An offroad rockbouncer with pure logic bricks. Layer2: full-auto shooting melee. I was so greedy to make the vehicle airworthy :-) .
Fly mode goes by rudder control configuration with no aileron surfaces, (like some rc toy planes) which means you must wait some second after hitting rudder for dihedral effect to cause the fuselage to commence rolling. After that, pull elevator for tight turning. It's somewhat unwielding trait but also kinda fun to maneuver, I think.
What goes by the name of "abusive spring" is abusive because it abuses an inherent limitation of constraint solver algorithm of real-time physics engines, including Bullet and others.
Unity - Stabilising Fixed Joint Logic - Compound Rigidbodys - YouTube https://www.youtube.com/watch?v=nArwDeA2Ko4
Its behavior is unstable and you may need to tweak mass, inertia and/or constraint configuration to fit your environment. ( I found it can act substantially different from layer to layer!! )
Aside from this abusive thing, I know a lot needs to be explained about my weird BGE contraptions. Hope I find enough time to elaborate on them. But for a while, I'm gonna prioritize publishing more and more bizarre BGE files I've been stacking on my hard drives :-) .