Re: Velocity 173 for FS 95

[Alan Shaw <wingco@iu.net>]

Lisa Boesen & Chuck Caldarale wrote:

> Don't have one for MSFS, but I have built a Standard FG for X-Plane. (This
> is not the very strange turboprop XL that comes with X-Plane.) The only
> real problem at this point is the performance is a little too good. I'm
> playing with prop and power settings to try to correct that.
>
>  - Chuck,

In the original proto type (slightly smaller and with a rounded windshield)
did 215 mph when our friends at NASA had predicted 180 mph.  The STD FG if
rigged and faired in correctly can be elusively fast.  One of the biggest drag
producers is the gear leg which is at a 15 degree angle of attack at cruise
unless superficially faired in too limit all this turbulence to the prop.
Reducing the arm pit cooling scoops down to no more than 4" width also cuts
drag and increases cooling efficiency.Another big speed mod is the air intake
for the engine.  The "standard" installation calls for no less than five  90
degree turns DECREASING the manifold pressure by at least 1" .  By bringing
the air in from right behind the speed brake,  through the fire wall just
below the gear leg arc, straight into the servo which is bolted straight on
the sump... the manifold pressure is INCREASED by  2".  The pressure increase
is generated by a simple venturi in that the intake is smaller than the
opening at the firewall where the servo is.
The resulting power increase at high cruise altitudes from 2+1=3" more
manifold pressure where the drag decreases translates to a substantial
increase in TRUE airspeed.  An RG with a CS prop can't catch it and his gear
is in the way of a possible ram air installation.
The biggest draw back is that you have to leave the speed brake down while
taxing to prevent the nose gear from throwing FOD into the intake.
In using X-plane to analyze the Velocities the first problem is that the
airfoils are hand drawn modifications....unprogamable.   Without known
airfoils we can't even figure out the coefficient of drag of the fuselage
through reverse engineering which makes for a lot of garbage in and garbage
out.  For the ram air mod try using 4000' for the "critical altitude" and see
what kind of true airspeed and fuel consumption figures you get at 12 to 18
thousand feet.   If you thought the performance figures were "a little too
good" before, now you will be convienced your computer is lying.

Alan Shaw