LOP Operation. Can someone explain for FI Lycon?

[Kahuna]

Having run LOP on both 4 and 6 cylinders, I can attest that the 6 certainly provides smoother operations in the LOP range. I think the following is required for success.

1. FI
2. Balanced ON THE ENGINE. matched injectors are not enough. Read my report on the matter.
3. Engine monitor for all cylinders accurate to single digits including fuel flow
4. I had better LOP operation with an electronic ignition on my 4 banger. Was not as smooth when running dual mags.

I ran LOP for the entire 1500 hour operation(where appropriate) on my 4 banger with great success. No engine trouble, no plug issues, great economy, high compressions. Im sold on the idea.

Best

[dan]

Originally Posted by gmcjetpilot

As far as way throttled back and LOP, I guess you could? I don't know why not. G

GMC, I run LOP 95% of the time, regardless of throttle position and RPM. Literally the only times I run ROP are:

• on takeoff and in the climb. I have done LOP climbs, but I did the math and found that I'm only saving 0.2 gallons on my average cross country by climbing LOP versus ROP. I have read Deakin's articles on LOP climbs and I subscribe to the theory, but in this case I want the extra HP on my climb, and 0.2 gallons is not extending my range significantly enough. I'm talking strictly about the initial climb to cruise altitude here, folks -- climbing from cruise to another altitude, I almost always do that LOP. As far as the initial climbout goes, if RVs didn't climb so quickly, or if I consistently flew up in the flight levels, it would make a bigger difference and I would climb LOP. But I don't on a normal basis. The exception is on the hottest summer day after a quick-turn, when oil temp is through the roof. I will climb LOP in that scenario to keep the engine cool.
• when flying as wingman in parade formation. In formation as lead, I always do fly LOP, but as wingman, I'm not able to devote my attention to my engine monitor, and the throttle is always moving. I fly ROP when wingman.
• when doing high power/low level tail chasing. Every once in a while you just gotta burn a little extra fuel and go nuts. We go out to the desert and chase each other around over the dry lake, or we find some lonesone meadow or hills and we have some fun. I'm running ROP for these shenanigans.
• on short final. When entering the pattern, as I reduce throttle below about 14" I simultaneously enrich the mixture to the rich side of peak. I NEVER ever land full rich as I know most people are taught, but I do run ROP in the last phase of the pattern.

At literally all other times I am running LOP. Cross country travel, lead in formation, in "route" spread in formation while traveling, and when just putzing around locally.

Reduced throttle LOP? When I'm putzing around and am in no hurry to do anything, I'm usually flying around 18" at 2250 RPM, 50-60 LOP, burning 5 gph...still doing about 140 knots true! My AF-2500 engine monitor has "miles per gallon" and "knots per gallon" modes, and I love watching the economy exceed that of my Tundra and then that of my Accord.

NOTE: I usually enrich the mixture during a prolonged high speed descent, i.e. at the end of a trip. I still keep it on the lean side of peak, but by enriching the mixture you actually raise the CHTs, or rather, you add a little heat to the mix and keep them from dropping. From LOP cruise, there's not very far for CHTs to go...that is, they're between 260 and 300 to begin with. But by pushing in a little more fuel, the CHTs stay put during the descent. I don't even believe in shock cooling, but you can't argue with temperature stability being a good thing regardless.

[f1rocket]

As Mike said, it is easier to run LOP if you have fuel injection. You can do it with a carb'ed engine but it's hard to get the most benefit from it since the flow to the individual cylinders is so variable.

I did not find it that difficult to balance my injectors. I did fly down to Airflow Performance to have them spend a day, but I had already completed most of the work myself. I don't think it's that important that each CHT peak at the same time, it's just important that each CYLINDER peak at the same fuel flow, or close to it.

The AP restrictor fittings are $25 apiece. By following the GAMI guidelines and playing with the restrictors, it can be done in about 6-8 flights. I do have a slight stumble at LOP in certain atmospheric conditions, but that is more a result of the F1 Rocket cowling design and the performance of the fuel distributor than anything else.

[gmcjetpilot]

Originally Posted by dan

GMC, I run LOP 95% of the time, regardless of throttle position and RPM. Literally the only times I run ROP are:

Makes sense to me, obviously as you point out "as we are taught". I am a creature of rules as a commercial pilot. Fly by the book and stay out of trouble, but everything you said makes sense.

Clearly you are safely and efficiently running way more economically with careful and thoughtful use of the throttle, prop and mixture. You gave me a few ideas and sure that it will improve fuel savings.

5 gal/hr and 140 kts is amazing. I think people will stop going from how fast they can cruise to how low they can get their FF in cruise with fuel prices as they are.

The only thing I question, since you don't mention it, is leaning above 75% power. That has been tribal knowledge and the Dogma. Thou shall not lean until below 75% power. You say the climb lean is not worth it to you for a small savings vs HP, but I would not do it out of "principal". I have seen engines with detonation damage, it ain't pretty. It can happen fast and be devastating.

Dan you have it wired, but I worry about some individuals not really understanding the concept, trying it and burning their engine up. If done right there is little or no risk.

I know LOP has value and safe if you can do it (below 75% power), so great, I need to go out and spend a few grand and buy a Airflow Perf FI or Precision FI so I can fly LOP and save $6.00 an hour. Actually pay back time is much shorter with high gas prices. G

[dan]

Originally Posted by gmcjetpilot

The only thing I question, since you don't mention it, is leaning above 75% power. That has been tribal knowledge and the Dogma. Thou shall not lean until below 75% power. You say the climb lean is not worth it to you for a small savings vs HP, but I would not do it out of "principal". I have seen engines with detonation damage, it ain't pretty. It can happen fast and be devastating.

I didn't mention the 75% rule (of thumb), because I'm not a believer in that rule being hard & fast.

Thing is, I never "cruise" at higher than about 70% anyway. I normally cruise between 8500' MSL and 12500' MSL. At those altitudes on any "normal" day I can't make 75% regardless. Since I climb ROP, when I level off and do the big pull, I'm already well below 75%.

And in the descent, as I get below about 8000' DA I'm usually throttling back to maintain a lower power setting LOP anyway.

And when I'm "cruising" (as opposed to putzing) down low (rare), I normally select a power setting that is well under 75%.

[AlexPeterson]

I second everything that Dan has said, it is truly about a 1.5 to 2.0 gph savings over running "the way we were taught", or 100 ROP. I have run LOP for probably 720 hours out of a total of 750 hours in my plane, and typical settings are 22", 2300rpm, 7.1 to 7.3 gph. This delivers a true airspeed of around 160 knots in the higher altitudes, say 7500'.

Regarding running at lower settings, 18" for example as Dan mentioned, there are cases when slowing down delivers a net faster airspeed. If one can avoid a fuel stop on a trip because of higher mpg and better range, the airspeed loss of perhaps 20 knots is more than made up for. I recently flew to southern FL from MN, a total of 1238 n.m. distance. On the way down, I stopped only once for fuel after 3:45 flight time and 635 n.m. After about 45 minutes, I was back in the air for another flight of 3:35 for the remaining 600 n.m. or so. The gs averaged 169 knots on the first leg (about 10 knots tailwind) and 167 the second leg. Departure to destination averaged, including the stop time, 156 knots! Again, these were with 10 knot tailwinds. But, if my burns had been around 9 gph, I would clearly have needed two stops (one hour is my minimum fuel).

So, my point is that sometimes going slower through the air will get you there faster. And, burning less fuel through proper LOP operations delivers more performance gains than simply saving, nowadays, about $5 or $6/hour fuel costs.

CHT management through these techniques is a whole 'nuther treatise.

Everyone who flies should read, or put it more accurately, study, John Deakin's writing on LOP. Very good stuff.

[George in Langley BC]

On a 30+ hour trip from Canadas West to East coast and return (via Osh 04) in my fixed pitch 0-320 (160) RV-6A I did not get as good fuel economy as expected, 7.95 GPH (US) and 145 Kt average running about 60% power.

To run LOP with a lack of instrumentation I leaned agressively to ensure I was in an area of cooler temps otherwise I stay ROP. I have no EGT or fuel flow instrumentation, so leaned for a 175 RPM drop which gives a 30 - 40 degree F drop in cyl head temp. Yes, my carbed 0-320 with electronic ignition (1 Lightspeed) will run smoothly right down to the point where the flame goes completely out.

On return I calculated the fuel burn from the log book and fuel pump readings, I had expected to average around 7 GPH but with it close to 8 I got looking at the Lycoming charts. Specific Fuel Consumption decreases with leaning into the Best Economy area and then it begins to increase again.

Lesson learned, I was over leaning. The 7A I am building will have more instrumentation.

George in Langley B.C.