I just got a call from a customer - he needs a new prop! I seems that one
of his
exhaust springs broke and went through his prop splitting the
wooden blade right at the grain which developed a crack on the grain all
the way back to the propeller hub.He hadn't even flown the plane yet, he was just
doing the break in!!! The problem
was that in his zeal to get into the air he forgot to safety wire his
exhaust springs.
But even if he had safety wired them he probably would have still had a
problem - because few pilots know how to properly safety wire and
"SILICONE" the exhaust springs.
In the his photo you see that the safety wire is wrapped around the
outside and through the inside of the spring.
I suggest that it should be routed so that BOTH pieces of the safety
wire go through the middle of the spring.
Note that the spring in the photo are all stretched. Rotax has a
recommended distance that the two hooks that the springs attach to be
placed.
Also note that the springs are NOT being pulled in a
straight line, which is how they are suppose to be pulling.
Now
even safety wired these springs will still damage the propeller!! When the
spring breaks it generally does so AT the ENDS, where they
hook on to the exhaust hooks! The safety wire DOES NOT stop these pieces
from going through the prop!
To prevent any part of the exhaust spring you have to SAFETY WIRE
and SILICONE the spring from one end to the other. This
helps prevent the spring from breaking by helping to prevent harmonics,
AND keeps all of the parts imbedded in silicone if the spring does break.
Now this might not look that great it does work!!!
Another suggestion is too install some "SHRINK WRAP" around you spring,
shrink it, install the spring, safety wire it, with the safety wire
running inside the spring, and then come along and place two balls of
SILICONE on each end of the spring - with the silicone running back up
inside the spring. Now the two balls will hold the spring ends if they
break and the shrink wrap will hold the pieces of the spring together.
Now the reason that my customers spring probably broke was that he used
a set of VISE GRIPS to install the springs - which weakened it when it bit
into the metal. You can use a number
of items to properly install you
exhaust springs.
If you son or daughter are into hockey they will have a lace puller for
their skates that works great.
While visiting a snowmobile shop I noticed one of the guys using an
emergency brake handle lever. It was about a foot long, had the regular
handle on one end and he had put a hook in the other by bending it in a
vise.
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