Cruise rpm

[RIVERFOX]

What do most of you with 80hp 912 use for a standard max cruise RPM?

[cap01]

with the pitch i have set in the prop , im a little shy at takeoff , 4900 rpm . at cruise i usually 5200-5300 burning 4.3-4.5 gph . i dont have the taper tips but will probably take the prop off this winter and get it shaved . so ill see what difference that will make ?

[DesertFox4]

5200 - 5500. 5500 when extra cooling was needed on a hot desert day.

[HighWing]

Standard max cruise on the 912 UL is 5500 rpm. I know a lot of guys that shy away from 5500 and some who will cruise higher. I flew at least above 5000 as I have heard that the gear box takes more load at lower rpms. 5500 max cruise is spelled out in the Operators Manual, but I would often be flying with friends and we would throttle back to the slowest airplane. When solo and wanting to get somewhere, 5500 was the norm.

Lowell

[cap01]

yep lowell , ive read that your not doing the engine any favors by running her slow . shes made to run all the time at 5500 .

[Av8r3400]

At my current pitch (tapered Warp 3-blade, 912UL 80 hp) I cruse at:

~5400 for 105 mph @ 3.25 GPH (Verified on my trip to S-n-F this spring)
~5200 for 100 mph
~4800 for 90-95 mph
~4500 for 80-85 mph

[sdemeyer]

I'm close to Ava8tor3400.

5200 = 105 MPH (ias) 3.5 GPH @1500ft
5000 = 102 MPH (ias) 3.2 GPH @1500ft

I generally cruise around 5000 rpm. I have a Warp standard three blade and 80HP 912ul.


Scott

[Newkid]

I think you can cruise at whatever RPM your heart desires just so long as it's above 5000 RPM. We used to have a little IV Speedster with a 912 UL and a Powerfin 3 blade, and we used to cruise at 5700 to 5800 RPM all day long. Full bore strait and level was about 6100 RPM. We have a friend that did the same thing in his Rans S-7 except he had a UL with high compression pistons. His motor now has 1600 hrs. on it and is still running strong. Both planes burned right around 4 gph.

[RIVERFOX]

Hey guys thanks for all the input. This time of year I do a lot of air to air photography of "birds of prey" along the St. Croix River and I spend much time at 4000 rpm and 40 IAS. One service center said stay above 4900 rpm and the other said 4000-4200 rpm was fine and no problem at all. Don't know who to believe. All my temps for coolant, EGT and oil are fine. I see no reason why those rpm's would be harmful. Can anyone give me a good reason why those slower rpm's would be detrimental?

[DesertFox4]

riverfox, years ago I was told to stay out of the 4300 to 4800 rpm range for continuous operation in the 912 series engines. You are below that rpm so from what I've understood you should be ok. You should be getting some incredibly low gals. per hour readings at 4000 rpms.