SAS/ASAS will not hold attitude on space planes

[KerikBalm]

First off, due to my OS, I'm still on 0.19.

I've made a number of spaceplanes that just didn't seem to fly, I'd get off the runway, pitch up, hit "t" to toggle SAS (with an ASAS module on the ship), only to see the nose swing down and the whole plane crash into the ground.

I've since made craft that I could mannually fly, having to constantly pitch up to maintain attitude, but I could fly them past 20km just fine, while the SAS/autopilot always nosedives....

I even made craft that had the CoL ahead of the CoM by a bit, and the SAS in this case seemed to maintaine attitude for a bit, then slowly starts pitching down, and then after some more time... nose dives....

Has anyone else had this problem?

This always seems to occur on my designs that have a spacecraft slung underneath a spaceplane - with an inverted gull wing, and engines inline with the craft slung underneath... the thrust lines and CoM match well, and its quite controllable without SAS.

I've made some small spaceplanes that handle just fine, and all my rockets, the SAS seems to work fine on.

I can't figure this one out.

[Penguinhero]

What os are you on And why can't you update to .22

[RocketPilot573]

The SAS is very different in .21 and .22, why can't you update?

[Johnno]

SAS relies on control surfaces, engine gimbal and reaction wheels to keep your heading. Add a reaction wheel or two plus some winglets (behind CoM) and canards (forward of CoM).

Edit: Since you're on 0.19 disregard the bit about reaction wheels. More control surfaces should do the trick.

[KerikBalm]

I'm on Mac OSX 10.5.8, hence no updates.

I added a ton of control surfaces... my earlier designs I thought this was a problem, as when the control surfaces were used for anything other than pitch (ie, roll), the nose dipped.... but now, when I need to hold the nose down... it makes no sense.

I have tweaked some stats/added some mods (in particular, back porting many .22 parts to .19, but nothing that I can think of that would affect the SAS.

[Cruzan]

What do your designs look like?