<If you are on the lean side of peak and you descend with out changing
the knob (forgot) the  engine gets leaner right away.  Up to peak EGT very
quickly.

You are confusing me here, Paul.  If you are lean of peak, and you get
leaner (by descending,) you move MORE leaner of peak, thus EGT should go
down.  And your next wake-up call is when the engine sputters!

Please don't ask me how I know about the very effective wake-up call.

Bob Darrah

You are absolutely right Bob. See how easy it is to get confused
over the mixture :-)>

Here is what I think happens. Correct me if I am wrong.
There could be other mistake scenarios.

Mistake conditions:

A. WOT, over 8000, feet power less than 75%. Engine leaned. 
Climb.. mixture goes leaner engine stutters. Descend... more air, mixture 
goes leaner engine stutters. Cowl flaps closed.

B. Less than 8000 feet. Throttle partially closed. Power less than 75% 
(No engine manufactures allows the mixture to be leaned at more than 75% power.
for Continental engines the number is 65% power.)  
Engine leaned. If you forget the mixture and open the throttle (more air) to climb
mixture goes leaner. Engine stutters. Adjust the mixture to less than full rich.
Valves overheat as more power and EGT is being generated. Cowl flaps closed. 

Descend, more air, throttle in same position, engine goes
lean, engine stutters. Adjust the mixture to less than full rich. Valves
over heat as too much power is being generated. Cowl flaps closed.

Descend, throttle closed, less air... engine goes
lean, engine stutters. Adjust the mixture to less than full rich.

There could be some combination of throttle, cowl flaps and mixture 
setting between these last two that is bad for the valves obviously.

C. Climbing through 8000 feet. Mixture knob set to full rich. Full throttle 
mixture gets richer and richer. Power goes down. Less air.  Plugs eventually foul
and engine stutters. Cowl flaps open.
 
I always have to think carefully about all this. It is easy to forget
something.  Flying in the congested So Cal basin is a full time job just 
looking out the window for other traffic. 

Here is another interesting chart from the Sky Ranch Engineering manual.
It would be so great if we had EFI on aircraft engines that kept track
of all this. I am sure they would charge $10,000 for a certified version. 
Perhaps a warning horn on the scanner when the EGT or CHT got too high.
Automatic thermal control on the cowl flaps would also help.

Is it bad pilot technique or is it bad human factors cockpit
design? Perhaps exhaust valves are just prone to failure no matter what.

Forget it. Just get a rotary :-)

Paul Lamar
 
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