soyAnarchisto wrote:pretty simple actually - more fuel going through a venturi lowers the temp (that's how carb ice is formed) and lowers the intake air charge - therefore lowering the cht.

It's actually not quite that simple... There are other more influential factors at play than cooler mass coming in a carburetor. Vaporizing fuel cools the charge regardless of the induction. More fuel = more charge, and more charge = more mass within the cylinder to scavenge heat as it leaves the exhaust. Which is why looking at actual EGT values (in our engines) is worthless for anything outside of trend monitoring.

I have an engine that will run LOP well for a carbureted engine. Having said that, I take in to account the reason I'm flying at that moment (mission, mission, mission with anything aviation) long before I set the red knob, and quite often I am more interested in making as much horsepower, or covering as many miles per minute than I am what it takes to make that happen (short of destroying my engine). If a few more gallons gets me to my destination 20 minutes sooner, there may be some value to that, there are only 1440 in a day, and no matter how you run an engine, you're not going to get a single minute more out of it, or a single minute back.

Waste is like beauty... it's all in your perception. One person 'wasting less fuel' may be 'wasting time' or 'wasting horsepower' in another's eyes. I choose not to diminish why someone elects to run their engine a certain way, and I have not the energy, time, or patience to try and instruct them to run it my way (whatever that means).

The LOP/ROP debates run long, and passion frequently gets in the way of common sense. By that I mean if you are doing something because all the cool kids are, or because a self proclaimed expert said it's the right way to do it, and you don't first educate yourself as to whether what's right for their situation is really right for yours, your really not using common sense.

Getting real time answers to your own situation has never been as easy as it is today. Get a good engine monitor, learn how to read it well (by read I mean interpret what it's telling you). And then utilize that information as it fits your MISSION.

Take care, Rob

Rob wrote:I have an engine that will run LOP well for a carbureted engine. Having said that, I take in to account the reason I'm flying at that moment (mission, mission, mission with anything aviation) long before I set the red knob, and quite often I am more interested in making as much horsepower, or covering as many miles per minute than I am what it takes to make that happen (short of destroying my engine). If a few more gallons gets me to my destination 20 minutes sooner, there may be some value to that, there are only 1440 in a day, and no matter how you run an engine, you're not going to get a single minute more out of it, or a single minute back.

Waste is like beauty... it's all in your perception. One person 'wasting less fuel' may be 'wasting time' or 'wasting horsepower' in another's eyes. I choose not to diminish why someone elects to run their engine a certain way, and I have not the energy, time, or patience to try and instruct them to run it my way (whatever that means).

The LOP/ROP debates run long, and passion frequently gets in the way of common sense. By that I mean if you are doing something because all the cool kids are, or because a self proclaimed expert said it's the right way to do it, and you don't first educate yourself as to whether what's right for their situation is really right for yours, your really not using common sense.

Getting real time answers to your own situation has never been as easy as it is today. Get a good engine monitor, learn how to read it well (by read I mean interpret what it's telling you). And then utilize that information as it fits your MISSION.

Take care, Rob

I agree with Rob

It’s all about mission

“ During World War II, engineers plotted their test results from full rich to lean, and the Army classified the chart as top secret. Charles Lindbergh taught fighter pilots in the Pacific how to run lean of peak EGT, a technique that helped him across the Atlantic in 1927. Max Conrad used lean of peak to set distance records in his Comanche in the 1960s when he flew over 7,600 miles nonstop.”
-plane & pilot mag article

For max range LOP makes heaps of sense, for me flying to a few lakes down low in my 185, with nornal 30-45min in cruise, meh, now if I was trying to fly the plane across the ocean to Europe for…well I don’t know why…LOP makes sense

Same with the work plane, we have high speed cruise settings and max range, unless we NEED that extra range we target just shy of the barber pole

There's more to the story about Lindbergh. When he accompanied a fighter group he was returning with 1/3 of his fuel when everyone else was empty. Those guys were spending long periods crossing open water in hostile conditions, so "mission, mission" included getting back to your base.

Update:

I tried running higher settings and I’m getting much less speed loss and the engine is running much better. Before I was testing using 23/2300 so my lop hp was probably 60%. At those low settings, the comparison wasn’t really fair because you can run rop 21/2300 (same speed as lop 23/2300) at very low fuel burn and low chts.

New test was at 24/2400 and 25/2300 and it ran much better and kept much better speed. At 24/2400 I only had a 5 degree difference in egt temps from peak, which made it really easy to safely pick a fuel flow setting. 25/2300 had a wider range of temps from peak. Both settings are approximately 65% hp.

I’ll probably run wot and 2400 or 2450 up high, and 24/2400 down low.

As they say, a step backward after a wrong turn is a step in the right direction. I’ll be flying lop when the mission suits it.

I enjoyed following this conversation; thanks to those that contributed. I’m still building experience with LOP. My engine doesn’t seem to like it much, likely because the injectors seem pretty far out of balance, but on the days it works I seem to only lose 4 mph while my fuel flow decreases by 1.5-2gph.

Lately I’ve been paying more attention to miles per gallon. I still haven’t found the most efficient setting because I’m usually trying to get somewhere but it is an interesting metric to monitor.

Jon - it's not expensive to get custom injectors. I suggest you would benefit from fixing just the worst couple of cylinders. You can also try swapping injectors around. They are all subject to the same shared distribution system (spider), so changing one can affect the others. Overall, spending $80 bucks and some fiddling for half an hour can be all the difference. The best part - it will rapidly pay itself back! Not a common thing in recreational aviation

Battson wrote:Jon - it's not expensive to get custom injectors. I suggest you would benefit from fixing just the worst couple of cylinders. You can also try swapping injectors around. They are all subject to the same shared distribution system (spider), so changing one can affect the others. Overall, spending $80 bucks and some fiddling for half an hour can be all the difference. The best part - it will rapidly pay itself back! Not a common thing in recreational aviation

I tried swapping the factory injectors around with little success. Gami injectors are $900 which is almost reasonable. I asked Airflow Performance if they could set me up with a custom set of injectors and they said they could but suggested I call GAMI instead. They said it would be cheaper from GAMI and a lot less effort.

You can order one at a time, at pre-measured sizes, to fix the problem. Much cheaper than $900, I am sure it was $80 plus shipping for an injector. I think they might have been Airflow Performance, or maybe GAMI. You just have to specify the size you want. The $900 - I think that's for a fully tuned set, so you are paying for a lot of labour there.

I know this thread is a bit old at this point, but thought I would contribute a note about turbo-normalized engines and LOP.

Turbo-normalized engines basically maintain sea-level manifold pressure as the airplane climbs, all the way up to their "critical altitude" where the turbo can no longer overcome the effects of thinner air, and MAP begins to drop off. These engines are almost ideal for LOP operations, with minimal pilot workload.

I had a Commander 114 (IO-540) with an aftermarket turbo-normalizer (Hot Shot). Even before I purchased it, I attended the APS course (in person, back when they were still doing that), and learned a LOT about operating engines - especially turbo-normalized engines.

With that knowledge in hand, I flew a few flights using "book" settings (<=75% power, per the charts), and was averaging about 157 KTAS while burning 14.5 GPH. Once I was comfortable with all the other systems in the airplane (new to me avionics, etc.), I switched to WOT-LOP operations, and analyzed the data from the CGR-30P after every flight.

I quickly realized I could cruise at ~156 KTS (the same as 75% ROP), but when operating LOP it would burn about 13 GPH, saving me 1.5 gph. Same speed on 11% less fuel? No brainer. I shared these results with the guy who taught the APS seminar, and he suggested I try operating at even higher LOP power settings (WOT-LOP), keep a close eye on the CHTs, and find my "go fast" settings through experimentation.

I learned that I could safely operate up to 90% power (LOP only, of course), but the CHTs were running in the high green range, and that made me a bit uncomfortable... However, at 85% power the CHT readings seemed really comfortable (well within the green range). That 85% power would produce ~168 KTAS, while burning that same 14.5 GPH. So roughly 6-7% improvement in speed at the same fuel burn. That became my "go fast" mode.

I didn't learn about "Carson speed" until long after I'd sold that airplane (mission change)... But I did some "loafing along" testing at 55% power settings, and at the same cruise speed as 55% ROP, I was again burning about 10-12% less fuel. When I took my wife sightseeing (looking at changing leaves, lake shoreline, etc.) I would use this mode to save gas.

There was a long cross-country flight (to visit family members) that we made fairly regularly. Flying book cruise settings (ROP) it required two fuel stops – one a complete fill-up, and one a "splash and dash" – to complete with my self-imposed 1-hour fuel reserve. Operating LOP, it was an easy one-stop flight. Stiff headwinds would encourage 85% LOP cruise (with equal fuel burn to "book" settings). More neutral winds would allow that flight at 75% LOP with attendant fuel savings. Tailwinds allowed 65% LOP cruise and saved a LOT of fuel.

Thanksa for the reply. Ive been meaning to jump on this thread again and ask..

What is the highest LOP power setting one could comfortable run?

You read my mind and answered that. Ive heard Busch say many times that we shouldnt be operating LOP at RPM higher than 2500. I've recently been running 24.5/2450 on my io520. CHTs never get above 350-360 and it seems like the hardest I can run it LOP down low. Up high and Im WOT/2450 obviously. Im usually 11.9-12.1 GPH.

After watching lots of webinars, ive started ging WOT the whole climb and pulling back to 2550 after the first 700-1000'. What a world of differene that is... then keeping EGT leaned to around 1300s for that climb.

I've got a question- I was under the impression that EGT's are only useful in finding exact peak, that we should'nt fly with a target EGT. I was under the impression that the hottest CHT is the critical number- seems to me the Gami folks, and pelicans perch guy have been telling me that.

I fly with a targeted hottest cylinder EGT at around 350- its simplified my engine management considerably. I do a thorough leaning with reference to EGT if I know I'll be at an altitude and a power setting for awhile otherwise I just mostly wing it- LOP-WOT, 2500RPM, hottest CHT at 350

Thousands of hrs in SR22’s of all kinds, turbo and not, I almost always run LOP besides takeoff and climb, unless I’m in a big hurry and a few knots matter.

Always WOT and 2500 unless Turbo. Then 30” and 2500 rpm.

Minimal speed loss with significant fuel savings LOP. If everything is set up right, you would be looking at 14.5 gph and 172 knots and 340 CHT on a standard day at 8,000 ft.

ROP would be around 20gph for 180 knots all else being equal.

I have found on my 185 on floats with a similar engine, I have to be more rich or more lean than a cirrus on a warm day, because of the slower airspeed.

The speed difference between WOT ROP and WOT LOP while keeping temps in check is significant on a warm day.

I’m often choosing between 13gph and 105kts or 22gph and 125 kts.

Despite the fuel bill, I often end up at 22gph because I’m impatient lol

I got a question for the LOP BCP Gurus. I do not need to be sold on the benefits of LOP operates. I fly my O520 LOP quite a bit. At low altitudes I have a narrow EGT spread and it flies really nice 20/23 LOP at 10.5 GPH. I feel safe flying it there because I am below 60 percent power and just figure I am out of the red box and can't hurt the cylinders with the mixture control. I don't have GAMIs or an injected engine so haven't really experimented outside of this one power setting mentioned above.

My concern for doing it above 60% power is the time required to see the LOP operations on the engine monitor and being in the red box during the movement of the mixture control through this area. It seems with the big mixture pull you might accidentally end up in an area where some of the cylinders haven't moved past peak EGT. I like to let my engine rip in smooth air from time to time and run it hard WOT/2600 RPM but I am running 20 gph. It would scare the shit out of me to pull the red knob back to 14 gph or whatever FF gives LOP at that setting. I would be scared doing it with a more reasonable setting of 23/23. At my 20/23 setting I throw the JPI into lean find mode and just slowly scale back the mixture. Is this what you guys are doing flying it 75% power or are you doing the big mixture pull and leaning for FF at a predetermine setting ?


Josh

Nothing bad is going to happen through the mixture knob sweep. Takes quite a while at peak EGT to cause harm.

If you have a full engine monitor, you can pull the mixture fast til the engine is very lean and runs a bit rough, then enrichen until the first peak, then lean from there to 25 or 50 or 75 or whatever LOP depending on % power. This minimizes time at peak.

Im obviously not the guru but I do a big pull on the mixture back to gph settings I have previously checked. I’ve written a few in my phone for reference so I don’t have to continuously find peak at high power settings.. 24.5/2450, I’ll pull it right back to 12 gph. For me, that is 25 lop on the richest cylinder.

ington6 +1

ington6 wrote:Im obviously not the guru but I do a big pull on the mixture back to gph settings I have previously checked. I’ve written a few in my phone for reference so I don’t have to continuously find peak at high power settings.. 24.5/2450, I’ll pull it right back to 12 gph. For me, that is 25 lop on the richest cylinder.

Works if the air temp is similar.

Going from extreme cold to extreme warm might be as much as 2 gph difference.

Good point. Maybe I need a summertime list and winter list. I noticed I was 12.2 gph at those settings when making my list originally. (Cold spell ) Then we have had a warm spell. I seemed to be running a little hot so I checked forpeak egt and was running about peak egt at 50 oat, 12.2 gph. Pulled back to 11.8 to settle around 25 LOP when slightly warmer.

It’s a great idea to check peak egt from the lean side, much less time in the box. When you think about it, you really only need your richest cylinder to find peak, then lean it out, rather than dragging all your cylinders through the box. In my plane, I could probably quickly find peak from the lean side, while the other cylinders are still -10 to -15 lop. Not so bad.

Yup that's the way to do it. We have such wild temperature swings where I live, you gotta check where peak is often.

Sometimes I take off when its -30F, then fly 5 hrs south where its +50. As the air gets warmer, it gets less dense, richening your mixture. So sometimes I need a peak check mid flight, or just nudge the mixture back a bit based on experience.