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Operating Lean of Peak at Lower Altitudes?

ChuckGant

Well Known Member
I am a new owner of an RV-7 with an IO-360. I am a professional pilot, but new to constant speed props on piston engines. My RV is equipped with a Grand Rapids Technologies Horizon WS and EIS 4000 engine monitoring system. I have read everything I can find from John Deakin and Mike Busch about flying lean of peak and feel like I have a pretty good understanding of the process and the "red box".
However...
Everything I've read talks about leaning as you climb and leaning at cruise altitude above 8000', where you know you are producing less than 60% power. My question is, how do you lean when cruising around at lower altitudes, like 2000-6000'? From what I understand, once you are below 60% power, you can do anything you want with the mixture control without hurting the engine, but none of the articles detail how you know when you are below 60% power. Are you guys just using the generic charts that many have in there POHs, such as 22" at 2350 rpm? These seem a little generic and inaccurate for something as important as avoiding detonation. Or, are you just doing a "big pull" on the mixture until it runs rough and then richening it up a bit? How do you safely operate if you want to run at a higher power setting? Please enlighten me on the best way to manage mixture down low.

Thanks,
Chuck
 
Remember, when you are LOP, FUEL sets your % power, not MAP. Here's my simple rule for my IO-360:

MAP 26.0" or below and 9GPH or below.

I fly LOP at 2,000' all the time. 9 GPH is 70% power so if you're below that you're pretty darn safe no matter what your MAP. My engine seems to run happier limited to 26" than trying to run 28" at 2K feet while also pulling the fuel.

If I want to go faster than that, then you need to be more careful or just go ROP when you're lower.

I'm sure lots of other people have their own methods...
 
Since you've got a GRT EFIS, you don't have to guess - you can configure it to display % HP all the time - accurate enough for determining that you are below 75%, the point where Lycoming says you can lean. The 60% number where you "Can't hurt the engine" is true, but it is REALLY hard to hurt it below 75%, and Lyc says you can take it to peak at that point and LOP is easier on the engine than peak by all measures - so have at it. If you are over 75%, just bring the throttle back until you are below it.
 
Lean all the time except on takeoff and below 3000 feet in the climb.
There is a document from Lycoming that says the same thing. Start engine, lean, runup lean, takeoff and climb rich, landing rich (in case of go-around). Lean in all other flight ops

Once Embry-Riddle followed (wrote) these rules, their engine reliability improved dramatically. Notice they don't say 'lean of peak'. I assume that they can't depend on engine analyzers on all engines so they say to lean it out then richen to smooth, which in our FI/EI engines is still LOP.

http://www.lycoming.com/Portals/0/t...Procedures for Flight Training Operations.pdf

I will caution, though, that this was developed for C-172s that probably can never put out more than 75% hp due to restrictive intake and exhaust, so the likelihood of being in the 'red box' is low. With our juiced engines, ram air intakes and efficient exhausts, I wouldn't be leaning to 'best power' at high power settings. I would never lean any richer than smooth operation dictates unless it was well rich of peak.

tumblr_mvxk3lUsFx1sgl0ajo1_500.gif
 
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Since you've got a GRT EFIS, you don't have to guess - you can configure it to display % HP all the time - accurate enough for determining that you are below 75%, the point where Lycoming says you can lean.
...
If you are over 75%, just bring the throttle back until you are below it.

Most EFIS systems don't factor in fuel flow, so it will make you think that you are in the danger area because your MAP is high, but your fuel flow is keeping you safe. 26" MAP at 4,000' is 85% power if you are ROP but can easily be below 70% power LOP.

If you want to be efficient at LOP, you don't pull the throttle, which increases pumping losses, you pull the fuel.

--Ian @ Dynon
 
Since you've got a GRT EFIS, you don't have to guess - you can configure it to display % HP all the time - accurate enough for determining that you are below 75%, the point where Lycoming says you can lean. The 60% number where you "Can't hurt the engine" is true, but it is REALLY hard to hurt it below 75%, and Lyc says you can take it to peak at that point and LOP is easier on the engine than peak by all measures - so have at it. If you are over 75%, just bring the throttle back until you are below it.

Also,

Make sure that you have put in the performance data for your engine. It may already be there. If not, there are some tables at the GRT site (I think).

If you only have one screen, you may at some time want to upgrade the WS to an HX so that you can do a lot of the newer stuff including split screen that shows engine data on bottom strip below PFD and MAP split screen.

James
 
There are tables at GRT. There are more table available than when I was in phase 1 in 2012. I mention it because the table available at that time, noted for O-360 was not even close to describing my IO-360-M1B correctly. The power levels were low, meaning the EFIS showed 75% but reality was a lower power level. Created my own chart via reference to Lycoming docs for the M1B.

And yes.... I run LOP all the time, excluding takeoff. Even at low altitude. I will pull the rpm way back in order to minimize any closure of the throttle plate.

A handy trick I have started doing recently is to go ahead and set the engine display on the 'lean' function prior to takeoff. As I climb, it will show a peak and it gives easy reference back to the takeoff EGT values since the EGT goes negative during climb. Simply lean back to zero and you stay at takeoff EGT.
 
I am a new owner of an RV-7 with an IO-360. I am a professional pilot, but new to constant speed props on piston engines. My RV is equipped with a Grand Rapids Technologies Horizon WS and EIS 4000 engine monitoring system. I have read everything I can find from John Deakin and Mike Busch about flying lean of peak and feel like I have a pretty good understanding of the process and the "red box".
However...
Everything I've read talks about leaning as you climb and leaning at cruise altitude above 8000', where you know you are producing less than 60% power. My question is, how do you lean when cruising around at lower altitudes, like 2000-6000'? From what I understand, once you are below 60% power, you can do anything you want with the mixture control without hurting the engine, but none of the articles detail how you know when you are below 60% power. Are you guys just using the generic charts that many have in there POHs, such as 22" at 2350 rpm? These seem a little generic and inaccurate for something as important as avoiding detonation. Or, are you just doing a "big pull" on the mixture until it runs rough and then richening it up a bit? How do you safely operate if you want to run at a higher power setting? Please enlighten me on the best way to manage mixture down low.

Thanks,
Chuck


Chuck,

Check your PMs.

Jerry
 
And yes.... I run LOP all the time, excluding takeoff. Even at low altitude. I will pull the rpm way back in order to minimize any closure of the throttle plate.

Just be cautious. High MP, low RPM is pro-detonation. In fairness, detonation would probably require one or more additional conditions (high CHT, high OT, high OAT, minimum spec fuel, advanced timing, or high compression ratio), but it pays to observe the general trend.

A handy trick I have started doing recently is to go ahead and set the engine display on the 'lean' function prior to takeoff. As I climb, it will show a peak and it gives easy reference back to the takeoff EGT values since the EGT goes negative during climb. Simply lean back to zero and you stay at takeoff EGT.

What a great idea! It's the "target EGT" method for climb leaning, with instrumented help. I gotta try it when I get out of annual.

Everything I've read talks about leaning as you climb

Chuck, note a detail that may help understanding.

Deakin's writing is understandably Continental-centric; it was GAMI's original and largest market. A basic Continental-type fuel injection meters fuel flow based on RPM. The basic system cannot detect a change in air density, thus it must be leaned in the climb if you wish to maintain anything like rated power for any given altitude. Some of the later systems do incorporate a form of density compensation, but it's fundamentally an add-on.

A Bendix-type fuel injection (Bendix, AFP, or Precision) meters fuel flow based on air density and throat velocity. You're not absolutely required to lean in the climb, as the system tries to do it for you. It is not completely successful, but gets close. Given a constant TAS climb at full rich, measured enrichment with the FM-200 on my own IO-390 is only about 12.5:1 to 10:1 for 13,000 feet of altitude change. Leaning in the climb is a tweak for max performance and lowest fuel burn, not a hard requirement.
 
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Just be cautious. High MP, low RPM is pro-detonation. In fairness, detonation would probably require one or more additional conditions (high CHT, high OT, high OAT, minimum spec fuel, advanced timing, or high compression ratio), but it pays to observe the general trend...

Also noteworthy is that really lean mixtures are anti-detonation (or detonation proof if lean enough). The trick is passing through the detonation zone quickly to get to the "safe side".
 
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clear as mud

Please continue these discussions....good stuff.

2 observations;
1. when I read 'casual' descriptions of this, perhaps some slang and semantics make it totally confusing. ....such as.....' I leave the throttle alone, but pull back the 'power'.
what magic knob is this?

2. I find it bizarre, how Lycoming comes out with 'bulletins' about a super-important, critical way to operate their engines (in 2011, based on the EmbryRiddle training ops) about sixty years after developing the injected engines. Kinda late eh?

I guess one day when I have the blue knob on my dash, and an injected engine, it will make more sense. Of course, I'll be scared spitless to touch any of the knobs!
 
2. I find it bizarre, how Lycoming comes out with 'bulletins' about a super-important, critical way to operate their engines (in 2011, based on the EmbryRiddle training ops) about sixty years after developing the injected engines. Kinda late eh?

What's really sad is that we're still talking about it on new airplanes with new engines...
 
Take a Look at the Training Syllabus

Located on this website here:

http://www.vansairforce.com/community/showthread.php?t=93661&page=6

Up to version 2.9 now. ~Page 219 or so give a great "Rule of Thumb" for estimating Lycoming power output called the "Rule of 48".

Additionally, it's just a dang good read, especially if you're used to the type of comprehensive flight manuals you're used to from Military/Commercial flying...i.e-USAF Dash One/51-xx series manuals or Navy NATOPS.

Loads of good gouge in it, many thanks to the author for the extensive work involved!

FYI, I am only slightly ahead of you in this game...same background (military/commercial) very limited GA time....as a new-to-me RV-7 owner, my SA curve has a steep slope upwards as I figure out recip engine/mixture/prop stuff while discovering how to use my feet again for something other than braking the aircraft!

Have fun with it and let me know if I can help in any way!

Rob S.
 
Please continue these discussions....good stuff.

' I leave the throttle alone, but pull back the 'power'.
what magic knob is this?

2. I find it bizarre, how Lycoming comes out with 'bulletins' about a super-important, critical way to operate their engines (in 2011, based on the EmbryRiddle training ops) about sixty years after developing the injected engines. Kinda late eh?


Great questions.... got me to thinking back on my career flying corporate, military and airlines.

Everything I ever flew had been in the inventory for years if not decades and we were always getting changes on how to operate the aircraft. Murphy rears his ugly head and pulls something that you never thought could happen, but it does.

Pulling back the PROP and/or mixture in effect dramatically changes the POWER output on these engines and I'm guessing that's what the original poster meant.

Lycoming, like Boeing, Lockheed, Northrop, etc, keep finding ways to improve efficiency and/or life span of engines and components, hence the changes to old time procedures that may make us scratch our heads as operators, but there is usually a good technical reason.

And then again, there's the lawyer effect... Don't get me going on that though..
 
So it is my opinion, based upon reading Bush and Deakon writings, that in the regimen in which we fly our RV planes we would have to work really hard at making our engines pre-detonate. There is a lot of concern about protecting our expensive investments that lead directly to events happening that actually have a higher potential for creating more risk than less. In the case of discussing LOP operations I do not feel we can even purposely make our engines pre-detonate if we wanted to. Oh , I am sure someone out there would disagree, and may even give me anecdotal examples, or may even provide me with some dyno info from some engine run, but the truth is, in our normal every day operations of our RVs, we are not placing our engines in an environment, nor sustaining them in such an environment, that would allow the engine to self destruct. That holds true for running them LOP at lower altitudes. Given that you can monitor all cylinders independantly for CHT, EGT, along with all other number of engine performance info, while grabbing and pulling the big red (or blue) knob, it is highly unlikely that any one of us would face much risk in making the big pull at any altitude.
 
Just be cautious. High MP, low RPM is pro-detonation. In fairness, detonation would probably require one or more additional conditions (high CHT, high OT, high OAT, minimum spec fuel, advanced timing, or high compression ratio), but it pays to observe the general trend.

When I attended Fuel Injection 101 at Airflow Performance, Don told us that in his years of working with Lycoming he learned that , "Lycomings do not like to be run lean above 24" MAP." That supports Dan's comment above. I run LOP in cruise at nearly any altitude, but I obey the 24" limitation. :)
 
So it is my opinion, based upon reading Bush and Deakon writings, that in the regimen in which we fly our RV planes we would have to work really hard at making our engines pre-detonate.

A reasonable argument...much as theory says we would have to work hard to exceed 6 G's and bend the wing, or be really dumb to exceed VNE in an RV-7. But it ain't so, because these things happen mostly by accident.

In the case of discussing LOP operations I do not feel we can even purposely make our engines pre-detonate if we wanted to.

Ahhh, a fun new game for next year at PJ! Can I fly your airplane? ;)
 
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When I attended Fuel Injection 101 at Airflow Performance, Don told us that in his years of working with Lycoming he learned that , "Lycomings do not like to be run lean above 24" MAP."

I run my Superior IO-360 at 26" LOP basically every time I fly it. It's smooth and doesn't complain at all either in feel or any of the temps.

I have balanced my injectors to a spread of 0.1 GPH, ironically using Airflow injectors.
 
Just be cautious. High MP, low RPM is pro-detonation. In fairness, detonation would probably require one or more additional conditions (high CHT, high OT, high OAT, minimum spec fuel, advanced timing, or high compression ratio), but it pays to observe the general trend.t.

Thanks for the warning. I'm not really operating outside the power chart envelope for the bone stock M1B. I have seen the charts you have posted about detonation limits on your angle valve. I would take them seriously too. I think I have a bit more margin with 8.5 pistons. So..... I run 2300 25" all the time. I start getting a nervous twitch at a 3" oversquare and I have a hard time setting a 4" oversquare even though Lycoming allows this at 75% at peak EGT :eek:. CHTs always good.

Heck, my motor has spent so much time LOP, it probably has a self image of being anorexic.
 
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Percent power when LOP

When LOP and WOT use the formula 15.9 X Fuel Flow / rated horsepower to determine % power, and yes, most of the monitors out there do not account for LOP ops to report percent power, nor do they perform the "Lean Find" function very well. At least try it manually and see how that compares to your monitor. My GRT EIS was reporting 40-50 LOP when in fact it was closer to 80-90. So I picked up a few knots once I learned that.
So example 0-360 180 HP engine @ 8 gph: 15.9 X 8 / 180 = 71%
This makes leaning dirt simple once you know the numbers for your engine. On my 0-360 if I'm between 7.4 gph (65%) and 8.5 gph (75%) I'm in the cruise range. Above 8.5 and I'm pushing things, less than 7.4 and wasting time but saving fuel.
Stay out of the "Red box" by simply pulling the MP back to less than 24" before you pull the mixture, then back to WOT.
Tim Andres
 
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When LOP and WOT use the formula 15.9 X Fuel Flow / rated horsepower to determine % power,

LOP HP on an 8.5:1 engine is generally considered 14.9 x flow not 15.9.

Stay out of the "Red box" by simply pulling the MP back to less than 24" before you pull the mixture, then back to WOT.

Depending on your fuel injection system, this is actually a bad idea. A lot of them have WOT enrichment, and you'll see that if you back off the throttle just a bit, they will lean considerably. Thus, if you pull back, adjust your fuel flow and then go WOT again, there's a very good chance that will drop you right at peak.

Personally, I pull the knob quickly until the engine noticeably reduces in power, then richen back up from there to the flow I want.
 
but the truth is, in our normal every day operations of our RVs, we are not placing our engines in an environment, nor sustaining them in such an environment, that would allow the engine to self destruct.

Care to define "normal operations"?

I consider my setup normal.... RV-10, IO-540 parallel valve with Bendix injection, One Bendix magneto, 1 lightspeed ignition, ~9.2:1 Compression.

Its not "Stock" but I think it would be categorized as "normal operations".

I can make it detonate slightly with 100LL fuel under specific operating conditions even at 7000 ft DA.
 
Depending on your fuel injection system, this is actually a bad idea. A lot of them have WOT enrichment, and you'll see that if you back off the throttle just a bit, they will lean considerably.

Good observation, but there are no "WOT enrichment" circuits in a Bendix-type (Bendix, AFP, or Precision) fuel control. The leaning is just a side effect of the operating scheme; throttling reduces both throat dynamic pressure and venturi pressure drop, closing the diaphragm ball valve and reducing deltaP across the main jet.

Just polishing the pins, old bean ;)

I can make it detonate slightly with 100LL fuel under specific operating conditions even at 7000 ft DA.

Hey Joel, Steve's 9 is fixed pitch, so I figure I'll just slow-flight it until the temperatures are high enough, then forget to push in the mixture when I simulate a go around. It would be a lot like flying the Ripon approach to the Sunday OSH runway rodeo, and getting a little distracted when the controllers call time out, eh?
 
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Good observation, but there are no "WOT enrichment" circuits in a Bendix-type (Bendix, AFP, or Precision) fuel control. The leaning is just a side effect of the operating scheme; throttling reduces both throat dynamic pressure and venturi pressure drop, closing the diaphragm ball valve and reducing deltaP across the main jet.

That's interesting to know, I'll have to look into it some more. I have a Precision fuel servo, and I know that just breathing off the throttle from WOT and full rich will reduce my flow from about 17 GPH down to 14, with only about 1/2" MAP change. The fuel flow change is much more than the mass air change. I get the same effect what altitude. I tend to fly at 26" MAP, and if I'm using the throttle to limit that, as a climb and reach WOT, I always have to jump on the mixture and pull it out since it will go from LOP to ROP on me.
 
So what does detonation look like...

1. So what does detonation look like on an engine analyzer?
2. What does pre-ignition look like on an engine analyzer?
3. Can we tell the difference?
4. How do you tell light detonation from serious about to blow the thing up in one nano second pre-ignition.

Are there tell tale signs?

Quickly climbing EGT's? Quickly climbing CHT's? Rapidly fluctuating EGT's & CHT's? Something else?

Anyone know for sure or care to Hazard a guess?
 
Hey Joel, Steve's 9 is fixed pitch, so I figure I'll just slow-flight it until the temperatures are high enough, then forget to push in the mixture when I simulate a go around.

No! dont. it will probably melt the ring lands.

1. So what does detonation look like on an engine analyzer? light detonation will make the CHT start increasing at a rate of something like 1 deg f per 2 seconds increasing in rate as it gets hotter. Also a keen ear will hear it pinging but you really gotta be on your game to hear it and probably need mufflers. I really doubt you can hear light detonation with an open exhaust RV.

2. What does pre-ignition look like on an engine analyzer? no idea

3. Can we tell the difference? dunno

4. How do you tell light detonation from serious about to blow the thing up in one nano second pre-ignition.

Are there tell tale signs? The rate of CHT temperature increase is a result but would be a slow indicator if you were to experience sudden sever detonation.



Quickly climbing EGT's? Quickly climbing CHT's? Rapidly fluctuating EGT's & CHT's? Something else?

Anyone know for sure or care to Hazard a guess?
 
Detonation

1. So what does detonation look like on an engine analyzer?
2. What does pre-ignition look like on an engine analyzer?
3. Can we tell the difference?
4. How do you tell light detonation from serious about to blow the thing up in one nano second pre-ignition.

Are there tell tale signs?

Quickly climbing EGT's? Quickly climbing CHT's? Rapidly fluctuating EGT's & CHT's? Something else?

Anyone know for sure or care to Hazard a guess?

Detonation typically results in abnormally high CHT and/or a trend of rapidly rising CHT, and somewhat reduced EGT. The detonation (or preignition) shockwaves result in high peak internal cylinder pressures (ICP) that drastically reduce the gas boundary layer that normally exist around the internal surfaces of the cylinder head combustion chamber and piston face. The high peak pressure and reduced boundary layer results in significantly increased heat transfer to the cylinder head (and piston face) resulting in the higher CHT, as well as reduced thermal energy (temperature) in the exhaust gases.

For normally aspirated aircraft engines with proper cooling and ignition timing, severe detonation and preignition is often related to cracked or damaged spark plug ceramic insulators.

Skylor
 
Pre-ignition usually takes off the ground electrode first and puts a big hole in the piston a few seconds later. Much more damaging and a much quicker failure than detonation which almost always breaks the piston ring lands first.
 
Detonation typically results in abnormally high CHT and/or a trend of rapidly rising CHT, and somewhat reduced EGT. The detonation (or preignition) shockwaves result in high peak internal cylinder pressures (ICP) that drastically reduce the gas boundary layer that normally exist around the internal surfaces of the cylinder head combustion chamber and piston face. The high peak pressure and reduced boundary layer results in significantly increased heat transfer to the cylinder head (and piston face) resulting in the higher CHT, as well as reduced thermal energy (temperature) in the exhaust gases.

For normally aspirated aircraft engines with proper cooling and ignition timing, severe detonation and preignition is often related to cracked or damaged spark plug ceramic insulators.

Skylor

Thanks Skylor,

I ask these questions because I have been on board an aircraft that was running hard, down low, on a very hot summer day while the pilot was trying to determine what his aircraft's maximum speed would be. He was leaning very slowly and engine became very rough. The engine monitor indications, (both cht & egt) began dancing very erratically. The best I can describe it is that it resembled a graphic equalizer display on a high end stereo system from the mid 1970's playing hard rock. The engine rapidly lost power and I suspect that detonation and probably pre-ignition were occurring. Needless to say, the mixture was quickly shoved forward and the throttle pulled back. The testing ended at that point and we ended up pulling the plugs and bore scoped the cylinders to see if there was any obvious damage. The pistons looked fine and the plugs looked fine but I wondered if damage to the crank or rods might have occurred. Here is a youtube video that helps explain things in layman's terms.

https://www.youtube.com/watch?v=ZWKRw0HmBLE

Here's a good "Savvy" link that is more in depth:

https://www.savvyanalysis.com/articles/detonation-and-pre-ignition

And here is a good Contact article:

http://www.contactmagazine.com/Issue54/EngineBasics.html

Needless to say, this experience made a believer out of me, but I'm not positive what I saw the engine analyzer doing was an indication of detonation or pre-ignition or both. I suspect others may have experienced the same thing but are reluctant to talk about it in public due to the possible effect on aircraft resale value. It has been my understanding that pre-ignition can destroy an engine in seconds.

I would be interested to know how the SARL or Reno racers approach this issue in flight. I'm not talking about changing colder range spark plugs or methanol injection, but do they ems indications or some other monitoring method to stop their leaning just on the safe side of detonation.

Joe
 
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Correct

LOP HP on an 8.5:1 engine is generally considered 14.9 x flow not 15.9.





Depending on your fuel injection system, this is actually a bad idea. A lot of them have WOT enrichment, and you'll see that if you back off the throttle just a bit, they will lean considerably. Thus, if you pull back, adjust your fuel flow and then go WOT again, there's a very good chance that will drop you right at
Personally, I pull the knob quickly until the engine noticeably reduces in power, then richen back up from there to the flow I want.

Thanks for the correction, your right, 14.9
Re rapid leaning, I use to do the same until I read this, now I'm not sure it's a good idea, check this out:
http://eci.aero/pdf/93-6-7.pdf

Tim Andres
 
Rough engine...

Thanks Skylor,

I ask these questions because I have been on board an aircraft that was running hard, down low, on a very hot summer day while the pilot was trying to determine what his aircraft's maximum speed would be. He was leaning very slowly and engine became very rough. The engine monitor indications, (both cht & egt) began dancing very erratically. The best I can describe it is that it resembled a graphic equalizer display on a high end stereo system from the mid 1970's playing hard rock. The engine rapidly lost power and I suspect that detonation and probably pre-ignition were occurring. Needless to say, the mixture was quickly shoved forward and the throttle pulled back. The testing ended at that point and we ended up pulling the plugs and bore scoped the cylinders to see if there was any obvious damage. The pistons looked fine and the plugs looked fine but I wondered if damage to the crank or rods might have occurred. Here is a youtube video that helps explain things in layman's terms.

https://www.youtube.com/watch?v=ZWKRw0HmBLE

Here's a good "Savvy" link that is more in depth:

https://www.savvyanalysis.com/articles/detonation-and-pre-ignition

And here is a good Contact article:

http://www.contactmagazine.com/Issue54/EngineBasics.html

Needless to say, this experience made a believer out of me, but I'm not positive what I saw the engine analyzer doing was an indication of detonation or pre-ignition or both. I suspect others may have experienced the same thing but are reluctant to talk about it in public due to the possible effect on aircraft resale value. It has been my understanding that pre-ignition can destroy an engine in seconds.

I would be interested to know how the SARL or Reno racers approach this issue in flight. I'm not talking about changing colder range spark plugs or methanol injection, but do they ems indications or some other monitoring method to stop their leaning just on the safe side of detonation.

Joe

What you describe sounds like "lean misfire" and not detonation. If the engine was overly-leaned (perhaps he was watching the wrong EGT) one or several cylinders likely started intermittently "dropping out" resulting in roughness and erratic EGT. It's hard to imagine the CHT's being too erratic though because the cylinder head mass tends to dampen rapid temperature changes...

For racing at Reno this year, detonation concerns were simply not an issue for me. I ran at best power EGT, yet never saw CHT's above 355 F even on the hottest days. It's pretty hard to make a stock IO-360 detonate at maximum RPM's with those temperatures.

Skylor
 
"Rapid Leaning"

Thanks for the correction, your right, 14.9
Re rapid leaning, I use to do the same until I read this, now I'm not sure it's a good idea, check this out:
http://eci.aero/pdf/93-6-7.pdf


Tim Andres

The whole point of leaning using the "big pull" method to get Lean of Peak (LOP) is that by rapidly pulling the mixture through the danger zone or "red box" the piston (and cylinder head) simply doesn't have time to heat up thus avoiding the issues that The ECI document wants us to believe exists. Also note that the linked ECI document is dated 1993, which is a bit before LOP ops became widespread and understood in the GA community.

Skylor
 
He was leaning very slowly and engine became very rough. The engine monitor indications, (both cht & egt) began dancing very erratically. The best I can describe it is that it resembled a graphic equalizer display on a high end stereo system from the mid 1970's playing hard rock.

That sounds like bad connections from the vibration. CHT is the measurement of 5 lbs of aluminum and cannot change more than a few degrees a second no matter what the engine is doing.

So without fuel flow and more data, how do you know this wasn't just lean cut off? All engines will start running really rough when you get them too lean, but this is not indicative of any damage to the engine.
 
What you describe sounds like "lean misfire" and not detonation. If the engine was overly-leaned (perhaps he was watching the wrong EGT) one or several cylinders likely started intermittently "dropping out" resulting in roughness and erratic EGT. It's hard to imagine the CHT's being too erratic though because the cylinder head mass tends to dampen rapid temperature changes...

For racing at Reno this year, detonation concerns were simply not an issue for me. I ran at best power EGT, yet never saw CHT's above 355 F even on the hottest days. It's pretty hard to make a stock IO-360 detonate at maximum RPM's with those temperatures.

Skylor

It was not the normal engine roughness one experiences when going too lean. By lean misfire are you saying neither plug was firing the overly lean mixture and the cylinders were rapidly dropping totally offline and somehow coming back online? That sorta makes sense. This took place about 6 years ago so I could be mistaken about the CHT's but I'm pretty sure they were also fluctuating. There were no bad connections. The airplane did have high compression pistons and was still running great last I knew.
 
Hi Chuck. My EFIS also gives me the confidence to regularly run LOP. From a practical standpoint, CHT will quickly tell you if you stray too close to the red zone on any cylinder. If I run high power too close to peak, CHT's immediately climb and would exceed redline if left uncorrected.

For low altitude leaning, I takeoff rich, then temporarily reduce throttle to about 23" before doing the "big pull" to the onset of roughness. I then increase throttle to almost full, and add fuel with mixture while monitoring CHT and fuel flow. I add fuel until I see CHT's stabilize around 330 degrees, which puts me well in the safe zone for LOP operation.

Jay
 
A reasonable argument...much as theory says we would have to work hard to exceed 6 G's and bend the wing, or be really dumb to exceed VNE in an RV-7. But it ain't so, because these things happen mostly by accident.



Ahhh, a fun new game for next year at PJ! Can I fly your airplane? ;)
Well Dan, actually I do believe your statements are supporting what I was saying. I did not say it wasn't "possible". I am quite sure you could set the ball in play. What I do believe is that you would have to work at it to make it happen. Yes accidental potential exists given certain parameters are present but my point is that we recreational flyers flying our machines from point A to point B in a normal operation of our machines (yes Weasel, I will define that term) are going to have to be extremely specific on what we do to make these things happen. So ultimately my point is; yes, there is a POSSIBILITY, given a "specific set of operating conditions", but the PROBABILITY is unlikely, unless we engine operators work to set those specific parameters in place. Your OSH arival example being one of those certain situations that could cause an issue. So knowing what those situations are, most certainly can be beneficial, but saying that detonation/pre-ignition could happen at any given moment without constant vigilance is not being realistic. Operating on the edge of performance without knowledge, monitoring, and appropriate engine manipulation is indeed jumping into the deep end of the pool without being able to swim, but I don't believe running LOP in a typical recreational flight is balancing on the precipice. If we learn and comprehend the environment that creates such a situation and we monitor and manipulate the engine in an appropriate manner there is very little potential risk in operating LOP.

Care to define "normal operations"?

I consider my setup normal.... RV-10, IO-540 parallel valve with Bendix injection, One Bendix magneto, 1 lightspeed ignition, ~9.2:1 Compression.

Its not "Stock" but I think it would be categorized as "normal operations".

I can make it detonate slightly with 100LL fuel under specific operating conditions even at 7000 ft DA.
Other than the size of engine (IO-340 vs IO-540) I have a similar configuration as you. However, when I said "normal operation", I was not talking about the engine configuration. I was talking about the engine operation. I do not believe that in our typical operation of recreational flying we are operating in extreme conditions or manipulating our engines on the extreme edge of performance that would set detonation/pre-ignition in motion. I openly acknowledge these could potentially happen but I don't think they are easily occurring without some specific parameters existing first.

Live Long and Prosper!
 
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One little point on this discussion, there is no such thing as pre-detonation. Let's strike that term from the vocabulary. :) The engine is either detonating or it's not.

While I agree, carefully monitored, LOP is usually safe even down low, throw in a bit more advance through an EI and operation on mogas instead of 100LL plus some 9 or 10 to 1 pistons and you certainly have a MUCH higher probability of detonation.
 
Sorry Ross. I will remove the "pre"-fix in front of the word detonation. The two phrases of pre-ignition and detonation have always confused me on which should have the prefix. You have cleared it up for me.
 
If we learn and comprehend the environment that creates such a situation and we monitor and manipulate the engine in an appropriate manner there is very little potential risk in operating LOP.

Specific to this thread, the risk relates directly to available manifold pressure. There is no risk in LOP operation at low altitude, if you keep it throttled. LOP is not an additional risk...but it's not a panacea either. It's just an operating condition.

The key is to understand the pro-detonation factors, as it's impossible to state specific operating parameters for all the hot-rodded custom engine configurations in the RV fleet. Like Ross said, there's a long list of wild cards. For example, your 340 comes in 8.5 CR or 9.0 CR. Obviously the 9.0 CR operators have less margin.

Returning to low altitude leaning, i.e. the manifold pressure factor....some charts here:

http://www.vansairforce.com/community/showpost.php?p=1038026&postcount=21
 
LOP is not an additional risk...but it's not a panacea either. It's just an operating condition.
Hey, I completely agree with this statement. I am not so sure we are talking on different sides of the conversation. I am just saying although the potential does exist for detonation to occur, the likelihood of doing so in the operating environment the vast majority of us fly in is very low. Even at low altitude. In my case I do run LOP at low altitude but would never do so WOT on a hot July Oklahoma day with a heat soaked engine in my fixed pitched machine. I would not run high MP while having the mixture in that RED BOX zone no matter what altitude because I know that is a recipe for disaster. Everyone should know what the operating parameters are for their engine. Doing so can alleviate much of the fear of the unknown.

Having one of those 9.0 CR 340s, I am very aware of its operating constraints. I keep close eye on the operating environment I run in. The truth is, I know to date 100% of the time I have run this engine I have not put it in the aforementioned operating environment and especially when running LOP. It is indeed up to us as pilots to keep our engines in the appropriate operating environment and we must be diligent about doing so.
 
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