Re: Grain Direction in Moulded Prop Blades

From: Mark <f1diddler_at_yahoo.com>
Date: Sat, 10 May 2008 22:54:03 -0000

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

<<I am just going to mould some blades for a 12" diameter indoor prop.
I have not done much indoor for a long time. I seem to recall it was
a good thing to incline the grain to the axis of the blade but when I
start looking some plans shew the grain inclined one way and some the
other.>>

Ah, what would indoor be without contradictory data? I have tried
all the above, and they all fly. Yogi Berra, "When you come to a
fork in the road, take it."

However, you can't go wrong to copy the grain direction shown in the
plans. When a blade needs all available *strength* due to its aiming
for minimal weight, as per Hobbyshopper EZB, (p.17, INAV 107,) then
the grain is slanted "upward" toward ceiling in front-to-back
direction.

<<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.

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

You won't find many many such plans. I do recall one in an INAV for
ezb, and after checking with designer, he said the "opposite grain
direction" was a copying mistake.

<<whereas the other way will make the
blade stiffer against flaring. >>

That's the popular way, as is also grain parallel to spar in the case
of LPP or OPP.

<<With the glued blade is there a problem with the glued joints during
soaking and baking.>>

With acetate based glues, no. (Amboid, Duco, etc.)
Mark F1diddler
Received on Sat May 10 2008 - 15:54:06 CEST