CS Prop/Oil Temperature

Ed Midgley wrote:

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 Ed,

Yes I am asking if there is a relationship (ie is my short observation valid?) as I expect between rpm/MAP - load - engine temperatures.

Your temperatures are very similar to mine (test flying new Sonex).

Fortunately, I don't have to contend with very cold winters - so no oil/coolant thermostat.

Your preset RPM's are, with the exception of Auto/Cruise, the same as mine.

Prop RPM changes - I have, the yet to be adjusted, fine/course pitch stops. I can go to Manual for in flight adjustments. I am peripherally aware that other adjustments exist (lap top?) but have no in depth knowledge at this time.

The Manual override gives me real world experience of changes to the WOT/RPM/MAP, engine behaviour. From this experience I intend to adjust my pitch stops accordingly - I hope the Forum can give me some insight into what I might/should expect.

I trial would be worth the test to see about your oil temp and cruise speed vs rpm's.

Try the increase in WOT rpm and see, but I think it would be better set to get 5500 rpm at WOT in cruise at your average altitude knowing that many times you may only cruise around 5200-5400 rpm while throttled back a tad. It's not just about rpm, but how hard the engine has to work to get to that rpm depending on the prop pitch. I'm a big believer in not over stressing the engine. I have friends with 3K - 4K hours on their engines and still going strong and I believe over pitched stress on the engine might not have allowed this??? I always worry about longevity and reliability. I really like the reliability part because I don't want to land in a mountain canyon or the middle of the desert. :) 

Forgive me if I have misunderstood you, I don't claim to be an expert but I do have a 912ULS with an Airmaster CS prop.

I think you are in danger of confusing between the microswitch pitch stops ands the electronic adjustment (for which you need a cable and a bit of software.)

The microswitch pitch stops are safe operation limit devices and should be set exactly as per the manual instructions, which can involve quite a bit of experimentation. They are not there to change normal operation conditions under constant speed control.

In electronic adjustment to the 3 presets, you can re-program as you wish. If you want to raise your cruise setting to 5200rpm, no problem. It just means that if one day you want a gentle bimble at low throttle instead of thrashing along, you'll be running with a very low pitch to keep the rpm up unless you go into manual control.

I've left the settings alone. According to the revised Rotax MAP curve, with the right octane fuel you can use WOT at 5000, but I wouldn't. If I'm in "cruise" rpm but find I want more than 26-27" MAP (unlikely in level flight), I switch to the 5400rpm "climb" setting. It's smoother.

The 3 presets are labelled T/O, climb and cruise but they might just as well be called R1, R2 and R3. They are just numbers, the default settings ex factory being 5700, 5400 and 5000, it's entirely up to you how you use them. They don't respond to MAP, they just try to hold constant rpm whatever you do with the throttle lever. If you prefer different numbers, change them - but with the software, not the pitch stops.

PS Are you sure of your tacho accuracy? My rpm in cruise setting tends to vary a little bit with 5000 as the minimum rather than between 4800 and 5000 as you suggest. The prop documentation will confirm what the controller was set to at the factory.

I have been using airmaster cs prop on my 912ULS for five years. I have my cruise set to 5200 rpm and use MAP of 26’ or 27’. This gives me a fuel flow of 20-22 lph and good temperatures. Also does not stress engine according to rotax chart. I would hot run engine below 5000RPM unless using reduced boost. Use the software to set your RPMs meanwhile use the “hold” selection on controller to set your preferred RPM. The manual override bypasses the CS function. The HOLD allows any setting of RPM and will hold that RPM with pitch change.

Hi Mike - Guess what? I have been fixated on getting the Cruise setting to numbers I am comfortable with. I never considered using Auto/Climb in straight & level (there is one born every day!) 

Tacho accuracy? - Yes this was an early, in the test program, check and adjustment. Checked with laser/optical tacho.

I am still getting used to the Sonex, so my straight & level is a tad erratic, hence the prop Auto/Cruise 4800-5000rpm cruise range. Even so when I went into Manual I easily changed to & maintained 5200 rpm at the Rotax recommended 27HG MAP.

I think a deal more in-flight experience is required before further adjustment.

What do you think about my oil temperature observation - true/imagination?