An old thread this, I know, but worth re-visiting from time to time.
My figures are within a knot or two of Graham Clark's. 'G-EMIN'
In fact 'IMHO' I wouldn't be surprised if classic 912 (Mark 1 Europa)
owners
find their best cross_country_speed for flight planning purposes is in
the region of:
105 -110 knots
122 knots is my fastest (though completely impractical) continuous
cruise in test.
Warp Drive fixed prop setting , just over 17 deg, RPM 5500 (max
continuous)
and accurate Flydat digital measurement.
At this speed however cockpit noise levels are high and the engine is
thirsty.
I'm convinced my aircraft is fairly typical. It has a top speed of
nearly
130 knots at 1000 feet (5,800 RPM 17 deg prop).
I've also heard from reputable sources that my figures are broadly
consistant
with other tested customer aircraft. (and with the original figures for
G-YURO,
allowing for some uncertainty over prop. setting and RPM measurement).
In my experience (I've tried lot's of times !), accurately calibrating
cruise T.A.S.
is difficult and prone to yielding optimistic results. Factors like,
density/altitude,
head and cross wind components, slow descent, inaccurate prop. setting
and
RPM measurement, course and variable throttle setting all conspire to
introduce
errors.
Repeated GPS calibrated, two-way runs at constant throttle/height on
relatively
calm days, between two fixed GROUND points have tended to give
consistant
results and revealed a slight over-read on my old ASI.
Regular cross-country flight experience also has a tendency to reveal a
useful
working cruise. (bearing in mind that it's very nearly impossible to
achieve in
practice what might be predicted in theory). My RELIABLE,
point-to-point,
'fast cruise' on flight plans submitted to ATC is therefore 105-110
knots !
Gramin@aol.com wrote:
> 120 kts at 18.5 deg. 17 ltrs hr
>
> How many revs. is that ? I can only get 120 kts (set at 17 deg) by
going
> up to 5300 where it is too noisy for comfort. To operate safely out of
short
> fields I put it down to 16 deg. last summer but the fuel consumption
suffered
> a lot in the cruise, so I have put it back to 17. I prefer to potter
along
> quietly at 100 to 105 kts under 5000 rpm (digitally measured) and get
> consumption down nearer 12 ltr/hr.
>
> Graham C G-EMIN
--
Alan. D. Stewart
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