Thank you for your reply and I began to understood the concepts of the heading hold system in nav mode but some of the autopilot system's properties are not so solid in my mind so I want to briefly summarase my understanding of the autopilot systems lateral navigation mode if there are mistakes which is probably the case you may tell me. Target heading is calculated by using ((nav heading - nav radial) x distance to the nav point) which is the adjustment part that I saw on newauto.cxx and target heading is target radial + adjustment. nav_heading is the heading difference between our plane's heading and the heading of the reference line which we want to align with for example the airport landing road for an ILS system which is commented out in source as
// determine our current radial position relative to the
// navaid in "true" heading.
cur_radial = current_radiostack->get_nav1_heading();


Nav radial is the angle between the reference line with that line's heading and the line from the plane to the ILS or VOR antenna no matter what the plane's heading is which is commented as
// determine the target radial in "true" heading


The nav_radial seems to be the target radial in newauto.cxx,
tgt_radial = current_radiostack->get_nav1_radial() and the heading needle deflection becomes the difference between our current heading and the line connecting our vehicle to the ILS antenna which is the line with the target radial and is handled in Cockpit/navcom.cxx as
r = nav_heading - nav_radial;
return r;
for the needle deflection and in autopilot code
in the comments it writes
// determine the target heading to fly to intercept the
// tgt_radial
TargetHeading = tgt_radial + adjustment;


In one of the mails I read something like
At 5 miles X 2 degrees deviation it was commanding a 10
degree turn so the order given by code to the aircraft is to turn with the amount of difference equal to the adjustmant part calculated in the autopilot code from its current heading to intersect the target radial.


Thanks

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