On Sat, 22 Nov 2008 00:22:49 -0800 (PST), "
wrote:

To All:


selecting goood propeller wood...

almost any wood has the tensile strength to keep a prop's blades on.

wooden props are bolted to the front of the aircraft with , typically,
6 bolts. those bolts hold the prop on to the prop driver by
compression and it is the friction generated between the prop and
driver that makes it do its stuff.

what I have found is that the arbitrating factor in whether a wood is
suitable as a prop wood is the compression strength of the hub.

on my O-200 powered Tailwind the wood prop is held on by a crush plate
and bolts torqued up to 120 inch pounds. the wood needs to be able to
withstand that compression without deforming or crushing.

also wood, no matter how well finsihed, will absorb some moisture in
wet weather and swell slightly, and conversely in dry weather it will
lose some moisture and shrink slightly.

the way to maintain the compression without having to continually
retorque the bolts is to use a sufficient stack of the conical
tempered spring washers called Belleville Washers. these have a known
compressive force and you stack them together to get the compression
needed. my prop uses 8 washers each bolt with 4 washers facing cone
up and 4 washers facing cone down toward each other to generate the
compression needed.
with these I need retorque my bolts only annually.

ol' snake unda the verandah.

(the belleville's are stacked like this...
^
^
^
^
V
V
V
V
with a bolt through the middle)