I have noticed a strange but reproducible issue with my TIT's (see EIS issues.pdf).  In cruise and with a steady state power setting (EGT's, fuel flow, fuel pressure, man. pressure, rpm all constant), the TIT's climb over 50 degree F over a 1 hour period.  They eventually reach 1650 degrees F and the alarms start to go off.  I richen the mixture to keep the temperature below the recommend 1650.  Once the mixture is richened and the TIT's fall below 1650, the TIT's do not continue to rise for the remainder of the flight.

 

I would like to start flying LOP but the TIT rise makes the issue a little confusing.

 

Anyone want to take a shot at this mystery? 

 

Steve Richard

 

Lancair ES

TSIO550

EIS 6000 engine monitor

 

Steve,

I fly LOP and observe that the fuel flow and EGTs/TIT  gradually rise in the first hour of flight.  I attribute this phenomenon to cooling of the fuel at altitude.  The fuel is metered by volume, but burned by mass, so as the fuel cools and becomes denser, the mixture becomes slightly richer.  When I reset the mixture after the period of initial cooling, the setup remains stable.

 

It is not clear to me if the data you presented is obtained LOP or ROP.  If you are ROP, my explanation could not be correct, but I would suggest that you run LOP and see what happens.  You’ve confirmed correct magneto timing, right? 

 

To operate LOP, set your MP and RPM where you want them (32/2400? I use 30/2500 in a TNIO 550), then prelean to 200 ROP, then use the lean find mode on your monitor and lean past peak until the richest cylinder is 60-100 LOP.  See where your TITs end up.  If your TIT exceeds 1650 (which I think will be unlikely in this regime), lean further.

 

Jonathan Fuller