Ailerons not working properly?

[drtricky]

So I have a plane and some of its ailerons are going in the wrong direction when applying pitch up...

...but the main wing is attached to the rearmost mk3 fuselage with the engines embedded in it. Is there a way for me to get the ailerons to work properly without moving the wing? I don't want to compromise its maneuverability.

Edited April 29, 2016 by drtricky

[A_name]

Well, I see on the first picture one aileron elevon, the innermost one, pulling in the correct direction, and another, the outer one, sitting idle (did you turn off pitch for it in the right click menu?). I also see the tailfins at the front apparently alos pulling in the correct direction. Then in the second the outer elevon is clearly sticking up, but I'm not sure what I'm supposed to see. I'm sorry I don't understand what's wrong.

[drtricky]

Just now, A_name said:

Well, I see on the first picture one aileron elevon, the innermost one, pulling in the correct direction, and another, the outer one, sitting idle (did you turn off pitch for it in the right click menu?). I also see the tailfins at the front apparently alos pulling in the correct direction. Then in the second the outer elevon is clearly sticking up, but I'm not sure what I'm supposed to see. I'm sorry I don't understand what's wrong.

All of the elevons except for the innermost one are pointing down on the main wing, when they should be pointing up because in that picture, I'm applying pitch up.

[A_name]

Are you sure they're pointing down? They look idle to me. Is pitch turned on in the right click menu? Or perhaps you set them to reverse in the right click menu by accident? I know this sounds obvious, but it's happened to me before

The other thing I can think of is that they are confused by the center of mass but it seems to be in front of all the elevons in the second pic, although it could be misleading because of the camera angle.

Did you already try to delete the elevons and attach attach fresh ones? Maybe do the same with the whole wing for good measure.

[Boris-Barboris]

Old bug. Squad's respone: set authority to -100%. Wich of course makes roll incorrect instead. I use corrected control surface module in AtmosphereAutopilot, just installing it shoud fix your problem (will need to reconfigure control surfaces on old designs).

[drtricky]

12 minutes ago, A_name said:

Are you sure they're pointing down? They look idle to me. Is pitch turned on in the right click menu? Or perhaps you set them to reverse in the right click menu by accident? I know this sounds obvious, but it's happened to me before

The other thing I can think of is that they are confused by the center of mass but it seems to be in front of all the elevons in the second pic, although it could be misleading because of the camera angle.

Did you already try to delete the elevons and attach attach fresh ones? Maybe do the same with the whole wing for good measure.

Trust me, they're pointing down, your perception is flawed. They're not set to inverted. As a matter of fact, setting the faulty elevons to deploy inverted does nothing. It only works if the elevons are set to always deploy, which is useless.

The CoM is indeed in front of all the elevons on the main wing. There is no camera tricks in the second photo, there isn't even that much of a deviation from a perfectly horizontal view. 

Rebuilding gives the same results. This issue was present when it was built in 1.0.5, and 1.1 did nothing to fix it.

Edited April 29, 2016 by drtricky

[Foxster]

I always seem to get the same problem with these wings and with the smaller swept wings too. I just don't use either of these wings. 

I don't know if this is a bug or I'm being dumb about some special treatment these wings need. 

[Plusck]

Yeah, definitely a bug. Or at least - it sure looks like a bug but it may be quite logical.

I tried to replicate the (basics of the) ship.

First attempt everything worked fine, but the landing gear was too far forward so I moved it back, but messed up symmetry so grabbed the whole wing assembly and reattached with mirror symmetry enabled. Next launch, some of the elevons were working the wrong way on pitch, the others were fine.

Tried rebuilding the wing. If the control surfaces are placed with angle-snap on and without using the rotation tool, they attach fine and work fine. However, rotating them into position caused some (the middle pair of elevons) to operate incorrectly while the inner and outer ones were fine.

Tried moving the wing back - everything worked perfectly. Moved it back to the original position, it bugged.

Final demonstration: attached two fuel tanks to the nose of the craft with radial decouplers. Launched. Result - elevons/ailerons all fine. Staged the hydraulic manifold thingies, result: middle sets of elevons going the wrong way.

Spoiler

Working correctly:

Not correctly:

 

So yes, with that wing, some control surfaces are getting confused about where they are with reference to the CoM. Oddly, they don't get confused if they aren't rotated into position.

However, this does suggest that the issue is less of a bug and more of a question of how the game works out what a control surface should do.

If you look at the second pic, the correctly-working outer aileron hasn't been rotated quite in line with the wing. Therefore its axis will pass through the ship behind its CoM. The middle sets have been rotated fully into position, therefore their axis passes in front of the CoM. Therefore, if this analysis is correct, this isn't a bug in a sense, but simply a question of control surface axis of rotation. Rotate your control surfaces slightly so that their axes pass behind the CoM, and everything should work properly.

Still, I'd say this wing should be used only for what it's intended: as mid-mounted wing with only ailerons (and therefore only roll authority, not pitch authority) and a separate tail assembly. It doesn't play nice if you try to use it as a delta wing.

Edited April 29, 2016 by Plusck

[Plusck]

One more test, and demonstration that this isn't a bug but a question of the axis of the control surface:

Middle control surface rotated so that it's axis (green circle) passes just slightly behind the CoM:

Spoiler

Outer control surface rotated so that it passes slightly in front of the CoM:

Spoiler

Result on the runway: The middle control surface works fine, the outer one doesn't:

Spoiler

So there you have it - it works as predicted.

So putting elevons on these swept wings is possible, as long as you are careful about aligning them properly with reference to the CoM. And special care will be needed to check how CoM shifts as fuel is used, to avoid catastrophic loss of control if CoM shifts backwards...

Edited April 29, 2016 by Plusck

[drtricky]

@Plusck You're right! Angling the faulty elevons so the green axis was pointing behind the CoM fixed the problem! So it's simply a flaw in logic that caused this.