Aerodynamic pitch control inversion

[arq]

It seems that the bug-report section of the forums was moved or deleted at some point after release, and this was the closest I could find.

There is a bug where control surfaces can end up with inverted pitch controls. I have attached a picture of a craft that produces this issue. It seems to stem from having control surfaces mounted at an angle too near the CoM. In the image, (counting inside to out) the 1st and 3rd control surfaces have the proper pitch deflection while the 2nd and 4th are inverted. All have the proper roll deflection.

Counting outward from the fuselage:

The 1st (innermost, inside the engines) set are mounted horizontal to the direction of flight and deflect properly.

The 2nd set are mounted at ~30deg (whatever the swept wing angle is) and have inverted pitch control.

The 3rd set are shifted further back using the offset tool. Any further forward than their current location will result in inversion, but they deflect properly where they are in this image.

The 4th (outermost) set are angled as well (but now using the Control Surface 1 part instead of 5) and experience inversion.

In fact, any surfaces mounted at that angle along that entire troublesome line (slanting back at 30deg) will experience inversion. An un-angled control surface causes no issue, and an angled surface sufficiently far back is fine.

Placing a large fuel tank on the front of the craft (to shift the CoM far forward) resolves the issue.

So it appears that this issue only occurs for control surfaces mounted with a rotation, and only when applying pitch input and if they are sufficiently close to the CoM. It does not seem to affect the roll axis, though it is possible an analogous configuration could produce this issue on that axis. Removing all mods from my install did not resolve the bug.

Edited August 16, 2015 by sumghai
Crossed out untrue statement

[sumghai]

[MOD - Moved to Support (unmodded install) subforums, which has existed prior to and after game release]

[WinkAllKerb'']

http://forum.kerbalspaceprogram.com/threads/103923-Problem-with-inverted-control-surfaces

[arq]

Thanks for the relocate and the link. Sorry I misplaced this. Glad it's already a known issue.