The combination of increased power with richer mixture and higher EGT
while descending is the valve killer while operating lean of peak.

OK we can now get off this subject as rotaries do not suffer from this
particular air cooled aircraft engine sickness.

Paul Lamar

Your example for "descent with mixture forgotten" is plausible, but in
the big scheme of things is not in the realm of reality of a prudent
pilot. The same pilot who "forgets" to adjust the mixture also forgets
the checklist... and one of these days may "forget" to put the gear
down. I guess a certain part of engineering is aimed at "idiot proofing"
the equation/equipment..

I suspect that if you are GOING to run LOP on an air cooled engine, you
need to have a well tuned and well instrumented engine, such as GAMI
Injectors and something analagous to a JPI engine monitor that gives
continuous multichannel monitoring of CHT's, EGT's and other selected
values. You set the values in your alarm parameters so that if you pull
a "forget to adjust the mixture" as the temps approach an undesireable
limit, the monitoring device makes a lot of noise and calls attention to
the oversight. This is the reality of the situation. If you try to do
LOP without the proper instrumentation, you WILL do more harm than good,
and while one cylinder might be LOP, the other might be in the danger
zone concurrently. Without the proper gauges to monitor, and without the
proper tuning to equal out the cylinders, attempting LOP is a crapshoot.

I actually think that some of the issues regarding this are pertinent to
rotaries - obviously not the valve issues, but the concepts of ROP, LOP,
Best power settings. The graph displays them nicely.

Do you have any numbers regarding expected Peak EGT's on the 13B 2nd
gen, or what the limiting temps are with regards to turbine inlet temps
for using a modified stock 13B turbo II's turbocharger? I intend to use
the same modification that John Slade did from the rebuilder down in
Oz... I cant find the immediate link at the moment. will follow.

Dave

Thanks for your input on this.
Dave..

What one needs for an air-cooled aircraft engine is a computer controlling the 
mixture based on the EGT. Heck I don't think there is a pilot out there that 
never makes at least one tiny mistake on every flight.

The older 13Bs are up to 1800 F. The RX8 a couple of hundred F cooler.
Most TIT are 1800 F or less. Depending on what the wheel is made from.
Not only does the temp kill the wheels a more important problem
is excessive RPM. In this respect they are a lot like exhaust valves.

Exhaust valve life is a combination of spring load and temp. Slamming an 
exhaust valve open and closed 1300 times a minute at 1500 F is a recipe for 
disaster. It always amazes me they last as long as they do.


Paul Lamar


 
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