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LOP Operation. Can someone explain for FI Lycon?
- Thread starter N62XS
- Start date
For the full explaination go to Avweb, click on columns, then on Pelican's Perch (John Deakin) and read all he has written on the subject. It will take you a while, so its difficult to do the subject justice in a few words here. Then taken one of the Advanced Pilot Seminars, and learn even more.
LOP = Lean of peak (EGT)
ROP = Rich of peak (EGT)
To simplify it in the extreme (and so not tell the whole story), leaning off the mixture will cause your engine to make more power, and so run hotter. When running with a rich(er than optimum for best power) mixture the excess fuel helps to keep the engine cool. At high power settings, say greater than 75%, there is a possibility of something called detonation happening - its to do with how the fuel & air burns in the cylinder - which is very bad news for the continued health of your engine. So the general recommendation is to run at least 50F below peak EGT on the rich side.
As you change the mixture from too much fuel to too little the EGT will increase to a maximum value, then decrease until the engine stops running. The absolute value of EGT is relatively unimportant as it is dependant on many things , including how far down the exhaust pipe the sensor is placed. CHT will follow EGT in general, but is much slower to react (as a large lump of meatl must heat up or cool down. However the absolute value of CHT is very important, the maximum CHT recommended by those who know is in the range 380 - 400 F. It is vital that CHTs do not exceed these values very much very often if your engine is to stand a good chance of reaching TBO.
To run LOP with any kind of success requires an engine monitor that displays each CHT and each EGT - in fact many would argue that to run your engine at all with any kind of success requires such a monitor.
The real reason running LOP is attractive is that it saves gas (1 or 2 gph in the cruise in RVs) and is better for the engine. A well balanced fuel injection system is required for really successful LOP operation - balanced means that each cylinder gets a equal dose of fuel and air. However, it is possible to run LOP with a carb - just not as easy.
During climb out leaning should be confined to keeping the EGTs around the take-off value, once in the cruise aggressive leaning can take place to reduce the fuel flow past the peak EGT (in every cylinder) and, say 50F, beyond it. Hence the term running lean of peak. It is also desireable to run with the throttle wide open (Wide Open Throttle) and regulate the power output with rpm using a constant speed prop - so called WOT LOP operation. John Deakin explains it much better than I can.
If you run LOP incorrectly it is possible to wreck your engine, if you do it properly it is possible to save fuel and extend the life of your engine. Engine manufacturers typically don't encourage running LOP as some skill is required to do it successfully (to avoid law suits). But read Deakin's views on the manufacturers' position.
I haven't found much difference in oil temp when running LOP, but it should be cooler as the engine is generating less heat.
Please read Deakin's articles for a much better account of this whole subject. I found them very enlightening.
Yours, Pete
LOP = Lean of peak (EGT)
ROP = Rich of peak (EGT)
To simplify it in the extreme (and so not tell the whole story), leaning off the mixture will cause your engine to make more power, and so run hotter. When running with a rich(er than optimum for best power) mixture the excess fuel helps to keep the engine cool. At high power settings, say greater than 75%, there is a possibility of something called detonation happening - its to do with how the fuel & air burns in the cylinder - which is very bad news for the continued health of your engine. So the general recommendation is to run at least 50F below peak EGT on the rich side.
As you change the mixture from too much fuel to too little the EGT will increase to a maximum value, then decrease until the engine stops running. The absolute value of EGT is relatively unimportant as it is dependant on many things , including how far down the exhaust pipe the sensor is placed. CHT will follow EGT in general, but is much slower to react (as a large lump of meatl must heat up or cool down. However the absolute value of CHT is very important, the maximum CHT recommended by those who know is in the range 380 - 400 F. It is vital that CHTs do not exceed these values very much very often if your engine is to stand a good chance of reaching TBO.
To run LOP with any kind of success requires an engine monitor that displays each CHT and each EGT - in fact many would argue that to run your engine at all with any kind of success requires such a monitor.
The real reason running LOP is attractive is that it saves gas (1 or 2 gph in the cruise in RVs) and is better for the engine. A well balanced fuel injection system is required for really successful LOP operation - balanced means that each cylinder gets a equal dose of fuel and air. However, it is possible to run LOP with a carb - just not as easy.
During climb out leaning should be confined to keeping the EGTs around the take-off value, once in the cruise aggressive leaning can take place to reduce the fuel flow past the peak EGT (in every cylinder) and, say 50F, beyond it. Hence the term running lean of peak. It is also desireable to run with the throttle wide open (Wide Open Throttle) and regulate the power output with rpm using a constant speed prop - so called WOT LOP operation. John Deakin explains it much better than I can.
If you run LOP incorrectly it is possible to wreck your engine, if you do it properly it is possible to save fuel and extend the life of your engine. Engine manufacturers typically don't encourage running LOP as some skill is required to do it successfully (to avoid law suits). But read Deakin's views on the manufacturers' position.
I haven't found much difference in oil temp when running LOP, but it should be cooler as the engine is generating less heat.
Please read Deakin's articles for a much better account of this whole subject. I found them very enlightening.
Yours, Pete
f1rocket
Well Known Member
gmcjetpilot
Well Known Member
It nice if you can do it, but than its not a big deal
Some engines and installations are physically incapable of operating LOP operations, especially with small cubic inch engines.
If the discussion is saving fuel, the best way to do that is SLOW DOWN and throttle back. If you are burning 8.5 gal/hr at 190 mph, go 150 mph get way better air MPG's, saving way more fuel than you could with LOP operations.
Most of the LOP topic is towards thirsty 260HP, 310HP and 350HP crowd. LOP can mean a lot more to them. Also with a bigger 6 cylinder it is easier to get smooth LOP ops. LOP is not new, 1950's big radials had LOP operations.
Also some talking about LOP are selling expensive "custom" fuel injectors. I am not debating if it can work and be safe, hey 50 LOP is cooler than 50 ROP, but I suggest is not alway practical for use little guys (but some are able to do it).
If there is ANY uneven fuel flow than LOP is hard to achieve, at least smoothly. The EGT spread must be small. Besides uneven fuel flow and EGT between cylinders, many (most) airplanes have exhaust systems that have uneven length pipe lengths between cylinders. This produces differnt power characteristics and does not promote smooth operations, again especially in 4 cylinder engines. Uneven fuel injectors and carburated engines are just unable to run LOP operations, typically.
In general you need a balanced fuel injectors engine and the bigger the better the engine. Lycoming's opinion is LOP is really only applicable or worth while on larger 6 cyl engines; although many individuals have claimed routine LOP ops with there little 360's in RV's. Clearly it can be done, but it takes knowledge, effort and skill.
I understand Lyc's comment and where it comes from. They know the average (General Aviation) individual is not willing to go thru the effort to groom their engine for LOP. Also you MUST HAVE an ENGINE MONITOR, with each cylinder instrumented with EGT/CHT. It was only in the last 10 years or so that these monitors have become common. I was thrilled when I was renting planes, if it came with a single EGT gage; WOW, that was hot stuff. Now 4 and 6 channel monitors are common. Also you have to have the knowledge and skill to read and set the engine. Many will find their EGT spread is too wide to allow smooth LOP operations.
Here is some reading:
http://www.lycoming.textron.com/mai...ons/keyReprints/operation/leaningEngines.html
100F ROP is best power, Peak EGT best economy. (personaly 75F ROP for me)
http://www.lycoming.textron.com/mai...ions/keyReprints/operation/properLeaning.html
Good info on EGT interpretation
http://www.lycoming.textron.com/mai...Reprints/operation/exhaustGasTemperature.html
Applies to TIO-540 but good general tips
http://www.lycoming.textron.com/mai...tions/keyReprints/operation/tboTradeOffs.html
If you can operate LOP (more than 50F lean and get even smooth operations with out large EGT spread between cylinders) than good for you. If you can't or have a carb, than by all means lean properly (as discribed above) or even better fly at 65% or even 55% power. You can always run 50F ROP, but clearly from the data 50 LOP is better (cooler). Again throttle back and get better gas mileage. If you are willing to go 130 mph than you can save huge fuel.
On large engines LOP pays back more, so it is worth the effort. On little engines 1% or 4% is not a big deal and chasing it may be more difficult. Just slow down. Van flew a RV-9A down to 3.2 gal per hour.
Cheers George
Some engines and installations are physically incapable of operating LOP operations, especially with small cubic inch engines.
If the discussion is saving fuel, the best way to do that is SLOW DOWN and throttle back. If you are burning 8.5 gal/hr at 190 mph, go 150 mph get way better air MPG's, saving way more fuel than you could with LOP operations.
Most of the LOP topic is towards thirsty 260HP, 310HP and 350HP crowd. LOP can mean a lot more to them. Also with a bigger 6 cylinder it is easier to get smooth LOP ops. LOP is not new, 1950's big radials had LOP operations.
Also some talking about LOP are selling expensive "custom" fuel injectors. I am not debating if it can work and be safe, hey 50 LOP is cooler than 50 ROP, but I suggest is not alway practical for use little guys (but some are able to do it).
If there is ANY uneven fuel flow than LOP is hard to achieve, at least smoothly. The EGT spread must be small. Besides uneven fuel flow and EGT between cylinders, many (most) airplanes have exhaust systems that have uneven length pipe lengths between cylinders. This produces differnt power characteristics and does not promote smooth operations, again especially in 4 cylinder engines. Uneven fuel injectors and carburated engines are just unable to run LOP operations, typically.
In general you need a balanced fuel injectors engine and the bigger the better the engine. Lycoming's opinion is LOP is really only applicable or worth while on larger 6 cyl engines; although many individuals have claimed routine LOP ops with there little 360's in RV's. Clearly it can be done, but it takes knowledge, effort and skill.
I understand Lyc's comment and where it comes from. They know the average (General Aviation) individual is not willing to go thru the effort to groom their engine for LOP. Also you MUST HAVE an ENGINE MONITOR, with each cylinder instrumented with EGT/CHT. It was only in the last 10 years or so that these monitors have become common. I was thrilled when I was renting planes, if it came with a single EGT gage; WOW, that was hot stuff. Now 4 and 6 channel monitors are common. Also you have to have the knowledge and skill to read and set the engine. Many will find their EGT spread is too wide to allow smooth LOP operations.
Here is some reading:
http://www.lycoming.textron.com/mai...ons/keyReprints/operation/leaningEngines.html
100F ROP is best power, Peak EGT best economy. (personaly 75F ROP for me)
http://www.lycoming.textron.com/mai...ions/keyReprints/operation/properLeaning.html
Good info on EGT interpretation
http://www.lycoming.textron.com/mai...Reprints/operation/exhaustGasTemperature.html
Applies to TIO-540 but good general tips
http://www.lycoming.textron.com/mai...tions/keyReprints/operation/tboTradeOffs.html
If you can operate LOP (more than 50F lean and get even smooth operations with out large EGT spread between cylinders) than good for you. If you can't or have a carb, than by all means lean properly (as discribed above) or even better fly at 65% or even 55% power. You can always run 50F ROP, but clearly from the data 50 LOP is better (cooler). Again throttle back and get better gas mileage. If you are willing to go 130 mph than you can save huge fuel.
On large engines LOP pays back more, so it is worth the effort. On little engines 1% or 4% is not a big deal and chasing it may be more difficult. Just slow down. Van flew a RV-9A down to 3.2 gal per hour.
Cheers George
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osxuser
Well Known Member
I don't know George, the Cardinal RG guys do it all the time, running the IO-360A1B6 (and A1B6D). Doesn't seem to be a big deal to balence injectors anymore either, GAMI will do it for you (they even provide a Lean Test on their website to see if you need Gaminjectors at all). Airflow Performance will also do it for you. Also, Powerflow claims that using their exhaust allows Carb'd engines to run LOP, and appartently proved it on GAMI's dyno, but I obviously haven't seen it personally. I don't think it's as big a deal as your making out.
gmcjetpilot
Well Known Member
Fuel Nirvana! perfect fuel distribution
I agree. I think the (200HP) fuel injected angle valve, counter weighted engine is a better candidate than say the (180HP) parallel non-counter weight engine. I am sure the 180HP could be tuned to do LOP ops as well, however the 200HP seems to be more suited. I am sure I did not say it can't be done, Dan C. does it all the time on his 200HP Lyc. We know how picky he is, which is good. He can get 40F LOP. He also says just a HAIR leaner the power drops radically. Like he said that is good. I am guessing but if his engine is that close to the "stochimetric" edge any little change, even turbulence would affect that delicate balance. Possible yes but its got to be right. The engine needs to be well tuned, adjusted, balanced and healthy, that is all.
I agree balancing injectors with Performance Airflow is pretty cheap verse the GAMI for Contenentals. I think he will do a data eval of you engine monitors output.
GAMI injectors are way too much. I understand the who, how and why of fuel balancing, and it is not big deal. However it is something that needs to be done on many engines to get LOP ops. It may need "re-tuning" from time to time to keep that tight tolerance in fuel balance. I agree it's not a big deal to you and I, but most GA pilots just want it good enough. However with fuel prices going up the interest will go up on saving fuel.
I did say the typical Cessna pilot is not willing or able to take the effort to run LOP, I stand corrected. Cardinal RG guys are hard core. I am sure there are many more Cessna drivers out there that take the time, but I bet most don't care or are clueless.
Powerflow is nice and I grant their right to Hype and advertise their product all they want. I have 4 into 1's and my pipes are all within an inch on my low tech carbed 360. I am going to experiment with LOP, but will not be heartbroken if I can't achieve perfect fuel Nirvana.
If I can get LOP ops I will be lucky. I have heard a Carb guy say he got LOP ops? Again it's a matter of practical. If mine will not, do I want to spend the time to trace the reason and solve it? I find most say they can't get it to run smooth LOP. If I can get tight EGT's spread (less than 100F) I will be happy LOP or not.
What is practical for the masses on all engines of various "average" tune and condition? What Lycoming suggest.
If you try hard I think you can get any engine to do it, but some are easier than others, like BIG Fuel Injected 6 bangers. Also, bigger 6 cylinders will benifit more for LOP ops. They are burning more fuel, so 4% on 15 gal is way more than 4% on 9 gal. At $3.50 a gal 0.30 gal/hr is a buck five. Five hours you got lunch!
Again to save way more than the 0.30-0.50 gal and hour LOP gives by cranking the RPM back and enjoying the ride. I will try for stochimetric perfection but will be happy with mediocre fuel distribution.
Cheers George
Many good points, lets see.....osxuser said:
I agree. I think the (200HP) fuel injected angle valve, counter weighted engine is a better candidate than say the (180HP) parallel non-counter weight engine. I am sure the 180HP could be tuned to do LOP ops as well, however the 200HP seems to be more suited. I am sure I did not say it can't be done, Dan C. does it all the time on his 200HP Lyc. We know how picky he is, which is good. He can get 40F LOP. He also says just a HAIR leaner the power drops radically. Like he said that is good. I am guessing but if his engine is that close to the "stochimetric" edge any little change, even turbulence would affect that delicate balance. Possible yes but its got to be right. The engine needs to be well tuned, adjusted, balanced and healthy, that is all.
I agree balancing injectors with Performance Airflow is pretty cheap verse the GAMI for Contenentals. I think he will do a data eval of you engine monitors output.
GAMI injectors are way too much. I understand the who, how and why of fuel balancing, and it is not big deal. However it is something that needs to be done on many engines to get LOP ops. It may need "re-tuning" from time to time to keep that tight tolerance in fuel balance. I agree it's not a big deal to you and I, but most GA pilots just want it good enough. However with fuel prices going up the interest will go up on saving fuel.
I did say the typical Cessna pilot is not willing or able to take the effort to run LOP, I stand corrected. Cardinal RG guys are hard core. I am sure there are many more Cessna drivers out there that take the time, but I bet most don't care or are clueless.
Powerflow is nice and I grant their right to Hype and advertise their product all they want. I have 4 into 1's and my pipes are all within an inch on my low tech carbed 360. I am going to experiment with LOP, but will not be heartbroken if I can't achieve perfect fuel Nirvana.
If I can get LOP ops I will be lucky. I have heard a Carb guy say he got LOP ops? Again it's a matter of practical. If mine will not, do I want to spend the time to trace the reason and solve it? I find most say they can't get it to run smooth LOP. If I can get tight EGT's spread (less than 100F) I will be happy LOP or not.
What is practical for the masses on all engines of various "average" tune and condition? What Lycoming suggest.
If you try hard I think you can get any engine to do it, but some are easier than others, like BIG Fuel Injected 6 bangers. Also, bigger 6 cylinders will benifit more for LOP ops. They are burning more fuel, so 4% on 15 gal is way more than 4% on 9 gal. At $3.50 a gal 0.30 gal/hr is a buck five. Five hours you got lunch!
Again to save way more than the 0.30-0.50 gal and hour LOP gives by cranking the RPM back and enjoying the ride. I will try for stochimetric perfection but will be happy with mediocre fuel distribution.
Cheers George
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gmcjetpilot
Well Known Member
More better info
As far as way throttled back and LOP, I guess you could? I don't know why not. G
Thanks I thought it was like 0.50 gal/hr, I had no idea, good info. Quite amazing. I assume your 10 g/h was 100F or best power.dan said:
As far as way throttled back and LOP, I guess you could? I don't know why not. G
Kahuna
Moderatoring
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
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
Well Known Member
gmcjetpilot said:
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.
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f1rocket
Well Known Member
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.
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.
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gmcjetpilot
Well Known Member
Sounds like a plan
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
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.dan said:
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
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dan
Well Known Member
I didn't mention the 75% rule (of thumb), because I'm not a believer in that rule being hard & fast.gmcjetpilot said:
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
Well Known Member
Fly slower to get there faster
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.
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
Well Known Member
Over Lean
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.
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.
