Hi Ira,
It is interesting to compare your computed figures with those from ROTAX
and DIAMOND.
Based on fig.14, page 10-8 of the ROTAX 912ULS Owner Manual, the engine
should be capable of producing 75 % power at 8000 ft at full throttle
and 5500 RPM. This is not 75% of 100 HP but 75% of the max continuous
power of 94 HP, i.e. 69 HP. At 8000 ft, full throttle, 5000 RPM, the
power is 59.5 %.
Below is what Diamond shows on the Katana DA20-100 Flight Manual. This
aircraft is JAR-VLA certified and uses the same 912S engine. The Manual
is available on line on the Diamond website. Below are their cruise
figures at 8000 ft. :
5500 RPM, 22 In.Hg: 75% of max continuous power (assumed to be at full
throttle):
5350 RPM, 21,7 In.Hg: 65% (probably not at full throttle)
5100 RPM, 21 In.Hg: 55% (probably not at full throttle)
The Diamond figures are consistent with the Rotax ones at 5500 RPM but
not for the other power settings.Your computed figures differ
significantly from both the Rotax and the Diamond figures.
One interesting thing is that Diamond provides fuel flow figures. This
confirms the higher you fly with the Rotax, the more fuel you use. A
typical exemple is 18 liters/hour at 75% at 0 ft and 23,6 l/h at the
same power at 8000ft. That is a 31% increase!
Regarding the advertised cruising speed of the Europa, I have made
numerous measurements using the 3 way GPS method and consistently get
135 kts TAS at 8000 ft, full throttle and 5000 RPM, which is about 60%
power according to Rotax. This is for an XS monowheel with 912 ULS,
Airmaster prop and speed kit. So it seems that the advertised 140 kts at
75% at 8000 ft are absolutely achievable, provided you accept to cruise
at 5500 RPM.
Best regards and Merry Christmas
Remi Guerner
F-PGKL
>>> At 8000' DA, the 912s can not make 75% power in cruise. Since the
Rotax factory does not provide sufficient data, I modeled power
Output with a simple linear model of MP and RPM. At 8000', at
takeoff rpm (limit 5 min) 5750 RPM, the engine provide 73%. At
5500 (constant pitch prop), the output is 70%, and at standard
cruise rpm of 5000 rpm, the output is 63%. That said, with the
speed kit installed and a fresh wash, I do see in the range of 135kt
TAS at 5000rpm at 8000'.
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