Center of Drag

[HQtopgun1]

Until the aerodynamics model is updated to be more realistic, I think it would be a good idea to have another option to display the center of force applied by drag at certain velocities along with the center of mass, lift, and thrust. This way it should be easier to judge if your rocket is going to instantly flip out due to, say, a large amount of very small parts on top of a tall lifter.

[Master Tao]

I think you've misunderstood the drag model in KSP. Because drag is directly tied to the craft's current mass, it's CoM and CoD are rarely significantly different, and that doesn't shift with velocity.

If you're rocket is flipping over, it sounds like the CoL is above the CoM. Try adding fins to the bottom stage. If that doesn't work, you could post pictures with the CoM, CoT, and CoL showing and someone will try to help figure out what's going wrong.

Also, FAR and NEAR both show the aerodynamic center, which is essentially both the CoL and CoD.

[MarvinKitFox]

I think you've misunderstood the drag model in KSP. Because drag is directly tied to the craft's current mass, it's CoM and CoD are rarely significantly different, and that doesn't shift with velocity.

If you're rocket is flipping over, it sounds like the CoL is above the CoM. Try adding fins to the bottom stage. If that doesn't work, you could post pictures with the CoM, CoT, and CoL showing and someone will try to help figure out what's going wrong.

Also, FAR and NEAR both show the aerodynamic center, which is essentially both the CoL and CoD.

CoD (Center of Drag) is really only pertinent to spaceplanes.

Planes tend to be asymmetric along the vertical axis.

Planes tend to use large numbers of non-standard drag items. such as

AIR INTAKES (0.3)

Parachutes (0.3)

Nosecones, of various types (0.1)

WINGS and control surfaces!(0.02)

This most definitely leads to a need to see if your drag, mass and thrust are suitably aligned!

For example, a plane with its COD ahead of its COM, will be inherently unstable, and prone to go into a flat spin.

Whereas one with CoD well behind the CoM is almost self-righting after a tumble.

[Master Tao]

Wings and intakes also have extremely low mass, so they have almost negligible drag anyway. Nose cones will only shift the CoD the wrong way if you stick them on the back of the plane. Parachutes, well, they're covered by "rarely" since they don't help much for landing planes without balancing them both forward and aft.

Feel free to show me an example craft where the CoD appears to be well ahead of the CoM, but the CoL is still behind the CoM. I'd like to see that contraption.

[MarvinKitFox]

Feel free to show me an example craft where the CoD appears to be well ahead of the CoM, but the CoL is still behind the CoM. I'd like to see that contraption.

*trivial*

Take one tube. Stick a turbojet on the arse, and 8 ram intakes on the nose. Add wings placed for good lift/mass balance.

CoD is **way** forward of the CoM

or an off-centre drag example.

Build one perfectly good plane of any design, with CoD and CoM and CoT all neatly aligned along the centreline.

Stick one radial scoop on the roof.

The CoM will shift upwards a little bit.

The CoD will shift up a third more. Even worse, the CoD will wobble up and down, depending on whether the intake is full or empty. Even worse, the CoD will wobble drastically up and down depending on whether the intake is open or not.

At high speed this plane will now want to backflip.

this is a VERY COMMON cause of first-timer plane crashes.

Edited August 19, 2014 by MarvinKitFox