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Dear Jim and All,

I looked at www.lycoming.textron.com/main.html -> Support ->
Publications -> Key reprints -> An Explanation of Power Settings.

It shows as an example, that a Cessna 177 RG using a Lycoming
IO-360-A1B6D, at 6000ft, can be ran in RPM ranges of 2100 to 2500 and MP
between 18" and 24" (disclaimer, not all combinations are necessarily
recommendable). It lists that for example, 66% power is available at
2100RPM and 24"MP.

They recommend that you should search for a power setting gives the
least vibration and the lowest noise level and that aditionally that
lower RPM means lower friction HP losses. This translates into a
slightly improved fuel economy.



There is another article on "Considerations for Low Power Low RPM
Cruise", where they discuss the pro's and con's on some engines of
operating them as low as 1800 RPM. The focus there is this low RPM
allied to low MP's might cause some problems exactly because in such
scenario the engine would be operated in too low of a power setting,
with lower than normal temps. Yes, too low CHT's and EGT's can be as bad
(in diferent ways) than too high CHT's and EGT's.

Continental engines have similar issues, I just haven't been able to
find their site. As a renter, still without a complex or
high-performance checkout, these readings have been mostly looking
ahead. I hope one day to have one of the new Diesel/Jet Fuel piston
designs on my Lancair 320, so we don't need to worry about leaning and
get more power, and less temps issue due to them being water cooled.

Some prop installations have a fairly high lower side of their RPM green
arc. Such cases are usually due to vibration or other similar issues.

Marcelo Pacheco
PP-ASEL IFR

LML website:   http://www.olsusa.com/Users/Mkaye/maillist.html
Builders' Bookstore:   http://www.buildersbooks.com/lancair

Please send your photos and drawings to marvkaye@olsusa.com.