Physics Question

bam0 said:
Saying that the force acts through the COM precludes any rotation, of any kind. The plane will always point the same direction, and eventually would be moving also completely sideways.
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Yes i agree and thats what i have expressed in path 3. But what i'm saying is were not talking about a forever falling object that never catches up with mavity. we're talking about a banked plane.
 
YZFAndy said:
Yes i agree and thats what i have expressed in path 3. But what i'm saying is were not talking about a forever falling object that never catches up with mavity. we're talking about a banked plane.
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No, because the banked lift is a constant acceleration, but only ever in one direction. Ignore the fact it's a plane because the model is so overly simplified it doesn't make any sense.
Instead you have an object with a constant velocity in one direction, while retaining that momentum you exert a constant acceleration at 90 degrees, this will give you path 1.
 
YZFAndy said:
And if you carry on path 1 forever it makes a circle
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How? The acceleration is only in one direction, how can it ever go backwards? The plane is always facing in the same direction, there is no rotation, not of the plane or the acceleration, it's an asymptote.
 
bam0 said:
How? The acceleration is only in one direction, how can it ever go backwards? The plane is always facing in the same direction, there is no rotation, not of the plane or the acceleration, it's an asymptote.
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Ok I've just gone back to original post and seen some new rules put there.

Definatly not going to be a parabolic curve with the nose point forwards( orginaly looked like it was quarter of circle and didn't quite notice plane nose wasn't following curve), and yes it would be a asymptote. That what i meant be corkscrew spiral, would have never remembered the name.
 
Tokenbrit said:
I think what matters is the position of the centre of lift in relation to the centre of mass.

If the lift is forward of the COM then it will drag the nose around and the aircraft will turn in a circle like path 2. If the lift is applied at the COM then there is no turning force and the aircraft will simply drift right as in path 1.

Lift going through the centre of mass is probably not an at all realistic assumption.
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Lift going through the centre of mass is completely realistic for a plane which is staying at the same altitude... Otherwise the plane would twist and completely change what way it is facing, and do all kinds of horrible things.

YZFAndy said:
But what force makes it steer out of the turn. The force that started the turn doesn't just vanish. its either there or not so it would Carry on in a direction unless acted on.
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The force doesn't make it 'turn'... It is still facing the same way, but it is not going in exactly the direction it is facing.

YZFAndy said:
Jesus guys don't you get it! Whats a curve called that goes on forever?
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Strictly speaking, a parabola goes on forever, and is always slightly curved (although it becomes incredibly slight after a while)

Jokester said:
Path 2 isn't constant acceleration!
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Well for it to go in a circle, it would require a centripetal force, which would exert a centripetal acceleration toward the centre of the circle

YZFAndy said:
Centre of mass hasn't much to do with making a wing work centre of mavity and centre of air pressure is.
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What exactly is the difference between centre of mavity and centre of mass? ;)


And for those of you mentioning asymptotes, I don't think that is right, as parabolas don't have asymptotes. Asymptotes are lines which the curve will approach, but never ever reach. e.g. The curve, y=1/x would have an asymptote of y=0, as no real value of x would give y a value of 0. There is however, no asymptote for the curve y=x^(1/2)
 
So, has the plane landed on a treadmill yet?

Another vote for path 2 simply because as the plane progresses along the curve it'll be continually turning off the current tangential line eventually following a vaguely circular path.

Path 1 would be wrong as it assumes the only important point is the initial point.
 
But what if the plane is standing on a large treadmill or conveyor belt and it moves in one direction while the conveyor moves in the opposite direction? ;)


e : Oh FFS, post #110 beat me to it :mad:
 
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Squark said:
No it doesn't
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Well quoting me a bit out of context, I was referring to my question where I explain what the question was asking, and seeing as the altitude stays the same, where do you suggest the lift acts though? If it acted anywhere else, with just the 2 forces included, the plane would effectively be hanging from wherever the lift is.
 
[FnG]magnolia;16616793 said:
But what if the plane is standing on a large treadmill or conveyor belt and it moves in one direction while the conveyor moves in the opposite direction? ;)


e : Oh FFS, post #110 beat me to it :mad:
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I was surprised it took four pages to get mentioned :p
 
So basically (judging by the OP), is this thread just: 'presuming there are only forces acting in one dimension, will other forces be caused in another if we arbitrarily draw a plane at an angle?'
 
Too many drinks to read the thread, but looking at the first few posts, the problem to me seems to be does the plane turn (rotate around the y axis). My gut feeling is that if you banked the plane in this way, you'd slide in the direction of the wing you lowered, and turn as you decend in a clockwise spiral, since as you start to fall, because you've decreased your lift (vertical force) by banking, the nose of the plane will dip.
I don't think that your altitude can stay constant in this example, unless you also change the shape of the wings as you bank, and/or the force of the forward thrust.
 
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