

iron eagel

Very true!
But airplanes need airspeed not ground speed.
At some point the belt is going to cause airflow in addition to the prop wash so the plane will still enter into ground effect then fly away from the belt.

Tall Paul

You're both over-thinking this!
Pushing that plane around on the ground takes little effort.
Anyone can do it easily.
The amount of resistance to rolling, from the landing gear is minimal.
Once that minimal amount of resistance is overcome by the thrust from the prop, -all- the rest of the power of the motor accelerates the plane, regardless of what is occurring between the landing gear and whatever surface it is rolling on.
It's that simple, no need to invoke anything else.

combatpigg

My Feedback: (3)

IronEagle, with a wide enough belt, you're right...the plane would take off.
If I was given the task to build the "unflyable conveyor", narrow spaced gear would be part of the program.

iron eagel

I'll build the plane if I get my choice of power....

LMAO

Gremlin Castle

My Feedback: (14)

Surely you jest. One thing that the multiple threads on this subject has brought to light is the dearth of physics majors that chose to involve themselves in this discussion.

I think that you should try to interest the Navy in conveyor belt landing systems and get rid of all those nasty tail hooks that mar the deck.[8D]