On Tuesday 04 May 2004 19:24, Jim Wilson wrote: > Lee Elliott said: > > Hello All, > > > > I'm having trouble with a couple of FG problems. > > > > The less serious of the two concerns the weather settings. I'm using the > > default weather settings, except that I've increased the visibility > > ranges but I'm finding that the actual weather 'level' I'm getting, apart > > from initial start-up on the ground, is pretty random. For example, more > > often than not, after taking off, as I pass through 500ft the weather > > settings transition to the 6000ft or 9000ft level so I'm getting up to > > 30kt crosswinds at a little over 500ft. > > > > I should point out that this is with airfields that are < 200ft alt. > > > > Sometimes it doesn't happen and the weather progresses smoothly through > > the 3000ft, 6000ft and 9000ft levels, but this is pretty rare. > > > > Opening the weather settings gui and selecting 'Reset' seems to be pretty > > random too - sometimes it'll correct the weather but quite often it'll do > > nothing or just select another incorrect level - for example, I can hit > > reset several times while at < 1000ft and I can see (and check via the > > property browser) that I'm getting the 6000ft or 9000ft levels. > > Frequently I'll get the right weather level by hitting reset only for it > > to jump back to the 9000ft level when I hit 'ok' to close the gui. > > > > Once I've finally got the correct weather for the level I'm flying at and > > closed the gui without messing it up, the weather then seems to behave > > itself. > > > > The more serious problem is with nav1 ils guidence. I can get the a/c > > onto the glide slope and following the nav1 heading nicely but at approx > > 1 mile from the runway the nav1-heading-error-deg can suddenly jump from > > < 0.01 deg to about 4 or 5 deg. While smaller aircraft can cope with > > this, something like the AN-225 can't. > > > > I can tune the pid controllers so it can cope with this jump but then it > > can't get on to the nav1 heading and stay there without badly > > overshooting (by up to a couple of miles) several times before it settles > > down, by which time it's almost on the runway. > > > > I've noticed that if there's any degree of crosswind, although the > > nav1-heading-error-deg might be showing < 0.01 deg, the hsi needle is > > clearly showing that I'm off to one side of the GS and I suspect that the > > jump I'm seeing is some sort of correction for this. > > > > Neither of these problems seem to be dependent on the a/c - I've > > experienced them with a variety of a/c. > > > > Is anyone else experiencing these problems? They aren't particularly new > > - I've been seeing them for quite a while and they're still occurring > > with the cvs update I did a couple of hours ago. > > Hi Lee, > > Sorry for taking so long to respond to this. Have you taken a look at the > 747 config? For AP using the nav1-heading-error I need to go back to that > and smooth out the transition a little so it isn't so sudden. Basically > once we get close enough to the ils (1 mile seems short, but maybe not at > some airports) the nav1 error output changes behavior slightly to give > reasonable performance close in. This tightening screws up the process of > intercepting the radial (automatic turn to final), hence the change at a > certain distance out. > > In any case it'd be interesting to know if this method is anything like how > a real AP works, both in the AN-225 and others, like the c172. My guess > is that it isn't even close, and the whole heading intercept espeicially > and nav1-heading-error method we're using is wrong. Maybe we can treat > interception and ils hold as two seprate functions. And end up with > something on ils that runs purely off the needle "deflection" value without > incorporating "distance" or converting to anything else e.g. degrees (might > have to "normalize" it based on "to/from"). Obviously if you have any > cross wind at all you don't want to be seeking radial heading which is > basically what the nav1-heading-error thing does. > > That said, I think that you'll find the 747's method (using the gps flight > path output to calculate flight track error) more effective. It manages to > plunk that pig right on the centerline even in a fairly brisk crosswind. > > Best, > > Jim
Thanks for the pointer Jim, I'll take a look at the 747. For a while I was wondering if it was an interception issue as I'd tuned/adjusted the controller pretty critically and it occurred to me that perhaps I hadn't actually crossed the radial at all, but was just running close along side - I tweaked it so it oscillated very slightly down the radial (+-0.1 nav1-error-deg) but it made little difference. It was getting pretty frustrating with the AN-225 - the B-52F can just about handle it, but then it's a lot lighter than the AN-225 even when the Myria is empty and the B-52F is fully loaded (the AN-225 could, in theory, carry a fully loaded B-52 of any Mk) and it just can't seem to cope with the change at such low speeds. I've not see the AN-225 but I recently watched an AN-124 as it flew over on approach into EGSS (London Stansted - about nine miles from me) and it was already lined up, with wheels extended (and that big low-pressure cloud of vapour over the wings). All the other stuff, 747's included are usually just turning in at the same distance. It was quite strange to watch the 'little' 737 following the AN-124 in - knowing it was at roughly the same distance really highlighted how big the AN-124 was. LeeE _______________________________________________ Flightgear-devel mailing list [EMAIL PROTECTED] http://mail.flightgear.org/mailman/listinfo/flightgear-devel
