very low power continuous operation

[prkaye]

First - i know, i ask a lot of questions here! And I thank all of you who continue to help me learn
After break-in, is there any detriment, from an engine longevity perspective, to routinely running at very low (40-50%) power settings? I'm rarely in a rush and like to save fuel. I wonder if running at very low power settings for a decade contributed to my early piston-ring failure.

 

[Untainted123]

Since you're up north, I would be concerned about running the engine TOO cool, instead of too hot. If I remember correctly, certain lead chemical transformations don't happen efficiently at too cool of a temperature, and you risk lead buildup and fouling. If you are running lead-free, this may not be a concern.

That being said, there's going slow and then there's going SLOOOOW. You should look into the Carson number for your airplane, and maybe shoot for that. If you are trying to build time, a Cessna 150 is probably cheaper

 

[prkaye]

Indeed, I'm familiar with Carson's number. Getting down to Carson speed is why i run at such low power!
In terms of Lead, i typically run 91 ethanol-free mogas, so no lead issues for me.
In terms of temps, i actually don't fly in winter, so maybe not an issue. And i'm actually at about the same latitude (very slightly north) as minneapolis, where i had my first RV-9A ride (thanks again Pete!)
I'm certainly not trying to build time (i have over 600 hours now, 500 on the -9A). I'm just trying to make my x-country flying as economical as possible, while factoring-in the costs of engine longevity (which recently bit me big-time).

 

[fl-mike]

just remember, to the log book and future buyer, "hours is hours".

I didn't build an RV to fly slow. WOT, lean of peak, and shop for cheap gas!

 

[Dan 57]

Being A/retired and B/an efficiency advocate, I usually cruise at Carson speed, which for my ship equates 114KIAS. At 4Kft I use 19" and 2K RPM, and this equates about 43% power, burning less than 5.5USG, and still returning a 130 or slightly less KTAS.
Another big benefit is noise, or better, the reduction of noise

We had a thread here covering the subject a couple of years ago... also looking for some articles by Mike Busch on over square ops etc, will demonstrate no ill effect.
Flown my engine this way for >1.2K hours during the last 4 1/2 years, and it loves it

And if I wanted to fly fast, I would certainly not have chosen an RV. There is a good choice of kitplanes made for speed and way faster than an RV...

 

[Scott Hersha]

I don’t think you can hurt anything by running low power settings, as long as you follow Lycoming’s recommendations concerning temps. OT 160-200, leaned properly. A Lycoming rep told me that you can’t hurt their engine with the red knob when below 65%. If it gets too lean it will just quit, or run very rough, but you won’t burn anything up.

 

[petehowell]

Low and Cold

Glad you are flying!

I fly low power in COLD temperatures here all winter using mogas. I've got 2700 hrs on my O-320, so I don't think it is too big of an issue!

Indeed, I'm familiar with Carson's number. Getting down to Carson speed is why i run at such low power!
In terms of Lead, i typically run 91 ethanol-free mogas, so no lead issues for me.
In terms of temps, i actually don't fly in winter, so maybe not an issue. And i'm actually at about the same latitude (very slightly north) as minneapolis, where i had my first RV-9A ride (thanks again Pete!)
I'm certainly not trying to build time (i have over 600 hours now, 500 on the -9A). I'm just trying to make my x-country flying as economical as possible, while factoring-in the costs of engine longevity (which recently bit me big-time).

 

[prkaye]

Thanks Pete! I still talk about that -9A ride in Minneapolis, when you went above and beyond to pick me up downtown, take me to the airport, take me flying, and drive me back downtown! I like to think that i have paid it forward to others a couple of times since. It's what this fantastic community is all about.
Interesting mogas observation - for my first 10 hours since IRAN, I ran 100LL. After 10 hours the oil was coming out pretty brown and opaque. After the 10-hour oil change i switched to mogas. Now 7 hours later the oil is still totally golden. I didn't realize how much the lead seems to be responsible for murking up the oil! Filthy stuff!

 

[Taltruda]

I feel that you should still run full power on takeoff, and climb to help keep the rings, ring lands and cylinder walls bedded and clean. I don’t believe reduced power takeoffs aren’t recommended by the manufacturer either.

 

[prkaye]

I feel that you should still run full power on takeoff, and climb

Absolutely agreed. I always takeoff full power and climb to 1000' AGL before reducing power. I only reduce power prior to that in the climb on really hot days after a long taxi if my CHTs approach 400.

 

[rmarshall234]

Doesn’t necessarily answer your early failure question but every engine I’ve ever operated, be-it airplane, motorcycle, car, etc. has seemed to have a “sweet spot”. A perfect blend of power, torque, temps, and *limited vibration. Sometimes it matches the recommended operating speed and sometimes not. That’s where I almost always operate, if the engine is happy I’m happy. Of course it needs to be set up and maintained properly, but I’ve had very good success over many decades. It comes naturally when you really pay attention.

 

[hoyden]

I regularly fly my IO-360 RV-6 at 30-40% power. 1800 RPM and 18-22" MP. For the same reason; I'm not in a hurry and I like the fuel economy. In the past two years I learned to do the mixture Big Pull. After takeoff and at about pattern altitude while WOT I pull the mixture to LOP at 90% power. Then I reduce throttle and prop to my climb or cruise setting somewhere south of 40% power. Oil and Savvy analysis always excellent results and no problems after more than 15 years and 1000+ hours.

 

[Richard RG]

Like the original poster, I'm interested in the most fuel efficiency whilst aviating and not so concerned about getting to my destination in any great hurry, or the increased engine/airframe times..,
Given that my estimated best glide in the RV3b is 95 mph, would suggest that my 'Carson Speed' would be 125 mph?
If throttling back to 125mph, would there not be a concern that damaging harmonic vibrations could take place in some engine/propeller combinations?
In past, having flown certified aircraft that were placarded against continuous operation within specific RPM ranges, I assume is to avoid damaging harmonic vibrations.
Also, for those that operate at such low power settings with carbureted engines, would you be using carb heat at all times? Carb icing would be a concern for me with such a large pressure drop across the carburetor throat and the moist air in my part of the world.
If carb heat is required for safe low RPM operation, would the heated intake air not negatively affect the fuel efficiency even if max leaned out?

 

[koupster]

Absolutely agreed. I always takeoff full power and climb to 1000' AGL before reducing power. I only reduce power prior to that in the climb on really hot days after a long taxi if my CHTs approach 400.

Phil,
My preferred climb (cruise-climb) is 120 KIAS. At that speed, I almost never have to reduce power to keep the CHT's in control. I lean as I climb to keep the EGT's similar to what was observed on initial climb - to keep the EGT's the same amount rich of peak as initial climb (I have a carbed O-360).

I would never pull to LOP at 90% power as one poster stated. I climb as above, reduce power for cruise, and then do the big mixture pull.

If you're recording Hobbs time, then hours is hours, but if you record Tach time, then the time aloft is recorded at a slower rate than the Hobbs meter would show.