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Is LOP worth it? - My test results

Webb

Webb

Well Known Member
Sponsor
I decided to bite the bullet and try out LOP.

First thing I did was started reading how to go about doing it properly so I wouldn't cook my engine.

Next, I ran fuel flow tests to determine the flow rate at peak. Then contacted Don at Airflow performance and he looked at my data and graphs and sent me a restrictor for cylinder #4. I re-ran the data and then decided to adjust 1 more restrictor (cyl #3). Peak is now about 0.1 gal/hr spread at 8,500 feet.

Here are the numbers at 8,500 feet I now have.

8500.png

I just took a trip and ran 50 LOP out at 9,000 feet. The flight went from Fairhope, AL to Naples, FL and flight time was 3.2 hours with total fuel burn was 25.2 gallons. Although I didn't write this down, it seems like the numbers for travel were - outside temp 37F, MP 21.7, and RPM 2250.

Once I had climbed to altitude, I went through the quick pull to the approximate temp and them tweaked it until I got the temp reading I was looking for.

Clinder head temps dropped. I didn't write them down but they were in the 340's and about 10 degrees cooler than 100 ROP.
Flow rate went from 10 gal/hr to 7.2 gal/hr.
TAS dropped from 163 to 158 knots.

My impression..........
The engine ran cooler - lower cylinder temps mean longer life
Endurance (taking reserves into account) went from approximately 3 hours to approximately 5 hours.
Range, increased from 550 miles to 900 miles.
Fuel burn was 28% better.
Speed decrease by approximatey 3%.

I also noticed that as you enrichen to just past 50 LOP the engine starts a nice pick up in power - somewhere around 45 LOP. I'ld call this the sweet spot and this is what I shot for on the trip to Key West we took, and the way back.

Is it worth it? Definately. To loose 3% speed and get 28% better fuel economy...not to mention a cooler running engine.
 
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1100 hours LOP and counting...

I also say welcome on over to the lean side!

My engine seems to like it so far - compressions unchanged at around 74 to 78, oil analyses with about half the usual metals (so I've been told), and oil consumption unchanged since the beginning. I'll report back in another 8 years...
 
Congrats and Welcome

If your airplane is the same as mine - just for the sake of a way to do some numbers - then the difference between 158 and 163 is worth about .5 or .6 gph and the rest is real savings for equal performance.

I took your reported altitude as pressure altitude and used the temp to get 9657 Density Altitude. Close, anyhow.

I tweaked my "model" to give 7.2 gph at 158 KTAS (I am taking your reported speeds as TAS). That gives the answer of a difference of 0.5 gph.

So for equal performance it would have been 10 vs 7.7 or a drop in fuel flow of 23% and an increase in NMPG from 156.3 to 21.2, a gain of almost 30% which is the same as range.

My numbers suggest that your BHP was only about 100 and since you were at an altitude that makes 75% impossible, you could push the throttle in to regain the speed and be well within safe limits. That said, the time to your destination would be almost the same.

As a reality check, my plane would burn 7.7 gph at the same altitude and TAS as your 7.2 gph. We are very much in the same ballpark with that, but your plane is performing measurably better than mine: .5 gph for equal speed and density altitude. It could be any combination of lower drag, higher prop efficiency or even slightly better SFC.

I use .40 for SFC in my model and the best you can do per GAMI is about .39. That can account for 0.2 gph. Your prop could be better, but I'm using 85% in my model (I would be at 2650 rpm at that altitude) and of course, your airframe drag could be a little lower. Whatever, you are getting terrific results.

Congratulations!
 
kevinh said:
Hi Webb,

What sort of engine? Carb/FI?
Click to expand...

Engine is a Superior IO360 with 8.5:1 pistons, MT CS 2 blade prop.
btw - when I fly back from Mobile to Jackson, I flew at 8,500 ROP and was cooking along at 169 knots TAS at 10.1 gallons/hr. I liked the speed and didn't mind the higher fuel burn for the short trip.

Key West.....Interesting trip. I would describe it as a cleaned up Bourbon Street. Next time it will be Marathon. Filed an IFR flight plan and went direct from Naples. Neat trip and the view was fabbo. These planes are great little travelers.

Funny story. On the way back, regional jet was approaching from the rear and he was told to look out for the RV at 14,000. His exact word was "cool". Gotta love it.
 
Great results and it shows the advantages of a balanced injected engine. I am not sure I agree with the reasoning behind your claim of 28% better fuel burn. You get this figure by comparing fuel burn at 100 degrees ROP to the burn at 50 degrees LOP. I have an 0-320 and am not familiar with the % power figures for an 0-360 but I am sure you would be in the power band where leaning to Peak EGT is allowed (about the best that can be done by us types with carbs or unbalanced injectors). So would it not be more realistic to compare the fuel burn at Peak EGT rather that at 100 degrees ROP? As an example, I know that I can manually lean my carb 0-320 to just before it gets rough (somewhere around Peak EGT) and get FF and TAS figures at 8,500 ft DA, very similar to your 158 kts @ 7.2 g/hr, 50 degrees LOP.

Fin
9A
 
Webb said:
Once I had climbed to altitude, I went through the quick pull to the approximate temp and them tweaked it until I got the temp reading I was looking for.
Click to expand...

Webb,
Since peak EGT changes significantly with OAT, how are you determining peak EGT using the big pull method?
 
Lean of Peak wanta be

Finley Atherton said:
So would it not be more realistic to compare the fuel burn at Peak EGT rather that at 100 degrees ROP?
Click to expand...

I agree.

Webb, Do you have the airspeed for each of those point in the table? I would guess you lost more then half the speed going from peak to 50 LOP.

I am toying with going over to the dark side but I have to get my injectors ballanced. I have 3 that are within a few degees of one another but one that is 80 degrees cooler then the rest.
 
Kahuna said:
Webb,
Since peak EGT changes significantly with OAT, how are you determining peak EGT using the big pull method?
Click to expand...

From what I can tell, the EGT varies more with power than with OAT. Past 8,000 feet, the peaks for each cylinder have not varied much. Below 7,000 peaks start to rise. If I was traveling at a lower altitude, say 6,000, I'ld be pulling my engine back to around 22/22 to keep the power around 60%. Then again, this could be the temps.

As far as OAT goes, when I was at 9,000, I was about 10F above standard and would have had to add 0.1" MP to the same amount of power. The rule of thumb I use is 0.1" of MP for each 10F difference from standard. When colder, subtract, when hotter, add.

For the big pull, I know that each cylinder will peak at 8,500 feet at approximately 8.6 gallons per hour and 50 LOP will be about 7.4 gal/hr and 100 ROP is 10.2 gal/hr. I pulled it back to 7.3 gallons per hour since I was at 9.000 feet and watched the EGT's. When they started to stabilize, I did the fine adjustment so I was around 50 LOP. Turns out the sweet spot was really about 45 LOP and that's where I left it and it was 7.2 gal/hr.

On my return trip, it was the same except I came back at 14,000 feet. I don't remember the exactly FF rate but it was slightly below 7 gal/hr.

plehrke said:
I agree.

Webb, Do you have the airspeed for each of those point in the table? I would guess you lost more then half the speed going from peak to 50 LOP.

I am toying with going over to the dark side but I have to get my injectors ballanced. I have 3 that are within a few degees of one another but one that is 80 degrees cooler then the rest.
Click to expand...

I don't have the speed at peak because I don't fly there.

As far as speeds, a lot of variables to deal with. It seems that all my travels are at gross.

Typically...in knots, I plan on 160TAS. If I fly at 75ROP, I get about 161TAS. If I go to 100ROP, then I get about a 2 knot bump to 163TAS. This holds true from about 8,000 to 10,000 where my plane seems to like it best. My 45-50 LOP gave me around 158TAS. I'm WOT generally and 2,500 to 2,700 which seems to be another sweet spot for my plane.

Yesterday, at 8,000, from 4R4 to M16 I as WOT at 2,400 and was dead on 169TAS running 100ROP.

Finley Atherton said:
Great results and it shows the advantages of a balanced injected engine. I am not sure I agree with the reasoning behind your claim of 28% better fuel burn.
Click to expand...

I guess technically, I need to knock off a few percentage points due to a 5 knot drop in airspeed. For round numbers, call it 25%. Remember, it's an estimate.
 
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Good report, Webb, interesting stuff.

If I may add, I think flying a long distance where a change in OAT is possible will necessitate monitoring or at least recording the initial OAT.

I was once cruising along at 9500' having set the mixture with the lean to rough, rich to smooth method, when the engine began to run very rough. Moving the mixture forward slightly fixed the rough engine, I had flown into some much cooler air.
 
Ops at Peak

Be careful about operating AT Peak EGT.... prolonged ops at Peak results in temps in that will burn exhaust valves.
 
plehrke said:
I am toying with going over to the dark side but I have to get my injectors ballanced. I have 3 that are within a few degees of one another but one that is 80 degrees cooler then the rest.
Click to expand...


You don't balance the injectors to an EGT or CHT temperature - the individual cylinders and EGT sensors are such that you will almost never have the same EGT at each cylinder even if you could use a magic wand to make them have the same mixture. Balance the injectors so that each cylinder reaches it's own individual peak EGT at the SAME FUEL FLOW, or as close to the same as you can get, preferably within .1 gph.

The absolute value of the EGT is almost meaningless for the purpose of balancing the injectors - the key is what the fuel flow is at the time that each individual cylinder reaches it's own peak EGT. That will ensure that all cylinders are reaching peak at the same time, and all are ROP or LOP together, reducing roughness and allowing you to run LOP without having one cylinder dangerously close to peak and cooking itself.
 
rv9av8tr said:
Be careful about operating AT Peak EGT.... prolonged ops at Peak results in temps in that will burn exhaust valves.
Click to expand...

Mike,

The statement needs qualification.

Lycoming has much to say about leaning their engines in the FLYER (Operations).

Operating at peak EGT will not burn the valves if done in accordance with their recommendations. But it will keep them very clean.
 
When do you go rich?

If you're running LOP at altitude and come down to pattern altitude, do you just keep the same fuel flow all the way down and adjust the throttle to maintain the same percent power? Do you go full rich on downwind or what?

Jerry
 
Jerry Carter said:
If you're running LOP at altitude and come down to pattern altitude, do you just keep the same fuel flow all the way down and adjust the throttle to maintain the same percent power? Do you go full rich on downwind or what?

Jerry
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I'm only using it at cruise. When it's time to come down, I put over to the flow rate that is around 75-100 ROP and slowly enrich as I get lower. By the time I'm at pattern altitude, I'm at full rich.
 
Webb said:
I'm only using it at cruise. When it's time to come down, I put over to the flow rate that is around 75-100 ROP and slowly enrich as I get lower. By the time I'm at pattern altitude, I'm at full rich.
Click to expand...

Some FYI

For those that are not use to higher mountain airports; we'll never go to full rich on landing. The red knob will usually be at least 3/4" out for landings and takeoff. My elevation is 4200', besides density altitude. In fact, the engine won't even run smooth for taxxing, if we don't lean right off the bat, after engine startup.

L.Adamson
 
Webb said:
First thing I did was started reading how to go about doing it properly so I wouldn't cook my engine.
Click to expand...

I too would like to run my engine LOP but I know I have some flow balancing that needs to be done. Do you have a reading list?
 
Jamie said:
I too would like to run my engine LOP but I know I have some flow balancing that needs to be done. Do you have a reading list?
Click to expand...


These are good:
http://www.avweb.com/news/pelican/182179-1.html
http://www.avweb.com/news/pelican/182176-1.html
http://www.avweb.com/news/pelican/182583-1.html
http://www.avweb.com/news/pelican/183094-1.html

Also read the post LOP, Do's and Don'ts. It has a lot of info in it.

After you check your flow rates, I would contact Don at Airflow performance and he can fix you up with the proper sized restrictors. They run $25 a cylinder. It will take you longer to get the top cowl off than it will to change out a restrictor.
 
Webb,

Thanks for the report, and for the links (and Jaime, thanks for asking the question about them). Great reading. I'm still getting to know my engine better all the time, but don't have balanced injectors or simultaneous digital EGT/CHT readouts on all cylinders (gotta cycle through them on the older VM-1000)...but I'm very interested in exploring this further, if I can do it while ensuring that all cylinders are out of the red-zone (might take some upgrades! ;)).

I found it interesting that in part 4, in those triangular red-box graphs with recommended LOP/ROP settings (the green lines), he espouses running LOP cruise to about 9K, then switching over to ROP cruise up higher for what sounds like power considerations. It may be due to his earlier stated bias towards the "go fast" mode. Wondering if any/many of the consistent LOP cruisers out there do that as well, or just go LOP all the time (at appropriate cruise altitudes/power settings, of course).

It was also interesting to read the recommendation to climb at (or near) max RPM. (WOT I get, and do), but max RPM is interesting.

His descent profiles and power management are also very interesting. Leaving mixture at the cruise setting, and adjusting RPM and MP to manage the descent speed, and leaving all three knobs back till landing is (as he seemed to say) different, and would require good discipline for go arounds (like he said, Red, Blue, Black knobs up, in that order...as it should be). I noticed you said you enrichen throughout the descent, as do I, but it sure looks like you've worked his procedures well in your testing and evaluation, managed your CHTs and EGTs well, and seen good solid results. Well done!

Some really good data, and the links gave some great thoughts on managing those temps with good ball-park numbers to use (he makes a good point about not having to be too anal, and gives good, safe ranges). I liked his simple climb temp management description.

I had the same thought as Kahuna about the big pull. You mentioned FF targets developed through good testing. I was wondering if you found that when doing the big pull, did those numbers correlate to "pull to a little rough running, and then enrichen slighty"...then perhaps approaching peak from the lean side and fine tuning the EGT from there? It might happen at different temps with different OATs (as Kahuna mentions), but the relative LOP and FF results might be same. Just wonderin'.

Thanks again...good food for thought (and experimentation)!

Cheers,
Bob
 
rvmills said:
Webb,
I had the same thought as Kahuna about the big pull. You mentioned FF targets developed through good testing. I was wondering if you found that when doing the big pull, did those numbers correlate to "pull to a little rough running, and then enrichen slighty"...then perhaps approaching peak from the lean side and fine tuning the EGT from there? It might happen at different temps with different OATs (as Kahuna mentions), but the relative LOP and FF results might be same. Just wonderin'.

Cheers,
Bob
Click to expand...

The ideal (as I see it) of going through the big pull was to avoid those high stress times on the engine. As you can see from my chart below, I know that 8.6 gal/hr at 8,500 feet is going to be that flow rate. I also know that somewhere around 10.2 gal/hr is going to be 100 ROP and just estimating, 7.3 is going to be the 50 ROP. I just pull the red knob back until I get the approximate flow rate and then let it start stabilizing. It takes about 20-30 seconds and then start tweaking until I'm happy. Like I said, the sweet spot for my plane is somewhere around 45 LOP.

ff8500.png


I quit using the leaning function on my Dynon because I have to go slowly through peak for it to do the proper job. If I do it too fast, the readings aren't accurate when I turn the lean function off and check it against the temps.

The procedure is pretty simple. Go up high enough you won't hurt your engine. Say 9,500 feet. Go WOT and 2,400 RPM. Chances are you will be somewhere around 22" MP. When I cruise, I keep my RPM's at 2250 but for this test, run it at 2,400.

Start with a flow in the mid 10's, then drop it by 0.2 gal/hr, let it stabilize for about 20 seconds and record the temp for each cylinder. Keep doing that until you get it down until it starts to run rough. Do this test twice, maybe the next one at 10,500.

Now you have your data. Contact Don and you can get the restrictors to adjust properly and re-run the tests after you get your new restrictors in.

I was lucky enough that my engine was close. I had to put a restrictor that was 0.005" larger in cyclinder #4 and 0.005" smaller in #3.

Here is something I learned from Don that I haven't seen in print. When the flow rates start getting low, the restrictors (0.028 standard size) won't keep the pressure up high enough for the nozzles to properly atomize the fuel. I don't remember if he said that the rate was less than 7 or 6 gal/hr but as you lean past there, that is when you see the issue. You would need to put in a complete set of smaller restrictors (0.022" is the number that comes to mind) and start the process over if you have to go that low on flow rate.

You can also fly over there to him and go through a custom tuning session. Cost is a few hundred bucks. Nice part is if you need to keep trying out different restrictors, the cost may be a wash. You'll also get a good education in the process.
 
I have found that the EGT peak changes based on alt, temp, power setting etc. etc., but if you're around 65% or less running at peak for a few minutes certainly is not going to hurt anything so I think the big "pull" to get past the peak area is really not an issue (per Lyc you can run at peak all the time at this pwr setting).

After doing my AFP cal I was going to change out 2 restrictors to balance them out. After talking with Don I decided to try some .025 injectors instead of the std .028, with those installed my system came in at .2GPH and also helped with the lower power setting flow and the hot idle issues/loping on the ground. You just have to be sure you have enough FF at full power to use the smaller injectors which means sufficient fuel pressure must be available which if I recall correctly should be in the around 28-30 PSI(or higher).
 
Question

On cylinder #1, I noticed at 10,500, the peak is 1416, at 8,500 it was 1432, at 7,500 it was 1434, and a quick look at 4,500 was 1450.

My question is, should we use peak as the highest temp we saw, or should we use the one for that flight level???

In the old airplanes I used to fly, we set the marker on the EGT to the area ROP of peak from the highest temps we saw and used it for all levels since we only had one cylinder with an EGT. That equates to the first thought of using the highest peak temps for all flight levels.

So.....does this mean that 50 LOP for 8,500 should be 1450-50=1400 or should we use 1432-50=1382?

Sometimes we think to much but what is it? I've been use the 1382 number but is it correct or too LOP?
 
It should be 50 LOP for that altitude, that flight, that OAT, that DA, that RPM, that MP.
Which is why one number will not work. It might seem fine right now Webb as your working this is a close regime. But as you travel across seasons, across altitudes, across extreme temperature ranges, a pull to a predetermined number will not work well at all Im afraid.
You should not be concerned about finding peak each time you fly as long as your below 24"mp.
Imagine how many planes for decades have been flying on the pull till its rough, and tweak back in a little, essentially running at peak. Rudamentary and crude, but been done for decades.

Now that we have outstanding telemetary, if you want to lay out into a nice long cruise, I recommend you find peak each time.

It would take a butt load of flight testing to graph the big pull properly.

I would swag my experience with LOP in the ~2000 hour range in both 4 and 6 cylinders from OATs -20F to +120F. I spend all my cruise time LOP. I would not be able to be accurate with a big pull, and I have flight data documentation comming out my ears.

Just my 2 cents.
 
Kahuna - I agree with you on the SWAG method. I've noticed that once I get above 9,000, the peaks seem fairly close. They go up down lower.

What I'm finding out is the flow rate that goes from rough to smoothing out and then all of the sudden is a bump in speed and power. Ironically, it's about 45 LOP. Like I said earlier...the sweet spot. I'll eventually get it down for the different altitudes. The only one committed to memory right now is 7.2 gal/hr at 9,000.

I have to say good stuff and I'm glad I did it.
 
Welcome!

Hey Webb,

Welcome to the club. The T-shirt, secret decoder ring, and the subscription to the monthly magazine "Lean on, Me" are in the mail.

I've been cheating death on the lean side for 500 hours now thanks to Alex P and some other good folks showing the way.

Clean, cool and efficient. Giddy Up!
 
EGT not too valuable other than..

to find the relative peaks between cylinders as they relate to fuel flow. In this role, however, it is invaluable. But, this can be done well once, and perhaps occasionally thereafter, to determine mixture balance between cylinders.

On an ongoing basis, I only monitor egt's to see if something is wrong with a given cylinder. I don't think I could tell you what egt would be expected in my plane for a given condition. From time to time I do the mixture vs egt charting to keep an eye on things.

I make it simple and generally fly at 22", maybe 23" MAP, where the mixture can be whatever you want it to be without harm. (I see a lot of discussion about altitude - the engine mostly doesn't care about that, only MAP.) Once the climb is complete (to whatever altitude) and the MAP reduced, I pull the mixture back until it starts to noticeably lose power, then dial it in until I see a fuel flow that I've determined, through experience and data collection, to be about peak egt to maybe 50 LOP. In my O360, it is about 7.2 to 7.5 gph at 22", 2350 or so rpm. I have found a bit more efficiency when I dial in the same fuel flow, but at 24". This is probably around 75 to 100 LOP, but it is more finicky as to settings, so I just stick with the 22-23 MAP. BTW, this delivers about 158 to 162 ktas in the 7 to 9k' range.

CHT's are a big indicator of mixture as well - I know I don't have the mixture set LOP if I see higher CHT's. Mixture is a very powerful input variable to CHT's. If I settle in with cruise settings, and I see CHT's hovering in the 350 or higher range (in the summer), I dial out a little mixture. If one believes (as I do) that higher CHT's shorten cylinder life, LOP is a very good thing.
 
rv9av8tr said:
Be careful about operating AT Peak EGT.... prolonged ops at Peak results in temps in that will burn exhaust valves.
Click to expand...

At the 8,500' MSL Web was running (peak EGT) it won't hurt the engine.

Great info Web! Welcome to the lean side! LOP ain't so bad. Did you notice the oil temp drop?
 
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Geico266 said:
At the 8,500' MSL Web was running (peak EGT) it won't hurt the engine.

Great info Web! Welcome to the lean side! LOP ain't so bad. Did you notice the oil temp drop?
Click to expand...

I think you meant IF Webb was running at peak. I was ~45 down from it. I haven't noticed the oil temp because I wasn't looking at it, but I can tell you the cylinder temps definately dropped.

I can tell you one thing. I really like the added flight time. I came back from Florida a few days ago and the weather was the pits around TLH. What should have been a 3 hour flight turned into a 3.8 hour flight with headwinds and lots of weaving and dodging cells. I landed with almost 2 extra hours worth of fuel on board. In the past I would have landed at 3 hours to stay within my personal limit of 1 hour reserve.
 
Geico266 said:
At the 8,500' MSL Web was running (peak EGT) it won't hurt the engine.
Click to expand...

Webb said:
I think you meant IF Webb was running at peak.
Click to expand...

So, I'll take the liberty to rephrase that. At the 8,500 ft that Webb was running at, leaning through peak EGT won't hurt the engine. I agree, however I think this would actually put the engine briefly in Deakin's Red Box. Using Webb's figures from post # 22, peak EGT occurs at 8.6 g/hr at 2,400 rpm. Now I only have the "Part Throttle Fuel Consumption" chart for a IO-320, but 8.6 g/h and 2,400 rpm at peak EGT produces about 121 hp. I presume this HP figure should be similar for the IO-360 (please correct me if the IO-360 chart shows differently) which means that Peak EGT occurred at about 121 hp or 67% power which is over Deakin's 60% limit for Peak EGT.

Fin
9A
 
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To beat the dead horse even further.

Lycoming operators manual, Section 3.1 Leaning to the EGT
Section A normally asperated injected or uncompressed carbs.
2) Best economy cruise (approximately 75% power and below) - Operate at peak EGT
 
Kahuna said:
To beat the dead horse even further.

Lycoming operators manual, Section 3.1 Leaning to the EGT
Section A normally asperated injected or uncompressed carbs.
2) Best economy cruise (approximately 75% power and below) - Operate at peak EGT
Click to expand...

Deakin is from MARS.

Lycoming is from VENUS.

Take your pick....
 
David-aviator said:
Deakin is from MARS.

Lycoming is from VENUS.

Take your pick....
Click to expand...

Deakin uses sound scientific measurements, basic physics, and shares his calculations and test methods.

Lycoming says "You'll die if you don't do it like we say"

I choose MARS.
 
airguy said:
Deakin uses sound scientific measurements, basic physics, and shares his calculations and test methods.

Lycoming says "You'll die if you don't do it like we say"

I choose MARS.
Click to expand...

Yes.

But Mr. Deakin does not warrantee his words or the engines.

Until I am out of Lycomings warrantee, I will try to abide by their version of the bible.
 
First of all, I'm not an engine expert but I look at it this way.

Metalurgically speaking, valves, pistons, guides, and whatever else is present there has a limit in which things will operate within the designed limits. Cranks are mean to handle the HP the engine puts out. Metal is designed to handle the expected temps that the engine will continuously run. And so on, and so on, and blah blah blah.

Just for a round numbers, lets pretend that your top EGT is 1450 and the max CHT that you want to stay below is 380. In other words, you can't make the EGT go higher, at any altitude but as we know, CHT's can be made to go higher without proper cooling.

If the owners manual says to run no more than 100 ROP for EGT's, then if you do not go above 1350, you should be staying within the temp requirments of the heat handling capabililities of your engine. If you keep you cylinder temps lower, that should be work also. Ideally, both should be under the limits.

Then does it really make a rat's rump if you keep it down below the stress limits of temps your engine can handle no matter what altitude, power, flow rate, etc....?

From a logical standpoint, this makes sense to me. Especially when you fly higher and can't generate as much power or as much heat. Internally speaking, 1300 degrees exhaust gas temp is the same no matter what altitude you are flying. Most of us lean agressively on the ground at idle so we don't carbon fowl the engine....same principle.....the heat produced at that power setting won't hurt the engine.

Right or wrong?
 
Right ... Sort of.
If you start with the premise that the purpose for LOP operations is to obtain max effeciency, MPG lets say, and you assume the red zone is bad (which at <75% power I dont ascribe to), then it is exaclty 50LOP that you after. leaner is loosing speed and power with no improvement in effeciency. Richer puts it in the red zone which some say is bad. (see articles on the subject)

So given that, you want to be at the highest effeciency and out of the red zone. Thats 50LOP. The only way to get exactly LOP on any given flight, or even close, is to find it each time. Peak EGT is a function of many things and must be determined each time.

The other benefits of cooler operations are nice. Safe LOP climbs are great, but hard for the novice to nail without many many hours of experience.
 
Very educational and eye opening. Just wondering, has any one used GRT Lean option to find the peak each time? It seems to work nicely and an easy way to give the peak and there after temp each time for any given altitude, AOT etc.

Thanks
Mehrdad - RV7A - IO360
 
GRT Leaning Option

Bavafa said:
Very educational and eye opening. Just wondering, has any one used GRT Lean option to find the peak each time? It seems to work nicely and an easy way to give the peak and there after temp each time for any given altitude, AOT etc.

Thanks
Mehrdad - RV7A - IO360
Click to expand...

I use it every time, it works great. No more math in your head, you get a direct display.

Hans
 
Sure - used it lots of times. Not so much lately though - cause it finally dawned on me that at 24 square, 50 LOP means 7.2 gph on my engine. So, now I dont bother - I just do the big mixture pull and enrichen up to 7.2 gph.

Note that while we all refer to 50 LOP, no one ever really gets that exactly on all four cylinders at the same time. I just kind of do a mental averaging of all the cylinders to get it close, while being carefull that the richest cylinder is still comfortably lean.

erich
 
So, let me pose this question to every one, would there be any advantage/disadvantage if you were running it at ROP but throttling back to achieve the same speed/FF ratio as oppose to LOP. Here is a made up example just for clarification: lets say at 10K feet, we and 50 LOP, we are getting 158 MPH and 7.7 FF. Can we achieve the same thing running it at 100 ROF and throttle back to get 158 MPH and hopefully the FF be about the same (7.7)

Is this possible and if so, is there any advantage or disadvantage?

Regards
Mehrdad - RV7A
IO360M1B
 
100ROP? Probably not.. You'd be burning more than 7.7 in that case at that speed.. Though, I have to say, I'm WAGing this one as I have not confirmed it.. this is more from memory of "transient state of things" as I'm on my way to LOP ops :)

PS.. I think you meant 158+kts not mph at that fuel flow :)
 
Bavafa said:
So, let me pose this question to every one, would there be any advantage/disadvantage if you were running it at ROP but throttling back to achieve the same speed/FF ratio as oppose to LOP. Here is a made up example just for clarification: lets say at 10K feet, we and 50 LOP, we are getting 158 MPH and 7.7 FF. Can we achieve the same thing running it at 100 ROF and throttle back to get 158 MPH and hopefully the FF be about the same (7.7)

Is this possible and if so, is there any advantage or disadvantage?

Regards
Mehrdad - RV7A
IO360M1B
Click to expand...

This doesn't work.

An easy way to think of this is that at peak EGT, the mixture is stoichiometric, which means that there are exactly enough oxygen molecules available to react with every avgas molecule.

If you are ROP, by definition there is more fuel available than oxygen, so some leaves the exhaust valve unburned.

If LOP, some oxygen molecules escape the chamber but all of the fuel is consumed.

The important difference here is that the oxygen is more or less free and unlimited, while you are paying for the fuel, and can only carry a limited amount onboard.

The only way to be certain you've extracted every last bit of energy out of the avgas is too have extra air around so no fuel is wasted (LOP).

Since the concentration of oxygen in the air is fixed at a given density altitude, the only way to be certain that the engine is making its maximum available power is to have extra gas around so no oxygen goes to waste (ROP).

You can cheat on the oxygen concentration (within limits) by compressing the intake air (supercharging) or add an oxidizer like nitrous oxide, but you have to also increase the corresponding amounts of fuel.
 
Thanks James,
I think you hit the nail right in the head... this makes sense. And I go further to contradict/correct myself in the earlier question, if I am ROP and throttle back to lessen the fuel flow? I am starving the engine even more for the air so even more fuel molecules are going to escape out of the exhaust, correct?

I have been flying ROP so far and hoping to give it a try this weekend to see what sort of FF I get.

Regards
Mehrdad RV7A
IO360M1B
 
Bavafa said:
Thanks James,
I think you hit the nail right in the head... this makes sense. And I go further to contradict/correct myself in the earlier question, if I am ROP and throttle back to lessen the fuel flow? I am starving the engine even more for the air so even more fuel molecules are going to escape out of the exhaust, correct?

I have been flying ROP so far and hoping to give it a try this weekend to see what sort of FF I get.

Regards
Mehrdad RV7A
IO360M1B
Click to expand...


If you throttle back, you reduce air and fuel roughly in proportion, so the ratio should stay pretty much the same.

An interesting side effect of this is that if you are lean of peak, you can determine power output by multiplying fuel flow by a constant. Since there is an excess of air (by definition) lean of peak, throttle and manifold pressure readings can be ignored, and you can calculate directly from fuel flow. This same trick doesn't work ROP, since you never can be sure exactly how much fuel is being wasted.
 
Bavafa said:
Can we achieve the same thing running it at 100 ROF and throttle back to get 158 MPH
Click to expand...

Three, possibly four reasons why the answer is no.

1 - You will increase pumping work by closing the throttle
2 - You reduce the ratio of specific heats of the working fluid (combustion products). This part is a bit of thermodynamics tech, but basically lean combustion is better than rich from a thermal efficiency PoV.
3 - Heat transfer (loss) to the cylinder head will be increased, since the mass of gas in the cylinder is lower and therefore is made hotter by burning and heating it with the same(ish) amount of fuel energy
4 - If ROP makes you run richer than stoichiometric, then significanly more CO is produced, which represents lost chemical energy.

A combination of all these reasons will give you a degradation in BSFC at the same shaft power level.
 
Riddle me This

flyeyes said:
If you throttle back, you reduce air and fuel roughly in proportion, so the ratio should stay pretty much the same.

An interesting side effect of this is that if you are lean of peak, you can determine power output by multiplying fuel flow by a constant. Since there is an excess of air (by definition) lean of peak, throttle and manifold pressure readings can be ignored, and you can calculate directly from fuel flow. This same trick doesn't work ROP, since you never can be sure exactly how much fuel is being wasted.
Click to expand...

Doesn't calculating HP from MP and RPM (modified for altitude) have to assume a given SFC implicitly? If so, is it best-power (around .50) or peak or what? So if I am right about that, why won't fuel flow multiplication work as accurately or inaccurately as the standard method when ROP (with a different multiplier than LOP, of course)? If I'm wrong that the standard method assumes some SFC, then how can MP and RPM in two cases, one at best power and one at full rich give the same horsepower (this assumes a CS prop - possibly for fixed pitch the case comes out differently)?
 
LOP

Just got back from a (Mapquest equivilent) of a 1235 mile journey...Did it in 6hours both ways and was making a TAS of 158 to 162 kts depending on altitude..All of this was flown at 2400 RPM and whatever MP pressure was available at 12K feet or above.

Fuel flow was about 7 to 7.3GPH. The first part of the trip was on Autofuel WITH ethanol..never taken E10 to 14.5k before but it seemed fine looking at the engine guages.

I do have a Sam James cowl so it might be a little quicker than stock but who knows for sure.

But anyway..we almost had enough fuel to do the trip without refueling.

LOP?..You know it makes sense...:)

Frank..still got this weired rocking sensation from the autopilot that continually gently rolls the airplane slightly right and left..:)
 
hevansrv7a said:
Doesn't calculating HP from MP and RPM (modified for altitude) have to assume a given SFC implicitly? If so, is it best-power (around .50) or peak or what?
Click to expand...
The power charts from engine manufacturers assume mixture set for best power. The Lycoming data I have shows SFC at best power of 0.49 to 0.5 with compression ratio of 8.5:1. It is about 0.48 with CR of 8.7:1.
hevansrv7a said:
So if I am right about that, why won't fuel flow multiplication work as accurately or inaccurately as the standard method when ROP (with a different multiplier than LOP, of course)? If I'm wrong that the standard method assumes some SFC, then how can MP and RPM in two cases, one at best power and one at full rich give the same horsepower (this assumes a CS prop - possibly for fixed pitch the case comes out differently)?
Click to expand...
If you are running LOP, you are burning pretty much every molecule of fuel, no matter where the mixture knob is set, so there is a fairly constant SFC. You can take fuel flow, multiply by a constant, and get power - this works reasonably well no matter how many degrees LOP you are, as long as the engine is not misfiring.

But, if you are running ROP, you are pushing unburned fuel out the exhaust, and the amount of unburned fuel varies as you change mixture. So, the relationship between fuel flow and power will change depending on how many degrees ROP you are. But, if you always run at XXX degrees ROP, the SFC at that mixture setting should be fairly constant.

Note: even when running LOP, the SFC is not exactly constant, as the power lost to friction is constant at a given rpm, and this becomes a greater proportion of the power produced by burning the fuel at low power settings. So, SFC when LOP will be best at higher powers, and it will get worse as power decreases.
 
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