Anyone good at physics, please clear this mystery

[Olethros]

The plane's mass, momentum and acceleration do matter. And for physics calculations they matter within the inertia system, NOT within the medium. And in this case this "inertia system" would be planet earth: the ground.

So problem still remains: The plane (more correct: its mass) has to be accelerated by 80mph within 30 seconds. By the force of the wind and by the force of its engine. (While the engine is "wasting" some of it's potential force by not applying it in the direction that matters at all times.)

In short: That webpage does use a simplification of the problem. And I am not fully convinced that it is a valid one.

For the love of your imaginary deity of choice, never, EVER attend flight school. The absolute speed difference (dV) from before and after the turn will actually be 160 mph no matter what direction or force the wind has. Hence, the change in inertia is also the same and has no influence on the plane's indicated airspeed during or after the turn.

Furthermore, your concept of an "inertia system" that holds the ground as a static reference point makes absolutely no sense at all! If it were so, then you would not be able to turn a rolling bicycle beyond 90 degrees without pedalling no matter what your speed was before you decided to change direction. (To name but one example.)

The plane doesn't take off. Lift is generated by wind flowing over the wings, not through the engine. The engine is providing thrust, but the conveyor is "magically" acting against it in equall and opposite direction, preventing acceleration. Unless the thrust of the engine is directed in a vertical manner (harrier) to some degree and with suffient force to actually lift the plane without the wings generating any lift will it get off the ground. but a traditional plane unable to direct it's thrust away from the ground is stuck.

Enjoying your McJob yet? If the conveyer where to counteract the thrust of the engines through the free-rolling wheels, it would have to accellerate insanely fast and not - as stated in the original parameters - match the aircraft's groundspeed in the opposite direction. So yes, the conveyer would indeed have to impose some "magical" kind of force on the aircraft, because the known laws of physics sure as fuck won't let it!

 

[ant75]

I like it when people hit the "reply" button without having read the whole thread.

 

[Sir_Brizz]

when did comedy gold enter this thread?

 

[geogob]

when did comedy gold enter this thread?

I would say from Post one, directly comming from post one on the BUF O/T thread.

 

[chuckus]

"The conveyor works on the wheels of the plane which are attached to an axis and can spin freely, thus making any effect the conveyor has on the plane negligible."

I GET IT NOW! I know it's been stated over and over again but for some reason wording that way just made it click.

 

[Hadmar]

Whoa, a usefull post by me. I must get old.

 

[geogob]

I have to say, that post was really an easy way to solve the problem.

 

[M. Fenix]

lol Olethros QED.
And BTH, as long as we're stating the irrelevant... Yeah, but what if the plane is a Harrier?
Well, maybe not so irrelevant if it's a riddle

 

[Harrm]

Yeah, but what if the plane is a Harrier?

I think this came up in the OT. The response was something akin to "shut up fag."

--Harrm

 

[M. Fenix]

Dude, that's the answer! And aren't these OT guys the very same people you're undermining

 

[geogob]

The REAL question, is why don't you rip your giant treadmill out of the ground, flip it over and make a giant snowmobile out of it. You'd be all set for the next ice age, or ready to crush a few villages.

 

[Pipe_Dream]

No it cant, The plane has to have momentum and air pressure under the wings to get off the ground.

This is one of the stupidest arguments i've ever heard.

If The propulsion was powerfull enough to lift the plane from the conveyor "witch basically has the plane at stand still" Then there would be no need for runways in the first place. But the propulsion is not that strong so a runway is necessary.

If you had the conveyor rotating in the same direction as the planes path then you could maybe have a shorter runway. like when you run on the long conveyors at the airport. It would sling the plane into the air quicker , and less distance would be needed to take off.

By Pipe_Dream

 

[Hadmar]

[...]the conveyor "witch basically has the plane at stand still"[...]

How does it do that? Via tractor beam?

 

[Farouk]

For the love of your imaginary deity of choice, never, EVER attend flight school. The absolute speed difference (dV) from before and after the turn will actually be 160 mph no matter what direction or force the wind has. Hence, the change in inertia is also the same and has no influence on the plane's indicated airspeed during or after the turn.

Furthermore, your concept of an "inertia system" that holds the ground as a static reference point makes absolutely no sense at all! If it were so, then you would not be able to turn a rolling bicycle beyond 90 degrees without pedalling no matter what your speed was before you decided to change direction. (To name but one example.)

Wow, you really managed to make me feel like an idiot for a while. I already had the beginning of a humble I-was-wrong reply formulated but then was distracted from finnishing and posting it. Now I have had more time to think about it and I still stand by my view.

I could be completely wrong wrong though. But you can be rest assured that I have nothing to do with flying. My background is in mechanical engineering. And so, I feel competent enough on Newtonian mechanics, altough I'm a bit rusty.

My inertia system does make sense. The plane's flight starts on the ground. So it IS the zero point. The plane, standing there on the runway, is considered to have zero momentum and zero kinetic energy. Correct?

Then it accelerates to take off. If there is no wind at all, it will actually accelerate to a higher velocity to gain the neccessary airspeed as if it will be starting against the wind, don't you agree?

But that automatically implies that the plane has a greater momentum and more kinetic energy than the one starting against the wind.

And the preservation of this kinetic energy makes the bike lose no speed in your example. Neglecting all the friction losses, it will be as fast as it was before the turn.
And exactly the same goes for the plane in the 80mph wind speed example. It has been accelerated to 40mph before the turn and will have 40mph after the 180° turn.
But it needs to have 120mph at the end of the turn. And the force of the wind and the engine have to provide the missing 80mph in these 30 seconds.

 

[Harrm]

I'm with Geo on this one.

Also, Olethros and Farouk, you guys have just entered a mobius circle. You're going to debate this and end up at the same place you started, just so you know.

--Harrm

 

[Pipe_Dream]

How does it do that? Via tractor beam?

http://forums.beyondunreal.com/showthread.php?t=170367
see post #2

 

[gal-z]

nice one. Pretty confusing as one would normally think that the conveyor moving back would counter the plain forward movement. This would've been true if the power would come from the wheels. However, the wheels have practically no friction and the power comes from the engines, and the wheels are just free spinning and therefore the conveyor and wheel speed have no effect on the actual plane speed, and the plane CAN definately take off.

 

[Olethros]

Wow, you really managed to make me feel like an idiot for a while. I already had the beginning of a humble I-was-wrong reply formulated but then was distracted from finnishing and posting it. Now I have had more time to think about it and I still stand by my view.

I could be completely wrong wrong though. But you can be rest assured that I have nothing to do with flying. My background is in mechanical engineering. And so, I feel competent enough on Newtonian mechanics, altough I'm a bit rusty.

My inertia system does make sense. The plane's flight starts on the ground. So it IS the zero point. The plane, standing there on the runway, is considered to have zero momentum and zero kinetic energy. Correct?

Then it accelerates to take off. If there is no wind at all, it will actually accelerate to a higher velocity to gain the neccessary airspeed as if it will be starting against the wind, don't you agree?

But that automatically implies that the plane has a greater momentum and more kinetic energy than the one starting against the wind.

And the preservation of this kinetic energy makes the bike lose no speed in your example. Neglecting all the friction losses, it will be as fast as it was before the turn.
And exactly the same goes for the plane in the 80mph wind speed example. It has been accelerated to 40mph before the turn and will have 40mph after the 180° turn.
But it needs to have 120mph at the end of the turn. And the force of the wind and the engine have to provide the missing 80mph in these 30 seconds.

Your reasoning isn't bad, but you have gotten one crucial detail wrong: The work-energy theorem (Wtotal = K2 - K1) is only valid in an inertial frame of reference. What this means is that since the plane is moving through a system (the air) that in istelf is moving relative to your reference point (the ground), you can't apply K1 = 1/2*m*V1^2 and K2 = 1/2*m*V2^2 with V1 and V2 measured relative to the ground. This would provide a disproportionate result since the equation is not valid for negative speeds (V is squared in the equations, making -V yield the same result as V). You have to use dV in place of V1 and V2. Therefore:

Wtotal = 0.5*m*dV^2

rather than

Wtotal = 0.5*m*V2^2 - 0.5*m*V1^2

Clearer now? It's an easy mistake to make, but a mistake nonetheless.

No it cant, The plane has to have momentum and air pressure under the wings to get off the ground.

This is one of the stupidest arguments i've ever heard.

If The propulsion was powerfull enough to lift the plane from the conveyor "witch basically has the plane at stand still" Then there would be no need for runways in the first place. But the propulsion is not that strong so a runway is necessary.

Man, you are just an entirely new kind of stupid, aren't you? Let me try it one more time: Because the wheels are free-rolling, the runway has no way of keeping the plane "at a stand still" because there is no horizontal force working through them.

Now make yourself a hat that says "moron" and wear it sitting in a corner for a while. Preferably a long one.

 

[Hadmar]

Well, considering that he just copied the post the hat better says "plagiarist" and possibly "troll".

 

[DEFkon]

what if the runway and wheels were replaced with a river (with a current that adjusted) and a set of floats?