Message-ID: <19990114074154.11348.qmail@www05.netaddress.usa.net>
Date: Thu, 14 Jan 1999 07:41:54
From: Dan Schaefer <dfschaefer@usa.net>
To: lancair.list@olsusa.com
Subject: Props, CS vs fixed pitch
Mime-Version: 1.0

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A comment in response to Sven (SE-XOP) regarding props. 

I'm not sure what kind of terrain and environment you are accustomed to
flying from, Sven, but here in the Western US, it's quite common to find
yourself stopping for gas at an airport sitting at an altitude up at
5000 to 6000 ft. and often in the summer (when one is likely to be out
and about going somewhere) where the temperatures can easily be 90
degrees (F) and higher. I've had my share of rejected takeoffs back when
I was flying behind a fixed pitch prop and my plane's seats have the marks
to prove it! Since I changed to a CS unit (MT two-blade), the problem went
away. I may not go any faster in cruise (though I actually do, a bit -
reflected in about a 10% higher fuel burn, indicating that I'm making,
and using, more power) but I'll take the extra performance on takeoff
any day!!

Just for reference, with a wooden, fixed pitch prop, I could get no more
than about 2350 RPM for a sealevel takeoff and takeoff was a bit on the
anemic side, to say the least. With the CS unit, I always get 2650-2700
 RPM and the takeoffs are now quite sprightly affairs.

Do the numbers; that's better than a 10% increase in takeoff horsepower
(HP = T x RPM / K [K is a constant around 5200 for these regimes]).
Nearly all of it is "excess power" needed to climb, which relates to
better takeoff performance.

Cheers,

Dan Schaefer