[Webb]

After researching lean of peak, info seems to be a bit sparse but after doing enough searching, this is what I've found:

- Don't do it below 6,000 feet. You can't run greater than 75% power above.
- Make sure you are WOT. Detonation can occur for 2 reasons, too lean or too low rpm.
- Shoot for 50F LOP
- Best if engine is fuel injected
- Engine monitor is needed to do it properly
- Temps should be fairly even
- Expect about a 10 knot drop in speed
- Lycoming does not recommend

Any more experience/advice for those that are in the know would be great.

 

[ronschreck]

After researching lean of peak, info seems to be a bit sparse but after doing enough searching, this is what I've found:

- Don't do it below 6,000 feet. You can't run greater than 75% power above.
- Make sure you are WOT. Detonation can occur for 2 reasons, too lean or too low rpm.
- Shoot for 50F LOP
- Best if engine is fuel injected
- Engine monitor is needed to do it properly
- Temps should be fairly even
- Expect about a 10 knot drop in speed
- Lycoming does not recommend

Any more experience/advice for those that are in the know would be great.

I have been running LOP at ANY altitude for over 600 hours. Just pull the throttle back to 75% power at lower altitudes. You do not need to be at wide open throttle. Agree with the rest of your post. BTW, Lycoming did not recommend MOGAS for their engines until last year!

 

[Russ McCutcheon]

This comes up often and has been beaten to death, but it is an interesting topic. I run mine LOP at any altitude and at less then WOT if I so desire, so long as it?s below 75%!

Yesterday we where going from Bend OR to The Dalles OR then down the Columbia Gorge to home in Vancouver WA. The first lag was at 9000msl, less then WOT, 22? and 2400rpm and LOP, I did a little checking to and all four where LOP buy 50 degrees or so, was burning about 7.4 GPH. On the leg down the river we where at 2000msl and it can be bumpy so we where going slow, still 22? and 2400rpm but once again LOP about 7.2 GPH this time, still running very smooth and far LOP, when we thought it was good to go faster (not bumpy) we went ROP to 8.5 GPH and we where ripping along, the same power setting was giving us 140 indicated very LOP and 160 indicated ROP, never changed the throttle or the RPM just the mixture.

200hp angle valve IO-360 A1A with CS prop, I do have 4 probe EGT but you have to switch between each cylinder to see there readings, not very high-tech, at 9000? I decided to check each cylinder, I had not done this in the past, so I leaned the engine four times, once wile looking at each cylinder EGT, sure enough even though each reads a different value they all went LOP 80+ before it would start to go ruff.

I only have one CHT probe and it runs cooler LOP then at peak or ROP, I will assume the other three cylinders follow the same pattern since they are all LOP they all will be making less power and less heat, not very high-tech.

The best thing to do for your engine is maintain it properly and fly it often, we did a very major OH 5-9-06 and the engine now has almost 700 Hobbs hours, 233 per year and no issues, should make TBO in 10 years at this rate.

 

[hevansrv7a]

Any altitude, any power below 75%

I'll just join the chorus. I do it all the time and most often at lower altitudes and power settings. I make sure the engine is at least as lean as GAMI says. On the GRT, that means that it will compute a SFC of 0.38 or less. The reading is lower than reality, but it's a good way to be sure. In Michigan in the winter that leaves the engine so cold I worry about that, not detonation.

 

[SebsRV7A]

John Deakin articles on LOP ops - great read!!

Link to John Deakin's articles on the subject. Long read, but my reference on LOP ops...
Note the Red Box power settings - I have them posted on my panel...

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

Seb Trost
RV-7A 325 hours
Boulder City, NV (BVU, formally 61B)
Always LOP at cruise, sometimes in climb, too!

 

[lucky]

what the deakin says about cruise seetings

http://www.warmkessel.com/jr/flying/td/jd/65.jsp

 

[erich weaver]

I commonly see folks here saying to limit people LOP to <75% power and have kept my LOP operations in that range, but I dont recall a specific limitation to that in the Deakin articles. In fact, there are a few places where he refers to going LOP during climb, using what he calls "the big mixture pull" (something like that anyway), to quickly transition from ROP to LOP. THis tecnique is distinct from the less aggressive one he describes in later articles, where you slowly lean as you climb by adjusting mixture to keep your egt approximately constant, then go LOP naturally above around 8ooo feet, or if below that, by leaning a bit more . By either method though, its always full throttle according to Deakin, as anything else would be "like operating with a dirty air filter".

Clearly you are not at full power anytime you are LOP, but it would seem likely that its at or above 75% using his "big pull" method, no?. And as he points out, the majority of the "red zone" is on the rich side of peak. Maybe it really can be done at >75% power??

I havent tried the big pull method myself, and Im not making any recommendations here either - just trying to promote further discussion and understanding.

regards

erich

 

[rv7charlie]

Lots of stuff about setting mixtures here:

http://www.lycoming.com/support/tips-advice/key-reprints/pdfs/Key Operations.pdf

While it recommends against lean of peak, it *does* recommend operation *at peak* for best economy cruise power settings. Interesting, since conventional wisdom for the entire time I've been flying has been to stay away from operation at peak in all circumstances.

FWIW, I've seen a document from Lyc in the past that actually details how to operate lean of peak, including the turbocharged models, but I can't find it now. Seems as if engine info is a lot like the weather. If you don't like what you see, just wait; it will change.

Charlie

 

[Webb]

I differ with Russ about this being beaten to death. I've learned more from these post with their the web links than I have anywhere else. I do agree with him that it is an interesting topic.

Thanks to the info. By far more complete than I've been able to find.

 

[Geico266]

After researching lean of peak, info seems to be a bit sparse but after doing enough searching, this is what I've found:

- Don't do it below 6,000 feet. You can't run greater than 75% power above.
- Make sure you are WOT. Detonation can occur for 2 reasons, too lean or too low rpm.
- Shoot for 50F LOP
- Best if engine is fuel injected
- Engine monitor is needed to do it properly
- Temps should be fairly even
- Expect about a 10 knot drop in speed
- Lycoming does not recommend

Any more experience/advice for those that are in the know would be great.

Webb, before you run LOP you need to "tune" or "balance" the injectors. They need to peak at nearly the same time. If you don't you run the risk of having a cylinder running at peak.

Call Don at Air Flow Performance and he will walk you though the procedure to gather the data, then you can replace the injector nozzles as needed.

http://www.airflowperformance.com/

 

[Ron Lee]

Is it not true that running at peak EGT is fine below certain power settings?

 

[rv7charlie]

Larry,

Take a look at the official Lyc document at the link I sent earlier.

Charlie

 

[Webb]

Webb, before you run LOP you need to "tune" or "balance" the injectors. They need to peak at nearly the same time. If you don't you run the risk of having a cylinder running at peak.

Call Don at Air Flow Performance and he will walk you though the procedure to gather the data, then you can replace the injector nozzles as needed.

http://www.airflowperformance.com/

Larry,

All cylinders peak at almost the same time. #'s 1,2,&3 almost exactly, #4 starts when the others have dropped about 10 degrees.

At cruise at altitude last night at 6,500 feet (23.5/2,250), my CHT's were 340, 342, 342, and 344 (#4) and the EGT's were all ROP with the 1,2,&3 about 88-90 and #4 was 80. Number 4 is my warmest and it's darn close.

I'm not sure that I can get it much closer. Next time I the cowl is off, I'm going to check and see it there are any air leaks near the baffle. As close as it is, I'm hestitant to touch a thing,

I'll try to remember to take a picture in flight tomorrow of the engine monitor so I can post verifiable numbers.

As close as the temps run, would you mess with it?

 

[erich weaver]

Is it not true that running at peak EGT is fine below certain power settings?

True according Deakin articles, as well as the Mike Busch (sp?) articles at Avweb. I remember Mike saying that he prefers to fly at peak.

Leaner is cooler when LOP, richer is cooler when ROP. So, according to Deakin, to stay out of trouble, you should:

stay richer than 100 degrees F ROP or leaner than peak EGT at 65% power
stay richer than 125 ROP or leaner than 25 LOP at 70%
stay richer than 180 ROP or leaner than 40 LOP at 75%
stay richer than 200 ROP or leaner than 60 LOP at 80%

So, at less than 65% power you should be able to fly at peak.

If you venture into the "Red Box" area between the LOP/ROP settings above you risk detonation.

At about 8000 feet and above, you can run any mixture setting you desire and not risk damage to your engine - without turbo power, you cannot have more than appx 60% power at this altitude and there are no mixture settings that put you at risk at this power rating or less.

regards

erich

 

[rwhittier]

Make sure your thinking FF

Webb,

I run LOP all the time, it is my preferred way to run the engine. I used to not feel this way believing all the old wives tales about LOP operation. To get the real truth I spent the money to go the the Advanced Pilot Seminars, at the GAMI facility. I have not been flying my Superior FI engine that way yet, only cause its not flying yet But I will. I now have over 700 hours LOP hours on a IO-550. I have had good oil analysis results and the engines TT is near 1000 hours. Compressions are all great, lowest one at annual this month was 72/80 all on original factory cylinders so I clearly am not hurting that engine.

So to your situation. It sounds like you are saying they peak about the same time. But one thing you need to watch is that its not important what CHT temperature they peak at, but at what Fuel Flow they peak at. Your last to peak is the one you have to set your LOP cruise FF to to protect it. Ideally all cylinders EGT would peak at exactly the same FF. In practice that's nearly impossible to do because all cylinders are just a tad different and can be baffled different.

In your case it does sound very much like number 4 peaks last. One thing I would do is the complete GAMI test. See http://gami.com/gamijectors/leantest.php After that is done you will know better. One trick I have seen to even out FF peaking is to take the first to peak cylinders injector and swap it with the last to peak cylinders injector. Then go repeat the test and perhaps do that again. That way your moving the injectors with minor size differences to the cylinders that can use the different size, in effect optimizing the extremely small production variances.

Just remember, the higher the output of the engine, the more LOP you have to be to protect your detonation margin. For example, at 75% (or at lower altitudes with a non aspirated engine) an EGT that's 50 degrees (or more) LOP is important. The new Turbo Normalized Cirrus SR22 runs 85% power LOP as the only approved way to operate the engine in cruise in the POH, so it can be done with balanced injectors. At lower power settings (when your 65% or lower) then 10 to 25 degrees LOP the last cylinder (#4 in your case) to peak would be fine. When your at 10,000 feet or below 60% you could run @ peak safely and never hurt the engine (it can't get enough air to produce enough compression pressure to detonate), but engine temps will be a bit higher so I don't do that. I feel strongly that one of the advantages of LOP ops is lower CHT, so I want to get that benefit.

If you would like me to look at your GAMI test results, I would be happy to do so. I have done this test on about 8 aircraft now. Good luck.

Larry,

All cylinders peak at almost the same time. #'s 1,2,&3 almost exactly, #4 starts when the others have dropped about 10 degrees.

At cruise at altitude last night at 6,500 feet (23.5/2,250), my CHT's were 340, 342, 342, and 344 (#4) and the EGT's were all ROP with the 1,2,&3 about 88-90 and #4 was 80. Number 4 is my warmest and it's darn close.

I'm not sure that I can get it much closer. Next time I the cowl is off, I'm going to check and see it there are any air leaks near the baffle. As close as it is, I'm hestitant to touch a thing,

I'll try to remember to take a picture in flight tomorrow of the engine monitor so I can post verifiable numbers.

As close as the temps run, would you mess with it?

 

[Kevin Horton]

At about 8000 feet and above, you can run any mixture setting you desire and not risk damage to your engine - without turbo power, you cannot have more than appx 60% power at this altitude ...

The air density at 8000 ft at standard temperature is 79% of the air density at sea level with standard temperature. RVs have very efficient air induction systems with very little air pressure loss, and quite good recovery of ram pressure rise. The theoretical ram pressure rise at 160 kt is 1.2 inHG, if the air box was perfect. Many RV flyers report cruise MPs that are higher than the ambient pressure. I believe that many RVs are able to achieve 80% power at 8000 ft.

 

[Geico266]

Is it not true that running at peak EGT is fine below certain power settings?

Larry,

Take a look at the official Lyc document at the link I sent earlier.

Charlie

It depends on what altitude you are flying at. Peak temps at lower alts are higher.

 

[Geico266]

As close as the temps run, would you mess with it?

Looks good to me Web.

The test I referred to is simple. Give it a try and see where you are at, if nothing else you have an excuse to fly again!

Here is the test from Airflow Performance.

Nozzle Tuning Data

The basis of nozzle tuning is to get each of the cylinder EGT’s to peak at the same fuel flow. Your aircraft must be equipped with EGT information on each cylinder and fuel flow information. A digital flow meter is preferred.

To gather correct data for nozzle tuning, set a cruise power setting. Typically 24” MAP and 2400 RPM. Set the mixture to be 0.5 GPH richer than peak on any cylinder. At this setting record all the EGT’s for each cylinder. Lean the mixture 0.2 GPH and record all the EGT’s again. Lean the mixture an additional 0.2 GPH; record all the EGT’s again. Continue leaning the mixture 0.2 GPH and record the EGT’s until all the cylinders have peaked.

An alternative method although not as accurate is to lean each cylinder to peak and record the fuel flow at that point. You will get the same data, but since the EGT reacts slower than the leaning process you may go past the peak and not know it. This is especially true if an engine monitoring lean find function is used. We get more accurate data taking the EGT data manually. If you use an automatic data acquisition function, allow 30 seconds or so at each fuel flow setting so the EGT value can stable out.

After the data is taken, we determine which nozzles to change to get all the cylinders to peak at the same time. You will notice that the EGT number at peak may not be the same for each cylinder, THIS IS NOT IMPORTANT. The cylinders that peak first (higher fuel flow) are the lean ones; the cylinders that peak last (lower fuel flow) are the rich ones.

Getting all cylinders to peak within 0.2 GPH is ideal.

 

[erich weaver]

The air density at 8000 ft at standard temperature is 79% of the air density at sea level with standard temperature. RVs have very efficient air induction systems with very little air pressure loss, and quite good recovery of ram pressure rise. The theoretical ram pressure rise at 160 kt is 1.2 inHG, if the air box was perfect. Many RV flyers report cruise MPs that are higher than the ambient pressure. I believe that many RVs are able to achieve 80% power at 8000 ft.

Hmmmm. Guess I better go even leaner then I was!

I tend to get lost in the math, but the above seems to indicate that 79% air density equates to approixmately 79% of full power at full throttle (neglecting any ram air effects or filter losses), no?. This conflicts with the Deakin articles where he claims you cant get more than about 65% of full power at this altitude. Doesnt make sense to me that this discrepancy could be explained by efficient induction systems - if its efficient at altitude, it is going to be efficient at sea level as well, so shouldnt you still have a consistent drop in power with altitude gain (assuming standard conditions blah blah blah)

Am I missing something?

erich

 

[Kevin Horton]

Hmmmm. Guess I better go even leaner then I was!

I tend to get lost in the math, but the above seems to indicate that 79% air density equates to approixmately 79% of full power at full throttle (neglecting any ram air effects or filter losses), no?. This conflicts with the Deakin articles where he claims you cant get more than about 65% of full power at this altitude. Doesnt make sense to me that this discrepancy could be explained by efficient induction systems - if its efficient at altitude, it is going to be efficient at sea level as well, so shouldnt you still have a consistent drop in power with altitude gain (assuming standard conditions blah blah blah)

Am I missing something?

The Lycoming power charts suggest there isn't an exact one to one relationship between air density and power available, but the relationship isn't too far off one to one.

Where exactly did John Deakin state that you can't get more than 65% power above 8,000 ft? I'd be amazed if he said that. The usual statements you hear people make are "you can't get more than 75% power above 7500 ft" (or maybe 8000 ft), but even those statements are not necessarily true for RVs. They may be true for Cessnas, which have less efficient air boxes, and less ram pressure rise available due to lower TAS, but I don't believe they are true for RVs. If you take the MP readings that many RV pilots report at full throttle at 8000 ft, and go into the Lycoming power charts, you will conclude that it is possible to exceed 75% power at 8000 ft at full throttle and high rpm.

 

[erich weaver]

I'll have to check the articles to find a citation - there may not be an exact quote, but I distinctly recall a reference to 8000 feet as the approximate point where you wouldnt have to worry about mixture setting any more. Let me see what I can dig up.

erich

 

[Webb]

Looks good to me Web.

The test I referred to is simple. Give it a try and see where you are at, if nothing else you have an excuse to fly again!

Here is the test from Airflow Performance.

Nozzle Tuning Data

The basis of nozzle tuning is to get each of the cylinder EGT’s to peak at the same fuel flow. Your aircraft must be equipped with EGT information on each cylinder and fuel flow information. A digital flow meter is preferred.

To gather correct data for nozzle tuning, set a cruise power setting. Typically 24” MAP and 2400 RPM. Set the mixture to be 0.5 GPH richer than peak on any cylinder. At this setting record all the EGT’s for each cylinder. Lean the mixture 0.2 GPH and record all the EGT’s again. Lean the mixture an additional 0.2 GPH; record all the EGT’s again. Continue leaning the mixture 0.2 GPH and record the EGT’s until all the cylinders have peaked.

An alternative method although not as accurate is to lean each cylinder to peak and record the fuel flow at that point. You will get the same data, but since the EGT reacts slower than the leaning process you may go past the peak and not know it. This is especially true if an engine monitoring lean find function is used. We get more accurate data taking the EGT data manually. If you use an automatic data acquisition function, allow 30 seconds or so at each fuel flow setting so the EGT value can stable out.

After the data is taken, we determine which nozzles to change to get all the cylinders to peak at the same time. You will notice that the EGT number at peak may not be the same for each cylinder, THIS IS NOT IMPORTANT. The cylinders that peak first (higher fuel flow) are the lean ones; the cylinders that peak last (lower fuel flow) are the rich ones.

Getting all cylinders to peak within 0.2 GPH is ideal.

I was playing with it tonight at a lower rpm. Alt was 7,000. All cylinders are very close and within 0.2 to 0.3 gph when they peak and change to monitor to degrees below peak instead of raw temp numbers.

Here is the picture at ROP.

I also tried LOP but it seems the engine runs a bit rough. Might be my imagination but I sure don't want detonation. Might just be uncomfortable and need to take an experienced "leaner" with me.

 

[Geico266]

I was playing with it tonight at a lower rpm. Alt was 7,000. All cylinders are very close and within 0.2 to 0.3 gph when they peak and change to monitor to degrees below peak instead of raw temp numbers.

I also tried LOP but it seems the engine runs a bit rough. Might be my imagination but I sure don't want detonation. Might just be uncomfortable and need to take an experienced "leaner" with me.

Do you have EGTs info? CHTs are not accurate enough to run LOP.

Detonation running LOP is rare due to the lower fuel mixture, and cooler running temps. It is running rough because you are "on the edge" of the lean mixture. If you have EGT info you would set it up 40-50F LOP of the 1st cylinder to peak. The Dynon will do this for you in the lean mode. There will be a slight loss of power and speed, but the fuel burn will be 1-2 GPH less.

There is a great manual to read about running LOP. Click on the link below and the 3rd link on the page is "Operator's Manual For Any EGT Instrument".

http://www.buy-ei.com/Pages/Masthead/Masthead_Downloads.html

 

[Webb]

Do you have EGTs info? CHTs are not accurate enough to run LOP.

Detonation running LOP is rare due to the lower fuel mixture, and cooler running temps. It is running rough because you are "on the edge" of the lean mixture. If you have EGT info you would set it up 40-50F LOP of the 1st cylinder to peak. The Dynon will do this for you in the lean mode. There will be a slight loss of power and speed, but the fuel burn will be 1-2 GPH less.

I was backwards. 40-50 on the last to peak like you do when you go ROP. Others got too lean, hence the rough run.

Just another excuse to go fly and try again.

 

[Geico266]

I was backwards. 40-50 on the last to peak like you do when you go ROP. Others got too lean, hence the rough run.

Just another excuse to go fly and try again.

Try running -50F on the 1st to peak at that alt. Should be smoother.

I re-read that manual I posted above and picked up (was reminded of) a few pointers about running LOP again. It is funny how I forget or get lazy about flying and managing the engine. Always good to re-read stuff like that and keep current after a long winter.

 

[frankh]

Webb Try this

First off you won't detonate on the lean side of peak..In fact the "danger zone" is around 50 degrees Rich of peak..And I doubt that would happen anywhere with such lower power numbers.

Anyway..Take the thing to altitude and set yer MP and RPM where you want them..I normally use 24sq and lean from there.

OK now do the big lean..pull the red know until it runs like bag of nails..It wakes your passenger up if nothing else.

You should be well LOP on all cylinders.

Ok now twist the knob back in until it just runs acceptably..A little bit of misfire is ok.

Now hit the leaan mode on the Dynon..Let the temps settle and start twisting the knob towards rich...What you'll do is to find peak egt from the lean side.

At one point (at 24 sq this will be 7 to 7.4 GPH fuel flow) the thing will run smooth as silk...Note where this is and keep twisting the knob until the Dynon indicates you's just gone ROP.

I will bet money that the point where it runs smooth is several knob twists away from where the first cylinder peaks.

Now you have the key to easy leaning..Once you have convinced yourself of the above..you will in future take off..climb (or set the throttle) to where mp<24", Rpm to 2400..then grab the red knob and haul on it till it complains and then just inch it forwards till it runs smooth..Should be around 6.8 to 7Gph...Peak will be about 8.2GPH so your well on the safe side of peak EGT.

So set the GPH to 7 to 7.5 and forget about it.

Have fun and save fuel..I fly everything this way including aerobatics, where i just manipulate the throttle.

Frank

 

[Jamie]

Webb:

Why do you not have the % of power displayed on your EMS? Turn that on and never have a doubt about the power you're running at. It may require a firmware update.

I have an EMS D-10 too and I really, really like it for it's simplicity, compactness and capability.

 

[erich weaver]

Where exactly did John Deakin state that you can't get more than 65% power above 8,000 ft? I'd be amazed if he said that.

Ok, found it - Check out his "Pelicans Perch #65 - Where Should I run My Engine? Part 3 - Cruise" available on the Avweb site. Under the heading "Cruise at Altitude" it says:

"Its important to realize that if you choose to run at full throttle in a normally aspirated engine (and you almost always should), then your only control over manifold pressure is altitude. The higher you fly, the less the manifold pressure, and the smaller that 'red box'. Its really simple if you climb above about 8,000 feet or so. The altitude will have reduced your power so that no matter what you do (normally aspirated), you cannot recover it - you cannot get more than 60% or so - and you cant hurt the engine with ANY mixture setting."

There are multiple other places in his collection of articles where you reach the same conclusion, but this is the most clear-cut direct reference I found.

Any thoughts?

erich

EDIT: SEE POST #55 ON THIS THREAD FOR A CORRECTION FROM JOHN DEAKIN ON THIS

 

[Radomir]

Best thing to do is to pull out the Lycoming power chart and figure out what power *your* engine is producing at said altitude.. These rules of thumb can work as very rough guides, but we are capable of knowing better (considering the instrumentation we have in our planes). But rest assured your RV can do more than 60% at 8,000 ft...

 

[erich weaver]

Try running -50F on the 1st to peak at that alt. Should be smoother.

Careful here - The first to peak, when leaning from ROP, would be the leanest cylinder. Therefore, when that cyclinder is 50F lean of peak, the others will be richer, possibly at peak or somewhat ROP. Depending upon the percent power being produced, that may well be in the 'red box' zone that should be avoided to stay clear of detonation. For LOP operation, its best to look at the RICHEST cylinder, meaning the other cylinders are leaner and further from peak pressures/temperatures and further from detonation.

Of course, if the engine is running rough because the injectors are not well enough matched, you will really have no choice except to enrich until all cylinders are far enough ROP to avoid the 'red box'. From the ROP side, the opposite is true - you would be most interested in the leanest cylinder, as that is the one closest to peak pressure/temperature.

erich

 

[frankh]

Its still easier

and less stress on the engine to find peak form the lean side....You can mess about over there all you want..But I would be leaving some of my cylinders on the just ROP side for very long..even at 24 sq.

Frank

 

[erich weaver]

Frank - did you leave out a word there in your post? I think you meant to say that you would NOT leave some of your cylinders slightly ROP for very long, no?

erich

 

[Webb]

Webb:

Why do you not have the % of power displayed on your EMS? Turn that on and never have a doubt about the power you're running at. It may require a firmware update.

I have an EMS D-10 too and I really, really like it for it's simplicity, compactness and capability.

I didn't see anything in the manual about this. Phone call coming next. Also, I did read about resetting the fuel flow rate but adjusting the K value. Mine is calculating high so I'll need to do a comparison next flight and make the adjustment.

For those that want to reset theirs, divide the computed use by the actual use and multiply that number against the value in the EMS for adjustment.

Geez, now I have ANOTHER reason to go fly. Will they never cease (lol).

Now to find out how to get the % power to show up....ho hum, the lazy man's way.....

 

[Finley Atherton]

% POWER DISPLAY

Be careful relying on % HP displays when LOP. Maybe the Dynon is accurate, but I have a newer version VM1000C with the JP innards and I am fairly certain that the % HP display is only accurate for ROP mixture settings. For example, my typical cruise setting at 8,500 ft is 2,250 rpm, about 15 to 30 degrees LOP (carburetor so can't go leaner) and this gives a fuel flow of 6 G/H. Using Curve # 12883 from the Lycoming 0-320 Operators Manual, 6 G/H at 2,250 rpm at "Best Economy" mixture (peak EGT) gives about 78HP or 49%. At this setting my engine monitor is displaying 60% power. The above mentioned graph shows HP at "Best Economy" (peak EGT) and admittedly going LOP could produce slightly more HP for the same fuel flow, although the Lycoming graph that shows "Representative Effects of Leaning on CHT, EGT, etc. indicates there is little improvement in Specific Fuel Consumption leaning beyond peak.

Tell me if I am missing something here.

Fin
9A

 

[erich weaver]

Fin:
I think you are pretty close here. Hate to beat a dead horse here, but take a look at the Deakin article I previously referenced. Graphs are presented there displaying EGT, CHT, ICP (internal combustion presssure) and BSFC (brake specific fuel consumption) curves together. The curves move the same relative to each other with different power settings, except for BSFC, which apparently shifts left and right just a little bit. According to Deakin, "At lower power settings, optimum BSFC occurs at about 10-20F LOP, and at higher power settings, as much as 80 LOP. But the BSFC curve is so flat in that area, it really doesnt make that much difference...."

A lot of folks seem to shoot for about 50F LOP. Of course, you cant really expect to have all cylinders at exactly 50 LOP simultaneously - how close you get will depend on how well balanced your fuel distribtuion is.

For maximizing your flight range, Deakin recommends operating at full throttle while leaned to best BSFC, then reducing RPM as much it takes to achieve the desired range. If you have any information about the efficency of your prop at different RPMs, this should also be taken into consideration.

erich

 

[vlittle]

Be careful relying on % HP displays when LOP. Maybe the Dynon is accurate, but I have a newer version VM1000C with the JP innards and I am fairly certain that the % HP display is only accurate for ROP mixture settings. For example, my typical cruise setting at 8,500 ft is 2,250 rpm, about 15 to 30 degrees LOP (carburetor so can't go leaner) and this gives a fuel flow of 6 G/H. Using Curve # 12883 from the Lycoming 0-320 Operators Manual, 6 G/H at 2,250 rpm at "Best Economy" mixture (peak EGT) gives about 78HP or 49%. At this setting my engine monitor is displaying 60% power. The above mentioned graph shows HP at "Best Economy" (peak EGT) and admittedly going LOP could produce slightly more HP for the same fuel flow, although the Lycoming graph that shows "Representative Effects of Leaning on CHT, EGT, etc. indicates there is little improvement in Specific Fuel Consumption leaning beyond peak.

Tell me if I am missing something here.

Fin
9A

Most horsepower computers only work at rich settings, using manifold pressure and rpm. For lean settings, it's fuel flow and BSFC consumption that determines horsepower.

The explanation is pretty simple. If you have excess fuel (rich), then power is determined by the amount of air pumping through the engine (rpm, map). If you have excess air (lean), then it's the amount of fuel flowing that determines HP.

Vern

 

[Kevin Horton]

Ok, found it - Check out his "Pelicans Perch #65 - Where Should I run My Engine? Part 3 - Cruise" available on the Avweb site. Under the heading "Cruise at Altitude" it says:

"Its important to realize that if you choose to run at full throttle in a normally aspirated engine (and you almost always should), then your only control over manifold pressure is altitude. The higher you fly, the less the manifold pressure, and the smaller that 'red box'. Its really simple if you climb above about 8,000 feet or so. The altitude will have reduced your power so that no matter what you do (normally aspirated), you cannot recover it - you cannot get more than 60% or so - and you cant hurt the engine with ANY mixture setting."

There are multiple other places in his collection of articles where you reach the same conclusion, but this is the most clear-cut direct reference I found.

Any thoughts?

That statement certainly disagrees with the Lycoming power charts. The exact MP required for 60% power at 8000 ft varies a little bit depending on which power chart you look at, but generally speaking 18 inHG at 2700 rpm will be 60% power or more. If you drop the rpm to 2500 you need to add about another half inch of MP. If you can't get a lot more than 18 inHG at full throttle at 8000 ft, there is something wrong with your airbox.

Maybe there was some sloppy editing in those articles. I doubt John Deakin really intended to disagree with the power vs rpm, MP and altitude curves that Lycoming and Continental publish.

 

[Finley Atherton]

Be careful relying on % HP displays when LOP. Maybe the Dynon is accurate, but I have a newer version VM1000C with the JP innards and I am fairly certain that the % HP display is only accurate for ROP mixture settings. For example, my typical cruise setting at 8,500 ft is 2,250 rpm, about 15 to 30 degrees LOP (carburetor so can't go leaner) and this gives a fuel flow of 6 G/H. Using Curve # 12883 from the Lycoming 0-320 Operators Manual, 6 G/H at 2,250 rpm at "Best Economy" mixture (peak EGT) gives about 78HP or 49%. At this setting my engine monitor is displaying 60% power. The above mentioned graph shows HP at "Best Economy" (peak EGT) and admittedly going LOP could produce slightly more HP for the same fuel flow, although the Lycoming graph that shows "Representative Effects of Leaning on CHT, EGT, etc. indicates there is little improvement in Specific Fuel Consumption leaning beyond peak.

Tell me if I am missing something here.

Fin
9A

Most horsepower computers only work at rich settings, using manifold pressure and rpm. For lean settings, it's fuel flow and BSFC consumption that determines horsepower.


Vern

So, It seems I am correct not believing the % HP readout at peak EGT and leaner? Lately, to determine HP when cruising at peak or leaner, I have been using a table I drew up based on the curve mentioned in my post # 34 and my typical fuel flows and rpms. The benefit being, what I thought was 60% power (based on the engine monitor) was actually only about 50%, so, if I want to go faster, I can now cruise at higher power settings without exceeding my self imposed limit of 60% power when operation at peak or leaner.

Fin
9A

 

[petehowell]

Dynon LOP HP%

As I understand it, the Dynon guys adjust their HP % for LOP conditions.

It seems to check out for me:

Here I am at 6GPH at 6 lbs/gal = 36lbs/hr. Using a LOP BSFC of .41, that gives 39/.41 or ~87HP. 87HP/160HP = 55%

I think that checks.

 

[fishguy]

I can't get 50 lop!

I have just gone through the nozzle tuning program with Airflow Performance and although I need one more flight to verify, I think I am within about .3 gph for all peaks. The funny thing is that when I get more than about 20 to 30 degrees LOP the temps begin to rise! Ron at Airflow explained the reason-- the cumbustion event is happening slow enough that it is still happening when the exhaust valve opens, thus higher temps--but it is unsettling to see the temps going up when it seems like they should continue going down. Maybe I should be using the absolute value away from last to peak, the combination of down and then back up? Does anyone else have this happen?

FG

 

[Finley Atherton]

As I understand it, the Dynon guys adjust their HP % for LOP conditions.

Hi Pete,

Using your figures of 5.9 G/H and 2,200 rpm, Lycoming Curve #12883 gives about 78 HP or 49% power. This is based on HP at peak EGT. Your actual figure could be a little higher because you are LOP, however as stated previously BSCF does not appear to improve much past peak. Another factor is your dual electronic ignition which is meant to give extra HP for the same fuel flow so maybe your 55% is not far off the correct figure.

Fin
9A

 

[hevansrv7a]

HP goes up or down LOP?

Hi Pete,

Using your figures of 5.9 G/H and 2,200 rpm, Lycoming Curve #12883 gives about 78 HP or 49% power. This is based on HP at peak EGT. Your actual figure could be a little higher because you are LOP, however as stated previously BSCF does not appear to improve much past peak. Another factor is your dual electronic ignition which is meant to give extra HP for the same fuel flow so maybe your 55% is not far off the correct figure.

Fin
9A

His 5.9 gph x 6#/gal /0.4 SFC = 88.5 HP = 55% of 160 while LOP. So far we agree. The Dynon says "LOP" so if they know that, they could do it and appear to do it right. Excellent.

But lowering the SFC does not increase the HP as compared to peak. BSFC gets better for a while - I think more than 5% based on my GRT experience - as you move away from peak but while you do that, you are reducing fuel flow and the airplane is slowing down a little. In theory the same fuel flow with a lower BSFC gives more HP but in practice you set the throttle and pull the mixture, so you get less HP. That's especially true if you are already WOT. As Vinnie (John Travolta) used to say, "I'm so confused".

 

[Webb]

Fuel PSI

Pete, I was looking at your engine monitor and was wondering about your fuel PSI. It looks low. What sensor type do you have inputted? Mine was low and then I found out I had the wrong # type in the Dynon. Now it's in the 20's. Just curious.

As I understand it, the Dynon guys adjust their HP % for LOP conditions.

It seems to check out for me:

Here I am at 6GPH at 6 lbs/gal = 36lbs/hr. Using a LOP BSFC of .41, that gives 39/.41 or ~87HP. 87HP/160HP = 55%

I think that checks.

 

[rwhittier]

A simple formula

that I learned from the GAMI guys to calculate HP is that when you are LOP HP output corresponds directly to FF. Take your FF and multiply by 15.

15 x 5.9 = 88.5. Pretty easy to do in your head. That does not work ROP, but it does work at any RPM, as long as you are LOP.

His 5.9 gph x 6#/gal /0.4 SFC = 88.5 HP = 55% of 160 while LOP.

 

[petehowell]

Hey Webb!

Pete, I was looking at your engine monitor and was wondering about your fuel PSI. It looks low. What sensor type do you have inputted? Mine was low and then I found out I had the wrong # type in the Dynon. Now it's in the 20's. Just curious.

Webb - I am running carb - low pressure fuel system......

 

[petehowell]

APRS

Webb - we need to get you set up with a tracker - buzz me again if you want more info or help.

 

[Finley Atherton]

that I learned from the GAMI guys to calculate HP is that when you are LOP HP output corresponds directly to FF. Take your FF and multiply by 15.

15 x 5.9 = 88.5. Pretty easy to do in your head. That does not work ROP, but it does work at any RPM, as long as you are LOP.

This has been discussed in another thread and I don't want to bore people but I would really like to be confident in the calculated HP figures when I operate LOP. Basically I am still not convinced about the accucracy of the "by 15" rule and that rpms make no difference when calculating HP, LOP. For instance, at what point LOP does this "multiply by 15" rule become effective? For example, IO-320 at Peak EGT, for 65% power (104 hp) you need a FF of 8 g/h at 2,700 rpm and a FF of 7.1 g/h at 2,000 rpm (from the 0-320 Lycoming Operator's Manual). The calculated multiplier therefore varies between 13 and 14.65. So presumably if you are operating at peak or maybe just on the lean side, you should ignore the multiply FF by 15 rule and use the Lycoming figures instead?? At what point LOP will the multiply by 15 rule become effective? The other thing I can't get my head around is that plumbing and frictional losses will increase with higher rpm even when LOP so how can a fixed multiplier be appropriate at different rpms when LOP. At peak EGT at least, rpms make a big difference to the multiplier as shown by the figures above.

Fin
9A

 

[hevansrv7a]

Walter Says:

This has been discussed in another thread and I don't want to bore people but I would really like to be confident in the calculated HP figures when I operate LOP. Basically I am still not convinced about the accucracy of the "by 15" rule and that rpms make no difference when calculating HP, LOP. For instance, at what point LOP does this "multiply by 15" rule become effective? For example, IO-320 at Peak EGT, for 65% power (104 hp) you need a FF of 8 g/h at 2,700 rpm and a FF of 7.1 g/h at 2,000 rpm (from the 0-320 Lycoming Operator's Manual). The calculated multiplier therefore varies between 13 and 14.65. So presumably if you are operating at peak or maybe just on the lean side, you should ignore the multiply FF by 15 rule and use the Lycoming figures instead?? At what point LOP will the multiply by 15 rule become effective? The other thing I can't get my head around is that plumbing and frictional losses will increase with higher rpm even when LOP so how can a fixed multiplier be appropriate at different rpms when LOP. At peak EGT at least, rpms make a big difference to the multiplier as shown by the figures above.

Fin
9A

I recently asked Walter Atkinson about the 14.9 (SFC=.40) as it relates to altitude HP gains. I was using SFC of .40 as a constant and wanted to know if it made sense. Walter's answer was "pretty doggone accurate". I used the constant in my "Model" which is posted at: http://www.vansairforce.com/community/showthread.php?t=42703
I would have thought that pumping losses could cause it to vary and I can't explain why not, but in using it as a constant, it does seem very precise.

 

[Geico266]

that I learned from the GAMI guys to calculate HP is that when you are LOP HP output corresponds directly to FF. Take your FF and multiply by 15.

15 x 5.9 = 88.5. Pretty easy to do in your head. That does not work ROP, but it does work at any RPM, as long as you are LOP.

This may work for a 4 cylinder, but it doesn't work for a 6.

 

[hevansrv7a]

I think I disagree abouat cylinders

This may work for a 4 cylinder, but it doesn't work for a 6.

Perhaps I'm missing the obvious, but this 14.9 multiplier is just a convenient way to express an SFC of 0.40. Why would it matter how many cylinders are in use? I think the rule that when LOP fuel flow is proportional to BHP makes good sense and putting a number into that concept merely makes it more precise. Heck, the rule would work ROP if we knew the SFC. If we would use 0.50 as the SFC at peak power (not necessarily peak EGT) we'd come pretty close, too.