follow up/Re: Grain Direction in Moulded Prop Blades

From: Mark <f1diddler_at_yahoo.com>
Date: Sat, 31 May 2008 14:04:25 -0000

John B, how did it go, if done? Need to recant something, below.

> --- In Indoor_Construction_at_yahoogroups.com, "newtongks"
> <john.barker783_at_> wrote:

<<It seems to me that one way will make the blade easier to
mould but more prone to flare ">>

If you are down to convential published blade thickness, and wood in
the 5 lb range, and you soak the wood, then "ease of moulding" should
not be much an issue.

Oops, I forgot that in the case of wide LPP blades, such as 2.5"
wide, the wood often doesn't want to twist without tearing unless you
relieve it with extra undercamber. This may (or may not) explain why
Mylar Doll article (2.6" wide) calls for 3/8" undercamber. So, if
using typical 20" pitch block, an under-pad that thick may face a
similar problem of cracking, regardless of grain direction. My
workaround is to just pin the outside edges of blade blank to the
pitch block, allowing the blade to "pop up" across its width. The
wood will sort of want to do this naturally (think oil canning) and
only 6 pins or so are needed all around, of course with little balsa
pads under the pins. (Pinning edges to touch block, not pins into
the prop wood.)

There's probably a better way; I'm not a LPP specialist. But a blade
as above gets easy 8 min flights in our 22 ft site.
Mark F1diddler
Received on Sat May 31 2008 - 07:04:29 CEST