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Lean of peak operation question

togaflyer

Well Known Member
I did my first LOP flight from Georgia to the Florida Keys. Four hours non stop. Just want to see if my numbers are in the ball park. So here is how she ran:

Altitude was 9,500, speed at 150 true, 9.9 GPH, 58 percent, manafold at 19.8 percent, prop at 2390, CHTs between 331 and 364, EGTs between 1325 to 1360, LOP was -43 to -64 degrees. Engine felt good.

Does this sound about right.
 
CHT

Mine runs much the same. I usually bring the prop back to 2300 in LOP cruise, see about the same FF (9.5 - 10gph), a little more speed at around 160ktas. The biggest difference is CHTs, I'm used to seeing around 300 - 320deg at that altitude and WOT, could just be your higher RPM, or my northern weather. What are your temps like on the ROP side?
 
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What engine do you have?

The fuel flow and power numbers depend on which engine you have, but no, I don't think your numbers sound right. In particular, your fuel flow is way too high to be LOP unless you have a bigger than typical engine. Or maybe you have an RV-10 with an IO-540? In that case your fuel flow seems better, but then why are you going so slow?

I have an IO-360 angle-valve engine. Here is what my numbers would look like at 9500 ft.

2400 RPM
MP= approx 21.0 -- 21.5 in hg something like that, WOT, of course.

170 kt true

Fuel flow 8.0--8.5 gph (depending on how far LOP I want to go)

CHT approx 290F
EGT approx 1275-1300F (again depending on how far LOP I want to go)

Now, two caveats:
1) Angle valve engines tend to run with cooler CHT because they put more heat load into the oil. I have a big cooler, so my oil temp would be 180F on a 'normal' day at this condition
2) EGT from one airplane to the next means almost nothing. It depends on where the probes are installed into the header pipes. What matters is where each cylinder temp is compared to its peak.
 
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Based on the slow TAS I?d guess you were too far done the LOP curve. In short, this means at that point you might be using a little less gas but power is dropping faster than fuel burn.

For 10GPH at 9500 feet you should have been over 160kts TAS. Try 15 to 20 degrees LOP, 2400rpm, WOT.

Did you balance the injectors?

Carl
 
You guys realize this is the RV-10 forum, right?

Pretty sure he’s running a IO-540, not a 360.

I’ll admit to thinking same thing until I saw what forum this post was in :).

Chris
 
I did my first LOP flight from Georgia to the Florida Keys. Four hours non stop. Just want to see if my numbers are in the ball park. So here is how she ran:

Altitude was 9,500, speed at 150 true, 9.9 GPH, 58 percent, manafold at 19.8 percent, prop at 2390, CHTs between 331 and 364, EGTs between 1325 to 1360, LOP was -43 to -64 degrees. Engine felt good.

Does this sound about right.


First things first. Did you use the lena find function to work out you were 43-63dFLOP? If so you were actually much leaner than that. Long story but basically, probes, algorithms and the fact when the CHT comes down it flows more air, and you will soon find that if you find peak again from the lean side, you were leaner than you thought. Lean Find functions are great concept teaching tools, but far from perfect operationally.

9500' depending on OAT would typically be a 10.5-10.7 GPH LOP setting. I get 9.9 at 13,000'

The fact your engine felt good suggests it has good F/A ratios and the GAMI spread would be 0.5GPH or less. So be happy!

Your TAS should be more like 160-164KTAS, so try getting more like 10dF LOP at that height (from the lean side) and see how you go. If the displayed TAS is not in the 160-164 range I bet you have a static source error. Then do a GPS box test. You are probably faster than you think.
 
You guys realize this is the RV-10 forum, right?

Pretty sure he?s running a IO-540, not a 360.

I?ll admit to thinking same thing until I saw what forum this post was in :).

Chris

Ah, yes, I see. My bad. When you look at "today's posts" it doesn't jump out at you which sub-forum it was posted under. I should have looked.

So your numbers look like they are in the ball park, except your speed. Check your static system as suggested
 
the fact when the CHT comes down it flows more air, ...

I am curious about your thoughts on how CHT impacts air flow into a cylinder. I understand how higher CHTs will marginally increase the air temp in the cylinder and how hotter air is less dense and therefore requiring less fuel. However, I am stumped on how CHT impacts the actual flow of air into the cylnder.

Larry
 
The volumetric efficiency changes slightly.......much smarter folk like George Braly could give you specifics, but go try this for yourself. Find peak from the rich side at top of climb, get appropriately LOP, then after CHT settles then find peak from the lean side and set the same amount LOP. The FF will be higher every time.
 
I have an IO 540 with 9:1 jugs. The plane is unpainted so that may account for the loss of a few knots. I have a Garmin G3X system and used the lean assist. My cylinders run 360 to 390 ROP. I showed -43 LOP on the last cylinder to peak, as my LOP setting. OAT was 10c at 9,500.


Question, how LOP do you go, -20, -30, -40 or ?. What power setting do you see. Are you looking for any particular numbers when setting to LOP. I was at 58 percent, is that about right or should it be set higher.
 
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Altitude was 9,500, speed at 150 true, 9.9 GPH, 58 percent, manafold at 19.8 percent, prop at 2390, CHTs between 331 and 364, EGTs between 1325 to 1360, LOP was -43 to -64 degrees. Engine felt good.

I have an IO 540 with 9:1 jugs. The plane is unpainted so that may account for the loss of a few knots. I have a Garmin G3X system and used the lean assist. My cylinders run 360 to 390 ROP. I showed -43 LOP on the last cylinder to peak, as my LOP setting. OAT was 10c at 9,500.

Question, how LOP do you go, -20, -30, -40 or ?. What power setting do you see. Are you looking for any particular numbers when setting to LOP. I was at 58 percent, is that about right or should it be set higher.

Let's tidy up a few fundamentals before moving forward.

Manifold pressure units are not a percentage. It is expressed in inches of mercury (abbreviated ""Hg"), typically measured at the intake port of the right rear cylinder.

You did not mention throttle position. We would generally assume you were at wide open throttle at this altitude. However, 19.8" Hg is a little low as compared to some other Vans examples. Could you confirm throttle setting?

Your exhaust gas temperatures do not matter in absolute terms, so knowing they were between 1325 and 1360 is useless information. Here the only EGT information of note is where you are relative to peak, and you've noted -43 to -64 degrees. As others have commented, there is nothing wrong with being that lean, but it puts you pretty far down on power, so airspeed will be reduced as compared to what most RV-10 owners post as normal LOP cruise.

Which brings us to your "How far to lean?" question. The answer is "As lean as you wish", the limits being (a) unacceptable loss of airspeed, or (b) engine roughness. What is practical? Lycoming has always suggested peak EGT as the economy cruise setting. Despite much rock throwing (at Lycoming), you'll note that LOP devotees very often suggest something like a whopping 10 degrees LOP at altitude. Neither is wrong.

At 9500 feet you should be at wide open throttle, and if so, the only way to increase indicated percent power (you reported 58%) would be to increase RPM. Again, there is no "wrong" RPM within the practical range one might select for cruise. More will require higher fuel flow, less will require less. You'll go faster or you'll go slower. Almost everyone has a favorite setting, usually based on comfort (like perceived vibration) or old belief (the way they always did it). Others enjoy mapping every possible combination, then developing an operating guide based on reams of data. That's cool too.
 
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Dan, I was not at WOT. I pulled back to 60 percent before doing a slow lean to peak. Once LOP I never push it the remaining throttle in I had left. I was a bit Leary of the red box syndrome. So I should be WOT. At 9.5 I was still up around 70 percent engine power, so should I do the big pull down to 10 gph, then enrich to see where peak is at. Sounds like I definitely gave up some speed by not being WOT and maybe too LOP.
 
It seems you never did a GAMI run to balance injectors. Do that before anything else. It only takes a few minutes and as you do it you will get experience with LOP operations.

On my IO-540 (new from Van’s) the initial GAMI spread was about 1 gph. LOP operation was horrible. It took just three iterations (and change out of four of the six injector nozzles) to get the GAMI spread down to 0.1 gph. Get your replacement injector nozzles from AirFlow Performance (I think $26 each). Don will help you figure out what size to get.

Typical LOP ops at 8K’ is WOT and 2400 RPM for 173kts TAS, 11.5gph. Above 12k’ it is WOT and 2450RPM to get the same 170+ speed but fuel burn is down to a little over 10gph. Drop the RPM and you will save gas at the cost of some airspeed. Have the plane at max weight and you will of course lose some airspeed.

Go out, burn some gas and get some engine data. No better way to spend a weekend.

Carl
 
Dan, I was not at WOT. I pulled back to 60 percent before doing a slow lean to peak. Once LOP I never push it the remaining throttle in I had left. I was a bit Leary of the red box syndrome. So I should be WOT. At 9.5 I was still up around 70 percent engine power, so should I do the big pull down to 10 gph, then enrich to see where peak is at. Sounds like I definitely gave up some speed by not being WOT and maybe too LOP.


Until you throughly understand LOP, what's happening, now A/F ratio works, etc, you should not make power changes (throttle or RPM) changes while operating LOP.

Establish your cruise power setting, let your engine cool from the climb while ROP for 1-2 minutes. Then, start leaning to peak and move to LOP. If you need to descent, go ROP. If you want to climb, go back to ROP. Then when established level, repeat the LOP process.

Making power changes wrong can cause major roughness, or possibly wandering your way towards running at peak EGT, possibly above what's considered acceptable for extended periods of time. I'm sure it's a minor concern, but when teaching pilots about LOP operations, I strongly recommend keeping it as simple as possible. LOP for cruise, ROP for everything else.
 
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Until you throughly understand LOP, what's happening, now A/F ratio works, etc, you should not make power changes (throttle or RPM) changes while operating LOP.

Yeah, do it wrong and the scary clown pops out of the oil door.

Red%20Box.jpg


If you need to descent, go ROP. If you want to climb, go back to ROP. Then when established level, repeat the LOP process.

Descend LOP for as long it runs smoothly. I mean all the way to pattern altitude if you wish. It will run smooth way LOP when the prop is unloaded. Just go rich before pushing the power back in.

Climb LOP if you wish. Most RV altitude adjustments in cruise merely require raising the nose, no power change. Assuming constant flow injection, it will get richer as you go up. You may need to lean a bit as you go along, just like climbing on the ROP side.

Making power changes wrong can cause major roughness, or possibly wandering your way towards running at peak EGT, possibly above what's considered acceptable for extended periods of time.

There is no time limit on peak EGT, only a manufacturer-imposed percent power limit.

You want simple? If it runs well and temperatures are low, it's fine.
 
I agree with Dan. We have several users who fly LOP in the climb, descent and even while doing formation work- any time you want to keep CHTs down, save fuel and don't need max power.
 
I agree with Dan. We have several users who fly LOP in the climb, descent and even while doing formation work- any time you want to keep CHTs down, save fuel and don't need max power.


I've always wanted to try it in the climb, but the window to hit seems pretty narrow and always moving. Leaving it WOT and using fuel to control power means flying it like a diesel! If only we could actually get a good compression ignition engine.
 
...
There is no time limit on peak EGT, only a manufacturer-imposed percent power limit....

So is there a rule of thumb for that "percent power setting"? My -4 has an O-320 and F/P Catto three blade prop. I generally cruse at between 62-65% power and a little bit ROP burning about 8.2-8.5 GPH. At 9500' my MAP is indicating about 19.5". I would love to run LOP but my engine starts to spit and sputter if I try to go any leaner than peak. From what I've understood up until this point that running at peak wasn't heathy for the engine. At peak and at those flight parameters I can shave about another 1 GPH off of my fuel consumption. So once again, is there a rule of thumb that should be followed?

Thanks,
Mark
 
I just yesterday finished a rather long Baja trip in my RV10 with BPE IO-540 9.1

I have played around with LOP quite a bit, but the resultant loss of airspeed just doesn’t make the rather slight increase in nm/gal seem worthwhile to me unless specifically needing to extend range. The engine runs smooth enough but I always feel like I’m sitting on eggshells.
The big dog likes to eat. Feed it and it purrs like a kitten. and the few gallons that those precious last 15 knots cost seem well worth the sheer pleasure of passing the other aircraft in the group (210’s, Beech’s, Mooney’s) and really energizes the air to air trash talk.
 
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So is there a rule of thumb for that "percent power setting"?

65%, and it's not a hard limit, merely a recommendation.

I would love to run LOP but my engine starts to spit and sputter if I try to go any leaner than peak.

Then don't.

Personally I think roughness is about the only bad thing you can cause with a mixture knob at 9500 feet.
 
I've always wanted to try it in the climb, but the window to hit seems pretty narrow and always moving. Leaving it WOT and using fuel to control power means flying it like a diesel! If only we could actually get a good compression ignition engine.

Most of these folks are flying Rockets or light angle valve RVs with really good power to weight ratios. They actually use the prop pitch more to regulate power than mixture and the EFI controls the AFR while you climb and descend automatically.
 
It never ceases to amaze me how crazy LOP discussions get. My take away from reading this thread is "everyone, please, pay attention to what Dan H. is saying here. His input is what makes clear sense without all the mythology".

One thing that I think is exceedingly useful in getting past the mythology is to have direct access to A/F ratio. I have an article coming out in Kitplanes in a couple of months on my experience adding A/F ratio direct data (a display in my panel that I tune to my desired ratios for particular operating regimes), and it is a wonderful way to really know where you are operating, rather than the crazy dance of finding peak EGT, then leaning or enriching either side of stoichiometric mixture. And to pre-empt an uprising about how leaded gas trashes oxygen sensors, there are some sensors available that are tolerant to LL levels, particularly if running LOP.

Reinhard Metz
 
I don’t believe % power indications from an engine monitor will be accurate when LOP, at least the GRT’s use a Lycoming % power table that goes out the window when LOP.
15.7 x fuel flow / rated HP works when LOP.
Edit: that works with 8.5:1 compression ratio, I don’t know the number for others C/R’s
Tim Andres
 
I think that it is very important to understand these concepts and know what our machines can do. However, glancing through the latest (excellent) KitPlanes buyers guide has reinforced the idea that while every airplane design is somewhat of a compromise, there are still a wide variety of worthy missions and aircraft designed to fulfill them. An RV10 in particular is a marvelous machine, but I wouldn?t classify it as an economy ride.

If one has chosen a fast design, paid for a fast design, built a fast design, then by golly, it seems to me they ought to enjoy opening her up and letting the big dog eat.

Nobody buys a Corvette to drive like a Prius.
 
Reading all the post and doing some more read up on the red box theory, it has been very informative and helpful. I realize my mistakes and misunderstandings. Looking forward to my next flight and LOP. Thanks to everyone!
 
I've always wanted to try it in the climb, but the window to hit seems pretty narrow and always moving. Leaving it WOT and using fuel to control power means flying it like a diesel! If only we could actually get a good compression ignition engine.

I do LOP climbs when not in a hurry or when it's cool, producing more power. Don't be afraid, just pull the mixture to known LOP EGTs. The window doesn't move fast and it's not as dangerous as some would have you believe to be outside the window for short periods. Just keep leaning as you climb to maintain your target EGT. I tend to move to LOP climb after 3000' to avoid some risks.

Larry
 
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I'd be interested in the reasons the VE changes with CHT as well.

This question seems to have gotten forgotten as the thread moved along. I think what happens is that there is some conduction heating of the intake tubes from the cylinders that heats the intake charge as it flows through the intake tubes toward the cylinder.

I have certainly noticed that if I go LOP at top of climb and lean to a target fuel flow and expected EGT and CHT, then check back a little while later, there has been further drop in EGT and CHT both -- because it is now farther LOP. I usually just leave it, because exactly as Dan says, if it is running smoothly, it is fine.

While I am climbing at 100F or so ROP so the EGT's are lower, the CHT's are higher than the stabilized cruise LOP CHT's. So at top of climb, the cylinders are hotter than they will be once stabilized. After a few minutes at cruise, the cylinders are cooler, and so presumably the intake tubes are cooler too, so there is denser charge which makes it leaner for the same mixture lever position.

Make sense?
 
This question seems to have gotten forgotten as the thread moved along. I think what happens is that there is some conduction heating of the intake tubes from the cylinders that heats the intake charge as it flows through the intake tubes toward the cylinder.

Make sense?

VE is the actual mass flow pumped vs. the theoretical mass flow pumped based on the rpm and displacement. The heating of the charge air in the intake tubes either through conduction at the flange or from impingement of the cooling air from the fins above on the steel tube below would be virtually immeasurable given the short time duration the charge air is in the tube between intake strokes, the small surface to volume ratio and low thermal conductivity of the steel.

I don't see that CHT would have any significant effect on how much mass flow is processed through the engine which is determined by flow restriction within the head, valves, intake and exhaust systems plus the delta P inlet to outlet (sometimes we'll have favorable or unfavorable acoustic effects helping or hindering VE at certain rpms).
 
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VE is the actual mass flow pumped vs. the theoretical mass flow pumped based on the rpm and displacement. The heating of the charge air in the intake tubes either through conduction at the flange or from impingement of the cooling air from the fins above on the steel tube below would be virtually immeasurable given the short time duration the charge air is in the tube between intake strokes, the small surface to volume ratio and low thermal conductivity of the steel.

I don't see that CHT would have any significant effect on how much mass flow is processed through the engine which determined by flow restriction within the head, valves, intake and exhaust systems plus the delta P inlet to outlet (sometimes we'll have favorable or unfavorable acoustic effects helping or hindering VE at certain rpms).

Completely agree.
 
I'd also add, to clarify, that once the air passes the throttle plate, it's been inducted and that air will be exhausted a few milliseconds later.
 
I do LOP climbs when not in a hurry or when it's cool, producing more power. Don't be afraid, just pull the mixture to known LOP EGTs. The window doesn't move fast and it's not as dangerous as some would have you believe to be outside the window for short periods. Just keep leaning as you climb to maintain your target EGT. I tend to move to LOP climb after 3000' to avoid some risks.

Larry


while at WOT?
 
Ram Air Effect

I'll offer that the ram air effect is the primary reason for the (small) increase in MP value at top of climb as the aircraft accelerates after the comparatively slower airspeed during climb. As a result, the mixture gets (a little) leaner once cruise speed is established.
 
I'll offer that the ram air effect is the primary reason for the (small) increase in MP value at top of climb as the aircraft accelerates after the comparatively slower airspeed during climb. As a result, the mixture gets (a little) leaner once cruise speed is established.

Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl
 
Servo Compensation

That's true - fair point, assuming that the servo sensitivity is fine enough to compensate. Consider also the injector bodies are subject to a relatively higher air pressure in the cowling as airspeed increases, so there might be a correlation there with a tiny fraction more air in the atomization stream compared to that in the climb. Interesting to ponder if nothing else... :)
 
That's true - fair point, assuming that the servo sensitivity is fine enough to compensate. Consider also the injector bodies are subject to a relatively higher air pressure in the cowling as airspeed increases, so there might be a correlation there with a tiny fraction more air in the atomization stream compared to that in the climb. Interesting to ponder if nothing else... :)

At WOT the bleed air delta is very low, not that it matters in this context. Pressure increases on both sides of the nozzle (cooling plenum space and within the cylinder head intake tract), thus velocity change doesn't change the delta. There is no additional bleed air to lean the mixture.
 
Bleed air delta

I see that a bit differently, Dan. The bleed air delta is bound to increase as a function of airspeed in a standard induction RV10. This is because the ram air applied to the upper plenum is virtually unimpeded (disregard nacelle inefficiency), compared to the induction path to the engine. The small inlet, air filter, throttle body and relatively complex/curvy path to the cylinder head all contribute to dynamic pressure drop . The faster you go, the larger the delta between plenum and manifold pressure. This is intuitive, however I believe you may have empirical manometer data from your excellent exploration of cowl exit design that would support the numerical relationship between MP and plenum pressure.
 
while at WOT?

Yes. I will be WOT and ROP in climb after take off. I stay ROP at the lower altitudes as more power is produced and more risks. Around 3000, I just pull the mixture to a FF of 8 GPH or so. 8 GPH is is 75% power for the 160 HP 320. 8 is a target and I don't worry if I am a bit higher and I don't worry about time spent in the leaning process, though I do it in one session to get where I want to be. I also watch the EGTs to confirm that I have settled into know LOP ranges.

No sudden engine failures nor any indication of detonation or other problems in 600 hours.

Larry
 
Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl

From my experience, the servo doesn't compensate in a linear fashion when manually leaned with the mixture control. Next time you are in cruise, add a bit of throttle. You'll notice that you get leaner and leaner the more you add. The mixture adjustment is not linear with air flow based fuel control in the servo. Increases in throttle or MP seem to require enriching the mixture to maintain the same AFR.
 
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This is intuitive, however I believe you may have empirical manometer data from your excellent exploration of cowl exit design that would support the numerical relationship between MP and plenum pressure.

Actually, I directly measured average bleed air deltas about two weeks ago, and expect to measure on a per cycle basis in the near future. The differential pressure transducer got here last Wednesday, but this past weekend I was sidetracked by experiments involving balloons and Jameson.
 
Not exactly.

A MP increase by ram air is the same as adding throttle to increase MP. Your servo will add more fuel. Effect on mixture will be in the grass (assuming constant altitude).

Carl

I think that is true when ROP, but my observation of the Bendix servo behavior when LOP is that it does not change fuel flow to match changes in MP in a way that keeps mixture even approximately constant.
 
I run a carbeurated O-540 (250 hp) and see about the same numbers as the OP. I add another 1/2 gph and cruise at 160 knots at 10.5 gph. Our claim to fame is the low drag airframe. I can still get 160 true at almost 20,000? DA making less than 50% power. I have tried it as high as 22,000? DA and was at 154 KTAS enjoying a 40 knot tailwind burning 8.7gph.
 
I don?t believe % power indications from an engine monitor will be accurate when LOP, at least the GRT?s use a Lycoming % power table that goes out the window when LOP.
15.7 x fuel flow / rated HP works when LOP.
Edit: that works with 8.5:1 compression ratio, I don?t know the number for others C/R?s
Tim Andres
Actually the number for 8.5 to 1 is 15.0 x FF= HP, HP/rated power equals % power. For 200 hp IO360 that is 10gph when LOP for 75%. For 260HP IO540 that is 13 gph =195 hp = 75%.
It looks to me like Dynon is using a FF ratio to MAP and RPM to determine % power. I had a problem with my fuel flow, indicating much higher than actual, and it wouldn't show LOP when so lean engine was stumbling and losing power. Now that I fixed the FF, the LOP/ROP indications appear to match the above calcs. You can't hurt a normally aspirated engine at any mixture setting if you have RPM and MAP where they fit the 65% setting. Once you have achieved LOP with a fuel injected engine, you can add throttle to WOT and you will still be LOP regardless of power generated.
For climb I just roughly adjust mixture to maintain EGTs between 1200 and 1300 until I level off and lean to LOP.
 
Just to add another data point, I get 171 kt TAS at 9500 ft PA, 5 degC, 21.5 in MP, 2300 rpm and 10.7 gph. I think my instrumentation is accurate and the speed is confirmed by GPS speed check.
 
Kelly, do you have a source for that? Not arguing, just want to know which is correct. I?ve seen 15.7 quoted for years, never seen a multiplyer for other CR?s.
Tim Andres



Actually the number for 8.5 to 1 is 15.0 x FF= HP, HP/rated power equals % power. For 200 hp IO360 that is 10gph when LOP for 75%. For 260HP IO540 that is 13 gph =195 hp = 75%.
It looks to me like Dynon is using a FF ratio to MAP and RPM to determine % power. I had a problem with my fuel flow, indicating much higher than actual, and it wouldn't show LOP when so lean engine was stumbling and losing power. Now that I fixed the FF, the LOP/ROP indications appear to match the above calcs. You can't hurt a normally aspirated engine at any mixture setting if you have RPM and MAP where they fit the 65% setting. Once you have achieved LOP with a fuel injected engine, you can add throttle to WOT and you will still be LOP regardless of power generated.
For climb I just roughly adjust mixture to maintain EGTs between 1200 and 1300 until I level off and lean to LOP.
 
Kelly, do you have a source for that? Not arguing, just want to know which is correct. I?ve seen 15.7 quoted for years, never seen a multiplyer for other CR?s.
Tim Andres
Yes...Gami/Advanced Pilot Seminars. I've only seen 14.9 or 15.0 for our compression ratio. Have used that figure reliably for around 18 years, or shortly after John Deakin did his Pelican's Perch articles.
Turbo-charged with around 7:1 compression use 13.7 multiplier.
I have been searching to get you the actual reference. Taking longer than expected.
 
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