Today's Message Index:
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1. 05:13 AM - Re: Allegro Cruise Speeds (Thom Riddle)
2. 06:47 AM - Re: Allegro Cruise Speeds (Aero Siam)
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Subject: | Re: Allegro Cruise Speeds |
Paul,
The airspeed varies approximately with the square root of the power.
The 912UL engine has a maximum continuous rating of 79 HP at 5,500 rpm.
The 912ULS is rated at 95 HP at 5,500 rpm, also max. continuous.
95 / 79 = 1.18987 18.99% greater max cont. power
1.18987
.5 = 1.0908 9.1% approx. expected speed difference
Since the torque and horsepower curves over entire RPM range are
similar for the two engines, it is reasonable to expect about 9%
difference in airspeeds between the same airplane with different
engines. If an Allegro 2000 with the 912ULS engine and a three blade
Woodcomp prop is pitched for best cruise, then this airplane under the
same conditions could expect True Air Speeds (TAS) of about 9% higher
than the figures in the table I provided. Examples shown below.
Zero Density Altitude
Actual Aircraft Flying Weight 940 lb. or 427 kg.
RPM 912 UL 912 ULS
5,500 126 mph 137 mph
5,000 112 122
4,500 102 111
4,000 92 100
3,500 73 80
I hope this helps.
Thom in Buffalo
Message 2
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Subject: | Re: Allegro Cruise Speeds |
--> Allegro-List message posted by: "Aero Siam" <paul@aero-siam.com>
Thom
Thanks for the info. I will update the Performance page to incorporate the speeds
for the 100hp.
Is it possible to extrapolate the figures for fuel burn at various RPM to complete
the picture? Rotax's website has a graph for fuel consumption. Can the figures
be used directly or is there a difference between bench tests and actual
in-flight results?
Paul
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=9316#9316
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