(LOP) Experts Are Everywhere – The Rebuttal By John Deakin ©June, 2013

[comanchepilot]

Don't confuse him with facts.

You come fly my airplane and then you can insult me, fair enough?

I have a GEM in my airplane. As Geoff notes, there are 4 points there and he is generally right on. . .

about 125ROP I get 160ktas at 2500rpm, about 15.6 gph at 7500. I RARELY fly there. BTW - that is a POH BOOK number - try that with your 1971 airplane. . .

I can lean to about 14.5-6 gph, at 7500' and see just rich of peak - the dreaded red box - and get 157ktas - as he notes - a small reduction in airspeed for $6-7 an hour less DOC.

I can lean to 50LOP - I then see about 146ktas. fuel flow is about 12.5.

However, and this is where we need to chat when I lean per the DEAKIN recommendations to 75-100LOP I'm down near 140-142ktas. This is 11.3gph. Sure - its 4.3gph less - $25 an hour in DOC - and after 4 hours I've added more than an hour to range - but I'm down 16knots per hour plus what ever the head wind component ends up being. We get a head wind component 60% of the time.

What I can do in the Comanche is what many cannot do - climb to 10500 or 11500, STILL be burning 11.5gph but be seeing 153 ktas. Take a non-high hp airplane up there and you're way down in speed even with the thinner air - but a low drag airplane loses alot less speed from the reduction of power over 10k than a draggier airplane like a Cherokee, Skyhawk/Lane, Grumman etc.

And no - LOP does not generate a headwind - don't be dumb - but it is obvious if you are slower to begin with a headwind component takes a bigger chunk of your groundspeed . . . .

PS: I'm not GAMI'd but I've done the poor man's Lycoming injector balancing - taken the hottest and coldest and swapped injectors, did it again, and then again - and my EGT's are completely flat when leaned, as are my CHT's - so its as good as it would get with GAMI's - Lycs seem to have that ability.

 

[Ted]

I can lean to 50LOP - I then see about 146ktas. fuel flow is about 12.5.

However, and this is where we need to chat when I lean per the DEAKIN recommendations to 75-100LOP I'm down near 140-142ktas. This is 11.3gph. Sure - its 4.3gph less - $25 an hour in DOC - and after 4 hours I've added more than an hour to range - but I'm down 16knots per hour plus what ever the head wind component ends up being. We get a head wind component 60% of the time.

75-100 LOP is too lean on your engine. For a big turbocharged engine, might make more sense. Not for yours. 50 LOP is the leanest you want to go.

PS: I'm not GAMI'd but I've done the poor man's Lycoming injector balancing - taken the hottest and coldest and swapped injectors, did it again, and then again - and my EGT's are completely flat when leaned, as are my CHT's - so its as good as it would get with GAMI's - Lycs seem to have that ability.

Flat EGTs by themselves aren't necessarily what you're after, it's EGTs that all peak at the same point. But if you're able to lean to 75-100 LOP, then you've got them well balanced. It's just that 75-100 LOP is too lean on your engine. In the Aztec more typically I was about 25-50 LOP.

 

[kyleb]

I've always understood LOP from an engineering/chemistry perspective, and from both of those perspectives, it makes sense. However, advocates rarely talk about both the fuel savings and the performance loss in the same discussion.

The real question IMO, is "What is your fuel burn at (say) 65% power when the engine is 50* ROP, and what is your fuel burn at the same power setting (same prop HP) when the engine is 50* LOP. Without clearly quantifying that (every time you discuss the topic), the discussion is meaningless.

 

[alfadog]

I've always understood LOP from an engineering/chemistry perspective, and from both of those perspectives, it makes sense. However, advocates rarely talk about both the fuel savings and the performance loss in the same discussion.

The real question IMO, is "What is your fuel burn at (say) 65% power when the engine is 50* ROP, and what is your fuel burn at the same power setting (same prop HP) when the engine is 50* LOP. Without clearly quantifying that (every time you discuss the topic), the discussion is meaningless.

No expert here, but it seem obvious to me that both rich burn and lean burn will result in a loss in volumetric efficiency from an exact stoichiometric intake mixture. And, as you know, one difference is that in rich burn, excess fuel is providing the cooling of the EGT while in lean burn it is excess air. Equally obviously, one will yield better specific fuel consumption.

 

[kgruber]

PS: I'm not GAMI'd but I've done the poor man's Lycoming injector balancing - taken the hottest and coldest and swapped injectors, did it again, and then again - and my EGT's are completely flat when leaned, as are my CHT's - so its as good as it would get with GAMI's - Lycs seem to have that ability.

Having equal EGTs and CHTs means nothing. No wonder you are confused.

 

[Ted]

I've always understood LOP from an engineering/chemistry perspective, and from both of those perspectives, it makes sense. However, advocates rarely talk about both the fuel savings and the performance loss in the same discussion.

The real question IMO, is "What is your fuel burn at (say) 65% power when the engine is 50* ROP, and what is your fuel burn at the same power setting (same prop HP) when the engine is 50* LOP. Without clearly quantifying that (every time you discuss the topic), the discussion is meaningless.

When you look at your BSFC (brake specific fuel consumption) you can expect to see a significant difference for the same power settings. Figure around a 15% reduction between best power and best economy (actual will vary).

 

[Capt. Geoffrey Thorpe]

The real question IMO, is "What is your fuel burn at (say) 65% power when the engine is 50* ROP, and what is your fuel burn at the same power setting (same prop HP) when the engine is 50* LOP. Without clearly quantifying that (every time you discuss the topic), the discussion is meaningless.

Even the Lycoming chart appears to be done constant manifold pressure which makes it more difficult to compare the actual BSFC changes at constant power.

In general, if you can open the throttle to maintain constant power, your actual BSFC will show more improvement than it would at constant manifold pressure because of reduced pumping losses. However, if you have a naturally aspirated engine and are at altitude, it may not be possible to maintain the power level.

From 50 rich to 50 lean is only going to get you a couple percent - you are pretty close to stoichiometric to start with. How close is impossible to say given just the data provided in the Lycoming service bulletin that started this thread.

edit: Ted threw out 15% from best power - but that is (I assume) significantly richer than just 50 degrees rich hence the difference in assumed improvement.

 

[alfadog]

When you look at your BSFC (brake specific fuel consumption) you can expect to see a significant difference for the same power settings. Figure around a 15% reduction between best power and best economy (actual will vary).

Does peak EGT correspond to a stoichiometric mixture?

 

[Ted]

edit: Ted threw out 15% from best power - but that is (I assume) significantly richer than just 50 degrees rich hence the difference in assumed improvement.

It's been a few years since I've been running through dyno charts, so I forget. But most naturally aspirated Lycoming engines were rated at a best power of 0.50 lb/hp-hr and best economy ended up being about 0.42 lb/hp-hr. As far as what EGT that was, I honestly don't remember with any certainty, but I think something like 100F would be a rough order of magnitude.

 

[timwinters]

You come fly my airplane and then you can insult me, fair enough?

I don't HAVE to fly your airplane to know that the Light and Sporty Guy stated a simple fact tht you didn't understand...you proved that with a previous post.

 

[comanchepilot]

flat egt's will peak roughly at the same time - and the lean finder function of the GEM swaps cylinders every time I use it - so while a different cylinder may peak each time - that seems to indicate that the engine is running fairly evenly. Flat EGT's are meaningful.

Ok - so 75F LOP is too lean for my engine - but it runs smoothly at that point - again - decent mixture distribution.

My point here is simply to make the argument that LOP slows you down and it can end up costing you more. Everyone agrees that if you can restore manifold pressure with a turbocharger [or fly low enough to have throttle left] you can offset the LOP slow down, I owned a turbocharged airplane [Viking] and I would fly it at 26" of MP and 2200 RPM - it was nice and smooth at that RPM but if I wanted to increase the speed back to the ROP point - I would need to go to 27" of MP - which is max sustained - and then to 2400rpm - which was nowhere near as smooth and is also max sustained - and I would get within 5 knots of that cruise but fuel flow was within 2 gallons per hour - its just not worth having to pay that much attention to the engine all the time - and really pay attention during descents and power change points -

LOP:
Lower fuel burn
Cleaner burn
Less residue - meaning less 'gunk' accumulating
Lower internal cylinder pressures
Less engine stress
Slower speeds.

ROP:
Faster
Dirtier
more costly

I get it - I AGREE with everything the LOP people say - but with a normally aspirated engine you lose 15% of your speed. If you are ok with that - then do it.

 

[Ted]

flat egt's will peak roughly at the same time - and the lean finder function of the GEM swaps cylinders every time I use it - so while a different cylinder may peak each time - that seems to indicate that the engine is running fairly evenly. Flat EGT's are meaningful.

What do I know, I only spent 2,000 hours sitting in front of a dyno running these things.

I hear a lot of people saying "My EGTs are flat, therefore they're good and even." Well, they might be, might not be. These EGT probes aren't very good and the readings they give aren't always as accurate as you'd like. For example, on the 310 the left engine doesn't look even at all, the right one does. It follows the probes and has been the same through a complete engine overhaul, but this time with GAMIjectors. Both engines will run smoothly until they quit running.

Ok - so 75F LOP is too lean for my engine - but it runs smoothly at that point - again - decent mixture distribution.

Correct. And your engine will run fine there, but you'll have lost a lot of power and actually be running less efficiently than you would be had you stayed at a more optimal leaned out setting.

My point here is simply to make the argument that LOP slows you down and it can end up costing you more.

I've never seen any math that supports that when done properly.

I get it - I AGREE with everything the LOP people say - but with a normally aspirated engine you lose 15% of your speed. If you are ok with that - then do it.

If you lose 15% of your speed, you're doing it wrong.

 

[gismo]

flat egt's will peak roughly at the same time - and the lean finder function of the GEM swaps cylinders every time I use it - so while a different cylinder may peak each time - that seems to indicate that the engine is running fairly evenly. Flat EGT's are meaningful.

Sorry but that's just not true. "Flat EGTs" simply mean the various factors that affect EGT (e.g. mixture, probe location, valve timing, ignition timing, airflow over the exhaust, and CHT to name a few) happen to conspire to yield equal EGTs. There's nothing wrong with equal EGTs but they don't by themselves indicate how well balanced your cylinder to cylinder air fuel ratios. What does matter is the FF that each cylinder reaches peak EGT at.

Ok - so 75F LOP is too lean for my engine - but it runs smoothly at that point - again - decent mixture distribution.

That is indeed a very good indication of "decent mixture distribution".

My point here is simply to make the argument that LOP slows you down and it can end up costing you more.

It is true that at any altitude you can make more power ROP than LOP but in most NA powered airplanes approximately 65% max rated power is a "sweet spot" on the speed vs economy curve and most of those can make 65% power at typical cruising altitudes in the 4000-9000 MSL range. And if you can make 65% power LOP you will be going just as fast as you would making 65% ROP. Now if you want to flog the horses to 75% or more you're not gonna get there LOP above about 5000 DA and your notion that LOP costs you in terms of speed becomes more of a reality.

Everyone agrees that if you can restore manifold pressure with a turbocharger [or fly low enough to have throttle left] you can offset the LOP slow down, I owned a turbocharged airplane [Viking] and I would fly it at 26" of MP and 2200 RPM - it was nice and smooth at that RPM but if I wanted to increase the speed back to the ROP point - I would need to go to 27" of MP - which is max sustained - and then to 2400rpm - which was nowhere near as smooth and is also max sustained - and I would get within 5 knots of that cruise but fuel flow was within 2 gallons per hour - its just not worth having to pay that much attention to the engine all the time - and really pay attention during descents and power change points -

It is true that some LOP pundits offer a nonsensical representation of the economy gained by running LOP with statements like "I use 10% less fuel on a trip and only lose 5Kt". The truth is at least half of that economy improvement could be had by reducing power while remaining LOP. But if you compare ROP and LOP fuel flows at the same airspeed you will still see at least a 5% improvement (or more if you also follow the APS recommendation to use a higher fuel flow than 50 ROP).

LOP:
Lower fuel burn
Cleaner burn
Less residue - meaning less 'gunk' accumulating
Lower internal cylinder pressures
Less engine stress
Slower speeds.

ROP:
Faster
Dirtier
more costly

I get it - I AGREE with everything the LOP people say - but with a normally aspirated engine you lose 15% of your speed. If you are ok with that - then do it.

15% is way more than anyone operating LOP properly will ever experience. The reduction in power from best power to min BFSC is about 10% and since at typical cruise speeds below 10K MSL speed is approximately proportional to the cube of power. That means a 10% power reduction should result in no more than a 4% loss in speed (cube root of .9 is .965) and your 15% loss in speed represents almost a 40% decrease in power. This suggests that you were leaning way beyond min BFSC.

 

[comanchepilot]

I will run some practice flights when it cools off with a friend who can keep a decent record and knows what I am trying to do - and we'll try to lean it to 25-50 lean of peak and see what TAS I get -

 

[Capt. Geoffrey Thorpe]

When anyone asks "what airplane should I buy?" there is a chorus of "What is your mission?" The same thing applies here.

If you are renting wet, hobbs, then the only reason to touch either the red or black knobs is to reduce the CO in the cockpit from the cracked exhaust system to acceptable levels.

If you are building hours in your own airplane, then you fly Vy at best BSFC.

If you want to get from point A to point B with minimum fuel, you fly Vy +- 1/2 wind speed (and again, lean).

If time = $ (and there is a proof of that somewhere on the web), then it's run the esso bee right up against the wall.

But, for many of us, the cost function is not quite as straight forward or as well defined - and even may vary from day to day. How high am I? What's my schedule? Personal perspective, etc. Now, if you are running less than WOT then it makes sense to lean and open the throttle to maintain speed in many cases. But if you are at altitude and the throttle is at the stop you now have to trade off fuel for time (but you would want to lean to at least best power - where that is depends on your engine).

As an automotive powertrain control guy, the assumptions behind the control systems I designed was that the operator is going to to travel at some given speed (that varies with time) and my job was to provide the necessary power to teh wheels with the lowest fuel consumption (as constrained by tailpipe emissions). So, my bias is to look at data from the perspective of best BSFC at constant torque.

 

[Ted]

But, for many of us, the cost function is not quite as straight forward or as well defined - and even may vary from day to day. How high am I? What's my schedule? Personal perspective, etc. Now, if you are running less than WOT then it makes sense to lean and open the throttle to maintain speed in many cases. But if you are at altitude and the throttle is at the stop you now have to trade off fuel for time (but you would want to lean to at least best power - where that is depends on your engine).

I think that sums it up well for many of us who put some extra thought into our costs.

It costs about an extra 4 GPH (15% ish) combined in the 310 to go 187 KTAS vs 177 KTAS, both LOP. So about a 15% fuel burn increase for a 6-7% speed increase. The dollars per mile end up being about the same since the airframe hours go down for the given trip, but because of the accounting functions have more hours purchased than we'll use, so hours don't matter a whole lot cost wise, but fuel costs we see.

What we end up doing is we'll fly slower and save the fuel when the time difference is small. Going to Wings, we flew slower. Coming home (with headwinds) we flew faster. On my marathon Canada trip a few weeks back I flew faster the whole time, which saved about 30-45 minutes on block time for the day. Ends up working out nicely. With a lot of our trips being very long, fast cruise does make a difference at the end of the day for us.

 

[brywd]

I will run some practice flights when it cools off with a friend who can keep a decent record and knows what I am trying to do - and we'll try to lean it to 25-50 lean of peak and see what TAS I get -

You mentioned in an earlier post that swapping around your injectors has left you with flat EGT's, but that isn't really the goal. While it is nice to have even temps, what you are looking for is for each cylinder to peak at the same time/fuel flow while leaning so "No cylinder is left behind" on the rich side when going LOP and so that none are starved on the lean side causing roughness. So really you need to determine if you have this, not even temps.

Assuming that all of your cylinders peak at the same time you can forget about your GEM and just use your airspeed indicator, and the seat of your pants to go LOP. Once level let your airspeed stabilize and then just give the mixture knob a manly pull until the airspeed just begins to drop. You can feel it, and see the result on your airspeed indicator as well. If the speed drops you are LOP. Now you can play with your GEM and slowly chase peak to find it precisely and then back off 20 degrees or so. Once you have this dialed in you can take your GEM and cover it up because you can just set to FF from then on, or yank the mixture until the speed drops.

Go up to 8,000' or higher (density alt) where you can't hurt anything and get the feel of things. Take another look at the red box as well. Above round 8,000' you can run peak if you want for best power and not hurt a thing.

BTW, I love Comanches. We've had two in the family including a C model. Really, no reason to give up more than a few knots to run LOP. Really, try again, it's worth it when you get it right.

 

[Skylane81E]

When anyone asks "what airplane should I buy?" there is a chorus of "What is your mission?" The same thing applies here.

If you want to get from point A to point B with minimum fuel, you fly Vy +- 1/2 wind speed (and again, lean).

If time = $ (and there is a proof of that somewhere on the web), then it's run the esso bee right up against the wall.

Here is where it can get "fun" depending on specifics. In my plane there is no economic advantage to flying slowly when going some where. From about 100-130kts true my MPGs are nearly the same. Slow further and they start to get worse, push to go faster and they really get ugly in a hurry.

Now I do have to shed a lot of speed to fly really LOP, about 15%. I can tell you why however, I have to throttle down that far to get the crummy intake on my engine to let me do it without shaking fillings loose. So it isn't that the LOP cost me that much power, its that the damn thing won't run LOP at a "normal" cruise power setting. Swapping to bendix mags did let me get closer than it used to though.

 

[Sac Arrow]

When I got my Turbo Arrow, economy while leaned 50 degrees ROP was horrid, which is why I started playing with LOP. A 5-10% loss in speed coupled with a 25% reduction in fuel burn (9 gph vs. 12 gph) translates in to significantly better economy.

Plus, on a long trip, if that saves at least one fuel stop, it significantly improves total travel time.

 

[Bill Watson]

Plus, on a long trip, if that saves at least one fuel stop, it significantly improves total travel time.

At 10k or above I can get to KEYW without a refuel or sometimes better, get to Fort Meyers for a cheap fill before getting to KEYW. That capability and choice is a big $$ and time deal.

Or, not having to stop in the SE, especially in FL, often means not having to revisit a lot of weather on the way up and down.

 

[Palmpilot]

If you are renting wet, hobbs, then the only reason to touch either the red or black knobs is to reduce the CO in the cockpit from the cracked exhaust system to acceptable levels.

Well, there's also the matter of not wanting to run out of fuel if it's a long cross country flight.

Besides, if renters never leaned, that would eventually show up as higher rental rates.

There are also a few pilots for whom ethical standards come into play.

 

[Jaybird180]

I've always understood LOP from an engineering/chemistry perspective, and from both of those perspectives, it makes sense. However, advocates rarely talk about both the fuel savings and the performance loss in the same discussion.

The real question IMO, is "What is your fuel burn at (say) 65% power when the engine is 50* ROP, and what is your fuel burn at the same power setting (same prop HP) when the engine is 50* LOP. Without clearly quantifying that (every time you discuss the topic), the discussion is meaningless.

Has anyone made a nmpg graph for thier installation to assist eith determining best settings to assuage Commanchepilots concerns, which I believe to be valid.

 

[wabower]

Can we establish an anal-retentive award to be named for the first volunteer?

Has anyone made a nmpg graph for thier installation to assist eith determining best settings to assuage Commanchepilots concerns, which I believe to be valid.

 

[Tony_Scarpelli]

I will run some practice flights when it cools off with a friend who can keep a decent record and knows what I am trying to do - and we'll try to lean it to 25-50 lean of peak and see what TAS I get -

When I run 25-40 d F LOP I lose about 5-7 knots. If I pull back the gas ROP I loose the same 5 knots and still save 2 gph so I cannot decern a difference.

Henning says he is going to fly with me and show me how to do it, but so far this is what I witness with my plane.

 

[poadeleted21]

Can we establish an anal-retentive award to be named for the first volunteer?

For $995, a few days of your time, and a trip to OK, you can see the chart in person this October. Which is about the only motivation I can see for digging up a 13 year old Lycoming paper and publicly whining about it like an 8 year old who didn't get an ice cream cone.

 

[Capt. Geoffrey Thorpe]

For $995, a few days of your time, and a trip to OK, you can see the chart in person this October. Which is about the only motivation I can see for digging up a 13 year old Lycoming paper and publicly whining about it like an 8 year old who didn't get an ice cream cone.

Ice cream? There is ice cream? No one told ME about the ice cream!

 

[comanchepilot]

When I run 25-40 d F LOP I lose about 5-7 knots. If I pull back the gas ROP I loose the same 5 knots and still save 2 gph so I cannot decern a difference.

Henning says he is going to fly with me and show me how to do it, but so far this is what I witness with my plane.

I see the same thing as you Tony - except I've not run it 25-40F LOP because that is in the 'Red Box' that Deakin tells us to NOT run an engine in - which is why I cranked it back further - sure - I do it ROP but temps are much more stable that close to peak when you are rich . . .

Now - moving on to this bashing I get because th EGT's and CHTs are level and thats not a good indication of a well running engine . .. seriously people? Everyone's EGT probes are put in the same place in every engine. I'd say 95% of the probe's I've seen are the same darn place in the exhaust stream. Again more or less- we're talking what? less than a 25F difference over the engine?

Sure I"m stupid, I'm ignorant - but when you swap the injectors and get the engine to look like this - its plain runs better too . . . but ok. I"m an a clueless non-engineer how did he get this far in life stupid humanities major . . .

 

[Ted]

Now - moving on to this bashing I get because th EGT's and CHTs are level and thats not a good indication of a well running engine . .. seriously people? Everyone's EGT probes are put in the same place in every engine. I'd say 95% of the probe's I've seen are the same darn place in the exhaust stream. Again more or less- we're talking what? less than a 25F difference over the engine?

Sure I"m stupid, I'm ignorant - but when you swap the injectors and get the engine to look like this - its plain runs better too . . . but ok. I"m an a clueless non-engineer how did he get this far in life stupid humanities major . . .

25-40 ROP is red box. 25-40 LOP might be for some high power settings on highly turbocharged engines. Lance knows what Deakin calls the red box more regularly, I honestly don't bother reading his stuff.

What us engineer types were pointing out is that EGTs being level by themselves does not mean that everything is as it should be. Probe placement isn't just how many inches from the exhaust port, it's also how deep into the exhaust stream it is. Did you know that temperature varies with distance from the wall as well as distance from the exhaust port? Then there's the matter of even distribution of air, not just fuel. And the fact that these probes really are pretty junky and are not always consistent.

Nobody's saying that what you did didn't work or not to do it, and I didn't see anyone bashing you, just trying to give you some additional education. If you're not interested, then that's your prerogative, but you need not bash the educator.

 

[flyingcheesehead]

I get it - I AGREE with everything the LOP people say - but with a normally aspirated engine you lose 15% of your speed. If you are ok with that - then do it.

I think it was stated that you lose 15% of your *power* compared to best power mixture, not 15% of your speed.

85% of power = 94.7% of speed.

I run LOP in the Mooney because I get 170 KTAS on 12.2 gph. I can get 180 KTAS ROP, but it takes an extra 5 gph to do so - So, about 5.6% less speed for 29% less fuel burn. I'd have to be in a 145-knot headwind before that extra fuel burn would make sense economically. :hairraise

 

[tmyers]

Moose tracks please!!!

 

[flyingcheesehead]

When anyone asks "what airplane should I buy?" there is a chorus of "What is your mission?" The same thing applies here.

An interesting analysis.

If you are renting wet, hobbs, then the only reason to touch either the red or black knobs is to reduce the CO in the cockpit from the cracked exhaust system to acceptable levels.

"Full rental power" definitely has its origins here...

If you are building hours in your own airplane, then you fly Vy at best BSFC.

As long as the engine is cool enough and you have the patience - I've never met anyone with that kind of patience.

If you want to get from point A to point B with minimum fuel, you fly Vy +- 1/2 wind speed (and again, lean).

Shouldn't it be Vg? And I think there's probably more to it than that - Wind speed vs. airspeed, for example - If Vy is 60 and the headwind is 60, 90 KTAS (or 30 knots over the ground) is going to leave you in that headwind for a LONG time, whereas speeding up will increase fuel burn per hour and per indicated/true knot but may decrease fuel burn per mile traveled.

If time = $ (and there is a proof of that somewhere on the web), then it's run the esso bee right up against the wall.

Well, depends how much $ the time is worth - Flogging an aircraft engine to death could easily double the hourly cost of flying with the drastically increased fuel and maintenance costs (and early overhauls) but only gain you a 5-10% advantage in time.

But, for many of us, the cost function is not quite as straight forward or as well defined

Understatement of the year. Which is probably why most of us don't run "right up against the wall" or at Vy ± 1/2 wind.

 

[Bill Watson]

Now - moving on to this bashing I get because th EGT's and CHTs are level and thats not a good indication of a well running engine . .. seriously people? Everyone's EGT probes are put in the same place in every engine. I'd say 95% of the probe's I've seen are the same darn place in the exhaust stream. Again more or less- we're talking what? less than a 25F difference over the engine?

I don't know how engines in various planes are delivered but I'm flying a self-build experimental and had to install my own EGT probes in my new IO-540. As hard as I tried, I couldn't get all my probes exactly the same distance because there is no such thing. The exhaust manifold pipes start bending pretty much upon exiting the cylinder and there are obstructions that force certain minimum distances on some cylinders. I never found any documentation showing 'standard locations'. Does Lycoming even deliver engines with 6 probes installed at the factory? I don't know.

So, while I don't know how certified engines are setup but I suspect that many have mechanic installed EGTs and that they did something similar to what I did. But I'm just guessing.

Then I'm thinking that if you start chasing even EGTs with even slightly varying EGT locations, you can start detuning the whole thing relative to LOP ops. But again, I don't really know.

Getting all cylinders to peak at the same time using engine log graphs is interesting because you begin to see that each cylinder behaves a bit differently.

There's also some dynamic variance on any given cylinder due to ambient under-the-cowl pressure fluctuations, at least on normally aspirated engines. Some experimental guys that are a bit obsessed with LOP ops have taken to installing the 'air pressure shrouds' that are part of turbo-charged injector installation, on their normally aspirated engine's injector installation. It apparently smooths out the ambient air pressure fluctuations and makes the injector tuning/swapping more precise. I had to tune those guys out though... that's just a bit over my anal pain tolerance (sorry if you guys are reading this, just being entertaining).

Question; how does swapping injectors serve to improve balance if all the injectors, as delivered by the factory, are the same? Is QC such that the injectors vary enough to provide some tuning capability? Seems like someone said something like that in this thread but I didn't know it was bad enough to actually facilitate tuning.

 

[Ted]

Does Lycoming even deliver engines with 6 probes installed at the factory? I don't know.

The only engine Lycoming will deliver (if it ever makes it to market) with EGTs from the factory will be the iE2. It requires EGTs for the computer.

Naturally aspirated engines are typically delivered without exhaust. Turbocharged engines are delivered with exhaust in most cases, and will have a TIT (Turbine Inlet Temperature) port.

So, while I don't know how certified engines are setup but I suspect that many have mechanic installed EGTs and that they did something similar to what I did. But I'm just guessing.

Correct, that is what typically happen. The mechanic installs them as closely as possible, but variables in the install, probes themselves, and even in the wiring (thermocouples are sensitive to wiring) can impact the indicated temperature.

Some experimental guys that are a bit obsessed with LOP ops have taken to installing the 'air pressure shrouds' that are part of turbo-charged injector installation, on their normally aspirated engine's injector installation. It apparently smooths out the ambient air pressure fluctuations and makes the injector tuning/swapping more precise. I had to tune those guys out though... that's just a bit over my anal pain tolerance (sorry if you guys are reading this, just being entertaining).

That's a really interesting concept, and one I never messed around with.

Question; how does swapping injectors serve to improve balance if all the injectors, as delivered by the factory, are the same? Is QC such that the injectors vary enough to provide some tuning capability? Seems like someone said something like that in this thread but I didn't know it was bad enough to actually facilitate tuning.

I think stock injectors will have a variability of something around +/- 1% when properly cleaned. Continental started selling some engines with "tuned" injectors (trying to dethrone GAMI) but as far as I know Lycoming sends out the same injectors in each cylinder. There is something to the idea of being able to swap them around for optimum performance. I never messed around with it on the Aztec. Maybe if I had, I could have gotten it to run LOP better than it did, but it did it well enough for me. Worked for 1,000 hours worth, anyway, and got the 25-40ish LOP that I needed.

 

[Bill Watson]

Correct, that is what typically happen. The mechanic installs them as closely as possible, but variables in the install, probes themselves, and even in the wiring (thermocouples are sensitive to wiring) can impact the indicated temperature.

Yes, I didn't know that until studying the installation requirements for my EGT proges. After taking the time to route my probe wires around so that their full length was retained, I'll be looking at other installations to see if the same care was taken. I suspect that some mechanics may do some snipping to make the installation easier and neater.

But as has been stated, the actual EGT matters little - it's the peak temperature for each probe/cylider and number of degrees ROP or LOP.

 

[Skylane81E]

Yes, I didn't know that until studying the installation requirements for my EGT proges. After taking the time to route my probe wires around so that their full length was retained, I'll be looking at other installations to see if the same care was taken. I suspect that some mechanics may do some snipping to make the installation easier and neater.

But as has been stated, the actual EGT matters little - it's the peak temperature for each probe/cylider and number of degrees ROP or LOP.

And for the EI IIRC you can set each bars limits differently so that you can get the display to show a flat line despite different values (assuming they maintain the same relationship to each other)

 

[N175PT]

Hi everyone! First post here.
I would agree with Comanchepilot, if your slowing 15% you're probably behind curve in the economics of LOP ops. On my plane 50 ROP @ 8-10 K msl it will true out at 180-181 kts. on ~10 gph.
Or set at 50~75 LOP and true out at 168-170 on 7.8-8.0 gph.
That's 7% loss of speed for ~20% less fuel. On a typical 200 nm trip it then takes 5 min longer but burns 2.2 fewer gallons and I lose a good 30 degrees on the CHTs to boot.

Once LOP you can use fuel flow to calculate percent power, ie 14.9* FF / rated power = % power. So for the LOP cruise above: 14.9*7.9/180 HP=65%

I think I disagree that flat EGTs also equal balanced flow. It where they each peak relative to the fuel flow, we don't care a bit what the actual temperature is. That's more a function of where the probe is placed in the pipe as well as the flame/gas flow dynamics inside the pipe.
With an engine where the EGTs all peak within .1-.2 gph of each other you really can run wot all the time and set power / speed with the mixture.
Fuel injection and electronic ignition make a sweet combo.
Tim

 

[azure]

I think I disagree that flat EGTs also equal balanced flow. It where they each peak relative to the fuel flow, we don't care a bit what the actual temperature is. That's more a function of where the probe is placed in the pipe as well as the flame/gas flow dynamics inside the pipe.
With an engine where the EGTs all peak within .1-.2 gph of each other you really can run wot all the time and set power / speed with the mixture.
Fuel injection and electronic ignition make a sweet combo.
Tim

That's my understanding too, and why I really can't run LOP at all in my Cardinal (200 hp IO-360) with my stock injectors. The cylinders peak in pairs, and the richer pair peaks about 0.8-1.0 gph leaner than the leaner pair. By the time my richer pair is LOP, my leaner pair is already 100 LOP and falling, and I'm getting roughness. Lean any further, and my leaner pair's EGTs start rising again, apparently due to flame front retardation causing fuel to be sent through the exhaust valve unburned and combusting in the exhaust pipe. Obviously, I need GAMIs to do this safely, especially at higher power settings. Only at altitude or well below 75% power do I lean to put my leaner cylinders LOP, basically using the "lean to rough, then enrich to smooth" method since I can't hurt my engine anyway there, and there is no point to fine tuning.

As a (trivial) counterexample to Joe's assertion that flat EGTs indicate good tuning, before my mechanic swapped injector pairs the last time, there was a point in leaning where my EGTs were absolutely flat. But two of them were coming down on the LOP side while the other two were still rising ROP. Not exactly where I want to be running my engine.

 

[tmyers]

There is a good question in Azures comment. What is an acceptable gami spread?

 

[azure]

There is a good question in Azures comment. What is an acceptable gami spread?

GAMI aims for < 0.5 gph.

 

[gismo]

GAMI aims for < 0.5 gph.

0.5 is "adequate" but 0.2 is noticeably better. Keep in mind that even without induction leaks the mixture balance will vary with RPM and throttle settings.