Hi Remi,
The table is engine performance with a constant speed (AirMaster) prop.
All certificated manufacturers provide a table like mine which shows
the relationship between throttle, selected RPM, and power output.
Rotax does not. The graph is useful to select which combination
works best under specific circumstance, particularly when fuel flow
and TAS are added to the table. My data collection is unfinished for the
bigger version of the table. In this version of just engine, not airframe
performance, density altitude is unneeded. No matter what density
altitude, throttle sets manifold pressure, and obviously without a
turbocharger/supercharger, the maximum MP declines with altitude.
The desired rpm is set on your prop control. Green is the usual
operating range, the other colors are not important here.
Example: 75% power is obtained at 27.5" and 4800 rpm or
26" and 5000 or 24" and 5500 rpm. The "standard" cruise setting
on Continental or Lycomings of 25 squared (or 2500 rpm @ prop at
25" MP) doesn't work out for Rotax because 2500 rpm would be over
6000 engine rpm, but by extrapolation would be over 80% power.
Or, if you set your prop to 5000 rpm for cruise, then you get 75% at
26" (only possible up 4000' DA), and 65% at 23" MAP.
While there are small inaccuracies due my simple model of the Otto
cycle, so far as I know, this table I created is the only published
attempt to provide guidance for 912s drivers with a constant speed
prop.
Cheers,
--------
Ira N224XS
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=221142#221142
|