On Tue, 2007-01-23 at 18:48 +0100, Roy Vegard Ovesen wrote:
> Just updated from CVS (HEAD (OSG)), and it seems to me that the
> autopilots are
> working. I tried the KAP140, and the generic in the pa28-161. Both
> worked
> fine in heading mode, and the followed the bug on the HSI.
>
I just did a cvs update -dP for both simgear and the fgfs source (osg
branch) and the "new version" kap140 works with the one quirk; to get
the heading bug to work requires going to the debug gui and reloading
the autopilot config.
Here is the version with the differential approximation for altFt. I
think this is exactly what you asked for in
> What I'm asking for is an equation to convert from pressure altitude
> to ASL
> altitude. Something like
> ASL_alt = f(pressure_alt, ref_pressure)
>
1) Add the partial derivative function before altAlert:
hPartial = func {
p0 = arg[1]; # Units of p0 must match units of delta p
p = arg[0]; # Units of p must match units of delta p
t0 = 288.15; # [K]
LR = -0.0065; # [K/m]
g = -9.80665; # [m/s²]
Rd = 287.05307; # [J/kg K]
gamma = (Rd*LR)/g;
z = -(t0/LR)*gamma*pow((p/p0),gamma)/p0;
return z;
}
2) Replace the computation of altFt in altAlert with
pressureAltitude = getprop(encoder, "pressure-alt-ft");
hPartBaro = hPartial(baroSettingInhg, 29.92) / 0.3048006;
# print("hPartBaro = ",hPartBaro);
altFt = pressureAltitude + hPartBaro * (baroSettingInhg - 29.92);
Notice:
1) altFt = f(pressure_alt, baro_setting)
2) requires only one call of pow (i.e. exp and ln)
I will send you the working kap140.nas with these changes off-list. It
is working well here.
Regards,
--
Dave Perry
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