Leaning at full power?

[Nuisance]

OK, you low level flyers...

How do you lean if you are flying at sea level, lets say in a race, and you want to set the mixture at 150 ROP, at full power? Do you dare lean to peak EGT at high power? Will the engine melt pistons, etc. in a flash at 100% power?

Or, can I just lean to peak fairly quickly, and then richen from there?

TIA, John
Pagosa Springs, CO (7650 msl.)

 

[Bob Axsom]

Well John ...

This should bring in some good information.

It is not a problem in my little 8.5:1 O-360-A1A so I figure you are probably asking about a race prepared IO-360-XXXX. I had plenty of fuel so with wide open Throttle and prop just under 2700 RPM, I went up into the nominal running area of the EGT with the Mixture, then dialed the mixture it back in until I got the top speed at 1,000 AGL. When I went in either direction from the final "best speed" mixture setting or reduced the RPM the speed dropped off 3 or 4 kts rather quickly and it was hard to get it back. With mine it just starts getting rough at peak EGT with the single probe from Alcor under these conditions. I bought the 4 probe EI EGT system from Aircraft Spruce at Oshkosh so I will have a better picture in the future if there is an AirVenture Cup in 2007.

With 55 gallons I had plenty for an all out run but I was down into the low single digit numbers on the gauges on the downwind at Fond Du Lac. What was you fuel experience? Oh that's another question - never mind!

Bob Whitehouse seems enthusiastic as the new AirVenture Cup boss and Eric Whyte said he will stay on as an operations man - both plusses in my opinion. If there is no 2007 AirVenture Cup I plan to fly the US Air Race Inc. cross country air races (http://www.us-airrace.org). They are handicapped but ... Pat Purcell told me that head-to-head class racing would be made available if they have interest (entries) and sponsors. Their 2007 Race is going to start at Whicita and there is a proposed finish in Florida but that is just a possibility at this point. I don't really like the handicap because it is so hard to assure validity but if it is the only game in town I'll do it.

Bob Axsom

 

[Walter Atkinson]

Leaning to Peak EGT on the ROP side at full power is not advisable. You will quickly eat up the detonation margin which may result in serious problems. Leaning the FF by 15% of the max FF IS tested and *should* avoid detonation. Leaning further is risky and unless you have pressure sensors in the combustion chamber, you cannot monitor the effects.

Walter Atkinson
Advanced Pilot Seminars

 

[Fitz]

Probably the best way to do it is with a wideband O2 sensor in the exhaust system. This has become something of the norm in high performance automotive racing.

The sensors use a pump cell and a Nernst cell to measure 'Lambda'. A lambda of 1.0 is "stoich" or "stoichiometric", essentially peak EGT. Numbers smaller than 1.0 are rich of peak, larger than 1.0 are lean of peak. If you know the stoichiometric value for a fuel, you can calculate Air Fuel Ratio (AFR) by multiplying it with Lambda. For example, MoGas is about 14.7. So at stoich, AFR is 14.7:1 (1 x 14.7). At .85 lambda, AFR is about 12.5:1 (.85 x 14.7).

The advantages of lambda measurement are that it is very fast (it is used to 'close the loop' for EFI and emissions control on modern cars), requires no peaking (you can dial in best power without having to run near peak) , and is fuel independant. That is, if you've determined that your best power is generated at .85 lambda and best economy occurs at 1.05 lambda, those remain the values for best power and best economy even if you switch from MoGas to 100LL, etc. Also, while it has its own 'gotchas', it is not subject to some of the main gotchas with EGT (ex. EGT drops in response to preignition).

The disadvantages for general aviation are that most widely available lambda meters use O2 partial pressure of air as a fixed value so they become inaccurate with altitude. Also, the sensors do not have very long lives in leaded fuel (Bosch specs a low cost one at 200 hours, but somewhere between 100 and 200 is more realistic). And, like partial pressure, many meters become less accurate as the sensor ages because of a fixed calibration for output.

We've had a few users put our automotive wideband controllers to aircraft racing use. And, at relatively low and relatively constant altitudes we are very confident in the measurements they are getting. That is because we can be field calibrated for partial pressure and our measurement principle does not become less accurate as the sensor ages.

We've talked about adding altitude correction based on some experiments I ran in a Skylane and a Mooney 231. This would make for a pretty nice GA lambda meter, but it has remained a very low priority. I'd buy one, but in a world where a heck of a lot of engines are leaned without even the benefit of a single EGT probe and where engine makers give recommended leans that put CHTs near their highest, I might well be alone.

Still, it is an area that interests me personally. So, aside from the question at hand I'd be very interested in talking to anyone else who has experimented in this area.

-jjf

 

[gmcjetpilot]

Just say NO

Probably the best way to do it is with a wideband O2 sensor in the exhaust system. This has become something of the norm in high performance automotive racing.-jjf

Fitz, that is interesting and most of it was over my head, but I agree with Walter, NO to leaning at full power. Just a side note O2 sensors don't last long with leaded av fuel (100LL has lots of lead despite the Low Lead moniker). Reason for saying NO, severe engine damage due to severe detonation and pre-ignition. Air cooled engines with huge bores are not like small bore water cooled engines, which can tolerate detonation better. 75% power (based on manifold pressure and RPM) is a safe bet ROP. At 75% power consider 100F ROP. (LOP operations see Walters excellent post on the topic, AVweb articles and Advance Pilot Seminars web site.) G

 

[Fitz]

Fitz, that is interesting and most of it was over my head, but I agree with Walter, NO to leaning at full power. Just a side note O2 sensors don't last long with leaded av fuel (100LL has lots of lead despite the Low Lead moniker). Reason for saying NO, severe engine damage due to severe detonation and pre-ignition. Air cooled engines with huge bores are not like small bore water cooled engines, which can tolerate detonation better. 75% power (based on manifold pressure and RPM) is a safe bet ROP. At 75% power consider 100F ROP. (LOP operations see Walters excellent post on the topic, AVweb articles and Advance Pilot Seminars web site.) G

No one is saying LOP. You want to be at best power, generally about 125-175 ROP. It is a race. You can't easily do this with an EGT gauge because you would need to 'peak' first to find a temperature relative to it. This potentially puts the engine just rich of peak, were pressures and CHTs soar (lots of heat, lots of fuel, means ripe for detonation).

But if you are looking at the relative pressures in the exhaust, you can find max power with great precision (say .001 lambda increments) without ever having to go near stoichiometric (peak). Throwing still more fuel into the mix beyound max power is just a waste. Charge cooling is basically a myth. Fuel does not really act as a coolant, changes in mixture just alter the speed of the flame front. Slowing the flame front beyond a certain point is counter productive because timing is typically fixed on an air cooled aircraft engine.

O2 sensing would be even more beneficial for finding and tuning best economy because the of the EGT curve of avgas LOP. But I hadn't really brought that up because many GA engines do not distribute fuel evenly enough to run well at peak, let alone lean of peak - at least not without upgrading the injectors.

Yes, the sensors die in leaded fuel, but consider the application proposed here. You want to fine tune best power, at wide open throttle, without ever exceeding the engine specs. It would take a lot of $40 sensors to equal one overhaul!

What I found with the 231 is that if you stay with a set TIT, the detonation margin actually shrinks with altitude. Again, here might be a case where measuring the composition of the exhaust, instead of just it's temp, might be an advantage. Or think of climbing like you would a race. You don't want to throw fuel and efficiency away, but it is dangerous to see where the peak is...

I'm not saying that the GA public is ready for O2 sensing - I've been following John Deakin's crusades to get people to properly lean with EGT for years! I'm just saying that one of the limitations with EGT is that it is a relative scale and the only way to find the reference point is to run the engine at stoichiometric, very near peak pressure and temperature. IE, the problem isn't leaning itself, but the instrumentation available.

Look at some of the AdvancedPilot samples on their website. They have a great presentation where you find the absolute EGT reading on your normally aspirated plane that equates to best power at a low altitude, then advise you to re-lean to that absolute temperature when operating at a much higher density altitude. This theory is correct. Wideband sensing is just a much more accurate and responsive way to find that point. It also can do so without ever having to run at peak and can continue to find the point even if you change the blend of the fuel.

-jjf

 

[rv6ejguy]

So, aside from the question at hand I'd be very interested in talking to anyone else who has experimented in this area.

-jjf

I've had a WMS wideband installed on our Sube Turbo 6A for a while along with 4 probe EGT. It is very interesting to have this info available as we can tweak ignition timing and mixture inflight with our EFI and look at rpm / TAS gain/loss at many different settings. This allows us to get optimal settings for speed and economy. Widebands may be the best way to tune for best power. The WMS meter uses the actual Bosch chip for internal calibration so does not need the free air hassle.

Using Decalin TCP has our O2 sensors lasting in excess of 40 hours now.

 

[Walter Atkinson]

Some facts of physics:

Best Power is found at between 75 and 80dF ROP.

It is only going to be about 2-3 degrees F cooler on the CHT's than 40dF ROP where CHTs are peaked.

The difference between Best Power and 100-125dF ROP at max rated power is very little on CHTs and ICPs.

Leaning to Best Power at max rated power is a really good way to experience detonation.

We used to Race at Reno. We only needed the engine to last for six laps. We couldn't do it at Best Power. It took a lot more FF than that to keep the engine together for six short laps.

Take those facts for what they are worth and make your own decisions.

Walter

 

[Fitz]

I've had a WMS wideband installed on our Sube Turbo 6A for a while along with 4 probe EGT. It is very interesting to have this info available as we can tweak ignition timing and mixture inflight with our EFI and look at rpm / TAS gain/loss at many different settings. This allows us to get optimal settings for speed and economy. Widebands may be the best way to tune for best power. The WMS meter uses the actual Bosch chip for internal calibration so does not need the free air hassle.

Using Decalin TCP has our O2 sensors lasting in excess of 40 hours now.

FWIW, the Bosch chip uses a fixed calibration curve - based on a group sampling. So it does become less accurate with altitude and age. On the Megasquirt web page there is a long white paper on this. They are trying to develop a different measurement principle but I have my doubts about its practicality.

I've also tested the impact of partial pressure of fixed current measurement with calibrated gases. I don't have my lab notebook handy but the difference between the beach and my house (at an elevation of about 2,000') was pretty signifcant. But, it is important to keep that in perspective. We are trying to provide accuracy in the .001 to .002 Lambda range, even on our lowest cost controller. Most controllers offer on the order of .025 - .1 lambda accuracy, and only really promise that near stoichiometric. So loss of accuracy, etc. is relative and may not matter for many applications.

I did have one thought about where our speed and accuracy might be useful for aviation. I once saw a pro racing engine builder configure one of our controllers for full speed (we always measure hundreds of times per second but users typically set our outputs to slower updates based on average). He then viewed our analog output on a o-scope and used the peaks and valleys to tune valves. This inspired me to experiment with multiple cyl measurements. I tapped the ignition pulse of one cyl to give me a reference, which I used to trigger my own scope (with offset), then compared the readings from the manifold to individual widebands on each cyl. The results were very good. I also found that I could detect individual miss fires based on the puff of O2.

All this only worked at lower RPMs, which limits its use in automotive. But all the GA engines that I have used typically operate below 3000 RPM. Getting cyl by cyl lambda with one or two sensors, instead of 4-6 seemed like a possible benefit when working with leaded fuels. I averaged quite a bit better than 40 hours in my tests, probably because of the measurement principle used, but life was still limited.

Sorry to sound like an ad! I actually joined the forum because I've recently been flying a friend's 10 year old RV-6A and have been giving some serious thought to building an RV-8. Of course, as soon as I saw an area for engines I just had to take a peek...

Your use of EFI intrigues me. I'll do a search for other threads, but do you have any other web links, descriptions, etc.? Also, if you don't mind my asking, how much Decalin TCP are you adding to your AvGas?

-jjf

 

[rv6ejguy]

We are using about 1/4 oz Decalin per 10 gallons of 100LL.

With our EFI and the WMS wideband, we can datalog AFRs at each rpm range to be able to reprogram the fuel values to the desired ratio.

Some of our clients are running our system on Lycos and able to get very good economy at 50 to 75F LOP, 20F spread between hottest and coldest EGT. One fellow leans in the climb to around 100F ROP. He has over 350 hours now on an O-320 in a Glastar.

Your experiments with individual O2 probes is interesting. I always wanted to do that but I have enough hardware on our mule already.

You should build that 8!

http://www.sdsefi.com/aircraft.html

 

[Fitz]

Some facts of physics:

Best Power is found at between 75 and 80dF ROP.

It is only going to be about 2-3 degrees F cooler on the CHT's than 40dF ROP where CHTs are peaked.

The difference between Best Power and 100-125dF ROP at max rated power is very little on CHTs and ICPs.

Leaning to Best Power at max rated power is a really good way to experience detonation.

We used to Race at Reno. We only needed the engine to last for six laps. We couldn't do it at Best Power. It took a lot more FF than that to keep the engine together for six short laps.

Take those facts for what they are worth and make your own decisions.

Walter

FWIW, Best Power is actually around .85-.86 Lambda, though as lean a .9 Lambda on some Porche engines. The EGT temperature will depend, among other things, on the fuel. The reason that I said 125-175 degrees ROP is that is generally what I see targetted in the service manuals for WOT operations on aircraft engines running 100LL. It is richer than 'Best Power' (in the engine builder sense), but by 'best power' I meant 'the best power available for the operation without exceeding the engine's ratings'.

My point was that with the mixture knob shoved in you are virtually always richer than the engine maker's spec and what is ideal for the fixed timing in the engine. An O2 sensor was the only way I could think of to very accurately lean in flight to the rated optimum. Other methods of leaning, like EGT and fuel flow, seemed inappropriate or too course. High performance auto racing has rapidly shifted from EGT based tuning to lambda based tuning for those reasons - but, of course, those engines run at higher compressions so the detonation margin is often smaller.

Again, my *only* point was that you need a better measurement mechanism to tweak to precise mixtures at high powers in flight. It was certainly not my intent to forward a strong opinion on what those mixture points should be.

Detonation is not a simple subject. It involves heat, pressure, timing, and chemistry. Why your engine tore apart at Reno is a more complicated subject still. Fuel distribution, back pressure, valve variance... there are countless factors. I am sorry if I irritated you, especially since I agree whole heartedly with virtually everything your group has been preaching. The best places to run aircraft engines *are* very lean and very rich. Our fuel distribution systems are simple, our timing is fixed, we are typically air cooled, and the manufacturing tolerances are generally very poor.

Again, with apologies,
-jjf

 

[gmcjetpilot]

No argument

No one is saying LOP. You want to be at best power, generally about 125-175 ROP. It is a race. You can't easily do this with an EGT gauge because you would need to 'peak' first to find a temperature relative to it. This potentially puts the engine just rich of peak, were pressures and CHTs soar (lots of heat, lots of fuel, means ripe for detonation).

manufacturing tolerances are generally very poor-jjf

No offense was meant and 125-175 ROP is fine, just my suggestion for 75% power leaning is 100F ROP; I was not talking about racing at this point. At full power in my opinion (that is all it is, an opinion) do not lean at full power, don't even think about . That is all.

At full power I have no idea how ROP you are? Some where I read it's in the 200-250 ROP range at take-off? I don't know or want to know for reasons you mention, you can't lean to peak to find out with out major hazard to engine health and longevity (and yours). Thus the advice, never ever lean at full power.

I know people get sick of me saying this but for the record, "Lycoming says only lean when at 75% power or less". Clearly they are working to worst case all engines and conditions. This is from lots of test data and no doubt has some margin of safety.

As far as LOP I only mentioned it because Walter found you can lean at higher power LOP. When I say higher power I don't mean 100% I mean something a little over 75%. I am no LOP expert and don't practice it because my engine (O-360) does not like it.

It would be cool if you could come up with some O2 gauge for aircraft use with altitude compensation. I find your comments interesting. I have plans to make a stand alone O2 gauge for about $20 + probe. The only thing holding me back is drilling and welding a bung to my exhaust pipes. It would be interesting to go up and fly and compare the O2 reading as you have. Do you think it's practical or a big improvement?

Your last comment "manufacturing tolerances are generally very poor" I don't agree with or I don't understand. The tolerances are by design.

I know you know air cooled engines (piston/cyl) tolerance are larger because they need to be (thermal expansion). The gaps are there by design for oil control. As far as gears, cams, cranks, case flatness, bearing journals and so on, the tolerances are very tight in every respect. I have an overhaul manual in front of me and I see 0.002 and 0.005 all over the place in the tolerance limits. That's tight. They make tolerance as tight as they need to. It's a pet peeve that there is this pervasive attitude that air cooled engines are crude, poorly made or lacking sophistications. Yes water cooled engines are tighter, but than they carry 100 lbs of stuff we don't need to carry a loft in my opinion. The tolerances and simplicity are by design. I think some see the external rough finish of the engine case halves or heads, which are castings, and think crude, comparied to a CNC hogged out aluminum block. They are precision high quality structural castings because they are lighter than hog outs. They are works of art. The rough finish belies what's inside the case or head. Just my little rant, sorry. G

 

[BOBM]

I know people get sick of me saying this but for the record, "Lycoming says only lean when at 75% power or less". Clearly they are working to worst case all engines and conditions. This is from lots of test data and no doubt has some margin of safety.

Doesn't Lycoming say to lean for T/O at 5,000ft?

 

[rv6ejguy]

FWIW, the Bosch chip uses a fixed calibration curve - based on a group sampling. So it does become less accurate with altitude and age. On the Megasquirt web page there is a long white paper on this. They are trying to develop a different measurement principle but I have my doubts about its practicality.

-jjf

I believe many of the early widebands used the free air method to calibrate however the later sensors use a precision resistor located in each sensor connector which the box can talk to so there is no more "group" calibration. A magazine test a couple years ago found a whole point variation in AFR between free air calibrated wideband units. I couldn't find any reliable information discussing variations with altitude in any Bosch literature I have.

Here is the basic info supplied from Bosch: http://www.wmsracing.com/o2/tech.htm

Leaning at full power (ie sea level) could be damaging due to high temps and possibly detonation. If you are already at 7500 feet, you can only develop 75% power anyway so technically you could lean there. Operating Lycos here at 4000 feet MSL requires some leaning for takeoff to get best power and smoothest operation on some aircraft due to variations in carbs and the AFR delivered at full rich settings.

Below 75% power and with CRs under 8.5 and 100LL and reasonable total timing values of under 28 degrees, it should be impossible to get detonation because the PCP is not high enough, irregardless of AFR.

 

[Fitz]

I believe many of the early widebands used the free air method to calibrate however the later sensors use a precision resistor located in each sensor connector which the box can talk to so there is no more "group" calibration. A magazine test a couple years ago found a whole point variation in AFR between free air calibrated wideband units. I couldn't find any reliable information discussing variations with altitude in any Bosch literature I have.

Here is the basic info supplied from Bosch: http://www.wmsracing.com/o2/tech.htm

No, the resistor has always been in the Bosch wiring harnesses. Remember, the sensors were built for a mass production application. The trim resistor essentially places stoich at the proper point. The assumption is then made that the sensor can generally be fit to a calibration curve that was established empirically with a sampling of like sensors.

The Bosch sensor with the Bosch driver does what Bosch says, but it is not a high speed, precision wideband controller. Again, I'd send you to the Megasquirt site. Bowling and Grippo started working on a precision wideband controller some years ago. They lay out pretty clearly why the stock Bosch solution was not sufficient for their needs and put together some very nice documentation on the sensor technology itself. As I've said, I have some questions about the practicality of their measurement principle. If you look at their calibration page, you will see what I mean. Each sensor must be calibrated with precision gases and they have a Windows application to help you factor in atmospheric factors in calibrating the lean side with free air.

I am not endorsing the Megasquirt do-it-yourself EFI! But not only has their 'open' work on precision wideband measurement been interesting, they have made practical demonstrations of the limitations stock implementations like the Bosch one you referenced with their AFR auto-tuning features. Users can successfully close the loop with a precision wideband controller like ours, but not with the stock Bosch driver. Understand, regardless of how fast someone samples the outputs of the Bosch chip, measurements themselves are limited to about one every 100 to 200 mS because of the measurement principle used. And, the sensors virtually never fit the fixed calibration curve exactly, so measurements always become less accurate the farther you go from stoich.

I'd be glad to go into why all Bosch sensor applications care about changes in partial pressure, but I'm already writing a book here! In brief, it is a consequence of the way Lambda is actually measured. Like sensor to sensor variation, the impact on accuracy becomes greater as you move from stoich. You don't free air calibrate because you 'have to', for example, we could easily use a constant like Bosch. You free air calibrate when you are looking for maximum precision from a given sensor under specific atmopheric conditions.

I would be interested in any magazine article you still have. Again, I'm falling into ad mode, but we believe strongly in our patented measurement principle and have kicked serious tush in every speed/precision shootout that I am aware of over the last few years (including some big dollar lab stuff).

Shifting gears...

*I am very sorry to have seemingly annoyed so many people in such a short time!!!*

I'm extremely interested in your work with experimental aircraft EFI. I'd love to see some of your logs. Since you have a bung installed, etc. I'd also be happy to arrange for a loan of a wideband controller and sensor for you to play with. Just email me with the lambda or AFR range you are using (tell me what stoichiometric multiplier you are using for 100LL if AFR) for your analog input and I'll pre-configure it for you.

*Regarding leaning (again)!!!*

I'm not encouraging anyone to Best Power or Stoich at max power. I started with the context of racing, and edging towards best possible power.

In the auto racing world, this has been done for years with EGT and stories like Mr. Atkinson's are common. I'm NOT saying that this is what happened to Mr. Atkinson in Reno, but the typical scenario goes something like follows:

* The tuner tries to get as close to Max Power as possible without the engine self destructing

* One cyl (or more) is slightly leaner, hence closer to peak pressures and temperatures

* That cyl starts to detonate

* EGT goes down slightly

* The tuner interprets this as indicating a richer mixture than desired

* The tuner leans a little more, taking things closer to peak pressures and temperatures...

Right or wrong, I translated this scenario to my own GA experiences. When the mixture knob is all they way in, the engine is almost always running needlessly rich. This is not nec. a bad thing, better too rich than too lean, but in a high performance application you would want to bring this back to the optimum level that is sustainable by the engine.

We do this in, say, a new 206. We go to a fixed fuel flow for takeoff in a new T206, and use the placarded fuel flows for altitudes on a non turbo 206 for "Max Performance Takeoffs".

But this is fairly imprecise and, again, typically errors on the side of rich. My only point, really, was that I'd want an O2 sensor to tweak to the optimum point for a max performance application. I would not trust absolute EGT in this case, because there is not a really good way to derive it, and I wouldn't trust fuel flow alone. I'd actually want to combine individual cyl lambda with individual CHT and EGT, since it would give me more clues about preignition and detonation, but that is almost another discussion.

My preference for true lambda measurement probably comes from my work. If you have a big hammer, the world seems full of nails... But I did try to point out the limitations for aviation applications!

BOBM: Over 5000', a normally aspirated engine can't generate enough power to easily do harm with the red knob. That is why POHs have long been OK with it. Leaning for cruise at any altitude is a (relatively) new addition. Engine makers presumably bowed to pressure from plane makers - who care about speed and range. If you head to Mammoth Lakes, Tahoe, Flagstaff, etc. in the summer - check density altitude and performance and definately lean for takeoff.

gmcjetpilot: I hope some of the top of this covers your questions about O2 sensing. We can discuss pros and cons, but I'm trying to not hopelessly hijack the thread *and* tick everyone off! My comments about tolerances relates to manufacturing quality. I had a horrific experience with a factory reman'ed engine. Lycoming did replace it, since there were some obvious manufacturing flaws. But I still think a lot of engines fail prematurely because of things not to being manufactured to proper tolerances.

Mr. Atkinson: Again, I'm sorry to have irritated you.

In fact, I'll extend that to everyone. I am interested in the use of O2 sensing in GA, especially with 100LL at $4.50 at my home airport and the whole future of 100LL up in the air. But I'm not even completely convinced that it is either widely practical or beneficial.

My main interest is, as a long time GA pilot, if I can realistically build an RV-8 and if 180-200 HP is enough. I recently transitioned back to conventional gear after years of tricycle, but my midlife crisis is still not fully appeased. An RV-8 sounds like a possible ticket and aircraft construction and snap rolls are both a lot safer (at least in my house) than a girl friend half my age!

-jjf

 

[chuck]

Fitz:

It is nice to hear from a 'car guy' with aircraft experience. You certainly have not annoyed me, and I suspect othes share that feeling.

Walter, rv6eguy and you (and others) have done a great deal in expanding the knowlege base here, keep it up! I think we all know there is more to the read knob than the lycoming manual tells us.

 

[aadamson]

Fitz:

I think we all know there is more to the read knob than the lycoming manual tells us.

Ooooo, I really like those "play on words" ...

 

[rv6ejguy]

Fitz, thanks for the detailed reply on widebands. I searched the MS site for about a half hour yesterday but it is a mess and could not find the article you described.

I'm not sure that the sampling rate is very important here in an aircraft application due to the constant power setting scenerio plus the delay in the response due to distance from the port. For what you are attempting to do, perhaps. I think the design of the sensor and it intended application needs to be kept in perspective- OE wideband closed loop (slow) control, for which it works well in my experience.

The WMS unit reported stoich at 14.7-15.0 AFR in flight at 8500 feet, confirmed by peaking the EGT so it seems accurate enough for my purposes. When we AFR datalog with SDS it is not to a laptop, it is to the handheld interface- much faster and easier. This feature was primarily developed for auto use with the wide and fast rev range. Aircraft engines are much easier to tune because it is steady state and you have a dyno- er prop out front to absorb the power. I had my engine mapped in less than 5 minutes on the ground and barely touched it after that. Total programming time less than 15 minutes including the in-flight ignition timing experiments.

I am happy with the results and fuel flows now so that testing phase is over with but thanks for your offer. I'd be interested in hearing anything more from your experiments in the future.

 

[Walter Atkinson]

jjf:

**Detonation is not a simple subject. It involves heat, pressure, timing, and chemistry. Why your engine tore apart at Reno is a more complicated subject still. Fuel distribution, back pressure, valve variance... there are countless factors. I am sorry if I irritated you, especially since I agree whole heartedly with virtually everything your group has been preaching. The best places to run aircraft engines *are* very lean and very rich. Our fuel distribution systems are simple, our timing is fixed, we are typically air cooled, and the manufacturing tolerances are generally very poor.**

No problems. No irritations! We agree. We never cratered an engine at Reno--I think the combusiton Gods must have felt sorry for us! (We cratered a couple during research.) As far as we can tell, there are basically three hard factors in detonation margin: heat, pressure, and fuel latency. All other factors act to affect one or more of those three. For example, timing alters heat AND pressure. Uhg. Lead affects the latency period of the fuel--*exactly* how remains a mystery.

As for your comment about being very rich or very lean at veyr high powers, you are dead-on correct. Being "not rich enough" when ROP is a bad concept with bad results.

Thanks,

Walter

 

[Nuisance]

We used to Race at Reno. We only needed the engine to last for six laps. We couldn't do it at Best Power. It took a lot more FF than that to keep the engine together for six short laps.

Walter

Walter, if you never hurt an engine at Reno, then how do you know this?

John

 

[Walter Atkinson]

George:

**No offense was meant and 125-175 ROP is fine, just my suggestion for 75% power leaning is 100F ROP; I was not talking about racing at this point. At full power in my opinion (that is all it is, an opinion) do not lean at full power, don't even think about . That is all. **

Agreed. Don't lean at max rated HP, OR be very LOP. The later is not yet availbale to us, but will soon be. I've made several proof ofconcpet lfights taking off LOP on a specially set-up engine.

**At full power I have no idea how ROP you are? **

Depending on the enigne and the induction and fuel, it can be from about 250dF ROP to as much as 300+ ROP. My personal engine is TC'd and set up to be MORE THAN 300dF ROP at max power.

**"Lycoming says only lean when at 75% power or less". Clearly they are working to worst case all engines and conditions. This is from lots of test data and no doubt has some margin of safety. **

That's very good advice when ROP. I generally run at 90% power in cruise and well LOP. So, yes, I lean above 75%------ BUT never to a ROP mixture above 75%. My IPCs at 90% LOP are lower (by measurement) than they are at 75% power ROP. That is the difference. Unfortunately Lycoming does not specify that the issue is being ROP.

**As far as LOP I only mentioned it because Walter found you can lean at higher power LOP. When I say higher power I don't mean 100%**

We have made a few flights where we took off at 100% power, LOP. It works great, but requires a special set-up. It is not possibel they way our engines are set up fomr the factory. I don't recommend trying it unless you have a very good handle on the issues incvolved.

There are some really impressive technological advances taking place that will allow this type of operation. It will be done without mulitple sensors which present interesting single point failure modes. An acceptable failure mode in a car is quite different than when it occurs in an airplane. <ng>

Walter

 

[Walter Atkinson]

**Doesn't Lycoming say to lean for T/O at 5,000ft?**

Yes, in NA engines; no, in TC'd ones (it always thinks it's at sea level, remember?).

The most accurate and reliable method for accomplishing Lycoming's recommendation to lean for high DA takoffs is to use the Target EGT method we devised. It works at all altitudes at all OATs, winter or summer.

Walter

 

[Walter Atkinson]

**Walter, if you never hurt an engine at Reno, then how do you know this?**

Well, we didn't GO to Reno and get into four straight Gold Races and keep the engines together without having done some serious testing. <g> It was expensive testing in some cases. <ng>

On the other topic, keep in mind that O2 sensing in the auto world is to a very different end. Everything there (not Racing) is designed to meet emissions requirements and not performance or maintenance issues. Our needs in aviation are quite different.

One thing I've noticed in this thread is an inconsistency in terminolgy. Best Power is a terrible engineering term. It should have been optimum power, or maximum, or something else. It ain't "BEST" in many cases. Someone earlier said that they wanted the Best Available Power and that that was at a mixture leaner than full rich and richer than Best Power. That is a reasonable goal that accepts that there are limitations to what's available.

We develped a concept called The Red Box, which is based on ICP and CHT and addresses the ability to set the mixture ROP or LOP outside the conditions of temps and pressures being higher than are acceptable for longevity concerns. This concept cleanly addresses much of what is being discussed in this thread. It answers why Lycoming doesn't want pilots monkeying with the red knob above 75% power when ROP.

A BIG part of the confusion on this topic is clearly a poor set of terms and loose use of them.

This is really interesting stuff which DOES have a real-world application.

Walter

 

[Nuisance]

thanks!

Thank you all for this fine discussion. Someone apologized for hijacking the thread I started...NO PROBLEM!!! I have been loving it. Fitz, I sent you a PM.

I was actually referring to a situation I found myself in at the Airventure Cup race on July 23rd. We were running at low altitude, due to headwinds that increased with altitude. I know that if I run full rich at full power, I will run out of gas before I get to the finish line. Since it is warm out, I am actually running at a density altitude of 3250 ft. So, I should be able to lean a little. Also, I am not running wide open, but more like 90% power. So, I should be able to lean a little, and still remain 150 to 200 degrees rich of peak...but what is peak?

Now, Walter might say I should be running lean of peak...50 degrees or so? Well, that is fine...what is peak?

Now you might say just stay full rich...it won't make much difference.

BUT, UNDERSTAND, I lost the race by 5 seconds over 408 nm.!!!

John

 

[Walter Atkinson]

John:

My wife has raced our Bo. She had the same question you do. We do know how to calculate the starting FF for maximum available power while not getting too far "not rich enough" or without finding peak. You can work that off of the BSFC numbers or you can use Target EGT as a starting point and tweak less FF to achieve that end while keeping CHTs under the max you are willing to run them.

A BSFC of about .68 would be a good place to start. That's calculated on the FF and HP being produced (we use 5.87#/gallon as the weight of the avgas). Your final acceptable BSFC number and FF will be based on the power being produced. In an ideal racing world, you would want to be the least ROP that will be tickling the detonation margin and hope that something doesn't change to make it go south. That will very soon be available as soon as we have the pressure sensors and the cockpit display of knock installed. It's working, just not yet certified. One could lean till it knocked or until 80dF ROP, whichever came first. If it knocked, you could richen till it went away. THIS is what you want, right? <vbg>

This is a VERY different concern when racing than most would use where longevity concerns are more important than the 5 seconds.

If you would like to discuss this in more depth, feel free to contact me off-forum.

Walter

 

[Fitz]

Someone earlier said that they wanted the Best Available Power and that that was at a mixture leaner than full rich and richer than Best Power. That is a reasonable goal that accepts that there are limitations to what's available.

That was me, and I think that referring to it as 'best power', easily construed as Best Power is how I felt I put my foot in it.

You can work that off of the BSFC numbers or you can use Target EGT as a starting point and tweak less FF to achieve that end while keeping CHTs under the max you are willing to run them.

That is the point were I think wideband sensing has value. It lets you tweak directly to, and maintain, a very precise metric.

O2 sensing for emissions is primarily narrow band sensing, the car only cares about running at stoich, to hold emissions down.

Wideband sensing, precise measurement of lambda over range, in high performance racing, is used pretty much as we are describing here. Actually, on both sides. When you turn on the Speed channel and see a winner, there is a very good chance that the car had at least 8 of our widband controllers hooked to it on the dyna for experimentation and tuning, and that it has 8 of our wideband controllers permanently installed to log actual performance in a race.

Rather the application (GA) is demanding enough to warrant some of the hurdles (ex. sensors eventually die in leaded fuel) is a legitimate debate. But I don't think it makes much sense to argue that analyzing the content of combustion results is not at least theoretically useful in a situation where we are trying to infer combusion results based on the temperature of the same exhaust. After all, EGT is what the auto world used for high performance tuning until precision wideband became readily accessible.

Nuisance: I responded to your PM

rv6ejguy: Understood, it certainly may be suitable for your application, but don't confuse stoich with the absense of partial pressure error. At stoich, the sensor is in balance. It is only off stoich, where partial pressure alters current in proportion that there is additional error.

But, again, we are talking about different scales. Stoich is where the sensor is at its absolute best. 100LL is still gasoline, so peak (1.0) should be displayed as 14.7 AFR. 15.0 is 0.02 Lambda off, or about 20 times the smallest increment we measure. This is very typical for the basic Bosch setup.

Sample rate is only a benefit (I think) in aviation if you try to do missfire detection and get multiple individual cyl measurements off one sensor. In car closed loop, it is another story.

Last, no criticism of your setup intended! Like I said, we are in the business of very precise measurement. I'm very interested in your work.

All: Thanks, I got the impression that, as a newbie, I walked into several long standing debates.

-jjf

 

[rv6ejguy]

Knock sensing

We have a couple of clients who have used the device desrcibed in the link here on air cooled Corvair and Porsche engines for individual cylinder knock retard with good results: http://www.jandssafeguard.com/

The Porsche chap was running a thermally challenged 2.2L turbo at very high boost and won many endurance and sprint races and he swore by it. Neither user has reported any problems with the knock sensor being fooled by high mechanical noise although this can be a problem in some cases.

May be applicable to racing aircraft applications.

The comment about auto vs. aero apps and racing and best power/ emissions is not really valid in my view. Racing is racing and best power AFR is the same regardless of application. Temperature stability may be another concern on some engines at certain AFRs. Emissions are no concern in auto racing. Having built and run my own dyno for many years, combined with recent testing on our 6A mule, we generally find best power occurs between an AFR of 12.7 to 13.3 to 1 on most engines (according to the WMS wideband???)

We never concern ouselves with AFR variations of .1 or even .2 as the curve is so flat in this range, hp difference is virtually nil. This is confirmed on the many dynos I have done pulls on and texts on the subject. In any case the ability for even high end EFI systems like Motec to control AFRs day to day within .1 AFR is unlikely in my experience mainly due to sensor lag (IAT especially). Bottom line- mixture control this fine is unimportant.

 

[Fitz]

Having built and run my own dyno for many years, combined with recent testing on our 6A mule, we generally find best power occurs between an AFR of 12.7 to 13.3 to 1 on most engines (according to the WMS wideband???)

With gasoline, 12.7 would be a lambda of about .86. A value of .85 to .86 is very typical. 13.3 is a lambda over .90. That is very lean. I would believe it on a few Porche engines, but as a general rule I would be suspicious of the measurement.

We never concern ouselves with AFR variations of .1 or even .2 as the curve is so flat in this range, hp difference is virtually nil. This is confirmed on the many dynos I have done pulls on and texts on the subject. In any case the ability for even high end EFI systems like Motec to control AFRs day to day within .1 AFR is unlikely in my experience mainly due to sensor lag (IAT especially). Bottom line- mixture control this fine is unimportant.

Agreed. Overall variations of .007 to .014 Lambda are not going to have a significant HP difference on the rich side. Analyzing lambda more precisely has advantages for things like balancing cyls or tuning valves, but serves no particular purpose here. Still, even measuring airfuel in .1 AFR increments would be greater precision than is easily obtained using EGT.

On the lean side, if your objective is true best economy, I would think you would want to try to hold AFR to about a .06 AFR (.004 lambda) range, somewhere near 1.05 lambda (about 15.4 to 1) for best results. But I haven't done any aircraft testing in that area.

Regarding closed loop EFI, In general I would agree, though we are doing some joint work on fuel efficiency projects that are pushing that technology envelope a little further.

FWIW, I tend to use Lambda because A) that is what is really being measured and B) it is fuel independant.

-jjf

Edit: The knock sensing stuff looks interesting. Thanks!

 

[gmcjetpilot]

Lycomings 5,000 foot rule and 75% rule

Doesn't Lycoming say to lean for T/O at 5,000ft?

Yes in their key reprints Lyc talks about 5,000 ft (landing and T/O from high elev airports). Lycs general recommended leaning in general is Leaning Textron Lyc Engines. If you have not read this, it is good to do. Just be sure you separate out the bits about turbocharged engines. One more article is Proper leaning. Interesting in that they talk about running at peak EGT for economy. That is a differnet debate.

The above has good advice for anyone. However the "5,000 foot" rule has some draw backs for RV drivers frankly, but I think there are pearls of wisdom and good advice in the above references.

Assuming your manifold pressure is the same as ambient, std day 5,000 ft, you would see about 87.5% at full RPM (assuming you had a constant speed prop, i.e., 2,700 rpm). This is theoretical max and unlikely, even for a RV.

Now subtract power for lower RPM for a typical fixed pitch prop and restrictions of airbox and exhaust, which are severe on production planes. The power may be down to 75% or even way less? Who knows for sure, but we can estimate for grins and giggles. A RV however may be well over 80%.

How does 75% power compare to the "5,000 foot" rule (Ldg/TO at high alt airports). We can assume Lycoming primarily writes about typical production planes, not our HOT homebuilts.


FACTORY PLANES
On a typical Cessna or Piper you see 1" to 1.5" drop in manifold pressure from ambient due to poor airbox design, unlike our RV's, but more about RV's later. At 5,000 feet the typical GA plane makes less power than a RV, even with the same engine, by a large margin. It's amazing looking at a 150-160 HP Cessna or Piper, that the rated HP, what it made on the test stand, not on the plane is quite different. That is why after market exhaust manufacture POWER FLOW EXHAUST claims they gain 23.75 HP on a 160HP C-172, because the stock exhaust is so very bad. Now the gain of 24 HP does not mean they are now making +180HP. Wish it was that easy. What it means is Power flow exhaust is only getting back near the engines potential or rated 160 HP. So 100% power in a C-172 is really like (160-24=) 136HP, or about 85% on sea level take off.

With a typical GA single engine, add altitude affect, lower RPM for takeoff (fixed pitch prop), poor airbox and exhaust, you are pretty safe leaning at 5,000 feet since you well under 75% power, may be as low as 65%. However for a RV you may have to fly to 8,500 feet to get 75%.


NOW THE RV
We have air boxes that drop zero to 1/2 inch-hg manifold pressure, some installations even provide a small "RAM air" pressure gain at high speed cruise. Now we add crossover or 4-into-1 exhaust, we are seeing the engines full potential, may be more? Oh yes, electronic ignition adds 1% or 2% power just by virtue of their fatter spark, even without the advance.

Lycomings 5,000 foot advice may not be so conservative for RV's. At 5,000 feet a RV might still make 85% to 83% power in theory. With a fixed pitch prop, 81% on takeoff? All this is a swag and some RV's no doubt make less power, but illustrates the point, 5,000 feet is fairly safe to lean, If you all other limits are nominal. Even with a RV you're way closer to 75% than 100% at 5,000 feet.


REAL WORLD and THEORETICAL
Poor performing GA planes at high density have little Perf to spare, so you MUST lean to get near the AFM specs. A RV has 4 time the performance, even if we ran overly rich on a high Alt take off. Therefore the operation techniques may vary.

Sometimes test pilot's do things during certification that does not make it into the AFM; so the "average" pilot can't attain the performance in the book, without knowing special techniques or skills. This also happens with big jets. Jet stopping distance are based on new brakes, with a test pilot that knew what was coming. They de-rate the performance to match used brakes and the reaction time for a surprise situation. GA plane AFM's can be optimistic.

Obviously you can choke an engine off if the fuel/air mixture is too rich, but I don't think we are close to that at 5,000 feet, but no doubt we are a little "WET". Wet engines do loose power.

I can tell you we (the flight school/club I once flew at) lost several Cessna's in mountain strips because they could not out climb the trees. May be leaning for max power was not done? +2000 feet/min in RV's makes you spoiled (and smile).


LYCOMING RULES!
Lycoming has to be conservative and simplify, but I think the 5,000 foot rule is an extension of their 75% rule. Feel free to disagree. It's MY reality or understanding of what Lyc is saying. Other insights are an engine on test stands does not EQUAL that when on an airframe. Different prop, fuel system (carb/FI) affect the way we operate an engine. So the 75% rule is a safe bet for lowest common denominator.

There's room for Target EGT and LOP in my opinion, for some but not all. We clearly can "trim the fuel mixture" with a full meal deal "engine monitor", which gives us way more data and control. We can also talk about the holy grail of inflight instruments, ICP (internal combustion pressure) and O2 data, which is even better. However the simple 75% rule is elegant for all occasions and a CYA deal. It's all relative. Every installation, engine, flight condition and instrumentation is different. Play by the rules you want to, but know why.

Leaning at 100% power is a hard no no rule for me. That little "fuel trim" is not worth the potential damage that can be done. May be if you have ICP, O2 and torque gauges you could do it safely? Since we don't have these special parameters in the plane, it's a moot point.

 

[Walter Atkinson]

George:

**Leaning at 100% power is a hard no no rule for me. That little "fuel trim" is not worth the potential damage that can be done. May be if you have ICP, O2 and torque gauges you could do it safely?**

That's very good advice--especially since we are now relegated to ROP operaton at that very high power setting. Being LOP at that high power is actually safer with a wider detonation margin--if only we could accomplish that. In the not-so-distant future we will be able to do it. As I said, we've already made some proof of concept flights and it works beautifully.

All in good time. <g>

Walter

 

[Joey]

Do you do it by adjusting the ignition timing?

 

[David-aviator]

Do you do it by adjusting the ignition timing?

This thread has gradually risen to level 401. Very interesting for this novice.

Don't know if the above question applies, but the answer with Subaru is injection time is ECU managed and by reducing fuel pressire less fuel is injected. As I recall, the Subaru H6 manual states 42 or 47 psi is normal (can't remember which). We are running as low as 28 inflight, 24 at idle. It makes quite a difference in fuel consumption.

Ignition timing is moving all the time controlled by a number of engine to ECU inputs, whether in closed or open loop, and other factors unknown to me.

I can induce closed loop only by reducing prop rpm to 1700-1900 and closing the throttle slightly. With higher rpm's it is in open loop except with the throttle almost fully closed and producing very little power. So, the method to reduce "table" induced fuel flow at higher power settings is to reduce fuel pressure.

But as I said earlier, this has to be done with a wide band O2 sensor to monitor A/F ration so as not to burn up the engine while determining a best fuel pressure. Robert Paisley did the original work in this area with his tail tied down on the ramp.

dd

 

[Fitz]

I can induce closed loop only by reducing prop rpm to 1700-1900 and closing the throttle slightly. With higher rpm's it is in open loop except with the throttle almost fully closed and producing very little power. So, the method to reduce "table" induced fuel flow at higher power settings is to reduce fuel pressure.

If there are more threads on efforts to use the Subaru engine in aviation, I'd be interested in reading them.

FWIW, closed loop's main goal in life on the stock ECU is to hold a mix that is ideal for emissions control. It uses a 'narrow band' O2 sensor which is used only to find 'stoich', or 14.7:1 AFR with gasonline.

If there is no catalytic converter, there is little incentive to run there. In an aircraft install you may well want to make closed loop 'auto lean' for ground ops. You can do this with some wideband controllers. Just program an analog output to simulate the narrow band signal for the ECU (car enthusiasts do this all the time so they can use just one O2 sensor). But, instead of 1.0 (14.7:1) you can set the actual mix much closer to best economy.

I'm really curious why you are chosing to override the fuel map with pressure changes? I would have examined AFR over RPM ranges and then calculated a new fuel map. In an aircraft application I might have also looked at some of the piggyback ECU's, since some can run closed loop in boost with a wideband controller.

-jjf

 

[David-aviator]

I'm really curious why you are chosing to override the fuel map with pressure changes? I would have examined AFR over RPM ranges and then calculated a new fuel map. In an aircraft application I might have also looked at some of the piggyback ECU's, since some can run closed loop in boost with a wideband controller.



For now, the stock Subaru ECU is used because of its redundancy and memory features not written into less complex programs. It's use is an Eggenfellner policy.

Why hasn't the factory map been rewritten? No one has figured out how to do it (and some smart people have looked at it). I can only guess Subaru has a proprietory code to make it next to impossible to rewrite the tables.

It is my understanding that if the system is in closed loop, it does use O2 sensors to compute injector timing for fuel flow rather than the tables. This is my usual local area cruise mode and I assume it is efficient as can be. The airplane will settle on 143 mph at 5.5 gph in smooth air.

dd

 

[Fitz]

Why hasn't the factory map been rewritten? No one has figured out how to do it (and some smart people have looked at it). I can only guess Subaru has a proprietory code to make it next to impossible to rewrite the tables.

Not really a hush/hush secrecy thing, just technology. When ECUs were simple almost any yahoo with a simple programmer could dump a PROM and decipher tables.

As ECUs have increasingly switched to RISC microcontrollers, it has gotten much harder. The 'table' often resides in the firmware. If the fuse bits are set on the processor, the firmware cannot be readily extracted for hacking. This leaves either complete reverse engineering of the ECU's conditional behavior and writing replacement firmware, or deciphering the ECUs ODB-II updating, which may or may not be implemented.

It is my understanding that if the system is in closed loop, it does use O2 sensors to compute injector timing for fuel flow rather than the tables. This is my usual local area cruise mode and I assume it is efficient as can be. The airplane will settle on 143 mph at 5.5 gph in smooth air.

Yes, when an ECU is closed loop an AFR sensor is used. There are also normally corrections for atmospheric conditions. However, exactly what closed-loop means varies with the ECU.

The simplest and most widely available form uses a narrow band O2 sensor. Think of it as a digital signal 0=rich of peak, 1=lean of peak. The ECU uses this to keep things at peak. The main reason is emissions control. Some setups use wideband sensing. Think of an analog signal 0V = 7:1, 5V = 21:1. These ECUs generally combine a map (target AFR) and closed-loop (adjusting to the target based on actual readings). Still, they generally go open loop (table only) at high boost or WOT.

Unless you have deciphered the ODB-II variables for a given ECU and are monitoring it, it can sometimes be tricky to tell if an ECU is in closed-loop or not. Even map values are sometimes 'corrected' based on various sensor inputs.

My worry with mucking with fuel pressure to fool a modern, stock, ECU is that you don't know all the fuel-cut conditions. When you are in a street car, shutting off the injectors to save the engine is probably a good thing. In an airplane, there are times I'd rather take my chances on burning up the engine and keep the fan running a few minutes longer...

-jjf

 

[walkman]

I realize this is an old thread, however I'm wondering if the participants are still around.

After a couple of years learning curve designing and installing a Microsquirt-base package in my Porsche 930, I'm considering using two of those ECUs in my RV-8 (IO-360 8.5:1).

 

[rv6ejguy]

Bob and David have sadly flown west some time ago.

We've been supplying EFI for aircraft since 1995. We will reach an estimated 1 million flight hours on the fleet in 2024. The 6th Gen SDS ECU has targeted closed loop and LOP functions developed just for aviation.

Give the MS a try. EFI is the future...

 

[koupster]

Wide-band oxygen sensor with Bluetooth

Just became aware of this product. The air fuel ratio can be displayed on your phone, so no through firewall wiring required. Hope this helps someone.

https://grassrootsmotorsports.com/articles/avoid-turbo-induced-disaster/?mc_cid=65f0f586ed&mc_eid=e123d8fda6
https://pe-ltd.com/product/wideband/

 

[lr172]

I realize this is an old thread, however I'm wondering if the participants are still around.

After a couple of years learning curve designing and installing a Microsquirt-base package in my Porsche 930, I'm considering using two of those ECUs in my RV-8 (IO-360 8.5:1).

I have installed the megasquirt on my turbo upgraded 911 and also use them on the 6 and the 10. However, they only provide ignition in those applications. With the porsche I could tune the fuel delivery with a drive observe change approach to get the AFRs where they needed to be in each situation. I was also able to rely upon wide band AFR ((quite difficult with leaded fuel). That approach just seemed to scarry for me to do on a flying engine. To me, the benefits of EFII over a well tuned mech FI were just not great enough to be worth it. If I could get an engine on a stand for setup that would be a whole different matter. With an airplane, you can't just pull over and tweak a setting.

 

[N49ex]

Air/Fuel ratio monitoring for aircraft engines

It's been over 4 years since I installed O2 sensor based air/fuel ratio monitoring on my Lyc I/O-390, and it is still working perfectly after about 350 hours. It is an absolute pleasure to handle leaning with it - I have two numbers to deal with - Lean to A/F ~12.5 for max power at 75% power, and A/F ~ 15.5 at <= 65% for lean of peak. No need to go find peak EGT.

What makes it survive the lead in the fuel is the NGK O2 sensor, which is known for its tolerance to lead, compared to the Bosch sensors. I am using the Ballenger Motorsports AFR500v2 unit. When I started down this path, it was an experiment, and just in case, I bought a spare sensor, and haven't had to use it yet!

Should you be motivated to try A/F monitoring in your plane, I wrote a Kitplanes article on my experience, as well as various aspects of engine operation, and including lots of test data: https://www.kitplanes.com/adding-direct-air-fuel-ratio-monitoring/

Reinhard Metz

 

[walkman]

I have installed the megasquirt on my turbo upgraded 911 and also use them on the 6 and the 10. However, they only provide ignition in those applications. With the porsche I could tune the fuel delivery with a drive observe change approach to get the AFRs where they needed to be in each situation. I was also able to rely upon wide band AFR ((quite difficult with leaded fuel). That approach just seemed to scarry for me to do on a flying engine. To me, the benefits of EFII over a well tuned mech FI were just not great enough to be worth it. If I could get an engine on a stand for setup that would be a whole different matter. With an airplane, you can't just pull over and tweak a setting.

Love to hear more about your pcar project. Are you on Pelican forums?

I don't plan on using WBO2 or closed loop for operation, but expect to use WBO2 during tuning. Currently running one impulse coupled mag and one Protek EFII ignition only on the RV.

Once I sell my boat I was considering picking up an engine and stand for testing, willing to split the cost? lol

 

[walkman]

It's been over 4 years since I installed O2 sensor based air/fuel ratio monitoring on my Lyc I/O-390, and it is still working perfectly after about 350 hours. It is an absolute pleasure to handle leaning with it - I have two numbers to deal with - Lean to A/F ~12.5 for max power at 75% power, and A/F ~ 15.5 at <= 65% for lean of peak. No need to go find peak EGT.

What makes it survive the lead in the fuel is the NGK O2 sensor, which is known for its tolerance to lead, compared to the Bosch sensors. I am using the Ballenger Motorsports AFR500v2 unit. When I started down this path, it was an experiment, and just in case, I bought a spare sensor, and haven't had to use it yet!

Should you be motivated to try A/F monitoring in your plane, I wrote a Kitplanes article on my experience, as well as various aspects of engine operation, and including lots of test data: https://www.kitplanes.com/adding-direct-air-fuel-ratio-monitoring/

Reinhard Metz

Curious, how do you know its still working perfectly and you don't have some drift. Did you calibrate against fuel flow and keep comparing those? Some other way?

I will defintely check out your article, Thanks.

EDIT: Read, bookmarked, thanks.

I have several Bosch LSU WBO2 sensors around, including on the MS in my car. I will try the NTK sensor, if possible I'll find a "blind" controller that provides a linear output and see if I can find a way to display that on my GRT EFIS.

 

[rv8ch]

It's been over 4 years since I installed O2 sensor based air/fuel ratio monitoring on my Lyc I/O-390, and it is still working perfectly after about 350 hours. It is an absolute pleasure to handle leaning with it - I have two numbers to deal with - Lean to A/F ~12.5 for max power at 75% power, and A/F ~ 15.5 at <= 65% for lean of peak. No need to go find peak EGT.

What makes it survive the lead in the fuel is the NGK O2 sensor, which is known for its tolerance to lead, compared to the Bosch sensors. I am using the Ballenger Motorsports AFR500v2 unit. When I started down this path, it was an experiment, and just in case, I bought a spare sensor, and haven't had to use it yet!

Should you be motivated to try A/F monitoring in your plane, I wrote a Kitplanes article on my experience, as well as various aspects of engine operation, and including lots of test data: https://www.kitplanes.com/adding-direct-air-fuel-ratio-monitoring/

Reinhard Metz

That's a very helpful article, Reinhard. Thanks for writing it.

 

[rocketman1988]

O2 sensor

I am using a PLX unit with a Bosch sensor. Is the NGK sensor a direct replacement? I don’t get much life out of the Bosch sensors.

 

[N49ex]

Air/Fuel ratio monitoring for aircraft engines

"Curious, how do you know its still working perfectly and you don't have some drift. Did you calibrate against fuel flow and keep comparing those?"

I periodically check the fuel flow as well as the EGT after setting mixture for the desired A/F ratio, and the numbers are pretty much the same as they were early on. It's a quick glance at FF, EGT, and % power per the Garmin display.

" Is the NGK sensor a direct replacement?"

I don't think so. The Ballenger electronic unit when I ordered it required specifying which sensor I wanted.

 

[lr172]

Love to hear more about your pcar project. Are you on Pelican forums?

I don't plan on using WBO2 or closed loop for operation, but expect to use WBO2 during tuning. Currently running one impulse coupled mag and one Protek EFII ignition only on the RV.

Once I sell my boat I was considering picking up an engine and stand for testing, willing to split the cost? lol

I did all that work on the porsche over 10 years ago and not active on any forums. You are welcome to reach out via PM.

 

[walkman]

"Curious, how do you know its still working perfectly and you don't have some drift. Did you calibrate against fuel flow and keep comparing those?"

I periodically check the fuel flow as well as the EGT after setting mixture for the desired A/F ratio, and the numbers are pretty much the same as they were early on. It's a quick glance at FF, EGT, and % power per the Garmin display.

" Is the NGK sensor a direct replacement?"

I don't think so. The Ballenger electronic unit when I ordered it required specifying which sensor I wanted.

The show three different NGK sensors of different claimed accuracy.

Which one are you using?

 

[N49ex]

A/F monitoring

The show three different NGK sensors of different claimed accuracy.

Which one are you using?

I have the least expensive one. Works fine. One thing to know is that probably due to the turbulence in the exhaust the indicated A/F number on the display will jump around about 0.1 while flying, but that's good enough to set the mixture. One check on calibration you can do (with power <=65%) is to set for 14.7 A/F and check that it coincides with peak EGT.

 

[walkman]

I have the least expensive one. Works fine. One thing to know is that probably due to the turbulence in the exhaust the indicated A/F number on the display will jump around about 0.1 while flying, but that's good enough to set the mixture. One check on calibration you can do (with power <=65%) is to set for 14.7 A/F and check that it coincides with peak EGT.

Good point

I was contemplating MAF vs MAP (speed/density) for mixture calculations. I see that the two commercial products are using MAP but on the face of it MAF seems a better choice given the wide and rapid changes in air density in an aircraft in climb. Why was MAP chosen and what are the drawbacks? Just installation constraints?

How is the VE table calculated? Just be doing an automated AFR-based tune aka VEAL in MS-speak?

 

[N49ex]

Good point

I was contemplating MAF vs MAP (speed/density) for mixture calculations. I see that the two commercial products are using MAP but on the face of it MAF seems a better choice given the wide and rapid changes in air density in an aircraft in climb. Why was MAP chosen and what are the drawbacks? Just installation constraints?

How is the VE table calculated? Just be doing an automated AFR-based tune aka VEAL in MS-speak?

I don't have any answers to these questions as they seem to be oriented to an assumed EFI environment. I have a normally aspirated mechanical Precision Automotive/RSA type fuel injection system on the I/O-390, and once an A/F ratio is set, the servo controls the fuel flow in step with the airflow as the plane climbs, keeping the A/F constant. That said, I will do a flight soon and verify the details of that - mainly I know I never seem to re-adjust mixture because the A/F changed. Of course, in a carbureted environment, it's a different story.

Using A/F in conjunction with one of the available experimental EFI systems - I don't know what they already do and what one might adjunct and the risks involved. But with mechanical fuel injection, the use of wideband A/F measurement and user's mixture control is low risk, apart from keeping track that the O2 sensor is still happy in the lowlead environment.