Lonnie Wood wrote:

Spring washers on the prop bolts of  wood props were discussed at one

time

on this
list. Has anybody tried this approach? If so, what part number and

spring

rates are you
using?
Lonnie Wood

Lonnie,
This might work.  To keep the bolt in tension to prevent fatigue you

would need

to stack up bellville washers (same direction) until you can reach full
rated torque
on the bolt without flattening the stack (they add spring rate this

way).

If there is
enough travel with a single (set) of washers this might be all you need.

If

you need
more travel to accomodate the wood expansion, you would make an

identical

stack to the previous one but revers the whole stack. This doubles the
travel with
the same spring rate. You'll need a thick HARD washer to top off the

stack.

  Imagine three (or whatever) washers cupped side down, then three

cupped side

up and then a large hard washer and then the nut.  Getting a bit
complicated, but
should work.  You also want a hard surface (hardened steel washer?) on

the prop

side.

Bill Freeman

Thanks Bill for your response. I am trying to figure out how much tension is
on a
3/8  by 24t prop bolt. I could not find any charts. In the "Firewall
Forward" book
Tony recommends 24-28 ft.lbs. but also says this may be too much depending
on the density of the wood.
Here are my calculations, correct me if I am wrong. 1" divided by 24tpi
gives a
nut travel of .0417" for one complete turn of the nut. If a 1 foot arm is on
that nut
then the end of that arm travels 75.384" (pie x 2' x 12")  to the nuts
.0417".
This gives a mechanical advantage of 1808 to 1. Assuming a torque on the
prop bolt of 25 ft.lbs. this is a bolt tension of  45200 lbs. I understand
that
only about 20% of  the torque goes into tension though from thread friction
and head friction, so that would leave 9040 lbs. That still sounds like  an
awful
lot.
I have downloaded some .pdf files from http://www.bellevillesprings.com/
but a weird thing happens when I view them. The charts go blank when I
scroll down. I am downloading the latest Acrobat reader to see if this will
fix that.
Lonnie Wood

 
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