Airplane rolling to the left

[pincushionman]

I'm having some control issues with an aircraft. It rolls constantly.

I don't mean "it rolls down the runway," I know about that. That's fine. It's also not about the landing gear flexing funny as I roll down the runway, it's pretty controllable on the ground. This is in the air. It constantly rolls to the left. Small roll, but enough that I can't keep a heading and I can't seem to trim it out.

The plane is otherwise stable, best I can tell. CoM is ahead of the CoL so we're cool in the longitudinal modes.

At first (with other planes I was trying to build) I thought I was simply unstable in roll, so I tried adding dihedral to the wings (as you can see). I'm not sure that even works in KSP, but it appears this isn't the issue. Then I thought maybe the jet engine applies a torque, but it does this no matter the throttle setting. I've been watching the control input indicators at the bottom left and this happens while the roll indicator is centered.

Here's the standard 3 views with the centers highlighted, but as I said it's not a stability issue.

And here's the .craft, in case any of you want to try to troubleshoot:

http://www./download/la7yyh9ma7asql8/Condor_LRF.craft

I have mods on, but only the following: In-Flight Waypoints, KER, Docking Port Alignment Indicator, ScanSat, StageRecovery, Trajectories, Kerbal Alarm Clock, TweakScale. As far as I know, the only one which should affect anything would be TweakScale, and nothing has been tweaked on this aircraft.

Any help would be appreciated!

Edited January 24, 2015 by pincushionman
answered

[NathanKell]

2-year-old bug.

[eddiew]

2-year-old bug.

In which case an internal strut along each wing may help. Perhaps an X strut between the tails too, make sure that one of them isn't flexing more than the other

[ratchet freak]

move the wings up a bit (or mass down) or angle the tip upwards (adding a dihedral to them) that will improve roll stability

[pincushionman]

2-year-old bug.

Eeenterrsting. So this seems to be a stiffness bug more than an aero one.

Each wing is two sections - I wonder if I could minimize the effect by placing the inner wing and tailplane from one side, then place the outer one from the other? Testing forthcoming…for SCIENCE!

In which case an internal strut along each wing may help. Perhaps an X strut between the tails too, make sure that one of them isn't flexing more than the other

I'll try something of that nature. Would you recommend a single long strut between the fuselage and wing tip or one from fuselage to inner section, then one between inner and outer? I'm a little constrained for parts in my career save so I'll have to see what I can sacrifice. If I even have struts yet in that save…I'll have to check.

move the wings up a bit (or mass down) or angle the tip upwards (adding a dihedral to them) that will improve roll stability

This is overwhelming any dihedral I'm trying to effect here. But you confirm it does work? That would help a lot; babysitting the heading all the way from KSC to the north pole where my survey contracts are is gonna get real old fast.

Thanks for the help so far.

[capi3101]

I would suggest moving the Elevon 1s you've got on the wings out to the outer edge of the outboard Wing Connector Bs you're using to try and improve your roll authority. Might not solve the underlying problem but you might be able to at least trim it out. Maybe try that in conjunction with what everybody else has suggested to this point.

[rynak]

Removing struts can also help sometimes. KSP is really annoying and bugged with this kind of stuff - been so for ages. Sometimes you need to add a strut somewhere, other times a strut actually causes it.

If you're not using it yet, i recommend KerbalJointReinforcement - i've had issues like this much less often since using it, plus no pancakes anymore.

[pincushionman]

I would suggest moving the Elevon 1s you've got on the wings out to the outer edge of the outboard Wing Connector Bs you're using to try and improve your roll authority. Might not solve the underlying problem but you might be able to at least trim it out. Maybe try that in conjunction with what everybody else has suggested to this point.

I gots more roll authority than I know what to do with already. I don't know how anybody flies planes with keyboard - the aileron moment arm is so long!

...I recommend KerbalJointReinforcement - i've had issues like this much less often since using it, plus no pancakes anymore.

I added some struts...and now it rolls the other way. I'll look into KJR.

[pincushionman]

Added KJR. Noticed still a slight uncommanded roll (right this time), but far smaller and now something I can manage.

Added some dihedral to the whole wing, but not any real effect with this much dihedral angle. Does it need to be way more to be useful?

[Foxster]

When I've had annoyances like this its usually been down to some invisible imbalance. Perhaps caused by using mirror rather than radial symmetry (or is it the other way around?) when placing a couple of parts. Often seems to creep in on a multi-revision aircraft i.e. one that's been tinkered with a lot. Only fix then being to start from scratch.

[rynak]

In the pic, i see SAS is disabled. If you enable it, that would probably get rid of the final minor imbalance. Not a clean solution, but practical if reassembling the craft would be a lot of work.

[ratchet freak]

Other wise use alt+e to trim roll to the right to overcome the tendency (alt+ command will add trim in that direction alt+x will reset it)