[jhb_airlines] Re: Autopilot APPR HOLD problem

  • From: "Bones" <bones@xxxxxxx>
  • To: <jhb_airlines@xxxxxxxxxxxxx>
  • Date: Tue, 18 Oct 2005 15:42:22 +0100

I doubt it but I've never delved into autopilot settings in the .air file as
they are quite complex. There are 112 separate parameters for the autopilot
and I've no idea what half of them do. Only a handful are now in the
aircraft.cfg file so the rest are still valid.

The .air file in FS2004 is a hugely more complex beast than in FS2002 and it
is now evolving into equations I have little knowledge of. It makes
performance tuning something of a specialist art now for proper
aerodynamicists as something like Cl_beta(alpha)Dihedral Coeff vs Body AoA
or Cm_de(q)Elevator Deflection (Moment) Factor vs Q are way out of my
league. There are a total of 32 Delta tables for control movements in FS2004
and I'm lost as soon as I open any one of them..


-----Original Message-----
From: jhb_airlines-bounce@xxxxxxxxxxxxx
[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
Sent: 18 October 2005 15:06
To: jhb_airlines@xxxxxxxxxxxxx
Subject: [jhb_airlines] Re: Autopilot APPR HOLD problem

I wasn't really interested in climbing at that speed, rather looking at
the throttle / power setup. Although the FS9 a/c clearly has the power
to climb at the higher speed, it doesn't attempt to go for full power,
to try to achieve it. It opens only to 65% thrust and doesn't fully open
the throttles either. This despite my fiddling the Aircraft.cfg to
accept 108% for Autoothrottle.
Is there a max limited climb speed built into one of the two files?

Gerry Winskill

Bones wrote:

>The normal climb speed for this aircraft is only 150kts IAS - it's Max
>Operating Speed is only 262kts IAS so you are trying to push it beyond
>it's capabilities.
>Don't forget that Cessna originally designed it as a sort of jet
>engined version of the King Air - a not very fast aircraft with the
>short field capabilities of a turboprop. They thought that owners would
>prefer a jet rather than a turboprop and that the Citation might eat
>into the King Air market - which it did beyond their expectations.
>Think of it more as a jet with turboprop performance.
>I've sorted the roll and speed problems - no need to touch speedbrakes
>unless you want higher than a 1500fpm descent.
>-----Original Message-----
>From: jhb_airlines-bounce@xxxxxxxxxxxxx
>[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
>Sent: 18 October 2005 10:11
>To: jhb_airlines@xxxxxxxxxxxxx
>Subject: [jhb_airlines] Re: Autopilot APPR HOLD problem
>I'm beginning to suspect there is something odd about this aircraft.
>Another FS9 lockup, over Turnberry, en route Glasgow. FS9 then refused
>to reboot, from the saved situation. Starting from a situation with a
>different aircraft was OK.
>Back to your thrust problem. I tried climbing, on AP, at 280 kias. It
>wouldn't go above 265 kias, even though only using about 65% thrust. On
>another check, it was rock solid on the GS, at 105 kias. It's quite
>reluctant to slow down to that speed and probably needs airbrakes
>deployed. At these speeds, with balanced fuel load, it's roll rate is
>disappointingly slow.
>Gerry Winskill
>Bones wrote:
>>At 85kts you are probably pushing into the stall envelope. The CJ1
>>table give a stall between 70 and 86 so that means minimum approach of
>>87kts to 107kts. Add maybe 5kts for the CJ2 which is about 35%
>>I've now got the thrust and balance working to a reasonable level and
>>100kts approaches are fine. The CG was indeed well out and once
>>brought back towards the wing the aircraft started to behave properly.
>>Unfortunately, as I warned Mike, it's opened up a few more cans of
>>worms because the rest of the aircraft's values are written around the
>>bad CG position.
>>Problem one cropped up after I decided to try a full weight landing
>>instead of the half empty weights I had been testing it with. At half
>>weight trim was nicely set up around 0.8 with this rising to about 1.7
>>at the lowest speeds. As soon as I put in 55% fuel (it can't go much
>>higher than this or you get an overweight landing) the pitch trim
>>jumped to a silly figure of about -4.2. This means the fuel tanks also
>>need shifting relative to the new CG - they should have minimal effect
>>on trim.
>>The second problem is more obtuse but it's down to the same thing. On
>>touchdown the aircraft now slams the nosewheel hard onto the surface
>>and it either breaks or starts a severe oscillation. I guess moving
>>the fuel tanks may cure this but I dread to find out what other
>>secondary problems will result from this..
>>I'm temped to go back to the original and just fly coupled approaches
>>at 120kts.. Or maybe buy the Eaglesoft version..
>>-----Original Message-----
>>From: jhb_airlines-bounce@xxxxxxxxxxxxx
>>[mailto:jhb_airlines-bounce@xxxxxxxxxxxxx] On Behalf Of Gerry Winskill
>>Sent: 17 October 2005 19:34
>>To: jhb_airlines@xxxxxxxxxxxxx
>>Subject: [jhb_airlines] Re: Autopilot APPR HOLD problem
>>Having finally got FS9 to work again, of which more anon, I tried a
>>flight and IOM 26 ILS, with wt shifted forward. As you say, it made
>>little difference to the AOA and I share your view that the C of G is
>>out. I'll leave you to fiddle with that.  On finals, all in APPR, I
>>progressively lowered the set speed to 85 kias. First noticeable fact
>>is its reluctance to let the speed decay that low. At 87, with even
>>higher AOA, it came slightly below the glidepath and remained stable
>>at that displaced position. The outcome was an undershoot of a few
>>hundred yards. Fair play, it did it gracefully. Highest trim readout
>>was 51; considerably lower than the pre tweek situation, where despite
>>that it couldn't remain on the glideslope.
>>Back to my FS9 bootup refusals. Having re installed the Radeon
>>drivers, which couldn't possibly have been causing the problem, done
>>the usual things like deleting FS9.cfg, I fell back on the mark one
>>eyeball method. Since all failures were accompanied by just one of the
>>GF MCP's lights coming on, I unpluged the Autopilot. FS9 then booted
>>OK. Switched it off and ran GFConfig and all in the garden is lovely
>>again. Another one to go in my fault box.
>>Gerry Winskill

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