Something to ponder... and I don't know the right answer

[Kaneda]

Lol thanks Train.


I like how Drop is getting all the credit for his answer...

I agreed with the a-a-tourney f-f-f-irrst 

[NightTrain]

Drop is an old roomate of mine.  He gets credit before some attorney.   

[Cole]

The jets are moving the plane relative to the earth independent of the wheels.

no it's not.  it's moving it relative to the conveyor and the earth....

replace plane with a car and it is the same answer the method of forward propulsion is trivial. 

[Mathius007]

i eat clay 

Hilarious.

And yes, iut will fly. While the conveyor belt is moving in the opposite direction, the plane is still moving. It appears to not move, and you would think that it would be stationary, but I don't think it would.

While the plane is going against the coveyor, it still, is in fact, accelerating. Think of it like this. If you run outside, in the wind, you will feel it. (duh). Now place a conveyor belt (reeeeally long one) outside and run on it. Guess what: the wind is still going past you at the same speed. Therefore, the plane, hypothetically, should be able to lift off, as the wind is still passing it, and, in theory, it is making progress towards the wind.


Of course, I'm no technical expert, or genius, but that is just my 2 cents.

[Cole]

OMFG no it won't.

Jesus christ people!

First Drop.

Then Night.

And now Mathius.

Who's next?

Try it this way guys.  Turn the plane around and turn on the conveyor.  The plane shall start moving with the conveyor.  If the conveyor goes fast enough, the plane will take off (and since it's not powered subsequtially touch down).  So....

matching speed in opposite direction = zero net speed.  I don't give a damn how you look at it.  that's logic.  Now without the air moving around the wing, you cannot fly the plane.  Unless it's a UFO.

[Cole]

Before the plane flys, it will will act like a car, it's propulsion system is just different.  IF the runway moves along, matching the speed (thus the acceleration too since it is matching instantaneous velocity) the plane never gets up to air airspeed where it generates lift.  Think of it this way, once lift is generated, the tranfser of energy changes from engine to ground to engine to air.  Actually, it is arguably engine to wing.

I think too many people think of this problem as hey, if a plane is flying, and its wheels touch down on a conveyor matching it's speed in an opposite direction, it can still fly. Or, they argue that the plane is flying in air.  The engines act upon the air.  It's not like a car where the engine turns the wheels and the engery transfer is tire to ground.  Well, I've got one for those people too.  Wrong!  The energy transfer is from Jet Rocket Ion Propulsion Fart Power to the ground in the plane too.  One word:  Gravity.  In normal operation, the plane goes fast enought to generate lift and overcome gravity.  On the conveyor, this of this discretely.  For every one "node" forward the engine pushes the plane forward, the conveyor pushes the plane back.  To the observer off the conveyor watching from afar, there is no net movement, but the tires spin twice as fast.  Thus the plane will not ever gain any velocity, and no flyie flyie fo' the poor little planey.

[Privateer]

cole is sitting at home... maybe watching tv... and then boom, another possible reason as to why it wont fly pops to his head...dilemma is does he leave the tv to go post it or does he just write it down on a piece of paper to then transfer it to the forums after the show.


We can clearly see that due to the excessive double posting by him that his favorite tv shows are not on

[Cole]

Ok.  I retract my statements.  All of them except the whole DOLPHINS BE SMART and shit. 


plane moves forward 40 miles per hour.  Conveyor moves backwards 40 miles per hour.  Planes groundspeed is now 80 miles per hour relative to the conveyor, but outside the inertial frame, the conveyor is moving at the same speed but opposite of the plane.  Plane's wheels are still going 80/2*pi*r but no problem.  The Plane is still moving forward since the engines are using the air to cause movement which is not attached to the conveyor.  Basically the cause of movement is outside of the conveyor-plane frame of reference, so it is not the correct reference to use.  So the plane does fly.

It is a very good thing I have no shame.  This character trait allows me to be wrong many times and still learn from my mistakes.  I don't know what the hell I was thinking.  My brain is fried from too much WPI Stratton hall crap.  Now back to Chapter 10 - Brownian motion.  woo hoo.

[Cole]

priv.  you ruined my triple post. 

[Spikeroo]

I'm afraid to take a stance on this one.  Instead, I'll post a question:

Tie the tail of a plane to a concrete block.  Now two assumptions - the rope/cable is infinitely strong and the block will not move under infinite force.  So, if the engines of the plane fire up, will the plane drift up in the air?

This is the same problem re-worded and I think, at least to me, it is a little simpler to thing about.  I know my answer but I'm not posting it...I'm too wimpy for the critics on this forum!!!

Maybe I'll hit the books a little later and post something but for now - nada.

 

[Spikeroo]

LOL...

http://forum.physorg.com/index.php?s=de677ccf0a75800be03ff934d999b080&showtopic=2417&st=0

You figure it out...

[Cole]

In your example Spike, the plane will not move.  You see, the rope and anchor are in the same inertial frame as the plane.  The rope directly opposes the force the engine puts on the plane.  In the conveyor example, the conveyor exerts force on the wheel, and the plane exherts force on the wheel, but those forces are additive.  the engine puts force/work on the plane, but there is nothing opposing it.  the wheels are not powered, that is they do not power the plane.  The plane powers the wheels sort of.  That's where I was confusing myself.  The conveyor just mkes the wheels spin two times faster.

Now another way to change the problem would be instead of a conveyor, you have a wind tunnel.  The wind velocity opposes the plane directly proportional to the plane velocity.  What happens?

lol.  The plane takes off sooner.  Basically it seems that planes are easy to get airborn, and the Wright brothers are hacks, just like everyone else from Indiana and Ohio!  That's right Wolvey*pie*, yum. 

[Spikeroo]

Nope - the conveyor and the wind tunner are completely different.  The wind tunnel will cause lift, as the air is cleary moving in relation to the wing.

My take on the conveyor case is the plane will not get off the ground.  What we are talking about is instantaneous velocity/speed of the wing in relation to the air - that is what the conveyor is adjusting to.  The average velocity/speed of the air with respect to the wing is zero, thus zero lift.  Just think about a plane - it doesn't get in the air the second it starts moving - it takes a significant trip down the runway with a lot of acceleration.  You can't have acceleration without a change in velocity - the only things accelerating are the belt and the wheels and the wheels are accelerating in a circular motion.  The minor velocity changes as the conveyor adjusts are not enough to give the plane the lift it needs.

I'm no brain surgeon, but I'm far from a dummy - I aced every Physics course I took - 2 at Tufts and 6 at WPI.  But this doesn't mean I'm right either.  I looked on the web and there are dozens of forums with hundreds, maybe even thousands, of posts regarding this exact problem.  The key is - who's got the right answer?

 

[Mathius007]

Guys...Cole has spoken.

He retracrted his earlier statement, and now says the plane will fly.

Hah. So, that has to be the answer, cus, Cole is smart (or at least sounds like it).

The plane will fly.



Besides Dropkick, Nighttrain, Cole and, Hey, me.




Some Smart dudes right there (well, maybe except for me.)

[Cole]

Nope - the conveyor and the wind tunner are completely different. The wind tunnel will cause lift, as the air is cleary moving in relation to the wing.

That was my point.


I was thinking the same way as you.  However, you're neglecting to consider the moion of the plane to it's surrounding air, which is like the rope.  The conveyor is outside of the inertial frame.

If you were inside the plane.  Fire up the engines.  you'd get thrust from the engines which are dependent of the air, and independent of the ground.  So, the conveyor doesn't even matter.  If you didn't look at the ground, you wouldn't even know that the conveyor was moving. 

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