w_benjamin

"If the conveyor is set to match the 'rotational speed' of the wheels.. as the airplane moves forward.. the belt will in turn mov forward to keep the wheels rotational speed at 0rpm, as that is the 'current speed of the wheel'. remember the conveyor is set to match the rotation of the wheel.. the wheel is not rotating unless the belt moves in relation to the wheel. "

A couple of problems with this. First, the conveyor rotates in the opposite direction. To visualize this, think of two gears meshed together. When one moves clockwise, the other moves counter-clockwise. Second it is not the wheel that rotates in relation to the belt..., it is the belt that rotates in relation to the wheel. I give you credit for trying to think it through though.

MinnFlyer

My Feedback: (4)

Congratulations WB, you have made 11 posts since I was gone and NOT ONCE were you able to give me the simple "yes" or "no" answer that I asked for.

However you did manage to type garbage like this:


If the belt is not turning the wheels, what is? Forward motion? Ah, but we can't have any forward motion or the plane would take off. So in order for the wheels to move, the plane must move forward, as it moves forward, then it must be... Hmm let me see... The BELT that's turning the wheels back? Ah, but since it is ONLY forward motion of the plane that causes the wheels to spin, the belt cannot increase speed until the plane moves forward some more.

Regardless of the time lag involved, (and there MUST be a time lag, unless your hypothetical belt can predict the future too), the plane will constantly increase speed as the belt tries to catch up.

And the plane will fly.

By the way. there IS no friction on the wheel bearings. I am using super-cooled magnets on my wheel hubs so that the wheel hub and the axle never touch.

I figure that if your belt doesn't have any friction, neither should the plane.

Unless, of course, if you want to continue to throw more conjecture into the mix.

BTW, please go back to my last post and answer the question or give up.

MinnFlyer

My Feedback: (4)

Yes yes yes, he read it wrong. We figured that one out already.

Now, Answer my question

David Cutler

No, because there is now rolling resistance that the sand has introduced into the situation. The sand absorbs energy because it is soft and energy is needed to distort it. The hard ashphalt surface (moving or not) doesn't, so therefore doesn't provide resistance. (except, yet again, for the very small bearing friction and inertia of the wheel itself).

The fact that you asked that tell me you haven't really grasped the forces that are around.

-David C.

gtmattz

Wait... where does it say the belt can only move one direction?

the belt is set to match the rotational speed of the wheels. right? well.. if the wheels start out not rotating.. what keeps the belt from moving with the airplane to match the wheels initial rotational speed????


And btw... what did I read wrong?

here is the original question again.. please read it:


where in that statement does it say that the belt can only move in one direction? it states it is set to match the exact rotation of the wheels at any time...

the wheels start out not rotating.. the airplane accelerates.. the belt moves with the plane to match the 0 rotation of the wheels???

thats what I see happening.

w_benjamin

Y'know, I have answered your questions. Check out post 191, 194, 199(for the SAME question), and finally post 238 and 243.

MinnFlyer

My Feedback: (4)

No you didn't, you typed a bunch of hypothetical nonsense.

YES or NO????

You have accused me of not being able to read, now show me how smart you are.

YES, or NO????

Pick one

w_benjamin

"the belt is set to match the rotational speed of the wheels. right? well.. if the wheels start out not rotating.. what keeps the belt from moving with the airplane to match the wheels initial rotational speed???? " When the wheels are not in motion the conveyor is not in motion. When the wheels are in motion, they are rotating in the opposite direction from the conveyor. so when the wheels roll in a forward rotation, the conveyor rotates in a backwards rotation.

w_benjamin

Sorry about putting the "uhh," in front of NO in post 243. Must'a thrown ya off with that hypothetical nonsense in 'uhh'.

gtmattz

why should they ever rotate? the belt matches the speed.. they move at 0 rpm.. the belt moves to match that 0 rpm.

whatever, i think some people just like to argue and once they have an idea in their head they cannot change their view to accept that their idea may possibly be wrong..

I am 99% certain that what I have come up with is a viable solution to this little problem.. I will argue no more.

David Cutler

All true.

As we have now said about 2,756,845 times, why are you fixated on the wheels when they have nothing to do with the motion of the plane (rolling resistance excluded as there isn't much to take into account on a hard surface)?

The wheels can be rotation at whatever speed the belt lets them, and it STILL won't affect the speed of the plane.

Say 100 times. "There is no friction to speak of from the wheels that retard the motion of the plane!"

-David C.

w_benjamin

I find it interesting, Minnflyer, that you used a scenario that does not reflect the question, yet may reflect your perception of the question. You're pulling a board out from under the planes wheels in your scenario. That makes the board the actor and the wheel the reactor. In the question they are the other way around, and they can't be interchanged.

David Cutler

Have you said 100 times that there is no connection between the speed of the wheels and the airspeed yet?

You can talk about the belt, wheels etc until the cows come home, and be both right and wrong about it. It still doesn't change the fact that it is irrelevant.

-David C.

w_benjamin

"The wheels can be rotation at whatever speed the belt lets them, and it STILL won't affect the speed of the plane." Again, we come to the misconception in the question. The belt DOES NOT act on the wheels, therefore the wheels don't rotate at 'whatever speed the belt lets them'. It's the OTHER WAY AROUND.

David Cutler

. . and still irrelevant to the airspeed of the aircraft, which is what matters in flight.

-David C.

MinnFlyer

My Feedback: (4)

Sorry, you did say "uhh - no" but it was in post 244 and I didn't realize that it was referring to my question since that was all the post said and it followed one of your own posts.

However, by saying "no" you have agreed that you observation that the wheels can't move faster than the plane is wrong.

At least we agree on that much.

Ok, now since your understanding of physics is so far superior to mine, then please explain something to me:

I place the plane on the belt. The engine is running at idle, so the plane is not moving, the wheels are not moving, and the belt is not moving.

Now I zip the throttle up to full.

Ok, here's the $64,000 Question:

What causes the belt to start moving?

MinnFlyer

My Feedback: (4)

Here's a hint:

If you say "Forward movement of the airplane" You lose.

David Cutler

me! me! me! Can I answer that question please?

.......Father Christmas?

He's very much into radio controlled conveyor belts ya know.

-DC

bucfan

My Feedback: (1)

Not being a physics major, I won't argue about wheel rotation and what not. All I know is that if there is no wind and the plane is basically standing still because of the conveyor belt then there is no airflow over the wings to create lift; Therefore no takeoff.

That doesn't mean the plane couldn't take off straight up from the airstream created by the prop, given a strong enough engine.

Liberator

Never mind

bucfan

My Feedback: (1)

Anyone seen the movie Flight of the Phoenix? The new one with Dennis Quad?
Remember the scene near the end when they are getting ready to shoot the model airplane engineer? Anyone recall what saves him?
They were all freaking out becasue they were sure his plane would not fly when this huge wind came up and what? Any guesses?

Thats right, made the stationary plane actually leave the ground. Please notice the word stationary, no wheels moving, at all.

To the guy who had his Physics teacher look at this and give that answer? Please, go in and ask him for your money back...NOW!
Again it required airflow over the wing to create lift and get it airborne![>:]

Liberator

So what is the prop providing in this example?

bucfan

My Feedback: (1)

Unfortunately, thats an unknown variable in this question.

Liberator

No its not, you even added it to your previous post after I had written in my example.

"That doesn't mean the plane couldn't take off straight up from the airstream created by the prop, given a strong enough engine."

The original question simply states an airplane. This could be any type of airplane including a 3D Foamy that could throw enough propwash to fly the plane, and they often do.

David Cutler

This is the whole point. The belt isn't, and indeed, cannot hold back the plane. Its only contact with the plane is through the wheels and they are running freely on their axles, hence any motion that is imparted on the plane by the prop (or, indeed, anything else) isn't hindered by the belt. Whether the belt is moving or not, it doesn't affect the plane's ability to reach a flying airspeed and hence take off.

Enough from me!

[sm=bananahead.gif]

-David C.