Hi Dave;
When you had all the smoke, did you happen to notice what it did to your
mixture display from the O2 sensor? Since mine is located just downstream from
the turbo I'm thinking that the oil burning in the exhaust would make it go
full scale rich. This would be an indicator if one happened to catch it in
time. On one of my initial flights, I had an oil pressure switch blow out oil
directly onto the exhaust, downstream of the O2 sensor. I had no indications
of it at all in the cockpit. The only reason I knew about it was I had another
RV flying chase with me. He said it looked exactly like an air show smoke
system. After I was told about it, I shut down the engine, set up glide back
to the runway and slowed down to stop the prop (so there would still be oil
incase I needed to restart to make the runway). Once I had slowed down, I
could smell the smoke in the cockpit.
So an unexplained full rich mixture reading could be telling us something we
need to pay attention too.
Todd
Bartrim
-----Original
Message-----
From: Rotary
motors in aircraft [mailto:flyrotary@lancaironline.net]On Behalf Of David Leonard
Sent: Saturday, June 21, 2008 6:40
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary]
Re: Another Turbo Bites the dust
Good point about the oil feed Ed. In
fact, when my first turbo went, the folks on the ground saw all that smoke and
reported that we were on fire... we were not on fire, but there was plenty of
oil both inside the exhaust on spilling onto the outside of it.
So after that I installed an electric switch that I can use to cutoff
oil flow to the turbo from inside the cockpit. Interesting, with
this failure there was no smoke or oil leakage (yet), but I will flip the
switch for the flight home and cut off the oil supply.
Thanks for the
reminder!
--
David Leonard
Turbo Rotary RV-6 N4VY
http://N4VY.RotaryRoster.net
http://RotaryRoster.net
On Sat, Jun 21, 2008 at 4:58 PM, Ed
Anderson <eanderson@carolina.rr.com> wrote:
In my opinion, one of the things
that we tend to not pay sufficient attention to is the extent of the demand we
are putting on turbos. Without getting into the specifics of boost
ratios vs ambient pressure, suffice it to say that a turbo compressor has to
work considerably harder at altitude to maintain the same pressure ratio in
the manifold.
The ambient
air pressure is of course less at 8000 MSL therefore density less as well and
the turbo simply has to turn faster to create the same amount of boost
pressure out of the less dense air. The only way the turbo can do that
is to turn faster at altitude. So you have that hot rotary exhaust
pushing those small turbine blades, faster and faster.
As we have
discovered, the stock RX-7 turbo succumbs quickly to those stresses (simply
not designed for them). Even with the TO4 compressor mod, which clearly
helps by reducing the turbine rpm needed to produce X boost, the stock turbine
and bearing just do not appear up to the stress for long duration – although
130 hours is better than I thought the stock bearings would
do.
A precaution I would
take before flying back with the turbo that condition is to disconnect and
plug the oil line to the turbo. Should the bearing have taken a worst
beating 0r continues to deteriorate, you would not want to be dumping that
precious engine oil into the exhaust – although there should be plenty of
smoke to tell you when that condition occurred – if there is anybody around in
West Texas to let you know {:>). So I would disconnect and plug the
oil line and coolant line to the turbo – just to make certain no leaks
occurred.
Just my 0.02.
Glad, nothing more happened to the engine or you, Dave.
Ed.
Ed
Anderson
Rv-6A
N494BW Rotary Powered
Matthews,
NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html
From: Rotary motors in
aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of George Lendich
Sent: Saturday, June 21, 2008 6:24
PM
To: Rotary motors in
aircraft
Subject: [FlyRotary] Re:
Another Turbo Bites the dust
It's amazing how fast 130
hrs goes when you are having fun.:-)
I took off the exhaust
today and too a look. One of the blades on the turbine wheel is gone,
but the axle seems otherwise intact, though it may be off kilter and that is
what is causing the resistance when I try to turn it. So I am to sure if
the problem was primarily the bearing, or overheat, or overspeed.
According to my calculations, turbine speed should have been well within the
green area. (way down around 60k RPM - near the bottom of the
chart.)
One difference with this fligh... I usually run well lean
of peak, but this particular leg I was running a little late so I decided to
push it up a bit by running a best power setting. I figured I was OK
because I was high enough that I was only showing 21" MAP. But the
failure happened in descent when I kept best power as I came lower and the
engine RPM came up to about 6300 (more exhaust available).
Combination
of higher than normal EGT's and 'you number is up, turbo'???
Dave
Leonard
Dave,
I follow your
threads carefully as you have put so much into the Turbo installation, I don't
know anyone who has done more but I'm sure there are, it's just we/I am not
aware of them. From what your saying, I think your right on the money -
heat is the killer (in this case).
I personally would
like you to try something remote as per suggestions by others. I think Paul's
idea is sound, but may be still to close to the heat for my
liking.
George (down
under)
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