Making wood propeller?

On Sat, 30 Jan 2010 18:15:02 -0500, wrote:

On Sat, 30 Jan 2010 17:58:32 -0500, Ernest Christley
wrote:

Stealth Pilot wrote:

the crush strength of the wood in the hub area is likely to be the
critical factor in selecting the wood species used for a propeller.


There's not a rule stating that you can't combine species. A lamination
of a harder wood on the front and back of the prop would improve the
props chances of survival.
But the expansion rates may be different enough to cause other
problems - and the CENTER would still compress.

thank you clare. the problem *is* that the softer laminations
compress.

On Sat, 30 Jan 2010 09:05:37 -0500, "Morgans"
wrote:


"Stealth Pilot" wrote



Maple is widely available as flooring. It might be the best choice for a
prop.

I have often wished I had it available.


I would add a point that nobody has yet added. It is that the orientation
of the grain to the face of the wood in your blanks is very important. The
plain sawed boards more often available will make the weakest blanks,
because of the way the wood changes with changes of moisture content. The
grain needs to be as close to 90 degrees to the face of wood as you can get
it. Also, alternate layers so the wood grain lines are opposite in each
layer as you go. Something like this:

////////////////////////
\\\\\\\\\\\\\\\\\\\\\\\\
///////////////////////
\\\\\\\\\\\\\\\\\\\\\\\
///////////////////////

agreed.

there was on my airfield a long time ago a 5/8th scale sidlinger
hurricane.
this eventually ended up in a museum after a very checkered safety
history.
at one stage of its life it had a prop made of the most amazing wood.
in parts the wood was a tightly curled grain that would probably be
described as cranky grain. there is no way in hell that a sane person
would have selected such twisted short grained wood in a prop.
the prop was used for about a year through the test flying when a
retract collapsed on landing. the aircraft described a semi circular
skid off the runway, through the dirt, over the taxiway, through even
more dirt and came to rest beside the airfield fence.
the prop had tried to do some considerable rotary hoeing during the
excursion and was smashed into many parts.
of course muggins here was fascinated by the cranky grain and made a
point of finding all the bits to confirm that it had let go where it
appeared to be the most deficient.

I was amazed. not one piece of deficient cranky grain had let go in
the entire prop. all the breaks were through areas of sound wood.
I'm never sure of these certainties any more.

btw I once encountered an ultralight at kalgoorlie that had been flown
across the nullabor in the middle of summer. according to the cockpit
placards the cruise speed was 68knots. it had a reduction belt drive
from a moto guzzi V twin.
the hand carved prop had a bloody big knot in it! it seemed to be
carved from radiata pine and was surviving the flying without a
blemish.
again certainties seem less certain with age!

Stealth (better to just get on with it)Pilot

On Jan 30, 2:49*am, Stealth Pilot wrote:

the crush strength of the wood in the hub area is likely to be the
critical factor in selecting the wood species used for a propeller.

The state of the art in prop bolts for wood propellers:
http://www.cozybuilders.org/Oshkosh_...lle_Washer.pdf

The better the prop is sealed, the less the variance in humidity will
be, so it's important to seal and finish a wood prop.

On Sun, 31 Jan 2010 19:07:19 -0800 (PST), flybynightkarmarepair
wrote:

On Jan 30, 2:49*am, Stealth Pilot wrote:

the crush strength of the wood in the hub area is likely to be the
critical factor in selecting the wood species used for a propeller.

The state of the art in prop bolts for wood propellers:
http://www.cozybuilders.org/Oshkosh_...lle_Washer.pdf

The better the prop is sealed, the less the variance in humidity will
be, so it's important to seal and finish a wood prop.

my tailwind has used belleville washers on the prop since it was
built.
first flight was october 1985.

without doubt you have the wierdest belleville washer setup on the
prop in the pdf's I have ever seen.
the old bellevilles on my prop are not much bigger than a standard
aircraft washer. the prop uses a steel crush plate. the bellevilles
are it under the bolt head. there are no other washers used.

....which reminds me that I need to replace them and I have no idea
what size was used. they work wonderfully! I use 120 inch pounds of
torque on each bolt.

Stealth Pilot