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Message
I finally got time
to get my failed 13b apart. The rear rotor was missing one apex seal, the other
2 were intact but jammed due to the fragments of the broken one. The rotor
housing has the classic chatter marks all around. Doing a Google of "13B apex
seal chatter" results in plenty of examples of this failure mode. Apparently the
chatter is from the natural resonant frequency of the seal, it eventually
fatigues the seal causing failure.
The front rotor was
in good shape, but the housing had the same chatter marks, but not as severe as
the rear rotor. The front rotor housing was brand new 150 hours ago when I
rebuilt this motor after the Grand Canyon forced landing. At that time the good
rotor housing had slight chatter marks but I reused it. The front rotor was
destroyed at that time due to foreign object entering the
rotor.
Both rotors were
missing the corner seal rubber plugs on the side with the short apex seal
segment. Perhaps the small segment vibrated more, disintegrating the rubber
seals?
The first 260 hours
of flying my rotary bird was with stock 3-piece seals, and I never saw any
chatter marks. The last 250 hours has been flown with 2 piece seals and now I
have chatter marks .
I now have Tracy's 2
piece apex seals and I wonder how they will perform, it appears that the heavier
weight of the 2 piece seals puts the resonant frequency in the cruising range of
6000RPM?
Chuck
Dunlap
RV6
13B
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