Re: prop size?


Ron Weiss <ronweiss4@...>
 

--- Awesome info!!!! Thanks,RonIn Q-LIST@yahoogroups.com, "David J.
Gall" <David@...> wrote:

Ron,

The spreadsheet Leon tried to send you is located here:
http://david.gall.com/files/Airplane/Prop-100.xls.
It is based on NACA Technical Memorandum 212. It should be
sufficient to get
you "into the ballpark" for your propeller selection. It can
recommend pitch
and diameter for either a two- or a three-bladed prop.

Your reported propeller failures sound like resonance problems.
With a 2:1
reduction, the propeller is in lock-step with the vibration of the
engine
from the power pulses. This is not due to "some reduction units"
but is
characteristic of the gear ratio and the orientation of the
propeller. Most
reduciton units use a different, non-integer ratio in an effort to
alleviate
this problem. Some use various vibration dampeners, but the real
problem is
the ratio and the orientation of the propeller.

For a reduction unit with an integer ratio or for a direct drive
engine,
(assuming a horizontally-opposed engine like a Subaru or
Continental) the
propeller needs to be installed in such a manner that it is
horizontal when
the power pulses occur throughout the crankshaft rotation. This is
referred
to as "clocking" the prop. Set the engine at Top Dead Center then
install
the prop with the blades horizontal.

If you install the prop with the blades vertical when the engine
is at TDC,
then the power pulses impart a bending load on the prop as they
move the
prop hub laterally left-to-right while the prop is aligned
vertically. This
bends the prop and sets it to oscillating. If the natural
oscillating
frequency of the prop is close to a whole-number multiple of the
RPM,
resonance may occur. Even absent resonance, large forces may build
up in the
prop or in the friction surface where the prop is clamped in the
prop
hub/crush plate, leading to prop failure.

See the file "Installing Wood Propellers.rtf" in the files area or
try this
link for more info:
http://f3.grp.yahoofs.com/v1/wP2ERN5XhWLms7lChuzq63Jm4Lag52JrmvgqpGHO
oOPIEPR
Np3D-AnqusooTSR48-zr837BdIKoeWR27ce1vF2SdJGKUea4G/Installing%
20Wood%20Propel
lers.rtf


David J. Gall

-----Original Message-----
From: Q-LIST@yahoogroups.com [mailto:Q-LIST@yahoogroups.com]
On Behalf Of Ron Weiss
Sent: Sunday, June 04, 2006 10:29 PM
To: Q-LIST@yahoogroups.com
Subject: [Q-LIST] Re: prop size?

--- Relax Steve, My attempt at humor wasen't very funny.
However here's my dilemma. In the last couple of weeks I've
been trying to get info on the airsoob site. I have a
Subie-Lyc 2.2. Apparently no one with this set up has logged
on in the last couple of weeks because all the info I can get
is that some reduction units don't like 2 bladed wood
props(harmonic issues). One guy used a Prince and liked the
performance, but, there was this vibration? He seemed to like
his Warp Drive, however, it didn't perform as well! Still, I
didn't get measurements for my motor( diameter, pitch, breast
size)?
I've been to many different propeller websites with the same
"aren't really sure" answer. Catto even flatly refused and
sent me to Prince! A@P's seem to twitch when I mention
Subaru. I don't mind paying for information, but, I can't
seem to find any. Leon sent me a "prop size sheet" that
didn't get through. Finley's website won't come up, however,
I do recall very few specs, mostly set up. I do remember him
running or ran a Warp Drive. So, if anyone comes across a
high performance airplane with a Subaru 2.2 in the nose, if
you could please take a moment and ask him or her....What
size prop are you running? I'd really appreciate it! Ron

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