very low continuous power operation lycoming

was not sure if this thread belongs to the engine forum section. If so... i kindly ask the moderator to move it.

recently we had a discussion in our flying club to define the flight operational rules for our club members in austria/switzerland/germany. one question was how to save gas without cutting flying hours. fuel prices in europe are higher (especially for avgas twice or even more) than in northern america. i think it's a good idea to evaluate any possible measure to keep flying on an affordable level. several involved in the discussion stated that it wouldn't be a good idea to run an lycoming 320/360 on 40/45% or so power for a long period of time, because the engine will suffer but no solid explanations why.
there are a lot of myths in general aviation, but most times there's also a grain of truth.

I'm not talking about power setting for best range, rather max endurance? so if you just want to enjoy the scenery and you don't care how fast your ship is moving: does a very low power setting hurt the engine? my understanding is that you can run the engine low as you want as long CHT's and vibration is ok.

What ya think?

best regards from lake constance
Kay
PS: replies like "did not build RV to go slow" aren't very helpful.

Low power

We used our Super Cubs with very low power settings for over 4000 hours between overhauls in predator control.

Training

I wouldn't think low power settings would be an issue (leaned properly, etc, etc). Lots of training situations (IFR training in particular) where you cruise around at low power settings. Lots of training aircraft with Lycomings that go to TBO. I have just about finished my IFR ticket in my -7 (same engine as yours) - and have spent many hours at 17 inches MP and 2350 RPM in practice approaches. No ill effects as far as I can tell.

Dan Langhout said:

I wouldn't think low power settings would be an issue (leaned properly, etc, etc). Lots of training situations (IFR training in particular) where you cruise around at low power settings. Lots of training aircraft with Lycomings that go to TBO. I have just about finished my IFR ticket in my -7 (same engine as yours) - and have spent many hours at 17 inches MP and 2350 RPM in practice approaches. No ill effects as far as I can tell.

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Hey Dan: nice to see your picture...

Engine:
why should it hurt the engine in some way or another? Assuming it was properly broken-in, the mixture properly set and the speed is not behind the power curve, all should be fine. The benefits should be economy and longevity thanks to lower revs and temps

Own experience (engine data contained in signature):
Flew close to 400hrs in 2019, 95% of those using the sedate settings of 19" at 2000RPM, equals 43% power. This gave an average consumption of slightly less than 21lt/hr (5.55 USG), all flight phases factored, at close to Carson's speed of 130kts TAS. Economy is one thing, another big benefit is the low noise level.
As for the engine, no ill effects up to now, borescope inspection at 100h intervals show no change. 3/4 of my flying is done on MOGAS, using the AVGAS tank for T/O, initial climb, approach and eventual G/A only.
Would avoid flying lower than say 95-100kts IAS as cooling might suffer, CHT to be watched.

To quote William Wynne https://flycorvair.net/2019/05/17/2000-mile-zenith-601-xl-adventure/:
If someone’s sole focus of building is to have a faster airplane so they can spend less time in it, perhaps they should honestly ask themselves how much they like the fundamental act of flying itself.

I suspect the idea of low power hurting aircraft engines comes from several sources of misunderstanding: 1. Past experience with 2 cycle engines where it is often helpful to "clear" the engine with throttle blips if idling too long and 2. fear of lead fouling spark plugs if temps run too low, and 3. a general distrust of engines used in line/pipe patrol aircraft.

As long as the engine is considered fully broken in, and oil temp can be maintained at normal operating temp, there is no reason that low power settings can't be used.

Good leaning techniques are even more important to prevent excessive lead build-up on plugs because of lower operating temps.

I have been flying my own RV-6A that way for many years.

If I am flying just locally, I often am at 17" MP and burning just a bit more than what an RV-12 would be (about 6 GPH) but still going faster.

I do it alot (Lyco 0320H2AD)

I have flow many,many hours doing group fly-outs in my RV-4 with everything from small helicopters to J3 Cubs. I have even gone slow enough to stay with a group of light sport Trikes. I often cruise at 1800-1900 RPM when sight-seeing and in no hurry. I have seen no negative side-effects, and as an APIA, I have not had any reason to believe any bad comes from it as long as temps and such are in parameter.

320 / 160 HP economy power

My RV-6 has been flying over 22-years and has flown over 3,400 hobbs hours.

One of my power settings is 22 inches and 2,100 RPM. At that power setting, I burn 6 GPH or less depending on how I lean. This was also the power setting I would set when I would lead a formation flight that had an RV with 160 HP or less with a fixed pitch prop.

I moved two years ago and the 22 inches / 2,100 RPM power setting is what is used most of the time that I am doing local flying.

I do not notice any change in oil consumption running at this power setting. Typically my cruise power setting is 2,300 RPM and WOT.

I believe that most of the people that have issues with low power settings have chrome cylinders. My experience has been that the chrome cylinder bores like a higher power setting to keep the rings sealed to keep oil consumption at a tolerable level.

Friends that have replacement cylinders with nickel ceramic cylinder bores also report using more oil use than the steel and nitrided cylinders. They also appear to like the higher power settings to keep oil consumption at a tolerable level.

As others have said, lean the engine at low power settings and keep temperatures in the normal green operating range.

rvbuilder2002 said:

As long as the engine is considered fully broken in, and oil temp can be maintained at normal operating temp, there is no reason that low power settings can't be used.

Good leaning techniques are even more important to prevent excessive lead build-up on plugs because of lower operating temps.

I have been flying my own RV-6A that way for many years.

If I am flying just locally, I often am at 17" MP and burning just a bit more than what an RV-12 would be (about 6 GPH) but still going faster.

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I fly just like this most of the time. I keep the oil temp high by adjusting my butterfly oil cooler outlet.
And I always lean to the max. burn is 5.5 gal. per hour at 150 mph.

Understanding

From what I understand of Lycoming engines, the cylinder pressure helps push the rings against the cylinders. So it makes sense that oil consumption will be slightly higher under low power conditions.

PilotjohnS said:

From what I understand of Lycoming engines, the cylinder pressure helps push the rings against the cylinders. So it makes sense that oil consumption will be slightly higher under low power conditions.

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I do not claim to have a very thorough understanding of engines but I don?t think the oil scrapper ring on a Lycoming is designed to use combustion pressure to improve its performance.
I have never notice a difference in oil consumption between low power and high power operations.

rvbuilder2002 said:

I do not claim to have a very thorough understanding of engines but I don?t think the oil scrapper ring on a Lycoming is designed to use combustion pressure to improve its performance.
I have never notice a difference in oil consumption between low power and high power operations.

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The oil scraper ring has nothing to do with compression so power setting would be irelevent for that ring type, it's the two compression rings that need to be forced against the cyl wall in order to seal properly. Glazing the bores is the biggest issue of low power settings, effects Conty's more. The poster would have been ref to the comp rings I'd say.

No expert here...

But same as the OP in Europe AVGAS saving is a thing so when I had the old Cessna with the IO360 210HP I flew her at 40% all the time. Couple hundred hours showed no signs of that being bad for the old girl. made for a very smooth ride.

Honestly I would argue that it is an advantage to running them at 75% at over 2600RPM. I think high RPM alone should increase wear on the parts.

Unless I can find any data to support the contrary I plan on flying the RV at low power settings as well. But I should probably get off the forum and into the shop

From dark corners of my cobweb mind I recall super low power settings can cause ring flutter or issues with ring seating. OVERALL caveat for sure is ALL pressures and temps are in the operating range.

rvbuilder2002 said:

As long as the engine is considered fully broken in, and oil temp can be maintained at normal operating temp, there is no reason that low power settings can't be used.

Good leaning techniques are even more important to prevent excessive lead build-up on plugs because of lower operating temps.

I have been flying my own RV-6A that way for many years.

If I am flying just locally, I often am at 17" MP and burning just a bit more than what an RV-12 would be (about 6 GPH) but still going faster.

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+1 oil temp is basic requirement.

I've been flying a T182T and run it 2000/28". Book numbers. Runs smooth and cool.

range, rather max endurance? so if you just want to enjoy the scenery and you don't care how fast your ship is moving: does a very low power setting hurt the engine?

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It does not.