If you are trying to form a prop blade from a flat piece of wood, you will always end up with the spar line bending or with far too much camber. I now make blades from narrow strips of balsa which are preformed to the block. To butt the strips together always requires wood to be taken out of the centre.
As has been pointed out, a blade has negative curvature, opposite to that of a sphere. To wrap a flat sheet round a sphere requires material to be removed from the edges, oposite to the reqirement for a blade.
The only way I know of alleviating this problem with a single piece of wood is to use, as Bernie Hunt recommended a long time ago, wood that is slightly off C grain. It can squash slightly to relieve the internal stresses built in when moulding.
Bob
----- Original Message -----
From: Timothy Chang
To: Indoor_Construction_at_yahoogroups.com
Sent: Saturday, July 01, 2006 2:02 AM
Subject: Re: [Indoor_Construction] Re: Prop Bending
Im not sure if this is what ur talking about but are you saying that your spars dont lay flat against the blades? If so, it means that the sparline on the block isn't level, you outta check to see if its flat with a ruler or straighedge.
Tim
Steve Brown <rtxc_at_yahoo.com> wrote:
If there is no glue involved then the only answer is the wood
itself. If the spars are warped or take a set when bent and won't
spring back then you'll need to make new spars from a different
piece of wood.
--- In Indoor_Construction_at_yahoogroups.com, "Nicholas"
<ndhuang83706_at_...> wrote:
>
> I'm sure it's not the glue- These blades have just come off the
block.
> I haven't attached them to the spars yet.
> Nicholas
> --- In Indoor_Construction_at_yahoogroups.com, "Steve Brown" <rtxc@>
> wrote:
> >
> >
> >
> >
> > --- In Indoor_Construction_at_yahoogroups.com, "Nicholas"
> > <ndhuang83706_at_> wrote:
> > >
> > > Hi All,
> > > I recently made a couple of props for my LPP, but when they
finished
> > > drying they were warped...
> >
> > Are you sure this isn't caused by glue shrinkage along the joint
where
> > the blade and spar meet? If you use much glue in this area you
will
> > get distortion of the spar and also may get excessive (and
increasing)
> > camber pulled into the "airfoil" of the blade.
> >
> > Try gluing the blades on with diluted white or aliphatic glue.
> >
>
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Received on Tue Jul 04 2006 - 03:25:56 CEST
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