On Thursday 20 January 2005 20:16, Andy Ross wrote:
> Lee Elliott wrote:
> > I don't think it quite reaches it's altitude performance yet
> > (I've been thinking about a PR version sometime).  However,
> > I once got the YF-23 > 200,000 ft (and still climbing at a
> > fair lick).
>
> YASim's atmosphere model table stops at FL620.  It doesn't try
> to extrapolate and just clamps the air density outside that
> range, so you were cheating badly by getting to that altitude.
> :)
>
> Andy

Ta for that.  IIRC the reduction in rate of climb did seem to 
level out at some point - at FL620 it would seem.

Although I don't know the YF-23's max ceiling I'd expect it to be 
> 62,000 ft so perhaps this problem with the fdm isn't quite as 
bad as I thought it was.

At the time I was using a 'mach-climb' hold AP function.  
Basically, this tries to get the max rate of climb while 
maintaining a set mach speed by increasing the target rate of 
climb when the target mach is exceeded in a sort of feed-back 
loop.  It seems to work well if it's engaged while the a/c is 
below the target mach but it's not so good if the a/c is already 
travelling at the target mach.

Something to look into some day...

LeeE

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