[Flightgear-devel] Ideas to stabilize c172p performance

[Tom B. <tb...@ne...>]

I found some of my notes regarding the changes I made to the c172p.xml
and c172p-set.xml files back in 2007. The changes that seemed to work
the best for me are in the -set.xml file:

1) Change the <aileron-trim> value from the default 0.027 to a value
between 0.030 and 0.032.

2) Change the <rudder-trim> value from the default 0.00 to a value
between 0.05 and 0.10.

I am still experimenting with changes to various values in the c172p.xml
files, as there are ample opportunities to further refine the flight
characteristics in several areas there.

But maybe John and Ron would be willing to test these rudder/aileron
trim numbers a bit and give me some feedback? Not surprisingly, I found
that the rudder trim value has the greatest impact on the effect of
P-factor. And indeed, on the real aircraft there is a ground-adjustable
trim tab on the back of the 172's rudder--and this is always bent
slightly in order to offset the need for right rudder in the climb. So
setting a positive value for rudder trim seems to emulate this effect,
and results in a less impressive left-turning tendency in the FG C172P.

As for the aileron trim, I found that a very small change seems to also
help the situation. My current settings are 0.05 for the rudder trim,
and 0.030 for the aileron trim--but I am not sure these are the best
values, and thus would like some input from other 172 pilots out there.
It make take retesting with a proper set of 3-axis flight controls to
make this determination; as it stands now, these have been tested using
an inexpensive joystick with auto-coordination turned 'on' to control
the degree of rudder input needed from the pilot.

If it's not too much to ask, I would also like someone to change the
name of the engine file to "eng_o320.xml." It seems like a small
(nit-picky) issue I realize, but the 172 never came equipped with an
Injected, Opposed (IO-320) engine. There were a couple of later models
with the Lycoming IO-360 engine, but the 172P had the non-injected
opposed (O-320) Lycoming engine. Again, it's a small point, but it helps
resolve confusion for those new to FG and trying to sort out the way
things work. And it only takes about 30 seconds to fix.

I am significantly impressed with the level of understanding shown by
people like Ron Jensen and John Denker, regarding the piston-engine
issues we are experiencing in the 172 model. I think that these guys are
really getting close to further improving the fidelity of the model, and
this will only make a great emulation that much better. 

Thanks in advance.

TB