On Wed, 2007-01-03 at 03:08 +0100, woodyst wrote: > I've arrived to that conclusion when I saw that the plain wasn't > unable of performing a 0-0 visibility approach with ILS.
The ILS minimums for non CAT II or CAT III approaches are usually no less than 200 1/2 (200 ft AGL decision height and 1/2 mile visibility). It is not legal to do a 0-0 ILS in the C172P with this autopilot. If you do not have the runway environment well in sight at the decision height (usually the GS intersects the DH at the middle marker), you are required to execute a missed approach. > I have improved the file (I think, I've never used a real Cessna 172 > with the KAP140, so I do not know if this result is more or less > realistic): > > - In the KAP140 manual there are a lot of references that indicates > the KAP140 uses elevator trim and not elevator for handling altitudes. > So I have adapted KAP140.xml file to use elevator trim. It results in > softer altitude changes and the autopilot does not conflict with > joystick or yoke. Note, page 7 of the KAP140 Pilot's Guide shows a pitch servo and a pitch trim servo as well as a manual electric trim switch on the yoke. There would be no pitch servo if the autopilot were "flying" the pitch with the pitch trim. Note also item 15 on page 85. "A flashing PT with arrows indicates the direction of required pitch trim." The pilot does not have the feel to set the trim, since the pitch servo is carrying the out-of-trim load on the yoke that the pilot would have to carry, were the AP not there. The PT annunciator provides this "feel" feedback. Also see page 89, voice message 2. If the autopilot were flying the pitch via pitch trim, this warning would be meaningless. It is especially important to pay attention to the PT annunciator (and correct any out-of-trim condition) when the GS is acquired. Otherwise, you will have a very nasty surprise near the ground when you disengage the autopilot (at or before the decision height is reached) with a significant out-of-trim condition. This has caused crashes for real. I recall reading a NTSB report for a Martin 404 crash caused by the pilot not noticing a stuck electric trim switch leaving the pitch trim in full down and then disengaging the autopilot at altitude. The ac tried to do an outside loop. > Also I am interested in the opinion of any pilot that has flown a > real Cessna and remembers the real autopilot performing. > I have not flown any Cessna autopilots, but I have flown several hi-performance Piper aircraft that have similar autopilots. The above comments agree with that experience. I added the KAP140 to the pa24-250 in FlightGear. I have done a number of ILS approaches in the fgfs pa24-250 using the KAP140. It does an adequate job down to just before the DH is reached. It does seem to "chase" the GS a bit more than I would expect from real experience for the last mile before the DH is reached. For whatever reason, the KAP140 gives more realistic performance in the pa24 than in the c172p. I did not include an autopilot config xml in the pa24 implementation, i.e. it is using the default configuration. The only surprise I have noticed compared to the Pilot's Guide is for the REV acquisition. The manual says after depressing the REV button, set the HDG bug to the front course inbound heading while the HDG annunciator is flashing. The modeled KAP140 requires the HDG bug to be set to the reverse heading (the reciprocal of the documentation bug setting). -- Dave Perry <[EMAIL PROTECTED]> ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ Flightgear-devel mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/flightgear-devel
