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List:       flightgear-users
Subject:    Re: Re: [Flightgear-users] How to land the C172 successfully?
From:       Tony Peden <apeden () earthlink ! net>
Date:       2002-04-28 20:24:55
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On Sun, 2002-04-28 at 11:25, Dirty Bear wrote:
> My previous reply to Tony can not be read by somebody, I rereply again.
> > The standard approach speed is 1.3Vs or 65 knots flaps up and 56 knots
> > flaps fully extended. 
> > 
> > So, you might try starting fgfs like this:
> > fgfs --glideslope=3 --altitude=1000 --vc=65
> > 
> > The pitch trim, throttle, and aircraft attitude should be set for you.
> 
> Thanks
> The option --glideslope seems not be recognized by FlightGear0.7.8.

Ahh, probably true.  It's a fairly recent addition.

You can answer your own question here though ... the --glideslope
option sets JSBSim to trim at -3 degrees of flight path angle.


> 
> I am using JSBSim 0.9.1 standalone for auto approach and landing. I 
impletmented some control laws to make the C172R auto-adjust head, 
auto-hold the altitude , auto-glideslope and flare, from the trimed state
that you teached me how to archieve. I also implemented an Genetic 
Algorithm for automatic parameters optimization. They all seems works 
well, but I wonder what I did is significant or not. and I wonder my 
methods are reasonable or not ... ... My interest is driving me.

Success with control laws is ultimately gauged by whether or not they
do what you want.  So, if they do what you want, they're probably fine.

It's hard to do something really radically wrong here since your code
can't directly change the physics.    

> 
> now I need a cross wind model to test my glideslope control law, but I 
do not know how to model it.

Constant crosswinds work fine in JSBSim.  No gusts or turbulence
available, however.

> 
> Tony, I found in FGAtmosphere.cpp that 
> (1) class FGAtmosphere is the implementation of  1959 standard atmosphere, 
the original data is from ICAO atmosphere model, where can I found it?

Well, let's see.  That model is actually the '76, I need to update the
comments.  It's available in many different texts, but I believe I got
it from Roskam's Airplane Aerodynamics and Performance.

The data and equations in the source *is* the model as defined by ICAO,
by the way.   

The tables you find in most texts were probably derived using code
similar to mine.

 
 
> (2) I found you commented out the turbulence temporarily, are you going to 
enable it ?  When I enable the turbulence in my project, the simulation would 
crush. Has the turbulence model been tested before?
> 
> 
> > 
> > 
> > 
> > 
> > On Sat, 2002-04-27 at 18:22, Dirty Bear wrote:
> > > Before gliding slope, my C172's speed is 80 knots, altitude is 1000  feet; When \
> > > gliding slope, try to keep the attack angle to be 2.5 degree. The total \
> > > distance of gliding slope is about 3.89 miles. Are all above reasonable?
> > > Thanks
> > > 
> > > 
> > > 
> > > How much should the altitude, speed be when begin to glide slope?
> > > How high when begin to "flare" ? "flare" means that pulling up the head to \
> > > decrease the vertical speed. who can tell me how to set the throttle ?
> > > Thanks
> > -- 
> > Tony Peden
> > apeden@earthlink.net
> > We all know Linux is great ... it does infinite loops in 5 seconds. 
> > -- attributed to Linus Torvalds
> > 
> > 
> > _______________________________________________
> > Flightgear-users mailing list
> > Flightgear-users@flightgear.org
> > http://mail.flightgear.org/mailman/listinfo/flightgear-users
> 
> 
> 
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-- 
Tony Peden
apeden@earthlink.net
We all know Linux is great ... it does infinite loops in 5 seconds. 
-- attributed to Linus Torvalds


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