I am confused by the SDK description of how the elevator, rudder, and perhaps
aileron controls are being simulated. The description of the htail_area
parameter says that the horizontal stabilizer is simulated as a single wing
with surfaces positioned in such a way that the overall incidence matches the
current control surface deflection. Furthermore, this surface will have the
area of the htail_area and the elevator_area combined. (A similar
description is provided for elevator_area, rudder_area, and vtail_area.' Does this mean that the flight model simulates a 5 degree elevator deflection as a 5 degree deflection of the entire horizontal stabilizer? The description goes on to say that "we recommend entering the exact area of each surface" because the respective pitching moments of the horizontal stabilizer and elevator will be affected. How can this be if the elevator and stabilizer are simulated as a single, uninterrupted wing? The description provided for the elevator_maxangle_scalar` adds to my confusion. It states that if the limit
angles match those of the real airplane, then this scalar should be smaller
than 1.0 because “the effective deflection will be aligned with the overall
htail and elevator chord.” I don’t know what “aligned” means in this sentence,
and I don’t believe the htail or elevator chord lengths are inputs. But this
again makes it sound like an elevator deflection is simulated as a movement of
the entire horizontal stabilizer. Otherwise, why should the scalar normally be
less than 1.0 if the elevator limit angles match those of the real airplane? I
guess this would explain why changing the slope of the elevator cl-alpha curve
affects the airplane pitch angle during level flight with no elevator input.
It appears to me from this description that the parameter identified as the
slope of the elevator cl-alpha curve is actually the slope of the cl-alpha
curve of the horizontal stabilizer. Similarly, the corresponding parameter for
the rudder appears to effectively be the slope of the cl-alpha curve for the
vertical tail, not just the rudder. If that’s true, it seems to me that it
might be an appropriate way to model an airplane that trims for pitch using
the elevator, but not for an airplane with a trimmable horizontal stabilizer.
Can you shed some light on this?