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1. 09:05 AM - torque of Model A prop bolt (Oscar Zuniga)
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Subject: | torque of Model A prop bolt |
--> Pietenpol-List message posted by: "Oscar Zuniga" <taildrags@hotmail.com>
Howdy again, low 'n' slow fliers; I got an excellent email from Delton Perry
regarding the prop bolt issue. Here's the info he sent me, including his
qualifications. I've rearranged and edited it a bit:
======================
I am a EAA technical counselor and Power Plant rated. I am retired and
building an RV6A. I am somewhat familar with the Pietenpol and A Ford
engine.
I will try to describe the arrangement of the prop hub make up according to
the drawing that I have. The plans that I have were drawn by Orrin Hoopman
for
Bernie Pietenpol. The flanged shaft that you refer to is an input shaft from
a
Model T transmission. There is also a five inch plate made from 12 gauge
steel
that goes next to the propeller. This plate is larger than the flange so as
to
support the back of the prop.There are four 7/16" studs for attaching the
prop.
I will describe the stack of pieces starting at the crankshaft flange. The
"T"
transmission shaft goes first, the 12 gauge plate next. The four 7/16" studs
go
thru the plate, T shaft flange and screwed into the crankshaft flange. The
studs
have jam nuts that tighten this stack to the crank flange. The prop goes on
next, the crush plate next, then retaining nuts. The drawing is a little
confusing. When you look at the drawing, it appears to have a nut on the
large
shaft. A closer look at the drawing actually shows the 7/16" nuts. The
alignment
of the nuts on the drawing makes it apperar that the large shaft has a nut.
I
have seen several Pietenpols with this basic arrangement. I not seen a large
nut
on the shaft. This may or may not agree with your drawing.
Actually a nut on the end of the of the "T" shaft would serve no purpose,
according to the drawing I have. If the 7/16" studs happened to break, the
"T"
shaft, prop and all would separate together from the crankshaft flange.
As general rule, the torque on wood props will run from around 12 ft/lbs to
16 ft/lbs. Much more than this will begin crushing the wood fibers. I don't
know
that I have seen a published torque value on the four 7/16" prop nuts.
Assuming
that the studs have a National Fine thread, I would suggest no more than 16
ft/lbs.
As a side note, I have seen some that have made a shaft/flange assembly
with a five bolt pattern for cub prop. I assume that these were machine shop
made as the Continental prop hub would not be easy to modify to fit the
Model A
crankshaft flange.
The corvair engined Pietenpol does have the center shaft with a castle nut
that is cotter pinned. The crank flange on the corvair is pressed on to the
crankshaft. The procedure is to cut an internal 1" thread into the end of
crankshaft. You then make a shaft to screw into the end of the crankshaft.
This
shaft serves as safety shaft to prevent the crankshaft flange from
separating
from the crankshaft. There is another way to accomplish this, but the safety
shaft arrangement is what you usually see on the corvair engined planes.
==============================
Thanks, Delton. I'm learning something new here practically every day.
Oscar Zuniga
San Antonio, TX
mailto: taildrags@hotmail.com
website at http://www.flysquirrel.net
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