RE: [Jsbsim-devel] C-172 Performance

[Jon B. <js...@ha...>]

> What parts of the 172p flight model are you uncomfortable with?
>
> > One test that I ran was a takeoff performance test to see how little
> > room is needed for takeoff. I set up a test with the throttle at full,
> > and the mixture set to 85%. There were no winds, and the runway was at
> > sea level. I got this:
> >
> > Takeoff roll: 886 ft (270 meters)
> > Over 50' obstacle: 1664 ft. (507 meters)
> >
> > The Cessna web site specifies this:
> >
> > Takeoff roll: 945 ft (288 meters)
> > Over 50' obstacle: 1685 ft. (514 meters)
>
> You need to control a few other parameters to make this useful.
> First, you need to make sure that the temperature is ISA (which
> FlightGear will give you by default).  Second, you need to make sure
> the plane is loaded up to maximum gross weight.  Third, you need to
> use proper short field takeoff technique.  I suspect that you used a
> very light plane but didn't use short field technique, so the two
> cancelled each-other out.

Before I say too much on what might be wrong, I'm going to run more tests. I have weighed
down the vehicle to a GW of 2450 lbs (per Cessna.com) and am trying to match the
performance from the Cessna web site. I can only make an attempt to match the takeoff
procedure, though, because I don't know it. I figure one notch (10 degrees) of flaps might
be worthwhile. Some enlightenment on validating takeoff performance is solicited.

One thing that I have noticed is that even at full power the IO360 puts out only 120 HP.
It is supposed to put out 160. I set the MAXHP setting in the engine config file to 185
and then I get 160. Maybe there is a scaling problem there. That seems to help
performance, and we are pretty close to matching takeoff performance at that point IFF we
also use the prop_generic2f.xml propeller file.

This one needs some work, but I think it can be fixed fairly easily.

Jon