Weird Left/Right Turn Tendencies (Even w/ Stock Vehicles)

[tsaukn]

I am having an annoying issue with planes. I am testing with a stock plane, The Bungalow. Stock, as-is, the thing has a massive tendency to pull right, as indicated in this photo below. Using RCS to show CoM, etc.

http://imgur.com/a/z20jo

Then, the only way to perfect it, so there is no turning tendencies is to do this...

http://imgur.com/a/2IzwY

I imagine it must be a mod I have installed, but the only one affecting physics, I removed, and the problem has persisted. (It was the Joint Reinforcement mod)

Any advice?

 

[StahnAileron]

If you have a propeller engine, it's not stock at all. You have FireSpitter installed and possibly a part mod that supplies a prop engine (apparently KAX from the craft name).

Judging from the images, all you really need to do is move the wings back a bit so the CoL (blue) is behind the CoM (yellow). That's basically what you're doing by adding that girder near the front (you moved the CoM instead of the CoL in that case). In the normal state, you have the CoM JUST ahead of the CoL, causing aero instability, i.e. the plane wanting to flip around. I'll yaw left/right because that's the axis with the least lift surface. (Other option: add more vertical fins to the back of the plane.)

You can mostly ignore the torque RCSBuildAid is showing because that's completely along your pitch axis (due to the wings adding mass below the engine.) It'll cause the plane to want to slightly pitch up naturally, but in this case it should be okay: control surface in SAS control should stabilize you.

You'll probably want to move the fuel to BEHIND the cockpit as well. With the tank up front, as you burn fuel, the CoM will shift rearward and can wind up behind the CoL once again. (RCSBA has an option to show the Dry CoM as well. Helpful for tuning long-term stability as fuel is used up.)

Anyway, long story short: Your CoM/CoL balance is wrong. Get CoL BEHIND CoM (and make sure it stays that way as you burn fuel).

Edited April 20, 2017 by StahnAileron