Go with the 1/2 inch US bolt. Much cheaper. Probably work with the two rotor as well.
As a quick check the bending stiffness is proportional to the
radius to the fourth power while the mass is proportional to the radius
squared so the resonant bending frequency of the 1/2 bolt will be much higher.
It will therefore be less likely to fatigue the 1/2 inch tension bolt.
Paul Lamar
I was thinking we could use long partially threaded 7/16 bolts cut down to the right length but then we would need someone to roll the 10mm threads for us. Might be easier than rethreading the front housing.
Fred O.
So tension bolts are 10 mm and not 12 mm? That would make it easier.
Paul Lamar
This may not apply to anyone but me, but the tension bolts on my 12A are
144mm long, the shoulder is 10mm, and the threads major diameter is
9.80mm, thus thread size is 10mm. We recently bought some bolts to bolt
a plate to the front housing so we could saw it. They are m10 x 1.25 x
25mm long.
The center housing is 50.55mm thick, and the 12A rotor housing is 70mm
thick. So a single rotor bolt length would be reduced by 120.55mm.
Making the bolt length 123.45mm. Or about 4 15/16. Not sure how much
thread is left at the bottom of the hole when the bolts are torqued.
Royce
That is it then. I made a mistake. The bolts are 10 mm. 1/2 inch
bolts will work fine and best of all solve the bolt breaking
problem in the 2 rotor 13B as they have a much higher frequency
than 10 mm bolts. This could be the answer to high cost Mazda OEM
tension bolts as well.
10 mm is only .3937 inches. Even a 7/16th should work and be an
improvement.
I used to think that stiff steel tension bolts were the problem with the
rotor housing shrinkage after the engine was overheated. Now,
with Perry's overheating his engine many times and not shrinking
the housing I am having second thoughts. I now think it has to do
with Mazda moving the O-rings slots from the rotor housings to the
end housings about 1986. When the slots were in the rotor housing there was
not much aluminum between the slot and the combustion chamber.
Consequently it was not hard to overheat this part of the rotor
housing and cause it to yield in compression due to excess thermal expansion
against the not-so-expanding steel bolts. I now think this problem
is gone forever and we can use stiffer and larger diameter steel bolts.
When I checked with ARP a year or more ago I specified the necked
down, less stiff, bolts of the earlier engines with this in mind. Perhaps
another check with ARP for simpler larger diameter bolts is called
for. On the other hand we don't need trick high strength bolts.
Any grade 8 - 7/16th or 1/2 inch bolt will be plenty strong enough.
All we need now do is find a supplier for the right length.
Paul Lamar
Just found my metric and english vernier calibers buried under a bunch
of papers on my desk. The holes in the rotor housings for the 10 mm bolts
is a good .5 inch. 10 mm is .3937 That gives at least .050 around the
bolt allowing it to vibrate in a bending mode. Not only would a larger
bolt have higher resonant frequency and be cheaper it would not have
as much room to vibrate. For this you would have to drill out and
re-tap the front end housing.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. Copyright 1998-2002 All world wide rights reserved.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org