Re: [indoor construction] VP or VD from Bill Gowen on 2006-10-22 ([Indoor

From: Bill Gowen <b.gowen_at_earthlink.net>
Date: Sat, 21 Oct 2006 23:48:43 -0400

I used VD props for a year or so before I learned to build VP hubs. The ones I made used sliding spars and were for PP and F1M. I've only heard of 2 people who were successful in using VD hubs for F1D - Jim Richmond and Richard Doig. These props were folders and use a very temperamental and delicate mechanism. Laurie Barr tried the mechanism but said he could never get his model launched without breaking the prop.

The VD props - at least the type I used - are not constant pitch. The blade angle stays constant as the blades shorten but this means that the pitch is going down as the blades shorten. For instance, my last prop was 16" diameter closed and 20" diameter open. If the pitch in the closed position was set at 26 (46 degrees at 4" radius) then the pitch when open would be 39 (46 degrees at 6" radius). The P/D open is 1.95 and the P/D closed is 1.625. I don't know enough about the geometry of the folding VD props to say how their pitch changes.

The sliding spar VD hub closes progressively as the torque drops off. I think most of the folding VD props fold all at once but I'm not sure about that. I know there has been some controversy about people making the props fold while steering the model.

For VP hubs I think almost all close progressively over a period of time. The spring rate and spring preload are used to control when this happens and over what time period.
Bill Gowen
Decatur, GA USA

  ----- Original Message -----
  From: Slobodan Midic
  To: Indoor group
  Sent: Saturday, October 21, 2006 1:12 PM
  Subject: [Indoor_Construction] [indoor construction] VP or VD

  Here are some thick questions, but perhaps ...

  1. There are two ways for reducing prop RPM
  in "low ceiling" space in the beginning of flight:
  VP and VD. From the point of prop efficiency
  what method has more advantages than others,
  and why? Under VD I means on the prop
  changing the Dia about 10%, and having the
  constant pitch absolutely (P=Const).

  2. Some people flying with VP prop says:
  Prop is now click on the minimal pitch. Is that
  change from max. to min. in one moment, or
  continually in some time interval...?

  Thanks,
  SloMi



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Received on Sat Oct 21 2006 - 20:53:18 CEST