Last Saturday I attended the Swedish Champs in Stockholm, and for the
occasion rushed to build a new VP hub for my F1M. I wanted to try the
"Ukrainian" approach, as it has some interesting features. I uploaded a
pic of my hub in the "VP-only" folder,
http://ph.groups.yahoo.com/group/Indoor_Construction/photos/view/ffe6?b=11&m=f&o=0
The most remarkable feature of the hub is that the torque from the prop
shaft is brought to the lever that changes the pitch by bending the shaft
backwards. The bent also acts as the surface where the pitch setscrews
rest against. This has two advantages. First there is no twisting force
onto the screws, only bend, which should make glueing them easier. Also,
there is no need to glue the lever to the shaft. The cosntruction has also
a few drawbacks: due to the bent shaft it is not possible to disassemble
the hub to change the VP spring. Also it is possible that the lever moves
back nad releases the tip of the shaft. This would result in a flight with
the prop at the low pitch setting throughout the flight.
I did some testing and flying with my new hub on saturday. On a few
occasions the shaft tip indeed dropped off the lever, but I discovered
that before start and did put it back in place. Also the current position
of my setscrews is not optimal, but turning them is a bit hard as blades
tend to be in the way. Short of that, the hub seemed to work OK. I have
plenty of room fr adjusting the pre-tension of the spring, so it may not
be such a huge disadvantage that the spring cannot be changed.
The material for the hub is mostly carbon. For the centre piece if the hub
as well as the holders for setscrews I used laminate for my F1B tailplane
trailing edge, one layer of uni-directional 100g/m2 carbon on both sides
of 0.5mm balsa. The lever is two layers of 80g/m2 carbon cloth, matrial
originally laminated for F1B timer access hatch. Wire in the hub is 0.4mm,
hinges brass tube (as can be seen behind the righthand setscrews),
setsrews M2 and prop hanger paper tubes 2.5mm ID. The hub is a bit on the
heavy side, 390mg. Sufficient for F1M, but I still have a long way to go
before I can build F1D to weight, I'm afraid.
-Tapio-
Received on Mon Aug 28 2006 - 00:31:58 CEST