Economic incentive for LOP
Hi David,
I ran my Barrett IO360 LOP alot, after installing a Lightspeed Plasma II electronic ignition on the lower plugs. At my preferred cruise altitude of +/- 12000' the spark was advancing to approx 37 degrees BTC. That permitted much leaner mixtures and thus made LOP really easy to do. Much of what I understand about this was by way of Klaus Savier who was very generous in exchanging knowlege.
The engine was an O360 that Monty added Bendix injection to, 9:1 pistons, and flow balanced. It had a fixed pitch prop. As you know about Barrett engines, it ran like a digital watch (for a Lyco).
For comparison with the mags, ROP ops routinely produced fuel flows in the low 8 gph range. After fitting the Plasma II, I could run LOP in the low 7's saving about 1 gph, with a small loss in power. Temps while doing that dropped a little too, like maybe about 10-20F on CHT. Oil temp didn't change noticeably. Leaning past peak aggressively was possible with the Barrett engine, but I ran into unacceptable power loss if I leaned too far. I found that at altitude with the PlasmaII advancing the spark so much, I could switch the mag off and it had almost no effect. The engine stayed smooth all the way to cut-off.
FWIW, I think the LOP operation didn't hurt anything while saving some fuel. I would add though, that its important to have a good engine monitor so you can see all the EGT's and find your peak point accurately. One cylinder probably will tend to peak first, even with a flowed engine. That's the point I used as a reference for LOP ops.
I'm not an expert at this either, with only one airplane to reference for information. None the less, I think its worth taking a look at, and offer these observations for reference.