COL Infront of COM and Vice versa

[Commander Jebidiah]

If my understanding of stock ksp aerodynamics is true then,

Planes with COL ahead of COM equals more agility

And COL behind COM equals more stability

Am I right?

Edited December 3, 2014 by Commander Jebidiah
Answered

[Alshain]

No, Center of Lift in front of Center of Mass equals disaster.

Center of Lift Closely behind Center of mass equals more maneuverable.

Center of Lifter Further behind Center of mass equals more stability.

And even further behind Center of Mass means the rear wheels probably won't leave the runway. If they do, you will go up and immediately back down again.

As far as stock and FAR go, this principle is the same. However degrees of maneuverability may be different.

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

Edited November 5, 2014 by Alshain

[BagelRabbit]

CoL in front of CoM is a bad thing. It basically means that the plane is unstable, and desperately wants to crash.

CoL and CoM in the same place is a pretty good thing. It means that the plane is 'marginally' or 'neutrally stable', which means very high maneuverability without instability.

CoL in back of CoM is a good thing, as long as the CoL isn't too far back. The plane will be stable and fly well... unless the CoM is too far back. In that case, the plane will be difficult to point in the direction you want it to.

[EDIT: Ninja'd, of course. I don't type very fast.]

[Commander Jebidiah]

Strangely my jet Biplane is very stable and its COL is infront of its com

Thanks for the answers though and upsilon I like claw game

[Alshain]

Strangely my jet Biplane is very stable and its COL is infront of its com

Thanks for the answers though and upsilon I like claw game

Post some screenshots with CoM and CoL showing. Typical biplanes have a heavy engine in the front which would bring the CoM forward. The fuselage in the back is usually pretty light. HOWEVER. Biplanes are also in a pull configuration. not a push configuration like a jet so it's a bit different anyway.

Edited November 5, 2014 by Alshain

[Red Iron Crown]

Biplanes are also in a pull configuration. not a push configuration like a jet so it's a bit different anyway.

Does that matter? My initial thinking says it shouldn't, but I could be wrong.

[Alshain]

Does that matter? My initial thinking says it shouldn't, but I could be wrong.

I'm not sure actually. From a theoretical standpoint I'm envisioning a force behind pushing and the lift causing it to be flip happy because the wings push the plane up too hard. The pushing force pushes it around because there is nothing holding it straight. In the case of pulling, the force itself is holding it straight, like a train. It makes sense in my mind from a physics standpoint but there might be something I'm not aware of.

I am by no means an expert on aerodynamics. I just try to share what I learn

Edited November 5, 2014 by Alshain

[Redshift OTF]

Pretty sure the CoM in a Bi-plane is in line with the two wings. When they flap their tails the tails move a lot while the wings don't.

[pellinor]

I'm not sure if l have fully understood what this CoL indicator actually shows. Can someone confirm or disprove my theories? Here is my understanding of how this CoL stuff works:

1) Imagine a plane in stable flight with constant velocity. Let us say thrust and drag are centered so they do not cause any momentum. If the forces of weight and lift would not be in line, the plane would turn around the pitch axis. Simple physics. So in straight flight something must happen to bring them in line.

2) The CoL arrow in the SPH doesn't point straight up, it has a light forward tilt. It always points up, even if you turn a wing upside down. So my theory is that the SPH actually calculates the lift force for an airstream that does not go horizontally but a few degrees upwards. So you see your plane at a fixed angle of attack (around 5°). This is even necessary for stock aero because at zero angle of attack there would be no lift.

3) If you turn the plane around the pitch axis (in the SPH), you see the CoL for different angles of attack. If a plane is hands-off stable in the pitch axis, the CoL must be behind the CoM at high angles of attack, and in front for low/negative angle of attack. The stable equilibrium is the angle where the CoL and CoM are in line (note that trim will move this equilibrium point, see #5). A stable plane will seek this angle of attack, resulting in a speed and climb/sink rate that depends on the thrust.

4) This shound work the same for other axes. So turning the plane around the yaw axis should simulate sideslip. If the plane is stable, the CoL indicator should create a momentum to turn the plane back.

5) If you attach control surfaces at an angle, the CoL indicator moves. This shows how the plane will react to control input.