Gert,
Your original post was asking how to figure out power settings for your 914 and
Woodcomp prop. Here is how we do it.
The 914 and 912 Operators Manuals give tables of suggested RPM and MP settings
for 115% (only for 914), 100%, 75%, 65% and 55% power. Fuel flow is related to
power. Assuming you have fuel flow measurement in your airplane, to choose
a set of operating parameters (RPM & MP), first fly the desired power setting
as given in the Operators Manual. Note the fuel flow. Now change one
parameter,
say RPM. Then adjust the other parameter until the same fuel flow is indicated.
That will be a new pair of operating parameters for that power setting.
Another way to do this and the way to calculate operating parameters for other
than the power settings given in the Operators Manuals, is to note that the
graphs
are related to each other. Say you wanted to develop operating parameters
for 40% power. Look at the Engine Performance graph and note that 40 hp (40%
of 100 hp) is 4100 RPM. Now look at the Manifold Pressure graph and note that
4100 RPM is 26.5 in Hg. Now look at Fuel Consumption graph and note that 4100
RPM gives 2.8 GPH.
Rotax SL-912-016 or SL-914-014, Essential Information, gives some operating
information.
These Service Letters state that WOT (wide open throttle) RPM should
not be less than 5200 RPM. This is to prevent excessive loading of the gearbox.
This is why many operators run their 914 or 912 at 5000 RPM or above. We
generally cruise at 5000 RPM, climb at 5500 RPM and use 5700 RPM for takeoff
in our 914 Airmaster equipped Europa.
Other portions of this thread concern IAS and TAS. TAS is IAS corrected for
density
(temperature and pressure). As Remi points out, TAS should be used when
making performance comparisons since it takes the variation in air density from
flight to flight into consideration.
For a given power setting, TAS will increase with altitude since the air becomes
less dense with altitude. This is why a turbo is nice, since you can develop
high power at higher altitudes. We typically operate at 5000 RPM and 30.5 in
Hg MP or about 73% power. We see TAS of about 145 kts at 8000 ft and 150 kts
at 12000 ft and our fuel burn is about 5.5 gph.
A normally aspirated engine (912S) loses power at higher altitude because the
air
becomes less dense so manifold pressure decreases. There is a graph in the
912S OM that shows this. You can develop 75% power (51KW) with WOT up to 2300
m (7000 ft) at 5000 RPM. You can develop 65% power (45 KW) with WOT up to 3500
m (10500) at 5000 RPM
Hope this helps.
Jim & Heather
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=430876#430876
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