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Message
Hi Chuck,
Sorry to hear about your engine troubles, but glad the
landing came out a bit better this time. It sounds like to me you lost an
apex seal. When I lost mine last April on way to Sun & Fun, I lost
power on one rotor, there was some vibration - but not bad, the EGT on the bad
rotor dropped to 1200F or below. Also, I could maintain 4800 rpm (enough
to keep me level at 6000 msl), but I had to turn up the fuel flow to 14 GPH to
keep that rpm. Normally, that would give me around 160HP, so figured I was
getting around 70-80 HP. I have found that 67HP will keep me airborne at
120 MPH IAS.
Be certain and check the wear of your apex seal
slots. If they get too worn the apex seal lacks support from the side
walls of the slot, will lay over and drag against the rotor housing until the
pressure simply becomes too much and they break.
When I tore my engine down I found what I believe was the
cause.
1. One apex seal had broken with the center section
of the seal leaving its slot and the two ends remaining.
2. That broken piece flew back and caught the second
apex seal down in its slot and smeared the soft iron over the lip of the
slot. That prevented the second apex seal from coming up - so had no
compression on that rotor.
3. I found that the apex seals on my used
rotor had wallowed out due to wear and the walls of the apex slot instead
of being vertical were sloped in a "V". In other words, the rectangular
shape of the slot had turned into a "V" with the tops wider than the bottom of
the slot.
4. The slots were worn out of tolerance which means
the apex seal had less and less support from the slot side walls and finally it
became too much and the seal broke. I was using Dave Atkins seals (same as
Hurley's) and when they were tested on a Rockwell tester the ones I had turned
out to be a bit softer than a comparison set they were measured against.
But, I think the main cause was the worn apex slots.
5. So I am convinced the use of worn rotors with
worn-out slots combined with softer seals was the end cause of the
problem. I was just not aware that there were limits on the slots (never
really even thought about it). But, after the incident, I did find in the
Mazda overhaul books a WARNING about using rotors with the "V"ing beyond a
certain limit - mine were.
6. I then purchased brand-new rotors and am using
Tracy Crooks new seals and thus far have had no problem.
I also had some of my flying friends try to talk me into
putting in a Lycoming, but I asked them how many lycomings had they seen fly
back with two cylinders out of operation. No, while I was certainly not
happy about it, the performance on one rotor convinced me that the rotary is the
way to go.
By the way, there was no damage to the rotor housings or
side housings in my case. The one rotor did have a corner cracked where
the broken part of the seal smeared over the following apex seal area.
Otherwise, I could have reused the rotor (NOT!) assuming it had not been worn
beyond the spec limit
.
Hopefully, you won't have that problem.
Good luck in your rebuild - its a pain doing it in a rotor
no-man's land. Been there, done that.
Ed
----- Original Message -----
Sent: Sunday, February 12, 2006 12:26
AM
Subject: [FlyRotary] Another rotary
failure
Sorry I didn't
make to Bill Eslick's for the Rotorfest, I missed by about one hour. About 30
miles north of San Angelo TX the RPM suddenly dropped and I could not restore
it with any of my emergency procedures. GPS told me nearest airport was Robert
Lee about 15 miles away. I headed there and landed without
incident.
Turning the prop
by hand shows almost zero compression in one rotor, indicating bad/broken apex
seals, quite similar to my engine-out experience 2 1/2 years ago which caused
a forced landing near the Grand Canyon. This time the vibration was not quite
as bad, and the RPM dropped to around 4300 which was still not enough to
maintain altitude. I called my friend with a Glasair and he cam got me
and took me home. I will have to find some time to build another motor and
drive 12 hours back there and swap motors. Or I might drive there, remove the
wings and trailer it back, have not decided yet.
My good
friend/mentor/flight instructor is trying to talk me into going back to a
Lycosaurus, and I have to think of some good reasons not to. Until I get the
motor back and torn apart, I wont know what caused the failure, but I
will post anything that I find.
Regards
Chuck
Dunlap
RV-6 13B 535
hours
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