On Friday, December 26, 2014 9:59:26 AM UTC-7, Dan Marotta wrote:
Hi Bill,



We run DA in the 8,500+ range in the summer at Moriarty; the field
elevation at Silver West (C08) is 8,290' MSL so I expect DA was
considerably much higher.* Back when the EGT and manifold pressure
gauges worked, I would lean on tow but, with a constant speed prop
it's better not to mess with it since cylinder head temperature is
too slow to respond.



Where are you flying?




On 12/25/2014 2:20 PM, Bill T wrote:



Roger on the leaning. Surprised you do not normally lean on tow. In summer temps here I start leaning at 200-500 AGL, even for a 2K tow.
I can watch the RPM come up when I lean. DA is already at 5500 or higher on the ground.





--

Dan Marotta

I once sat next to a Lycoming engineer on an airline flight. His advice for leaning an engine with CS prop at high DA was to ignore the gauges and lean slowly until you feel a light stumble then enrich just enough so that it smooths out.

Gauges, he said, can lead a pilot to do stupid things with a mixture control. He said there was no chance whatsoever of harming an engine by leaning above 5,000' DA. His main point is if an engine is running strong and smooth, it's happy and lean engines are happier than rich ones.

It worked for me over many thousands of hours. I could cover the engine analyzer and lean "by ear/feel" then look at the analyzer to find it was showing that the engine was perfectly leaned. If you really do over-lean an engine at high DA, it will just quit as you found out.

Still another tip from the Lycoming guy was to lean for taxi using the technique above so the plugs stay clean.

Finally, the Lyc guy made an interesting economic argument. (using current costs) If an O-540 averages 15 GPH and AVGAS costs an average of $5/gal then a 2000 hr TBO run will have burned $150,000 worth of gas. An O-540 overhaul is about $35,000 so it's easy to see one might burn more dollars in gas by running rich than what, if anything, could be saved at overhaul.