Neal:

***We set MAP and RPM per the charts to achieve the desired percent power. Then lean to achieve the recommended EGT (typically 75 deg F ROP or 50 deg F LOP). ***

Unfortunately, I see that you not one of the TCM reps who will be attending the APS class this weekend.  I had hoped to meet you.

If one sets the MAP and RPM per the charts for desired power, that will be the power produced ONLY when leaned to 75dF ROP--or essentially any useful ROP power setting.  That will NOT be the resulting power if one leans to a LOP setting (as you say is recommended at 50dF LOP).  MAP and RPM play no role in LOP power settings as power in a TCM TSIO engine is a function of fuel flow only--specifically 13.75 x FF = HP.

In addition, 50dF LOP is not the optimal mixture setting except at one power setting.  One flying a TSIO (at conventional high power settings might better choose 80dF LOP.  In these cases, one knows that setting to a specific FF does, in fact, get the desired mixture LOP.  For example, many choose to set MAP and RPM and simply pull to a conventionally known FF of, say 16.5 gph, where the known HP is 227 and that they are far enough LOP by reference to the appropriate CHTs having these as known, repeatable values.  If one does not have these known values (say, flying an airplane for the first time), then leaning by EGT will get one the FF values that can be used hence.  While using EGT and the slow leaning process does get you where you want to be, it is a sub-optimal practice since simply pulling quickly to a known FF by-passes the unhappy experience of spending a lot of time in the Red Box whilst ones heats up CHTs unnecessarily.

I hope to see you at an APS class soon.

Walter Atkinson
<walter@advancedpilot.com>
(225) 939-7508





On Oct 14, 2013, at 12:18 PM, Neal George wrote:

We set MAP and RPM per the charts to achieve the desired percent power. Then lean to achieve the recommended EGT (typically 75 deg F ROP or 50 deg F LOP).