VP-mechanism: geometry symmetry and bearing friction

From: Tapio Linkosalo <tapio.linkosalo_at_iki.fi>
Date: Thu, 14 Jul 2011 10:07:10 +0300

... it is about time to start building a few new VP hubs for Belgrade.
One thing to improve with my old hubs is the tracking of the VP arms; it
seems to me that the spring tends to incline the horizontal bar of the
hub, resulting in the blade-angle-changing arms become different length,
and thus the pitch change is not symmetrical. Further it seems to be
that the 0.3mm axle wire is not sufficiently stiff to resist the
bending. I was considering stiffening the axle from the horizontal bar
to the blade hanger with metal tube on the axle (and another tube over
that and glued to the hanger), but then worried about the friction
between the two parts becoming excessive. How do other people ensure
that the geometry of the VP arms remains symmetrical?

And talking about friction: I have considerations that my current setup
with carbon tubes over steel wires may have too much friction. At least
one flight in Belgrade last summer seemed to start sinking real fast
after peaking, until a minute or so later leveled out a few meters
lower. Seems to me as if at that point the VP "jumped" to a new setting.
Maybe piano wire / steel or brass tube bearings might be more sensitive,
providing more repeatable and continuous working of the hub?



-Tapio-
Received on Thu Jul 14 2011 - 00:06:27 CEST