Message-ID: <002501c1a7c4$a53f4420$1f499842@mshome.net>
From: "Robert Smiley" <rsmiley@tscnet.com>
To: <glcasey@gte.net>, <lancair.list@olsusa.com>
References: <NEBBIBKBKLGPNKKOGMMBEELCEEAB.glcasey@gte.net>
Subject: Re: constant-speed props
Date: Sun, 27 Jan 2002 23:25:56 -0700
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Reply-To: lancair.list@olsusa.com

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> On the other hand how many boats have variable-pitch props?

In an earlier teenage life, I raced outboard hydroplanes and utility
runabouts in the APBA in the Northwest.  Variable pitched props were not
available but we did use cupped blades.  The last 1/8th inch trailing edge
of usually,  stainless steel blades, had a slight increased curvature of the
blade to redirect the water in an aft direction.  Thus when you were flying
down the  straight-a-way. The full face of the blade was in contact with the
water.  The water was accelerated by the blade and redirected at a higher
velocity off the trailing cupped edge. When you approached the corners and
slowed down the water turbulated ever so slightly at the beginning of the
cup but not cavitate. It acted like a normal prop.  It kept the revs up yet
allowed all the power of the motor to convert to a slower efficient velocity
for the turn. Turning out of the corner and straight down the backstretch
the engine would rev up ever so slightly then suddenly shift down about 600
rpm and quickly lunge my craft forward about 6-10 mph.  What a thrill as the
prop grabbed solid water again and redirected the power in an aft direction.
That is about as close to a variable prop in boats as you can get.  We
called it shifting.  The trick was to match the right amount of cup with the
total rig setup.  Your motor, boat and water conditions.  We experimented
forever to get the right combination.

"It's all about  money and the compromises one makes because of the lack a
sufficient amount of it."  You are right.  It cost a lot of money and once
we got the right setup and prop; those props were guarded like gold and
brought out only on record courses.   It is not science in these areas;  it
is art. and once you have it you never let it go.

Why don't formula 1 racers use cupped props in air racing?

Bob Smiley
N94RJ

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