[jhb_airlines] Re: Autopilot APPR HOLD problem

  • From: Gerry Winskill <gwinsk@xxxxxxx>
  • To: jhb_airlines@xxxxxxxxxxxxx
  • Date: Tue, 18 Oct 2005 07:53:19 +0100

It sounds like the potential for yet another massive distraction. I'll settle for what I've got at the moment.
I tried down to 85 kias only because it's said to be possible. It certainly is in Manual mode, to which I'd drop anyway, in the last 3 miles. With normal finals around 106 kias, it should be OK.
I'll just stop looking from outside, when the AOA won't be a big deal.

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% heavier.

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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