Physics Question

Tokenbrit · 24 May 2010 at 19:51

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.

YZFAndy · 24 May 2010 at 19:56

Tokenbrit said:
. 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.

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.

Tokenbrit · 24 May 2010 at 19:59

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.

In Path 1 there is no turn, just a drift to the right, in the absence of any air resistance :rolleyes:

and no loss of altitude :rolleyes:

, it will drift faster and faster.

Jokester · 24 May 2010 at 20:00

YZFAndy said:
So then this assumes that it is constantly accelerating so it will now follow path 2 but in a cork screw shape.

No it's constantly accelerating in the x axis (path 1), path 2 has a continuously changing acceleration.

Edit: Path 2 is more akin to something in orbit round a mass

YZFAndy · 24 May 2010 at 20:02

Tokenbrit said:
In Path 1 there is no turn, just a drift to the right, in the absence of any air resistance and no loss of altitude , it will drift faster and faster.

Which take us back to what i said here

Jokester said:
Path 3 is fixed velocity, so that there is no unbalanced force, ie no lift developed by the wing. If the wing develops lift it will follow a path like that in 1 due to the acceleration it causes.

So then this assumes that it is constantly accelerating so it will now follow path 2 but in a cork screw/spiral shape.

LeJosh · 24 May 2010 at 20:02

You'd have to interfere with natural physics to achieve path 2 surely? Especially with zero acceleration/thrust.

YZFAndy · 24 May 2010 at 20:04

Jesus guys don't you get it! Whats a curve called that goes on forever?

Jokester · 24 May 2010 at 20:05

YZFAndy said:
Which take us back to what i said here

So then this assumes that it is constantly accelerating so it will now follow path 2 but in a cork screw/spiral shape.

Path 2 isn't constant acceleration!

Tokenbrit · 24 May 2010 at 20:05

YZFAndy said:
So then this assumes that it is constantly accelerating so it will now follow path 2 but in a cork screw/spiral shape.

The only force acting is lift.

It will not follow path 2 unless there is a rotational component to the force created by the lift.

If the centre of lift is the centre of mass (as in a particle) there is no such rotational component.

YZFAndy · 24 May 2010 at 20:06

Jokester said:
Path 2 isn't constant acceleration!

so it just accelerated for a little bit then stop? Rule 101

YZFAndy · 24 May 2010 at 20:07

Tokenbrit said:
The only force acting is lift.

It will not follow path 2 unless there is a rotational component to the force created by the lift.

If the centre of lift is the centre of mass (as in a particle) there is no such rotational component.

I said like path 2 but spiral shape because another factor of acceleration was added

Jokester · 24 May 2010 at 20:10

YZFAndy said:
so it just accelerated for a little bit then stop? Rule 101

No, the acceleration has to constantly change direction in order to achieve a circular or spiral motion.

Assuming that the force acts through the centre of mass, it will accelerate the particle in a constant direction at a constant rate. This is in effect what path 1 is doing.

Tokenbrit · 24 May 2010 at 20:12

YZFAndy said:
I said like path 2 but spiral shape because another factor of acceleration was added

Whether it is a spiral or a circle would depend on
1) The forward speed.
2) The amount of force created by the wings
3) The position of the wings.

Since the position of the wings is at the centre of the mass, there can be no turning force and we have the degenerate solution of lateral drift.

YZFAndy · 24 May 2010 at 20:19

Jokester said:
No, the acceleration has to constantly change direction in order to achieve a circular or spiral motion.

Assuming that the force acts through the centre of mass, it will accelerate the particle in a constant direction at a constant rate. This is in effect what path 1 is doing.

So whats the acceleration doing to answer the first part of what your saying? You're saying the acceleration isn't accelerating :confused:

"Assuming that the force acts through the centre of mass" We're not talking about orbits :confused:

"This is in effect what path 1 is doing" Multiply path 1 by 4 rotate it each time buy 90 degrees then we have a circle and are back in orbit with the forever accelerating / non accelerating particle

YZFAndy · 24 May 2010 at 20:22

Tokenbrit said:
Whether it is a spiral or a circle would depend on
1) The forward speed.
2) The amount of force created by the wings Not true
3) The position of the wings. Not true

Since the position of the wings is at the centre of the mass, there can be no turning force and we have the degenerate solution of lateral drift.

Degeneration :confused:

so now we're slowing down! Sprial goes other way

Sharpedge · 24 May 2010 at 20:27

Not 1 or 2. As the aircraft is banked over the amount of lift is reduced so the nose will drop. If left uncorrected the bank and dive will increase and the aircraft will eventually spiral into the ground. If you apply lift with the elevator to keep the aircraft level the turn radius will depend on the length of the wings. A short winged aircraft is easier to turn without use of the rudder than a larger aircraft like a Boeing.

YZFAndy · 24 May 2010 at 20:34

Aircrafts aren't turned with rudders, yaw is correct with rudders.

Tokenbrit · 24 May 2010 at 20:37

YZFAndy said:
Degeneration so now we're slowing down! Sprial goes other way

I can't tell if you are being wilfully ignorant or not.

YZFAndy · 24 May 2010 at 20:41

Tokenbrit said:
I can't tell if you are being wilfully ignorant or not.

Not at all, Flippant maybe but i'm being told to suck eggs and what your saying is wrong.
Centre of mass hasn't much to do with making a wing work centre of mavity and centre of air pressure is.

bam0 · 24 May 2010 at 20:42

YZFAndy said:
"Assuming that the force acts through the centre of mass" We're not talking about orbits

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.