At 05:31 PM 7/10/2002 -0400, you wrote: >Curt and I have been having a discussion offline about algorithms for >NAV mode on a simple autopilot (like those typically found in a light >Cessna or Piper). The current autopilot does not have a working NAV >mode -- it was just a quick kludge, with ability to correct for a >crosswind. > >What algorithms are commonly used to get and keep the CDI centered in >a simple AP? It should be easy enough to start with the rate and >direction of CDI deviation from center.
I'd say the simplest to implement, while still being reasonably usable, would be a "proportional plus derivative" law. Command a heading equal to the course, plus a factor times the CDI deflection, plus a factor times the time derivative of the deflection; with the right coefficients, that will damp out any overshoot. Provide an intercept mode that will follow a pilot-selected heading until the CDI comes off the peg. I flew a Cherokee back around 1970 that had an unbelievably crude nav mode: it was a single-axis autopilot that did nothing but command a bank angle proportional to the CDI deflection, truncated at about 15 degrees. If the needle was on the peg, the airplane would fly in lazy circles forever -- but if you did the intercept manually, it worked surprisingly well. rj _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
