Re: VP-mechanism: geometry symmetry and bearing friction

From: John Kagan <john_kagan_at_hotmail.com>
Date: Thu, 14 Jul 2011 18:13:07 -0000

Based on the photo, I'd say that your design definitely needs more space between the top and bottom bearing surfaces of the center portion - to resist twisting.

You could do something similar to the Hunt/Treger design and add a longer tube glued to the center piece.

--- In Indoor_Construction_at_yahoogroups.com, Tapio Linkosalo <tapio.linkosalo@...> wrote:
>
>
> ... 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 - 11:13:16 CEST