Airplane on Conveyor Belt Mythbusters 12/12

[Scythian]

That's the false constraint: the treadmill cannot prevent the wheels from moving faster in the forward direction as the plane zooms down the treadmill--the planes wheels just spin faster and faster as the treadmil speeds up--and faster still as the thrust powers it down the madly spinning treadmill.
The plan takes off--the treadmill cannot prevent it.

Of course it's a false constraint if you throttle up the plane's engine, but that doesn't change the fact that it's a constraint in teh problem. Are you gonna solve the problem as posed, or write a different one and then solve that?

Where does the treadmill preventing the plane from taking off come up in this? IT's the parameters of the problem that prevents it taking off -- in order to keep the wheels and treadmill at the same speed, the plane's wheels cannot go faster than the treadmill is going in the opposite direction. That means it is stationary.

I solved it as written, it has a false constraint: the plan takes off.

The speed, or the direction of the treadmill relative to the wheels of the aircraft has no bearing on the problem--"bearing!" get it!

Besides, what to you mean by 'speed'? Ground covered per rotation? or RPM?--it has no bearing....

The parameters of the problem cannot prevent the plane from taking off: they are false.

 

[exskibum]

JEBUS!!! Will you guys read the original post, please? See bolded provisions:

On a bunch of internet forums (fortunately, not here :yahoo: ), a ton of bandwidth was wasted on the hypothetical situation of the ability of an airplane to take off if it was on a conveyor belt spinning in the opposite direction of the wheels at the same speed of the wheels. Laypersons, physicists and scientists alike provided point/counterpoint with no clear cut conclusion (but, I think the majority leads to the theory that it could take off). Mythbusters is schedule to tackle the topic tomorrow. Check your local listings.

Where do you get that *I* am putting in an artificial constraint or changing the problem?!? Go ahead and design a test that has the bolded part satisfied and see what you get -- a throttled back airplane that isn't moving relative to the ground and has no airspeed over the wings. I'm all ears if you can design a test that satisfies the bolded part of this problem and generates ground and air speed (without rotary wings or wind tunnel fans, that is).

Whatever, if you need to "win", then go ahead and consider that you have.

 

[JimLor]

I'm with exskibum - per the post, the a/c wheels and treadmill are moving at equal speed in opposite directions. In relation to the earth, and more importantly to the "wind," the a/c is not moving.

So, how much wood could a woodchuck chuck if a woodchuck could chuck wood?

And thank you Randy!

 

[Scythian]

JEBUS!!! Will you guys read the original post, please? See bolded provisions:

On a bunch of internet forums (fortunately, not here :yahoo: ), a ton of bandwidth was wasted on the hypothetical situation of the ability of an airplane to take off if it was on a conveyor belt spinning in the opposite direction of the wheels at the same speed of the wheels. Laypersons, physicists and scientists alike provided point/counterpoint with no clear cut conclusion (but, I think the majority leads to the theory that it could take off). Mythbusters is schedule to tackle the topic tomorrow. Check your local listings.

Where do you get that *I* am putting in an artificial constraint or changing the problem?!? Go ahead and design a test that has the bolded part satisfied and see what you get -- a throttled back airplane that isn't moving relative to the ground and has no airspeed over the wings. I'm all ears if you can design a test that satisfies the bolded part of this problem and generates ground and air speed (without rotary wings or wind tunnel fans.

Whatever, if you need to "win", then go ahead and consider that you have.

if it was on a conveyor belt spinning in the opposite direction of the wheels at the same speed of the wheels.

Sure: It was on a conveyor belt spinning in the opposite direction of the wheels at the same speed of the wheels. Then the pilot throttled up and the plane took off the end of the treadmill.

--edit for exactness-- How would you specify the 'speed' of the treadmill vs wheels--'cuz if you go by RPM and the treadmill has much greater diameter, you'd have to argue that the plane would have to roll backwards to stay at the same RPM as the treadmill.

But now we are getting dumb--It's a false constraint:

The speed of the treadmill is immaterial to the action of the plane.

 

[ponyfool]

I'm with exskibum - per the post, the a/c wheels and treadmill are moving at equal speed in opposite directions. In relation to the earth, and more importantly to the "wind," the a/c is not moving.

Fine, they move in equal speeds in opposite directions. What about my solution? The wheels never rotate? The plane will still take off by sliding down the runway!

This IS a solution to the exactness of the question.

 

[exskibum]

 

[ponyfool]

Is that concession???

 

[exskibum]

Is that concession???

It can be anything you want it to if that works for you, but certainly not because you or Scythian have convinced me that you understood the problem or answered it correctly.
Why is it that neither of you has accepted my invitation to design a test (e.g., as MythBusters would have to do) that satisfies the stated constraint in the problem Randy posed of wheel and treadmill speeds being equal in opposite directions?

When you can do that and generate ground speed (from that, I'll concede that you get air speed and lift), then you will have proven something, and I will bow in deference (sorry, *** kissing is out for male winners). Until then, call it anything you wish, and I don't even mind if you confuse what I do for a living with an absence of math or engineering aptitude. Of the initial legions of us who got perfect 800 math SAT scores at 16 and were math and engineering majors at 17, a few of us have rotted our brains through repeated exposure to other subjects and have lost all such aptitude -- I am one of those, if you wish.

 

[RadioHowie]

Aaaaaaacccccccckkkkkkkkk.....

I did it again! I almost got caught up in this ******* of a conundrum!

(wiping hands derisively) I'm not coming back to this phuquer, EVER AGAIN!

 

[SouthernCruizer]

Reason I asked the simple question up front and have watched this free for all since is exactly what Southern Cruizer pointed out in the problem: the treadmill is MATCHING the speed of the airplane wheels.
There IS friction in the bearings of the wheel, and because of that, the treadmill exerts a backwards force on the plane. The question seems to be whether the forward vector of the plane created by the thrust of the prop or jet is equaled by the reverse vector of the plane created by the treadmill (given the friction of the wheel bearings transmitting some of the force of the treadmill to the plane).

Seems to me this question is answered in the affirmative by the problem, though, since the wheels and treadmill are defined to be moving at the same speed. If the airplane is moving forward (generating airspeed and lift via differential air pressure over and under the wings), then the wheels MUST BE spinning faster than the treadmill. To stay within the parameters of the problem, the treadmill needs to speed up to match the wheel speed, until the friction of the wheel bearings is sufficient to overcome the thrust of the plane and keep it at a standstill with no airspeed. No airspeed = no fly.

Looking forward to the namecalling to follow here.

*****************

That is the logical conclusion...so there are those that will HAHAHAHA it for sure

Jay

'04 FJR 1300

Yep. 'Cuz it's wrong. Do you really think an F-22, for example doesn't have enough thrust to overcome the wheel bearing friction no matter how fast the wheels were spinning?

I'll bet you could put the F-22 on its belly on a treadmill spinning the opposite direction to match, um, its bellyspeed or something--and it would still take off.

Oh, BTW: HAHAHAHA! :lol:

I love it. I love arguing this weird theoretical ****, especially on aircraft--it's what the Air Force pays me to do. If I can be right an hurt people's feelings, that's the best of all!

Still looking forward to my apology!

*******************************

After reading this post I find that I *DO* owe Scy an apology...you are NOT a moron...

....you are a wanna be Air force theortical blow hard internet pundit with delusions of pilot grandeur. Prolly a HD riding poser also! :assassin:

Go argue your wierd theoretical **** with your little gov't cubicle buddies LOLOL oops...i meant..HAHAHAHAHA

Merry Christmas! :glare:

Jay

'04 FJR 1300

P.S. wow, guess that does make me a name caller..my bad :dribble:

 

[jocko87]

I'm with exskibum - per the post, the a/c wheels and treadmill are moving at equal speed in opposite directions. In relation to the earth, and more importantly to the "wind," the a/c is not moving.

Fine, they move in equal speeds in opposite directions. What about my solution? The wheels never rotate? The plane will still take off by sliding down the runway!

This IS a solution to the exactness of the question.

But GUUUYS...per your own arguments of artificial constraints nothing in this situation would even move. What moves first? The treadmill can't move until the wheels on the plane move, being free-wheeling, the wheels on the plane can't move until plane itself moves. If the treadmill moves first the airplane falls off the back because it can't react independently to the treadmill.

Does spinning the treadmill oppose the force that made the plane move in the first place?

Nope.

It seems to me that those who originally piped up are now seeing the truth and are resorting to nit-picky analysis of the wording, instead of manning up and admitting they were wrong in the first place.

 

[Scythian]

Reason I asked the simple question up front and have watched this free for all since is exactly what Southern Cruizer pointed out in the problem: the treadmill is MATCHING the speed of the airplane wheels.
There IS friction in the bearings of the wheel, and because of that, the treadmill exerts a backwards force on the plane. The question seems to be whether the forward vector of the plane created by the thrust of the prop or jet is equaled by the reverse vector of the plane created by the treadmill (given the friction of the wheel bearings transmitting some of the force of the treadmill to the plane).

Seems to me this question is answered in the affirmative by the problem, though, since the wheels and treadmill are defined to be moving at the same speed. If the airplane is moving forward (generating airspeed and lift via differential air pressure over and under the wings), then the wheels MUST BE spinning faster than the treadmill. To stay within the parameters of the problem, the treadmill needs to speed up to match the wheel speed, until the friction of the wheel bearings is sufficient to overcome the thrust of the plane and keep it at a standstill with no airspeed. No airspeed = no fly.

Looking forward to the namecalling to follow here.

*****************

That is the logical conclusion...so there are those that will HAHAHAHA it for sure

Jay

'04 FJR 1300

Yep. 'Cuz it's wrong. Do you really think an F-22, for example doesn't have enough thrust to overcome the wheel bearing friction no matter how fast the wheels were spinning?

I'll bet you could put the F-22 on its belly on a treadmill spinning the opposite direction to match, um, its bellyspeed or something--and it would still take off.

Oh, BTW: HAHAHAHA! :lol:

I love it. I love arguing this weird theoretical ****, especially on aircraft--it's what the Air Force pays me to do. If I can be right an hurt people's feelings, that's the best of all!

Still looking forward to my apology!

*******************************

After reading this post I find that I *DO* owe Scy an apology...you are NOT a moron...

....you are a wanna be Air force theortical blow hard internet pundit with delusions of pilot grandeur. Prolly a HD riding poser also! :assassin:

Go argue your wierd theoretical **** with your little gov't cubicle buddies LOLOL oops...i meant..HAHAHAHAHA

Merry Christmas! :glare:

Jay

'04 FJR 1300

P.S. wow, guess that does make me a name caller..my bad :dribble:

It took a while, but I guess you finally realized you were wrong: It takes a big man with a bigger heart to make a forthright and honest apology without resorting to further insults.

I accept your apology!

 

[exskibum]

But GUUUYS...per your own arguments of artificial constraints nothing in this situation would even move.

Thank you -- you've proven the case in ONE velocity situation: where speed of the wheels = 0 = speed of the treadmill.

What moves first? The treadmill can't move until the wheels on the plane move, being free-wheeling, the wheels on the plane can't move until plane itself moves. If the treadmill moves first the airplane falls off the back because it can't react independently to the treadmill.

I didn't make up the constraints of the problem, which are that the speed of the wheels must equal speed of the treadmill, but in opposite directions. Let's assume for the sake of making it work that the pilot applying throttle can feather it to be very fine in accelerating the plane from a stop, and that the treadmill has some sort of servo that senses that acceleration and responds to that throttle position to keep the plane in one place. If the plane stays stationary compared to the ground, the speed of the wheels = the speed of the treadmill regardless of the speed of the wheels and treadmill, from 0 mph to infinity -- that's just mathematics. It seems to me that with enough room on the treadmill, equalizing the speed from a stop to whatever speed is feasible for the treadmill would be possible. If it's not, then what do you think the MythBusters program intends to do?

Does spinning the treadmill oppose the force that made the plane move in the first place?

Actually, yes, it does. It is relatively small compared to a full throttle aircraft engine pushing a propeller, but that's exactly why the prop needs to be throttled way back to meet the problem's central constraint of equal wheel/treadmill speeds. There is friction in the bearings, which allows a part of the force exerted by the treadmill to be transmitted to the airplane through the wheels. (Imagine what happens if the airplane is simply sitting on the treadmill without its prop spinning -- it travels backwards. That doesn't go away, or physics principles change to erase vectors of force, even if the transmitted treadmill force is small compared to potential output of the airplane's engine and prop.)

Can you overpower the treadmill with the prop? Of course, but as soon as you do, you are outside of the constraints imposed by the problem (equal wheel and treadmill speed) -- and your airplane wheels are turning faster than the treadmill. Why are you guys stuck on full throttling the engine when the problem insists that the speed of the wheels equal the speed of the treadmill? That's the red herring they want you to see, but in following it, you violate the central constraint of the problem. That's not "nit-picky analysis of the wording".

And WTF does a theoretical disagreement have to do with "manning up"? We're measuring cocks here? In my experrience, you're stuck with exactly what the problem says and you must solve it accordingly. I've never had a math, physics or engineering class that allowed me to decide that I didn't have to abide by what the problem said, just because I couldn't conceptualize a real world situation where I'd find those conditions or constraints. If you've had that experience, I'd love to know how that works. In particular, one thing that drove me nuts in differential equations: what does 8 or 10 or 14 dimensions look like? I'd have loved to tell the prof that he could stick those extra dimensions up his ***, because once we got beyond 3 dimensions (and grudgingly conceding a 4th for time), it didn't make any friggin' conceptual sense to me, so his problem needed to be changed back to 3 or 4 dimensions.

I won't measure dicks with you, but I'll cop to being a moron -- because only a moron would waste this much time on this after a couple days of successfully ignoring it. You guys think what you like and solve math/engineering/physics problems any way you want -- hell, substitute out the part of the problem you don't like or understand for all I care. I've got a ride to get ready for tomorrow, and a woman coming over to compare parts with.

Have a great weekend and a merry Christmas!