CS Prop/Oil Temperature

Rotax wants the oil temp at 100c every flight.

If your prop is an Airmaster you can adjust the fine pitch to raise the rpm. You should be at 5200 minimum for takeoff. 
Ed

Ed Midgley wrote:

Rotax wants the oil temp at 100c every flight.

If your prop is an Airmaster you can adjust the fine pitch to raise the rpm. You should be at 5200 minimum for takeoff. 
Ed

Hi Ed - the 100C is a peak temperature recommendation - not a constant. I look for/expect this temperature during climb out. I aim for a sub 100C temperature during cruise, with my preference being in the low 90c range.

Yes my prop is an Airmaster and yes I know that the pitch stops can be adjusted - early days in test flight schedule so adjustments yet to be done.

The above does not address my question, which is about the effect of pitch on engine load and oil temperature.

Its been a long time since I did my constant speed prop training - memory deficit, combined with the differences in an electric/Auto CS operation, has resulted in my uncertainty with the relationships of Cruise WOT:optimum RPM, not just best speed but also econamy (L/hr) and engine longevity(oil temp).

Over pitched prop can and will cause higher oil temps and more stress on the engine. With the older 1500 hr. engines too much over pitch (i.e. 5200 and below at WOT) could and did cause some crankcases to crack on top.

Having the engine get to 5800 is not over stressing the engine. There are safety margins built in for longevity and reliability. If you have just a ground adjustable prop 5600-5650 is a well balanced WOT setting at your average altitude. If you have a heavy plane, amphibian or need a short take off for some reason then that higher rpm up to 5800 is fine to get you better climb, but you'll lose some cruise speed. Over pitching under 5500 WOT has no redeeming qualities and causes loss in climb, loss of fuel economy, loss of speed, higher oil temps and stress on the engine.

Sorry I didn’t address the relationship between full throttle at 4800 vs higher rpm. It appears from your test that there is a relationship. 
In hot weather my oil will reach 115c on climb and cruise at 102c to 105c. I run Mobil 1 4T oil but Sport 4 should be safe at those temps also. I’m based in the Chicago area and if I install a larger oil cooler it will aggravate my winter temps even with an oil thermostat as they have a 10% bypass to prevent the oil from coagulation in the cooler. My engine is an Edge Performance 912 STI which has over 150HP. More HP more heat.
I have my Airmaster prop set for 5700 takeoff, 5450 climb and 5200 cruise. If I want to go fast I cruise at 5450. If I’m just practicing locally I use 5200. The rpm settings can be changed with a lap top computer.

Ed

Hi Roger,

This is a 2019 engine, started for the first time about 6 month ago.

Prop is a CS, as supplied from Airmaster, yet to have the pitch stops fine tuned (adjusted for my aircraft / flight regime).

Auto / TO gets 5700 rpm as per Airmaster commendation (100 rpm below Rotax recommendations)

Auto / Climb goes to 5400 rpm (as above)

Auto / Cruise,- this is where the questions lies, is 4800-5000 rpm

My little experiment - going to Manual and "fining" pitch to 5200 rpm/27Hg seemed to result in a reduced oil temperature - a plus in my book.

My questions are in part about my observation & the logic (if any) behind it (reduced load/oil temp???) AND would the "brains trust/Forum" think that a further increase in WOT RPM (to 5500 rpm) by further "fining" the prop pitch be a good/bad idea????