From: "Sven Jerlhagen" <svenjerlhagen@attbi.com>
To: <lancair.list@olsusa.com>
Subject: Re: Constant speed prop
Date: Thu, 24 Jan 2002 00:40:50 -0800
Message-ID: <ENEBKFGHGAOIHPPGCCBFGEOECBAA.svenjerlhagen@attbi.com>
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My 320 is equipped with a Warnke fixed prop. I can tell you my perfomance
numbers and try to put them in perspective, others will have to add CS
performance numbers. Most people who have CS will tell you this is the only
way, and it definitely gives advantages, but they are not that big.

My takeoff over 50ft barrier is 1360 ft at gross weight. Landing over 50 ft
barrier is 1720 ft, and I would never use less than 2000 ft anyway, so this
is not an issue. For grass fields a CS is a major asset though.

I get max climb rate 1400 fpm (gross, SL, std) at 110 kts. I like to climb
at 140 kts which gives 1250 fpm. The CS advantage will be hughe at Vx, but
small at cruise climb.

I get 193 ktas at 75% cruise at 10000 ft and 2700 rpm. A CS will not give
you any more speed or less fuel consumption, since you cannot get 75% at
10000 ft without reving 2700 (or adding a turbo). If I throttle back to 65%
182 ktas at 10000 ft and 2550 rpm. A CS will do this better by reving less,
it will take slightly less fuel, but you get a lot of fuel for the price of
a CS and its maintenance. Less rpm also makes less noise, especially if its
a 3 blade.

You will also lose a bit payload (same gross I assume). The MT 2-blade
weights 35 lbs, about 20 lbs more than a fixed. Hartzell is a lot heavier.
How much payload margin do you have on a typical trip ? If your CG is good
now, you will have to move something substantial or add ballast.

If you have a 320 you will get a better top speed increase by changing to a
360 with less weight increase and money. This should give 7 kts.

Sven J
SE-XOP

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