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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