I'll probably be away from my computer most of the day, but I wanted to voice my opinion on this. I don't think it will take off. I just don't see how it would move forward if it's on a conveyor belt matching its speed. I just don't see it.

Have a great day!

I think the people who assume the plane will take off are treating it as a simple rocket. If there is no vertical thrust component from the rocket (ie: all horizontal thrust), then the plane will be able to push itself forward, but there will be no lift to elevate the plane. Otherwise, their assumption is that the engines provide the downward exhaust to lift the plane, then the setup is that of a simple vertical rocket, but we know planes don't take off like that.

For those who think it will take off, where is the vertical lift coming from? I agree there is forward propulsion, but no vertical if there is no flow over/under the wings to create the differential pressure required for lift.

Then also, if this plane can take of regardless of the difference in wing/airspeed, why do planes take off in shorter distances when flying into the wind? If your assumption works, how does it agree with this common flight practice?

I'de be welcome for a response other than a sarcastic *sigh*.


*edited for proper nomenclature*
its early and coffee is yet to kick in

[This message has been edited by agrams (edited 10/25/2007 7:14a).]

Yeah, where's the forward lift coming from?

agrams,

What you have to understand is that the plane will be moving ... there will be airflow around the wings. The wheels do not propel the plane at all, they are supposed to be as closed to frictionless as possible. All the conveyor does is spin the wheels, but that will not move the plane.

What moves the plane are the engines. The engines provide a net force forward. In an ideal world, there is NO force backward (edit: other than drag), even if the conveyor is moving 91832409832 mph backward, because the wheels are frictionless.

Therefore, the thrust forward by the engines propels the plane forward the same regardless of whether the plane is on stationary ground or a conveyor moving 2039840823904832098423094823094823094823 mph, and the plane can takeoff normally.

However, in the problem statement there is something incorrect. If the conveyor was truly moving the same speed as the radius of the wheels times the rotational velocity of the wheels in a no-slip condition, then the plane COULD NOT BE MOVING FORWARD. The thing is, this is only possible if the net force on the plane is zero. If there is any net force on the plane, the wheels will be moving faster or slower than the conveyor. THIS is what makes this problem so retarded.

[This message has been edited by HotardAg07 (edited 10/25/2007 7:22a).]

quote:

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I just don't see how it would move forward if it's on a conveyor belt matching its speed. I just don't see it.

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Let's assume that we are using an F-22. Courtesy of wikipedia we know that the typical loaded takeoff weight is 55,352 lb, and that it has 2 engines, each capable of 35,000+ lb of thrust (total of 70,000+ lb). As you undoubtedly notice, the max thrust is greater than the weight of the loaded aircraft. Now, let's assume that you are able to somehow get the treadmill so fast that the tiny bit of friction being exerted on the wheels is sufficient to make it stay still as the engines increase thrust and that the wheels don't catastrophically fail... what do you suppose will happen once the amount of thrust becomes greater than the weight of the aircraft?

Here's a hint:




[This message has been edited by rustybq99 (edited 10/25/2007 7:21a).]

if you still don't understand after having it explained 934820394 times, then you are a lost cause and i pity your feeble brain.

that is all.

just give up trying to explain people - it has been explained as well as it can be and if they can't grasp the concept by now they won't ever understand it. They are either trolls or deserve the pity of God. There are some people who understood that it would take off without ever having anyone explain a thing (such as I), there are people who thought it wouldn't take off and then when others pointed out things they should pay attention to, they understood that it would take off. Then there are the people who had to be walked through the concept, didn't understand, then walked through again and again and again and finally just sided with the correct side so they didn't look like a dumb ass....and then there are the others

CopeIt,

You have to agree that the problem statement is flawed and leads to confusion though. If the conveyor was truly moving at the same speed as the wheels (rotational velocity * radius of the wheel), then it's impossible for the plane to be moving. However, if the engines were on at all, this condition would be impossible, because the net force forward would cause the wheels to move faster than the conveyor. I wish this would just die, personally.

so many dumbasses, so little time

The conveyor is moot!

CopeIt, I think you forgot about one more contingent, those that don't give a ****.

we know, lauren.

we know.

The conveyor is moot!

Well, at least I think i see the reasoning for those who say it will takeoff, but there is a clear different assumption from the two sides.

If the wheels are frictionless, then they don't matter, and the plane will be able move itself forward and eventually takeoff (given enough length).

But i think the assumption for those who say it wont take off are assuming that the plane only just keeps up with the velocity of the conveyor. My assumption was such, and of course the plane won't take off with 0 forward velocity.


BEER ME!

[This message has been edited by agrams (edited 10/25/2007 9:35a).]

quote:

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But i think the assumption for those who say it wont take off are assuming that the plane only just keeps up with the velocity of the conveyor. My assumption was such, and of course the plane won't take off with 0 forward velocity.

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And for the eleventy-billionth time, this assumption is wrong and is why your whole argument fails.

quote:

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But i think the assumption for those who say it wont take off are assuming that the plane only just keeps up with the velocity of the conveyor.

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The speed of the conveyor will only cause the wheels to turn faster.

Nothing more ... nothing less.

The assumptions relating to the speed of the aircraft and the speed of the conveyor belt are irrelevant.

The conveyor is moot!



[This message has been edited by IIIHorn (edited 10/25/2007 9:39a).]

After looking at this for so long, i cannot understand how it CAN'T take off....once you understand the engine thrust/plane movement thing its a given she's gonna lift off regardless of the treadmill conveyor thing.

well, whatever we do, lets assume that an internet forum message board is the most effective way to communicate an idea (/sarcasm off).

Fault my unclear assumption, but don't fault my results based on that assumption, which hold true given the assumption. If you read more closely cdub, you will see I agree that the assumption is wrong with the original intent of the problem (for the eleventy-billionth time)

[This message has been edited by agrams (edited 10/25/2007 9:48a).]

but i want to.

The internet forum message board is not moot!

why do you want to further an argument that is wrong?

That is just dumb. If you admit your assumption is wrong, then stop right there. It is stupid to continue to argue just to prove a point that has zero merit.

The assumption is moot!

The assumption is unclear (and wrong with the intended assumption of the experiment), and with the same assumption, we get the same results. No argument.

Why is it so difficult to recognize agreement?

i dont know man...if there is no wind speed i dont see how it can take off

The assumption concerning conveyor belt velocity is moot!

And that is why you have a degree where F=0 gambo.

quote:

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if there is no wind speed

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of course if couldn't take off if there was no wind speed.

but how in the hell will there be no wind speed? THE CONVEYOR DOES NOTHING TO EFFECT THE NORMAL TAKEOFF OF THE PLANE EXCEPT MAKE THE WHEELS TURN FASTER THAN THEY NORMALLY WOULD.

But,

How 'bout the proliferation of wind generators?

what cdub said.

what if the plane was made of cement. would you understand it then, bridge-boy?

[This message has been edited by flaith22 (edited 10/25/2007 10:18a).]

He just needs concrete evidence.

My assumption: Laith is a sparrow.
My conclusion: Laith can fly.

My assumption may be wrong in your eyes, but based on my assumption I am correct.

probably

im probably not understanding the experiment completely b/c honestly i havent read anything on this thread except for horn's puns

so there is probably something i'm missing about this whole thing