On Sunday 04 February 2007 09:07, Sébastien MARQUE wrote:
> hi all!
>
> I really find the Piper Comanche pa24-250 from Dave Perry wonderfull! I
> use it on cvs FG-OSG.
> But as I come from c172p, I'm a little confused with the engine,
> propeller and power controls...
>
> First for a 180 miles trip I use 3/4 of the available fuel (on the four
> tanks, ~7.000 ft ASL, ~130 KTAS), I don't know if it is normal, or too
> much, I personnally think it's too much, and I misuse the engine controls.
I found the following on the web:
Horsepower: 250 Gross Weight: 2800 lbs
Top Speed: 165 kts Empty Weight: 1690 lbs
Cruise Speed: 157 kts Fuel Capacity: 60 gal
Stall Speed (dirty): 53 kts Range: 630 nm
Takeoff Landing
Ground Roll: 750 ft Ground Roll 600 ft
Over 50 ft obstacle: 1650 ft Over 50 ft obstacle: 1025 ft
Rate Of Climb: 1350 fpm
Ceiling: 20000 ft
Are you sure that you have a full fuel load? At cruise you should be burning
something like 10 to 14 gal. US/hour which is over 4 hours plus reserve on a
full fuel load. Your 180 mile trip should use perhaps 1/3 of a full fuel
load. I usually only do shorter flights in the pa24 (<100 miles) so I have
not noticed how much fuel it is consuming.
>
> here's the trip:
> http://fgfs.i-net.hu/modules/fgtracker/?FUNCT=FLIGHT&FLIGHTID=10065&PHPSESS
>ID=fde9c270fdb27c820fde750dd1c9a31e
>
> Indeed, I can't succeed to find the good way to use the mixture control
> (on the c172 I used the fuel flow keeping its value at the minimum,
> don't know if it is the good manner, btw). for now I keep it at the
> maximum (except for switching off the engine).
On a real aircraft you would set the mixture using mostly the exhaust gas
temperature (egt). If you go too lean the egt will get too high and you can
damage the engine (it will burn out exhaust values). I don't think this type
of damage is currently modeled in FG. I just did a quick test flight in the
pa24 and the egt instrument does not appear to work. So your mixture
settings are at best a guess until such time as there is a working egt gauge.
>
> To climb or descend I was used to play with power control on the c172,
> on pa24 it is not that simple ;). so I try to play with n/N key to
> control propeller, putting the manifold pressure at 16 (for descent, as
> described in README.pa24-250), but I don't understand the effects both
> on propeller and rpm, and my descent is not very nice...
> for climbing I push the propeller control to the maximum, manifold
> pressure too, and I try to correct climb rate using the yoke and trim,
> so I can't keep a constant speed... and climbing is not "smooth"
> (neither descent) ;)
I have found the pa24 very easy to trim up for whatever flight attitude I need
at the moment (climbing, cruise and descending). "To climb or descend I was
used to play with power control ...." is the correct way of thinking about
your throttle controls. The throttle is for controlling altitude and the
elevators (and it's trim) are for controlling airspeed in normal flight
operations (non-aerobatic flight). With practice you will eventually be able
to maintain steady air speeds in different flight modes. So when descending
for example reduce throttle and then trim for the speed you want. This will
likely be significantly faster then your cruise speed even with the reduced
throttle setting. But try to keep it in the white. Also I have found that
keeping it near the bottom of the white is about the right speed for climbing
out once I am in cruise climb mode.
The correct way to trim an aircraft is to use the elevator control to hold a
steady speed and adjust the trim until you no longer have to hold any
pressure on the yoke/stick to maintain that airspeed. Again the pa24 trims
up nicely and once trimmed only requires minor adjustments to maintain the
trimmed airspeed and rate of climb (EI. it is mostly hands off at that
point).
You should be matching RPM settings to your throttle settings. So for higher
manifold pressures also set the prop for higher RPMs. You should also use
lower RPM settings at lower altitudes for the same MP setting. In other
words you are operating two controls when you make throttle changes on the
pa24 instead of one control like on the c172.
In normal operations you only use full throttle for a short time after take
off to get well clear of the ground and to get the aircraft well into it's
normal flight envelope. At that point you should reduce manifold pressure
and RPMs below full power but higher than normal cruise settings until you
reach cruise altitude. Then reduce throttle and RPM to your cruise settings.
As you are climbing you should also be adjusting your mixture.
When descending the reason for using a setting as high as 16 inches MP is to
avoid cold shocking the engine. With this throttle setting put the engine
RPMs at the bottom of the green. But remember to set the RPMs all the way up
as you enter the landing pattern so that you can quickly add full power if
needed. Also remember to increase mixture richness as you descend.
The pa24 is a wonderful high performance GA aircraft that is significantly
different to operate than lower performance aircraft like the c172. It likes
a light hand on the controls and really rewards pilots who operate the
controls with smoothness and finesse. It takes experience to learn these
skills. So keep at it and eventually you will get there.
>
> I'm not a real pilot, I only fly on FGFS, so sorry if I don't use the
> good terminology for these controls (indeed I don't know it in English,
> that is a problem to find infos over the Net).
>
> Any help is welcome to explain how to use these controls fine.
> Thank you.
>
> BTW, using this aircraft on my machine Debian sid, AthlonXP 1800+, 512MB
> RAM, Nvidia GeForce4 32MB VRAM with nvidia kernel 0.8774 (debian
> kernel), I get 35-40 fps, with --geometry=1024x768 and ATCChatter.nas
> disabled, which is enough for my use.
>
> regards,
>
> seb
>
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