Dick Sipp
Joined: 11 Jan 2006
Posts: 215
Location: Hope, MI
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 Posted: Fri Apr 28, 2006 7:14 pm Post subject: RV10-List :Fuel Economy |
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Tim & list:
Your comments on the operation of your airplane are great, good motivation
and insight.
With all the valid concern lately over fuel costs there are some operational
techniques that will help save fuel.
Many folks are uncomfortable with cruising "over square" (with the manifold
pressure higher than the RPM). This type of operation is permitted by
Lycoming (with limitations at low altitude) and does provide better fuel
economy. A side benefit is quieter operation and often less vibration. For
example, the same 65% best economy mixture power can be produced at both of
these fuel flows:
2000 RPM & 11.8 GPH
2600 RPM & 13.3 GPH
(page 3-35 operators manual)
the difference of course is the throttle setting. Think of shifting into
overdrive in a car.
the same 65% at best power mixture results in fuel flows of 13.6 & 15.2 GPH
for the respective RPM settings which demonstrates the importance of leaning
below 75%.
As for propellers, this should probably be in the catagory of whether or not
to prime, everyone has good reasons for their choice. In my case I'll be a
part of the minority using an MT; I'll accept a few knots less IF that is
the case for the smooooth, quiet operation. I understand that the 3 blade
props also become more efficient as altitude increases which is hopefully
where much of cruising in an airplane like the 10 will be done.
Dick Sipp
#40065
Many years ago a respected RV test pilot, Chuck Berthe, wrote a great
article in Kit Planes comparing constant speed and fixed pitch propellers.
The article contained lots of good cost calculations. I asked him if he
flew his airplane "oversquare" his answer was "as much as I can as much as I
can."
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