ROP versus LOP and the Lycoming IO-360

[jetdriven]

Good grief. This ol' thing again? My plane runs crappy LOP most days and chasing the illusive ideal GAMI spread and smooth ops deep into LOP is both very time consuming and can be pretty expensive. Fun hobby for the tinkerers, but I fly for fun so...

 

I run 65% at around peak most days. If I want to get somewhere faster I'll go 65%-75% 125 deg ROP. This means I do not run WOT and 2700 rpm. I have no issues what so ever with CHTs no matter what I do. Works well enough for now and I get the same 7.5 to 8.5 gph fuel burn everybody else gets, or I'll go up to the 10 if I want to faster.

Dave it should run smoothly to 50 LOP but best economy for speed is found at 15-25 LOP. 

[DaV8or]

Dave it should run smoothly to 50 LOP but best economy for speed is found at 15-25 LOP. 

 

Sadly, it usually doesn't. I rarely climb over 7500 ft, so that might be part of it. It goes down to about 10 degrees LOP and then gets real crappy and slow too. I've put all new intake gaskets on and new spark plugs too. Of course the injectors have been cleaned. The fuel servo and the flow divider have just been rebuilt. I have no idea what my GAMI spread is because my fuel flow indication is real erratic and since that one is a head scratcher, that would cost me a fair bit in time and money just to get that straight first. This up coming annual in July I'm going to rebuild the mags because they'll be at 500 hours. Curious to see if that makes any difference. Likely just unbalanced injectors.

 

Anyhow, at peak, or ROP, she purrs like a kitten. Like I said, when I have more money, I may pursue it again but as it is with my finances now, just keeping gas in the tanks and surviving the annual will be enough.

[aaronk25]

Sadly, it usually doesn't. I rarely climb over 7500 ft, so that might be part of it. It goes down to about 10 degrees LOP and then gets real crappy and slow too. I've put all new intake gaskets on and new spark plugs too. Of course the injectors have been cleaned. The fuel servo and the flow divider have just been rebuilt. I have no idea what my GAMI spread is because my fuel flow indication is real erratic and since that one is a head scratcher, that would cost me a fair bit in time and money just to get that straight first. This up coming annual in July I'm going to rebuild the mags because they'll be at 500 hours. Curious to see if that makes any difference. Likely just unbalanced injectors.

Anyhow, at peak, or ROP, she purrs like a kitten. Like I said, when I have more money, I may pursue it again but as it is with my finances now, just keeping gas in the tanks and surviving the annual will be enough.

Try backing off the MP 1/4-3/8 of a inch from full throttle at cruise then do the gami spread. If my indicated airspeed is over 125kts I can't seem to ever get a consistent gami spread. On my 77j the fuel injector nozzle bleed holes that are supposed to draw air in by the lower than ambient pressure inside the intake are affected by high speed air crossing over them creating low pressure on the backside which if down low at high power settings and high indicated air speeds fuel can actually be drawn out of the bleed hole. Besides creating a fuel stain mess if air isn't getting drawn in the bleed hole the fuel doesn't atomize as well and makes the cylinder appear as if it's running leaner because the combustion isn't as efficient.

John Paul at gami personally flew in my plane and had the number 2 and 3 cylinders running the largest nozzle possible which we both originally attributed to a intake anomaly. Actual what was happening is the bleed holes on both of the injectors weren't pulling air in with fuel, making it appear as if they were to "lean" so we consequently kept swapping them for larger "richer" ones until we were at a "j" gami injector, the largest one available.

When I crossed the gulf at fl190 and fl150, I could run full throttle with a .1 gami spread

because the indicated air speed was around 115kts...if I cruise at 6,000ft wide open the gami spread is .8 and I have changed injectors sizes at least 10 times trying to get it consistent but it's always a moving target. Back off.3 inch of M.P. and I have .1 to .2 gph spread at any altitude and rpm.....and airspeed increases about 2kts.

Not sure if this is happening with yours but it's a idea......and worth exactly what you paid for it .

B

[DaV8or]

Try backing off the MP 1/4-3/8 of a inch from full throttle at cruise then do the gami spread. ...

 

Back off.3 inch of M.P. and I have .1 to .2 gph spread at any altitude and rpm.....and airspeed increases about 2kts.

Not sure if this is happening with yours but it's a idea......and worth exactly what you paid for it .

B

 

Well, I have no idea what my GAMI spread is, like I said, my fuel flow indication is wonky. However, I will definitely try your suggestion of backing off the throttle a little bit. That would be a great fix if it works. I should also add, in a possibly related matter, when I use the ram air, LOP is much rougher. It does seem to work better LOP on filtered air.

[Shadrach]

Ross,

 

I am not sure what you mean, there is certainly differences in engines, but there is no difference in the science of combustion. Your earlier posts stated about the core being TCM focussed, but the funny thing is the Dyno runs and a lot of the data collected came off a Lycoming many years ago.

 

The class has some in flight video, turbo and N/A. We even just this year added a small section explaining briefly the conceptual difference between the TCM and LYC fuel systems and a carburettor.

 

So I am not sure what your concern is.

 

The vast majority of folk who have never taken the course have all manner of preconceived ideas and I am yet to have anyone explain precisely what the class is about, most think it is 2.5 days on how to run LOP. Oddly enough that is not it at all and is only a small part overall.

 

Once you are skilled up with the understanding, you can take this and apply it to any engine you fly behind.

 

Once you have done the course, you will understand what I mean. You could book in for the next one in Australia…I will make an extra effort to cover your questions….Its a long flight though 

David,

 

I think this is why Daren responded to you the way he did. You have no idea what my background is or what I know or don't know. The questions I've asked you have been reasonable enough for you to gleen to some degree my level of understanding, but instead of answering my question you reply with "I am not sure what you mean" and a pedantic "once you are skilled"... which leads me to believe you're more about parroting than listening. So I'll use an example to try and illustrate my question: 

 

A Jacobs R-755 normally aspirated 9 cyl radial engine has a CR of 5.4 to 1, is timed to 30d BTDC and makes a max continuous 225 HP at max engine speed (it's direct drive)  2000 RPM.

 

A lyc IO 390 normally aspirated 4 cyl opposed engine has a CR of 8.9 to 1, is timed at 20d BTDC and makes a max continuous 210 HP at max engine speed (it's direct drive)  2700 RPM.

 

A Conti TSIO550A Turbo Charged (Max MP 41") 6 cyl opposed engine has a CR 7.5 to 1, is timed to 24d BTDC and makes a max continuous 360 HP at max engine speed (it's direct drive) 2600 RPM.

 

Three different engines, all have very similar metallurgy and all will respond similarly to mixture adjustments. However, the "red box" is not the same for all of these engines...moreover, ICPs at say 100ROP and 75% are not the same either. The differences are significant enough to warrant different settings in relationship to stoic even though the same basic understanding is utilized to arrive at those different settings. ICP data on different engines tells us a lot about what can safely be done with the red knob. 

 

I have rebuilt and tuned a number of non aviation engines and I have turned a wrench or two on a few aircraft as well. I have a pretty reasonable understanding how combustion works...how ignition timing, CR, RPM, crank angle, fuel specs and combustion chamber design affect the flame front, ICPs  and thereby detonation margins.  Walter, John and George have been an excellent resource over the years as has Mike Busch.  One thing they all have in common is their ability to convey complex concepts without talking down to people. You seem to have mastered the inverse. I have yet to see you convey much in the way of a complex concept, yet you've managed to do a pretty good job of talking down to folks who likely understand more than you give them credit for.

 

I am not a propulsion engineer, but then I'm betting that you're not either, otherwise you would have understood my initial question.  Maybe I'm not the only one who needs to take a class... 

 

I think that many do see the APS seminars as classes about Continental engines with concepts that can be applied to the rest... It's likely more of a perception/marketing problem than anything else.  I have no preconceived notions about the APS class, just the APS based graphs that I've seen and articles that I've read, almost all of which are Conti Centric.  Does it matter with regard to the concepts being taught?...No, not at all.  Is it reassuring to see data derived from your own make and model engine?... Absolutely; especially when it is one of the most pervasive injected aviation engines in the fleet.

 

Do you think all of those Bonanza drivers would be happy looking at graphs and data from Lyc 4 bangers when reading tech articles or taking a course?    

[Shadrach]

Well, I have no idea what my GAMI spread is, like I said, my fuel flow indication is wonky. However, I will definitely try your suggestion of backing off the throttle a little bit. That would be a great fix if it works. I should also add, in a possibly related matter, when I use the ram air, LOP is much rougher. It does seem to work better LOP on filtered air.

 

I don't know what mine is either. But I do know I can smoothly run ~100LOP at high power on the richest Cyl. That may be a bit better than the norm, but running rough at 10LOP on an injected 4 cyl lycoming would have me looking for induction leaks.

[DS1980]

Ross...seriously. Don't bring back the troll.

[DaV8or]

Try backing off the MP 1/4-3/8 of a inch from full throttle at cruise then do the gami spread. If my indicated airspeed is over 125kts I can't seem to ever get a consistent gami spread. On my 77j the fuel injector nozzle bleed holes that are supposed to draw air in by the lower than ambient pressure inside the intake are affected by high speed air crossing over them creating low pressure on the backside which if down low at high power settings and high indicated air speeds fuel can actually be drawn out of the bleed hole. Besides creating a fuel stain mess if air isn't getting drawn in the bleed hole the fuel doesn't atomize as well and makes the cylinder appear as if it's running leaner because the combustion isn't as efficient.

 

I tried this two days ago and you know what? I think it does help. I noticed a weird phenomenon doing this too. When I pulled the throttle back a little bit, I noticed the fuel flow actually went up, so clearly my WOT is leaner than say 7/8th throttle. It still didn't run as smooth as ROP ops, but it did seem better. I will continue testing this out. I could only go up to 5500' because of overcast and I wasn't able to try it with the ram air on because I kept encountering rain. Thanks for the tip!

[DaV8or]

I don't know what mine is either. But I do know I can smoothly run ~100LOP at high power on the richest Cyl. That may be a bit better than the norm, but running rough at 10LOP on an injected 4 cyl lycoming would have me looking for induction leaks.

 

As of last annual, all of my intake gaskets have been replaced. I guess it could be leaking somewhere else, or who knows? It all comes down to how much money and time I want to spend chasing this thing. Since funds are limited and I really own and fly my plane for the actual fun of flying rather than to have yet another mechanical tinkering project on my plate, I'm not super inclined to go wrenching away on it. I can and do work on my own plane, but it's just to save money and be involved, not because I like it. Seriously, you have either a suspect EGT gauge, or seriously perfect engine. My airplane would be gliding probably somewhere around 60 deg LOP.

[aaronk25]

Plugs and mags have to be in tip top shape too if a couple of plugs have a bit to high of resistance it will miss. High hour plugs or as talked about "champions" have been getting a black eye for having to high of a resistance even on 100 hour plugs.

Check the timing too. If it's not advanced enough it will also miss. The lean mixture takes longer to burn so if the timing isn't in spec it won't work either.

[KSMooniac]

I'll add that new gaskets don't necessarily mean no leaks... next time you do a compression check, tape off the air filter and ram air, make sure the intake valve is open on the cylinder with the compression fitting installed, and then lightly pressurize the system.  Spray soapy water around all of the joints and see if you can find a leak... doesn't take much effort or time.

[DaV8or]

Plugs and mags have to be in tip top shape too if a couple of plugs have a bit to high of resistance it will miss. High hour plugs or as talked about "champions" have been getting a black eye for having to high of a resistance even on 100 hour plugs.

Check the timing too. If it's not advanced enough it will also miss. The lean mixture takes longer to burn so if the timing isn't in spec it won't work either.

 

The plugs were just replaced all new. No difference. However, I did go with the massive ones. Like I said before, my mags are due this annual to get the rebuild, so that is my next effort since it has to be done anyhow. It could be a mag issue, who knows? I'll find out in July.

 

The timing has been checked at each annual and it is always spot on. I doubt it's the problem.

[David Brown]

Ross,

 

I have no idea about your background, but it affects the science none, nor does mine.

 

You are correct in saying that there are differences in CR and RPM and ultimately the typical working pressures, but they vary the science of fuel combustion not one bit. Peak power is still achieved at around 75dF ROP no matter which engine. The fuel does not know which cylinder it is inside. The curves and data we use apply to all.

 

The red box theory is one which has very fuzzy edges, we actually teach this in the class. If you are operating one of the engines that has bigger margins, sure, poke away inside it, but use the concept to make an educated decision about it. If however it is a Chieftain engine, stick outside.

 

I think we both agree here, but I do wonder if you actually know what is taught in class, as the comments above indicate otherwise. As for having data presented for every engine in the fleet you have got to be kidding me. But we do teach with a focus on the science as it applies to all engines, where questions are asked specifically about a type it is rather funny how the answer still applies to the rest, except when say it relates to fuel delivery systems, which are different.

 

 

 

Do you think all of those Bonanza drivers would be happy looking at graphs and data from Lyc 4 bangers when reading tech articles or taking a course?  

Funny enough they are quite happy with the Turbo Lycoming, and the TN cross flow Cirrus engine on the stand at the moment. Even stranger the folk who have Carby O360 & 320 engines are just as happy. We even talk about fixed pitch props and carby engines at times.

 

 

I am not here to be prickly, nor upset you or anyone else, but perhaps my direct and less warm & fuzzy delivery is what is bothering you. Sorry if that is the case. John Deakin would perhaps be more softly written, and he does spend an hour carefully crafting what I type in 5 minutes. He has the luxury of time. Again I apologise for that. Walter however, you would either need your flame suit on or more likely he would ignore you. Walter is far more direct and far less warm and fuzzy. But a brilliant educator. We are all different, as are the folk here on MS. Some will be bothered by a direct response other not.

 

So unless I have missed the point again......what we teach in the APS class is deliberately not engine specific because it matters not. We do show data from various engines, and the course is not Bonanza/TCM oriented, despite what you think. But no amount of me explaining that will likely change your perception. Sorry about that too.

 

All the best.