I'm trying to model a spitfire as closely as I can (within certain approximations of course).
I have gotten a stable aerodynamic model by following the tutorial series, using the spitfire's wing span (~11m) and shapes, however I had to set the mass of the plane rigidbody to 300kg for it to become aerodynamically stable. When I set the mass to it's actual value (~2500kg) it becomes greatly unstable. I'm wondering if it's worth pursuing the actual mass or if I should be focusing my attention elsewhere. The main reason I'm doing so is because right now it's almost "too stable" and flies more like an acrobatic airplane instead of a heavier spitfire. Thanks! Really loving AO so far.
You have discovered the effect of advance ratio on propeller performance! Advance ratio is defined as the ratio of the forward speed of the aircraft to the tip speed of the propeller. As advance ratio increases (high forward speed or low prop rpm) the mean angle of attack on the blades decreases and at some point it will become negative, producing a net drag from the prop instead of thrust. At this point you have effectively a wind turbine on the front of the aircraft absorbing power.
The way past this is to increase the pitch angle of the propeller blades and/or increase the rpm of the propeller.
Note that at 3000rpm that is 50 revs per second and at the unity default fixed time step of 0.02 seconds that is one rev per time step so you would definitely have to use a rigid body (non kinematic) propeller to avoid interpolation errors. At the AO default fixed time step of 0.002 that would give 10 steps per rev.
One other thing is that you may wish to initially test your aircraft with an AO 'Simple Thruster' component (just add a SimpleThruster.cs script to )that just provides a force directly on the rigid body. This would allow you to sort out all the other challenges without worrying about propeller performance characteristics.
I just recently did some work on speedboat propellers that goes into a bit of propeller theory written up as a case study, see https://www.aerodynamicobjects.com/_files/ugd/28492b_86278d4cee3944e992afde104323a793.pdf Propellers are a bit of a dark art and its not as obvious as you would hope trying to choose the right one for an aircraft (or boat)
Enjoy experimenting!