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Bob; The only way to tell if the springs are bad is to jack the bird
up
and remove the outer cylinder on which the Belleville Springs are mounted.
If
they are really bad, it will be evident without taking the springs loose
from
the cylinder.
Below is a copy of the email I sent Kathy who also asked about the
springs.
"Hello Kathy: The Belleville spring is an excellent cushioning device.
They
are supposed to be removed and examined annually. They need some
lubrication
on the shaft in order to operate efficiently. If extra space develops
between
the springs, and the shaft is not lubricated, one or more spring may "hang
up." i.e. not hang perpendicular to the shaft. Then on landing, the
landing
force is not absorbed equally around the circumference of the spring and
after several of these occurrences, the spring starts to warp and will
actually come apart.
They are constructed using four large washers which are specially
cupped and heat treated. These washers are held together by a swaged piece
of
steel tubing in the center of the washers. The five pieces together make
one
spring. There are seven springs on each landing gear and supposed to be
enough shims to keep the springs in place without any appreciable up and
down
play when the landing gear is extended. Once a spring has come apart, it
really no longer functions as designed. I think as long as they are
checked
on a regular basis, (annually) and the shaft lubricated, they should last
a
long time. I have removed Belleville Springs from an Alon which had about
2500 hr. total time, with no indication in the logs of any of them being
replaced, and found that only three of the 14 springs were useable, and
they
were no longer properly held together. The tail height was only about 69
inches and the springs were hanging up badly and causing groves to be worn
in
the MLG tube.
When I put them back together after an inspection, I grease the
tube
lightly with white lithium grease. It adds an extra hour or so to the
annual
inspection, but I think it is well worth it."
I think if you purchase the spacers from Skyport, you will find
that
they will be just about right to get the tail height of your Alon back to
75
inches. Your calculations seem about right, but I do not remember how
thick
the spacers are that Skyport sells.
Lynn Nelsen
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