Flan told me before that the center of mass has to be adjusted for the planes to fly flat without any dipping of the nose of the plane after I said the lift value wasn't doing much.

I have no idea how to do this but I'm sure someone else can.

"The centre of mass is the position of the entity
To fix this, I would have to move the model up / down and then change the y values of all the origins in the type file. Not impossible, but time consuming"

The mass center can easily moved by translateAll(0, -2, 0); which now works on all 3 axis

Oh awesome!
I'll mess around with this and try and get it right :)

Since I have no clue how to do that I hereby assign this task to @jamioflan !

@Minecraft-SMP Sorry but I tried many different values for translateAll and in all occasions the plane seemed to still start aiming down.

Mind doing an example for me on the BF109 or something?

if i had to make a guess, then that the mass center is interacting somehow with the hit box stuff. so try to move the hit boxes (core/tail/wings) instead of the center

Had a play with this, we have two ways to fix this, make the engines all be at the same y value as the centre of mass (0), or the quick and dirty way which is to ignore the y value in the propeller position in the physics code.

Making a plane config option to ignore centre of mass stuff for the x axis (or whichever the one is nose to tail) could be good also.
Placing all engines at the same y is no good since that would mess up engines breaking I assume.
Ignoring the y value for the propeller would be undoing flan's new physics.

Some sort of toggle would be best, I'm not completely sure why the translateAll method never really had an effect.

At the moment any engine with a y > 0 will pull the plane's nose down, changing translateAll doesn't change the coordinates for the physics system, just the rendering

I was lied to!
It's a shame we can't make the tail heavier.

Not a good idea. What if the plane is a jet with the wheel to at the bow? Then the plane would look really wired.
In my opinion the mass center should be 0/0/0, no matter where the propeller is located

Not saying move the centre of mass, just where the physics calculations think the propellers are