On 1/3/07, Dave Perry <[EMAIL PROTECTED]> wrote:
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.
But then there would be interesting that the yoke, the pedals would not
produce interferences with the autopilot, because in a real plane, the yoke
moves when autopilot changes the pitch, but in flightgear it is not possible
because of the lack of force feedback in almost all yokes and pedals in the
market.
So I suggest that FlightGear could remember the last yoke and pedals
position and do not apply its values with the autopilot engaged when the
values of this devices didn't have changed. If not, whith the original
KAP140
config file, the plane is doing a lot of hard turns because the program
applies
autopilot's values and eventually yoke and pedals values too.
Do you agree with this reflexion? If you do, do you think it would be very
difficult implementing this solution? I ask it because I have almost started
looking at the code, and I do not know how things operate in FlightGear yet.
For the moment using trim for autopilot makes the fly more acurate because
it does not interfere with input devices. If this problem can not be solved
in FlightGear, I will remain with my config file, because I suffer very much
when I connect autopilot for making a rest and it starts doing very hard
turns
and plane's yoke vibrates a lot.
Do you suffer this effects too?
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.
I understand. But my trim indicator goes up and down all the time because
of the effect I have exposed before.
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.
Does in the real Piper improve the performance of the KAP140 compared
to FlightGear's one or it performs in a similar manner. I use FlightGear as
a
preparation for learning to fly before I start flying one day in real life,
because it is my passion. I want to acquire some experience and I
appreciate the more realistic experience with FlightGear.
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.
I solved it incrementing the proportional gain (Kp) from 2 to 3 in the
KAP140.xml file. Can you test if this works for you and if it makes this
autopilot more realistic?
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).
It can be fixed in "kap140.nas" file, I think. I would study that file well
and if I can, I will send another patch.
Thanks for your explanations.
As I have said, this game has made one of my more longed for dreams
real, so I am very agreed with all people that has contributed to the
making of this game. Thanks a lot.
--
Dave Perry <[EMAIL PROTECTED]>
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Woodyst.
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