Please Prop Pictch Mods

[Stan Griffiths]

>Message-Id: 1217_zs1ctc
>From: zs1afz@zs1ctc 
>To: w7ni@teleport.com
>
>Hi Stan,
>   I am very interested in your modification for modified prop pitch
>motors. If you can possibly forward a copy to me, I'll be very pleased ??
>Many thanks,
>73 Maria zs1afz@zs1ctc.ctech.ac.za)

Hi Maria,

I don't really have a write-up for prop pitch modifications, but I have used
several prop pitch motors over the years and have modified one back in the
'60s according to a magazine article I read then.  Unfortunately, I do not
have the article any more nor do I remember which magazine it was in.

The essence of the article was to suggest that the user of a prop pitch
disable one set of planetary drive gears in the prop pitch and therefore
change the gear reduction from about 10,000 to 1 to maybe 1000 to 1.  The
advantage claimed for doing this was that you would put far less voltage on
the motor since it now turns much slower than before.  This was supposed to
mean less power consumption, less noise (prop pitches can wake up your
neighbors at night!), and longer life for the bearings and brushes.  I did
this mod which involved hiring a machine shop to put part of the gear box on
a lathe and cut away a set of gear teeth.  In other words, it was not a
reversible modification.

The modification was successful in that it did everything the author claimed
it would.  Unfortunately, it did something exta he failed to mention.  With
only 1000 to 1 instead of 10,000 to 1 gear reduction, there was not enough
drag in the motor to prevent the antennas from rotating in the wind by
turning the motor through the gear box.  The system now needed a brake!  I
was sorry I did it but it was too late.

Another thing about prop pitch moters is the light weight oil that the gear
box is full of when they are original.  Some people say you should drain
this oil and use heavy gear grease.  Others say leave it there since the
designers of the prop pitch know best what kind of lubrication the gear box
needs.  My experience has been that, since the prop pitch is normally
operated in a "horizontal" position while on the aircraft and in a
"vertical" position while rotating an antenna, the seal that is supposed to
keep the light weight gear oil out of the motor is now working much harder
against gravity not to mention that seal is now 50 years old.

I have had sad experiences both ways.  I have had the oil leak into the
motor which required constant disassembly and cleaning of the motor.  I have
drained the light oil from the gear box and have had bearings, which used to
be immersed in oil, rust and freeze up.  I still think it is best to drain
the oil and take some more precautions to lube the gears and bearings better
with gear grease and try to keep the water out of it.

So I am certain there are dozens of really good prop pitch stories out there
and I hope this post will get some others to talk about their experiences.
Some will confirm what I have said and others will have a different set of
experiences.  I currently use one prop pitch, unmodified, with gear grease
instead of light oil, to rotate my 5 el 20 with a 46 foot boom.  It has been
working successfully at this job since 1975 without ever having to be
serviced at all since installation.

I hope this helps you some . . .

Stan  w7ni@teleport.com