Message-ID: <c=US%a=_%p=CDI_Corporation%l=CDIM-PTS-MAIL-981020182646Z-4709@cdim-pts-mail.ports-va.marine.cdicorp.com>
From: "Rumburg, William" <wrumburg@cdicorp.com>
To: "'lancair.list@olsusa.com'" <lancair.list@olsusa.com>
Subject: RE: Building Tip
Date: Tue, 20 Oct 1998 14:26:46 -0400
Mime-Version: 1.0

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For general information, here is a response that I sent to Greg 
Nelson
yesterday regarding my propeller and harmonic balancer...


Greg -

    I HAD an IvoProp (ground adjustable), until two years ago,
when it was damaged in an accident. I never flew with it. I did 
intuitively
feel that its thin blade airfoil (that composites make possible) was 
efficient
and well designed. I'd heard they were smooth and quiet and perceived
to be efficient on ultralights.
However, when I saw the internal blade twisting mechanism, I had bad
feelings about it. An aero engineer friend expressed similar 
misgivings.
It twisted the blades almost exclusively at the tip by imposing an 
internal
torsional force from an imbedded steel rod, bent into a "U" shape at
the tip. The rods were twisted from their roots, by a leadscrew in the 
clamping
plate at the hub. I felt that this method of twisting imposed possibly 
severe
torsional forces on a blade which is already carrying high shear 
stresses.
I had a LOT of apprehension about that.
The proper approach to pitch changing is to rotate the entire blade at 
the
root (my aero engineer friend explained that the ideal mechanism would 
involve a combination of twisting the entire blade at the root AND a 
slight
"Ivo-type" warping of the airfoil. That is, however, only possible 
with
composites and would be far too complex and costly).
   Also, at that time, the IvoProp neutral pitch was about 54", so 
bringing it up
to the Lancair cruise pitch of 80+" required a LOT of initial twisting 
(I believe
that Ivo has since redesigned the neutral pitch considerably higher).
     I now have a beautiful 62 x 82 three blade wooden prop by Colin 
Walker
of Surry, B.C. and I'm very happy with it. My engine is an IO-320 (160 
H.P.),
although I feel that with dual electronic ignition, no vacuum pump and 
Cermi-
Chrome cylinders, its actually producing 170-175 H.P. I spoke with 
Colin and
he said that if my engine can spin the prop a little over 2,900 rpm 
straight and
level, it is producing approximately 175 H. P.  Static is barely 2,200 
rpm and
actually drops to 2,050 rpm during takeoff roll and climbout. Still, 
at full gross
on a hot day, takeoff roll is less than 1,500 ft and is typically 
1,000 - 1,200 ft.
Climb is 160 mph IAS @ 1,200-1,400 fpm and cruise is typically 230 mph 
TAS @ 8,000 ft. Its an excellent all-around wooden prop.
    I don't have any before and after comparison of my harmonic 
dampener,
but I'm certain that it not only serves as a flywheel, but smoothes 
the
engine, as well as providing needed weight up front. Its a machined 
aluminum
ring, approximately 2" thick with outside diameter a little smaller 
than the starter
ring. It bolts to the front of the starter ring, utilizing the 
existing twelve holes
on the outside perimeter, filling the existing empty space on the 
front of the
starter ring which would otherwise be unused. My empty weight (fully 
painted
and upholstered), was 1,078 lbs. and I needed weight forward.
   It's disappointing that by now a domestically-produced electric 
variable
pitch prop is not available. The MT is OK, but MUCH too expensive. 
Besides,
I'd rather have a pilot-controllable variable pitch than a constant 
speed, with
its attendant complex, heavy and costly controller.
I'm happy to answer any further building or flying questions, just 
write !

                                                   Bill Rumburg
                                                   N403WR (Sonic 
Boom)