Engine questions, extended slow flight, M5-180-C

[merrymunks]

Is there any potential problem with flying at speeds of 90mph for a trip lasting 2 hours each way? The engine is a Lycoming O-360-C1F. Looking through the engine operator's manual, I can see values for Economy Cruise at 65%, but that's still around 110mph in this plane. Yesterday I tested running at 50% for a short period, with the engine monitor looking like this:


https://merrymunks.com/20190720_154627/

(Side note, the CHT on #4 shows lower due to sensor placement; manual temp measurement shows that cylinder has a similar heat profile to the others.)

50% resulted in a 105mph airspeed. Are there any potential hazards to reducing further to get 90mph? I can get to 90 in the pattern with full prop and manifold back to about 10-12, but have never tested running that way over an extended period of time.

[montana maule]

It's been my experience with the small Lycoming engines to get them to stated TBO they need to be run at 65 -70% power. You can run them at lower power settings but you won't get the life out of them. Lycoming says oil temps need to be at 180F for over an hour at a time to get the best life from the engine.

Also from what I have noticed if I lean to peak EGT I get the same MPG if I run at 65% or at 50% power. I just get get there quicker at 65%.

[Mog]

My assumption is you are trying to cruise with a cub or some other small light bird, not reduce fuel consumption?

[merrymunks]

My assumption is you are trying to cruise with a cub or some other small light bird, not reduce fuel consumption?

Yep, exactly.

[Mog]

I run a franklin which really likes high RPM. With a virtually stock M4 I found it very frustrating to operate in the 80-90mph cruise range. I would run this for up to an hour or more and i was constantly dropping in flaps for drag or making s-turns to keep in pace. Now, with big tires and a few other really draggy items I can certainly get down in speed a bit easier. But I don’t like pacing sub 90mph planes for very long.

[merrymunks]

It's been my experience with the small Lycoming engines to get them to stated TBO they need to be run at 65 -70% power. You can run them at lower power settings but you won't get the life out of them. Lycoming says oil temps need to be at 180F for over an hour at a time to get the best life from the engine.

Also from what I have noticed if I lean to peak EGT I get the same MPG if I run at 65% or at 50% power. I just get get there quicker at 65%.

Thanks Montana, really good information about power & engine temps. Didn't know about running over an hour @ at 180* with regards to TBO. I think I might be practicing landings too much, need to do more x-country...

[montana maule]

I use my MX7-160 for training. I finally installed a shutter in front of the oil cooler that the RV pilots use to control oil temperature. After the temperature goes below freezing I have to get more creative than that.

[VA Maule]

Duct tape works well to restrict air flow through the baffling to the oil cooler I've found about 2/3 coverage works well for my o360. Just don't forget about it on a warm day or you'll be looking for somewhere to land about 10 minutes into the flight