What is causing my plane to flip out?

[__Ultimatum]

I've had the game for about a year, I've really only gotten good in the past 6 months. I'm trying to build a fighter, loosely based on a F/A-xx, and it flies well, until I yaw. I recorded what happens. 

Can someone tell me whats going on and how to fix it? 

Craft file if needed:

https://drive.google.com/file/d/0B0k4mqYF2VKxMF9MdXFnTWR6Sk0/view

Edited June 8, 2017 by __Ultimatum

[Reactordrone]

I would suggest not enough vertical stabiliser so not enough natural stability in yaw, leading to a spin when you add large amounts of rudder input.

[Aegolius13]

Two thoughts:

First, where are your center of mass and center of lift?  Most of the time, instability issues are because your center of mass is too far back relative to your center of lift (or more technically, center of drag).  The heavy parts of the plane want to be in front, and in this case, that may be the relatively heavy engines mounted at the back of the plane.  If your COM shows behind your COL, you may need to redesign to move mass forward, move center of lift backward, or both.  

Second, in KSP as well as real life, aircraft do not like to be turned using the rudder / yaw.  More so than pitch or roll, yaw puts the aircraft in an unstable position (i.e., the plane is kinda flying sideways, with wings and control surfaces hitting at odd angles.  Turning by banking (and pulling up) is generally more effective.  

These two issues may be compounding.  Sometimes, even when an aircraft is unstable, you can maintain control by keeping it pointing prograde.  But once you far enough off of prograde, instability takes over.  It's kind of like balancing a bowling ball on a pin.  In theory it will stay as long as it's precisely balanced, but once it gets a little off center, things will spiral out of control.  

EDIT: one other thing - control surfaces can get a little confused when they try to do too many axes (yaw, pitch, roll) simultaneously.  Ideally you'd have three sets of control surfaces: a vertical stabilizer set to yaw only, some elevators (as far back and/or forward as possible) set to pitch only, and some ailerons (as far radially from the center of the plane as possible) set to roll only.  That might not work as cleanly with a diagonal tailfin design like yours.  But maybe you could try setting those fins to yaw only, setting your outermost elevons to roll only, and setting the rest of the elevons to pitch only, and see if that helps anything.  

Edited June 8, 2017 by Aegolius13

[DrLicor]

I totally agree with what @Aegolius13 said. Especially the last part. Also your yaw input is to big in 2 ways:

1. Too big surfaces yawwing too hard.

2. Too much tilled, resulting into an offsett pitch, resulting in your spin.

 

My solution for this would be to limit your yaw to 25% or even less, en tilt the surfaces a bit more upwards. 

Edited June 8, 2017 by DrLicor

[__Ultimatum]

1 hour ago, DrLicor said:

I totally agree with what @Aegolius13 said. Especially the last part. Also your yaw input is to big in 2 ways:

1. Too big surfaces yawwing too hard.

2. Too much tilled, resulting into an offsett pitch, resulting in your spin.

 

My solution for this would be to limit your yaw to 25% or even less, en tilt the surfaces a bit more upwards. 

Thanks! Lowering the tilt of the wings and limiting the authority of the vertical stabilizers has fixed all the stability issues. 

[DrLicor]

Glad to hear that.