Everyone always says “ I run LOP at 23/2300 and now I’m only burning 11.5 gph. Sure I lose a little speed”. Well isn’t this kind of stupid to equate engine settings and try to compare 23 squared lop and 23 squared rop? (Using 23/2300 as an example.)

What we need to look at is speed and mpg. When I’m running LOP on my io520 I’m around 11.5 gph. Leaving rpm the same, I will adjust my engine setting to the appropriate engine setting to match my LOP IAS. This seems to be lowering the manifold pressure two inches and moving to ROP. Now I’m running 21”/2300, same speed as my 23/23 Lop and doing it at 12 gph, So what’s the big deal? There is no real savings in gas besides maybe less than 1 gph.

What am I missing? Is it as simple as fuel =hp? I maybe I’m doing something wrong here. LOP newbie.

Drag increases with the square of airspeed, and thrust ~= drag.
ROP (true ROP) throws fuel away down the exhaust pipe, and usually people fly only a little faster. Even you fly at the same airspeed and same power setting, a ROP setting by definition involves throwing away fuel.... so you MUST be wasting fuel.

For the same distance travelled, it saves you A LOT of gas going 5 to 10% slower and burning 15 to 35% less fuel.....

ROP I burn 55 to 60 L/hr, airspeeds around 125 KTAS with 31" bushwheels equipped
LOP I burn 37 to 42 L/h, airspeeds around 120 KTAS with 31" bushwheels equipped

Am I saving fuel / money? Yes, in the last 1,000 hours flying I have saved enough money to buy a whole new engine.

I would add, that unless people are running a full engine instrumentation setup, they may "think" they are ROP, when in fact they are running at peak, or LOP. The way leaning is often taught, some people run LOP and don't even realise it.

At low power settings, like 17” 2300, I can get my fuel burn on my o520 down to 8.5 some days.
Still indicating 105mph. Allows me to see lots more country between fill ups.

Im losing pretty significant speed as well. I believe at least 10 mph moving to LOP so maybe there some something wrong with my procedure. The plane runs rough at anything less that 11.5 at 23/2300. I have Gamis and have had my spread verified. Maybe im running too lean? Then getting high drag and significantly more speed loss than the normal 4-5 knots.

It could be that my ROP setting are too lean as well. High temps and it’s just a quick check. Maybe if I settled in at that power setting and richness the temps would be busting 380 and I’d end up richening 1-2 gph to control it.

I do like running the engine LOP. My temps have been great, settling in around 350 in cruise with cowl flaps closed. I noticed my rop are much higher.

Why the 23 squared? I was told by the Gami people - wide open throttle 2500 RPM 25-50 degrees LOP.
I save a ton of gas and lose a bit of airspeed.

I was using 23 squared as a basis to stay around 65% power. WOT even below 5k? Wow

I’ll try again tomorrow with slightly higher power settings. Maybe that will keep me from big speed losses with that high drag cruise angle.

Thanks for the help. Definitely takes some time figuring out what the plane wants

I don't get below 5k too often- but I definitely stick to either wide open throttle or 25"- 2500 RPM- the procedure outlined in the Pelican Perch series of articles on Avweb really works for me. High power, high RPM, lean of peak with my hottest cylinder at around 350 or a bit less.

I will throw my 2 cents into the LOP debate.



LOP is more efficient. When on the lean side of peak there is more air than fuel. Consequently no fuel is wasted. CHTs are cooler and ICPs (Intra-cylindrical pressures) although not measured are lower. Theoretically leading to reduced heat, and less wear and tear on the engine. I took a screen shot of Mike Busch's slide from his engine leaning basic video. My take away from this slide is there is a 5% loss in airspeed for a 20% reduction in fuel burn for the same power ROP. I have a carbureted O-520 but I am able to fly LOP reasonably well. Usually down low I have a very narrow EGT spread less than 50F. I can run my engine 20/2300 LOP at 10.5 gph. I see 125 KTAS. ROP I see 135 burning 13.2. I am seeing about a 10% loss in airspeed for a 20% reduction in fuel burn.

It is a significant savings over the life of the engine to run it LOP. I see lower CHTs by about 5-10 degrees. I like running my engine LOP below 60% power. It is a very safe way to operate it LOP. No big mixture pull needed. I think with AVgas going into the stratosphere - it is a useful way to operate our engines.



Josh

I love how you click baited us with a title that says LOP doesn't save you any gas and you proceed to prove yourself wrong at the very onset with measuring 0.5 gallons per hour for the same IAS. I suspect you won't listen to anything if you don't even listen to yourself.

1) 0.5gph x 2000h x 7 $/h = $7000 just with your math. 7 grand (and your numbers are quite conservative) and I'd take that to help pay for my overhauls or buy even more gas.

2) IAS vs TAS vs G/S. I argue g/s is really what we care about, but TAS matters too - and your results will vary with alt so talk about TAS. Above 5k you cannot get into the "red zone" ever. You just don't need ROP unless max power is needed for climb out - never at cruise.

3) ROP is more lead, and wasting fuel for little power benefit except cooling the engine.

4) you don't need fuel injection to run LOP - you just need a 6 point EGT/CHT gauge and a reasonably balanced (I know) intake system.

I'm a LOP'er, fight me!

StillLearning wrote:At low power settings, like 17” 2300, I can get my fuel burn on my o520 down to 8.5 some days.
Still indicating 105mph. Allows me to see lots more country between fill ups.

You'll save more fuel doing this than anything, it does take restraint knowing that you could be getting where your going faster. I'm curious since the power setting is so low, if running near peak provides the most efficient combination in relation to MPG. I've started experimenting with reducing my RPM to 1900 with a low manifold pressure, roughly 45-50% power 10GPH at 25-40 degrees ROP give or take (IO-550, Gami's, MAC 401 combo). The engine is by no means lugging along, in fact, it is quite happy and extremely smooth. This works fine when I have no particular place to go...........but its nice to be able to shove the throttle to the firewall and make 145 kts to your destination. Gotta love the Skywagon. I'd imagine LOP when set up right could be a good balance of speed and efficiency. It takes some proper setup and a good engine monitor to do it safely IMO.

Well the original post was a little click baity but I’m realizing that for some reason I’m losing way more airspeed than most people. 10+ mph. And that’s not the norm. So I’m thinking I was just getting too slow and too lean with low power settings so the plane is just bumbling along in a high drag configuration. If I was running lop and only 5mph difference, that’d be great. Either way, thanks for helping me get to a conclusion.

soyAnarchisto wrote:I love how you click baited us with a title that says LOP doesn't save you any gas and you proceed to prove yourself wrong at the very onset with measuring 0.5 gallons per hour for the same IAS. I suspect you won't listen to anything if you don't even listen to yourself.

1) 0.5gph x 2000h x 7 $/h = $7000 just with your math. 7 grand (and your numbers are quite conservative) and I'd take that to help pay for my overhauls or buy even more gas.

2) IAS vs TAS vs G/S. I argue g/s is really what we care about, but TAS matters too - and your results will vary with alt so talk about TAS. Above 5k you cannot get into the "red zone" ever. You just don't need ROP unless max power is needed for climb out - never at cruise.

3) ROP is more lead, and wasting fuel for little power benefit except cooling the engine.

4) you don't need fuel injection to run LOP - you just need a 6 point EGT/CHT gauge and a reasonably balanced (I know) intake system.

I'm a LOP'er, fight me!

I like LOP, too, but your point about GS being what counts makes me wonder if there isn't a situation where headwinds are so strong that the efficiency advantage of LOP is offset by the additional time spent fighting the headwind. I roughed out some numbers for my plane for 30 and 50 knot headwinds, and LOP still came out ahead with greater range. So, maybe not a real world scenario for our planes, but I find it hard to stomach double digit groundspeeds on a long trip when I can get triple digits by pushing more gas through. (I'm talking about a 30 knot headwind, with GS of 90 vs. 100-105). I burn more gas, but, unless it's a max range flight where the extra fuel burn forces an otherwise unneeded stop for fuel, I get there sooner and feel a little better about it, particularly because high winds usually mean rough ride.




CAVU

OP,

You are a self proclaimed LOP newbie. From your initial post and subsequent posts, you confirm this. I would recommend taking a course offered through Advanced Pilot Seminars. I took the online one many years ago. I also read many of the Pelican's Perch articles on Avweb by John Deakin. I've also read many articles by Mike Busch. When you do this, you will understand what % power means when you are ROP and how to calculate it when you are LOP. There is a difference. Manifold pressure and tach combinations do not equate to power when LOP. Rather, HP is derived by multiplying FF x 14.9. In your post where you are using 11.5 gph (if you are even LOP at that point), the calculation would yield 171 HP. Depending on your engine displacement, you would divide that by your engines rated HP to get percent power. For a IO520 at 285 HP, 171 HP would be 60% power. You should know what your peak EGT is on your richest cylinder and lean to however many degrees cooler than that that you want to run. You achieve this EGT control by manipulating your throttle to give more air (make it leaner and therefore cooler EGTs) or give less air (make it richer and therefore hotter EGTs). I know my engine. If I'm running 11.5 GPH, I'm usually about 5 kts slower and burning about 4.5 GPH less. My MP is around 25" and my RPM is 2300 if I am at an altitude less than that required to still make 25". If higher, I would need to reduce fuel flow since I will be WOT and cannot increase MP in order to keep EGTs on the cool side of peak. For example...8000 feet, WOT, 2300 RPM, FF around 9 GPH.

LOP is for sure the way to travel when you have enough airspeed to keep cylinders cool (very reliant on air cooling since excess cooling fuel is not available). Floats and skis slow you down enough that CHTs rise due to the slower airspeed, and you might need to convert back to ROP operations if you can't keep things cool. Bonanzas flying at 180 kts usually have plenty of air cooling going on.

Good luck.

Oh, and to prove you wrong....

120 KTAS at 11.5 gph
124 KTAS at 16 gph.

In efficiency speak, that's a difference of about 2.6 extra nautical miles per gallon burned. I know this proof is just the math and you are probably looking for real world experience proof. Also, in my example, I didn't use the same HP ROP and LOP for a true HP comparison.

For that, take the plane up to cruise. Assuming you have an IO-520, you have to fly at a low enough altitude to run LOP at a FF of 12.8 gph.
Set yourself up for 23 squared (roughly 67% power) and enough fuel to run 150 deg ROP on the leanest cylinder. Record KTAS and FF.

Then set your FF to 12.8 gph (67% power) and your RPM to 2300. You will need to have enough MP to keep your richest cylinder more than 25 deg LOP. At that FF, you might need 26+ inches. Record your KTAS. You already know your FF.

There will be your real world proof and one that controls for HP.

Thanks for the info Squash. I’ve listened to all of the Busch webinars but am always willing to dive deeper. Your planes numbers seem to be different than mine so I’ll go back to the drawing board and try some different settings.

Really interested point about the hp calculation on lop. I always wondered if percentage power rop equated to the same hp lop in regards to the red box. It’s not like you can pull out a poh to get %hp at different settings. So essentially your rop 70% power setting might equate to 65% once you go lop even though your mp/rpm remain constant. Thank you for the knowledge. I’ll check out the course.

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I get LOP, I just don’t really sit in cruise long enough to bother with it

Kind of off on tangent here, but I read several references made to the term "Fuel Cooling", which, I hear a lot in conversations shot our aircraft engines. I understand that it does "cool", as richening does make temps go down, but how ? I understand how air cools, how water cools, but how does gas, which explodes into a ball of fire, cool ? The only way I can figure it, is it creates a mixture soo rich, that the engine is "blubbering" along, spitting out unburned fuel, as we've poured do much fuel in, that the inefficient spark can't burn it all. My o470 doesn't sound like it's blubbering on a wide open, full rock climb ? So, how is this exploding, burning liquid cooling my engine ?

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. In primary training we are trained watch engine cht temps and the fix is to enrichen mixture, open cowl flaps and lower the nose to increase air speed. Not sure the relative value but for sure more fuel cools CHT.

soyAnarchisto wrote:pretty simple actually - more fuel going through a venturi lowers the temp (that's how carb ice is formed)…

I was under the impression carb ice is formed purely by virtue of the temp drop of higher velocity air moving into the vacuum of the intake and that the fuel is just along for the ride. Lower pressure = colder air and condensing water vapor which then freezes and chokes off the carb throat.

Does the fuel atomizing contribute to this temp drop too?