Screwy center of lift / symmetry bug (FAR)

[Jarin]

Okay, what sort of FAR strangeness could cause my center of lift to be significantly off-center when everything on the aircraft is symmetrical? I'm at wits-end here.

[Hodo]

You are talking about in the SPH, when you attach a wing or something the CoL shifts to one side?

If so that is a minor bug, it often has no affect on the actual flight performance of the craft. You can check the numbers in the FAR testing graphs the craft will fly fine.

[Jarin]

Oooh, no. This is pretty solidly a misaligned CoL. My plane veers wildly off the runway as one wing pulls up harder than the other.

[Hodo]

hmm odd. I have only had this issue be a graphical issue not so much an actual problem in game. What version of FAR are you using?

[Wanderfound]

And are you sure you don't have an asymmetrically drained fuel tank or something?

[Jarin]

Latest version of FAR. I have flown an aircraft successfully exactly once since installing it. <.<

Center of gravity was spot-on. It was just lift that was weird. Don't have the files on-hand, but I'll see if I can post a bit more on it later.

[Hodo]

What other mods are you running?

[Stratzenblitz75]

I've had this happen to me before when using Pwings, B9-Aerospace and FAR in 0.25. CoL was offset in SPH and the plane flew horribly, if it even got off the runway. I found that taking off the wings, and replacing them (not reattaching them, completely replacing them) fixes the issue, most of the time. Sometimes I had to restart KSP completely to solve the issue.

I have no idea what is causing this. I'll have to make a craft that has a misaligned CoL and share it to see if this a bug with FAR, B9, or Pwings, or if one of my other mods is messing things up.

[Vectura]

I found, personally, that saving my craft then opening it again solved the issue.

[steve_v]

Alt-click clone also works for replacing a wing sub-assembly when this happens.

Hopefully it goes away when the shiny toys arrive with the next version of FAR

On an aside, my experimental VTOL trainer just pulled ~27G in a mach2 vertical loop

The crew did not survive.

These tweakable wing strengths are neat, if possibly a little OP at the default setting.

Edited November 22, 2014 by steve_v

[Redshift OTF]

Are you using Clipping? I have had big builds go wrong because symmetry mode has gone strange with clipping turned off, especially when using alt + click clone.

[The_Rocketeer]

I've had a similar problem caused by a bug when using SPH symmetry to get parallel symmetry for some wing-mounted parts and perpendicular symmetry for the wings themselves.

This may get a little confusing...

Lets say I want to add 4 engine nacelles to my plane. I want to have 2 per wing, with one above the wing and one below. I want them to line up neatly.

To make this work, I build one whole wing, with the nacelles, as a sub assembly:

First, I add at single wing to the top of the craft, pointing straight up. Then I use symmetry to add both nacelles to the 'left' and 'right' of the wing, which will soon actually become the top and bottom. Because the wing is aligned on the 'x-y plane' of the fuselage, symmetry works perfectly, and I end up with the nacelles looking very precisely aligned to each other (note in this context plane refers to a 3d plane and not an aeroplane).

Now that I have one wing, I can move it and use symmetry to duplicate the whole thing on the other side of the aeroplane.

This ^^ is where it goes bug-y.

For some reason, this "symmetry of symmetry" sometimes confuses the game. This results in not two but THREE versions of my wing being stuck to my aircraft. One is fine and normal, where I wanted to put it, but both of the other two are perfectly clipping each other, making it hard to notice at first that anything has happened. The result is that I now have twice as much lift on one side of my aeroplane as on the other.

I think this, or something similar, might be what accounts for your misaligned CoL.

Another symptom of this happening is that when you want to radially attach single parts elsewhere on the craft, you may sometimes find yourself stuck in symmetry mode. The only way to get out of this is to try to add an in-line part to a single attachment node, which glitches the game back into single-part mode.

The only surefire way to avoid this glitch is to make sure you don't use double-symmetry in the SPH. Another source could be using sub assemblies that take advantage of VAB symmetries which you then combine with SPH symmetry.

It may be worth noting that the VAB also has a similar bug that only seems to manifest when you try to add double-symmetrical parts to action groups. Then you find that only 3/4 parts, and not all 4 mirrored parts, have been assigned to the action group, and you have to add the fourth manually.

Edited November 22, 2014 by The_Rocketeer

[El wonso]

Using Mk2 Bicoupler causes CoL shift every time for me.

[Jarin]

For some reason, this "symmetry of symmetry" sometimes confuses the game. This results in not two but THREE versions of my wing being stuck to my aircraft. One is fine and normal, where I wanted to put it, but both of the other two are perfectly clipping each other, making it hard to notice at first that anything has happened. The result is that I now have twice as much lift on one side of my aeroplane as on the other.

This describes the effect of what I'm seeing, though not how I got there (no layers of symmetry or subassemblies in the wing design). But you can usually tell that's happened, and double-clipped parts often explode on launch anyway. Still, maybe I'll take a stab at that symmetry-stripping mod I saw earlier and see if that improves things any...

[numerobis]

Kraken stole my message

The symmetry bug is that if you symmetrically place an assembly where A and B are symmetric, you'll get C and D where A is marked symmetric to B and C ... but not D.

In other words, KSP has a bug where the symmetry relation in the vessel is not symmetric in the algebraic sense. A lot of code assumes symmetry is symmetric (which it should be), leading to weird behaviour.

[numerobis]

And you don't need to place assemblies -- just click on a part that has children that are placed symmetrically on it, then place the part with symmetry. When I first noted the bug, assemblies were just a rumour.

[Jarin]

And you don't need to place assemblies -- just click on a part that has children that are placed symmetrically on it, then place the part with symmetry. When I first noted the bug, assemblies were just a rumour.

Oh right... I remember doing this with asparagus staging. It had to do with flipping from single-place to symmetry placement after picking up an item or something.

[SpaceJuice]

The symmetry bug is that if you symmetrically place an assembly where A and B are symmetric, you'll get C and D where A is marked symmetric to B and C ... but not D.

In other words, KSP has a bug where the symmetry relation in the vessel is not symmetric in the algebraic sense. A lot of code assumes symmetry is symmetric (which it should be), leading to weird behaviour.

Thats true! But maybe not, it could be that KSP is not following FAR's aerodynamics.

[numerobis]

Another one that happens to me a lot is e.g. I place tanks with symmetry, radially from the main fuselage. Then on that pair of tanks I place radial intakes with symmetry. Sometimes, for reasons unknown, the radial intakes are placed with symmetry *around that tank*.

On its own, that will cause asymmetry. Or, if I then click on the tank again (perhaps by accident) and place it back where it was with the same symmetry, now there's an intake with recursive symmetry.

If I notice, I can hover the mouse over nothing, then back on the tank, and the intake gets properly placed one on the left tank, another on the right tank. But sometimes I don't notice.

[SpaceJuice]

Another one that happens to me a lot is e.g. I place tanks with symmetry, radially from the main fuselage. Then on that pair of tanks I place radial intakes with symmetry. Sometimes, for reasons unknown, the radial intakes are placed with symmetry *around that tank*.

Yup, that saying is a bug a in Ksp's editor. FIX IT SQUAD!

[Ace_Warbringer]

Have somewhat of a similar issue. Mods that seem to be interacting are b9 and FAR.

happens when I build off a central piece (usually a mrk 2 b9 lrg cargo bay for me, I like to try and balance the payload to actual ship center of mass) with just b9 wingtips. Now after I. Build said ships main shape I start adding on mission related items, still no movement of Com to Col.

as soon as. I add a large B9 airbrake to the side using symmetry and place on part, like a wing perhaps, the Col dives towards the placed part not its symmetrical counterpart. Each and every airbrake after worsening the issue.

however if I place on the opposite side after placing the first set, Col comes back to center.

I have not reliably replicated this phenomenon. Seems hit or miss.