Fix Coordinated Turns

[chrishajduk84]

Currently each coordinated turn only includes aileron and elevator action. Rudder action also needs to be included.

The rudder should MATCH the aileron action with some proportion.

Rudder = k * ailerons
Figure out k.
http://www.pilotworkshop.com/tips/rudder_coordinated_flight.htm

In a more complicated manner:
l = 1/2_ρ_V_a^2_S_b_C_l (β, p, r, δa, δr )
n = 1/2_ρ_V_a^2_S_b_C_n (β, p, r, δa, δr )
l and n are roll and yaw moments.
C_n and C_l are non-dimensional, non-linear aerodynamic coefficients dependent on δa, δr, pitch, roll and side slip angle.

We want the proportionality between δr,δa. This is difficult to solve for (there are a few other equations that we need to look at to do that, and it will be a non-linear algebraic system), therefore we need to make approximations.

Whenever the ailerons move, the rudder should also move to support the turn.
The elevator on the other hand (already implemented), is dependent on the roll angle (and not the roll rate). Higher bank angle = less lift = need for elevator

[CoatedMoose]

This is less relevant and/or inaccurate this time around as our new plane is inverted V tail.

[chrishajduk84]

There should be a Anaconda.c/.h config file in that case, which specifies these changes. (As well as Skysurfer)

[chrishajduk84]

Coordinated turns are still important on the Anaconda. We have elevator compensation, but no rudder action compensation for turns.

[ianjfrosst]

Could this be done using closed-loop control, instead of an equation model? Set desired pitch & roll angles, and a yaw rate.

[ianjfrosst]

Was thinking about this. I can add a configurable aileron -> rudder mix for the low-level orientation controller, and let the autopilot take it the rest of the way.

[chrishajduk84]

Yeah... That could work.

Also, ideally you would keep track of the gravity vector, and ensure that it's always pointing down in a turn.

Imagine a water bottle onboard. The water level shouldn't change during the turn.

[ianjfrosst]

Mmm, true. Your bank angle for a given turn would be proportional to your airspeed & your desired rate of heading change.

[ianjfrosst]

This is improved in #118 with simple output mixing. Could be a feedback control, though.