Leaning at full power?

[PilotjohnS]

just me

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.

I have the Bendix RSA clone on my stock Lycoming. It claims to keep a constant F?A mixture during climb but I find I need to tweak it as altitude or Baro setting changes. I typically run peak EGT cruise (65% power). And when I reduce power for descent, I need to richen and reset peak EGT once descent rate and power are reset. YMMV

 

[lr172]

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?

MAF is not feasible on a lycoming engine. Intake plenum is all but non-existent and fraught with turbulence. Don't know about microsquirt, but the megasquirt has baro compensation tables, but will need another sensor to deal with the changes. haven't done a lot of research on this but MAP alone may be adequate. Again more testing that cannot be done on a stand. Will also possibly struggle with accel enrichment. Pretty sure the COTS options use TP data to deal with this (alpha N in MS speak)

 

[walkman]

MAF is not feasible on a lycoming engine. Intake plenum is all but non-existent and fraught with turbulence. Don't know about microsquirt, but the megasquirt has baro compensation tables, but will need another sensor to deal with the changes. haven't done a lot of research on this but MAP alone may be adequate. Again more testing that cannot be done on a stand. Will also possibly struggle with accel enrichment. Pretty sure the COTS options use TP data to deal with this (alpha N in MS speak)

Figured it was installation constraints.

Yes Microsquirt has automatic barometric adjustment. Can be a single sample from the MAP sensor at start up or a close to real time adjustment using a second MAP sensor on the BARO port, which is what I do in my car. Seems to work great with the ~3,000' altitude changes I've done but the car climbs much slower and the service ceiling is lower .

There is also the MAT table to deal with.

Quad MAP sensors is no big deal, easy to build a manifold or T them together.

Not sure presence of a TPS necessarily means Alpha-N, could be used to accel enrichment or WOT enrichment.

 

[koupster]

O2 Sensor Spacer

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.

Bob,

Consider an O2 Sensor Spacer to get the sensor out of the direct leaded exhaust stream. The sensor might be slightly slower to react, but that shouldn't be a factor for aviation applications.

https://www.electrodyne.cc/product/130%2010%2010%20010.html?srsltid=AfmBOooUd7nU_-HNLDedQwFtw4F7mfDDjFn9vMIj5c04imQEo0OhSVd7z7g

https://www.garlaven.com/products/o2-sensor-spacer-extender-adapter-35s7?variant=012c3373-a89e-4705-ab6b-3eacf8e56307&gad_source=1&gclid=CjwKCAiAg9urBhB_EiwAgw88mZ699RZIgIcStMr_ymZ6HUkiuLCHO3V-VKdfjTtqmw1lfi8izpxolBoCuGQQAvD_BwE

https://www.walmart.com/ip/Car-CEL-Fix-Check-Engine-Light-Eliminator-Adapters-Oxygen-O2-Sensor-M18X1-5-2-Pack/699277702?wmlspartner=wlpa&selectedSellerId=101255041&adid=22222222227699277702_101255041_154879163646_20826618661&wl0=&wl1=g&wl2=c&wl3=683218793893&wl4=pla-2262296054290&wl5=9029755&wl6=&wl7=&wl8=&wl9=pla&wl10=666177212&wl11=online&wl12=699277702_101255041&veh=sem&gad_source=1&gclid=CjwKCAiAg9urBhB_EiwAgw88meJ-qrTe5BRjZkov6nCyi1beTeafefejKDTq6nkNitQ32uFLQwZ1kRoCNIYQAvD_BwE

 

[DanH]

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.

Interesting.

You have an EX-5 servo?

Plot below is density vs GPH (in effect, weight vs weight) for an AFP FM200 on a 390, constant indicated airspeed climb, full rich. Fuel flow does not precisely track rho.

I'd be tickled if you ran the same climb test (full rich, hold 125 KIAS, record fuel flow at each 1000 ft) while keeping an eye on the A/F meter.

 

[N49ex]

Interesting.

You have an EX-5 servo?

Plot below is density vs GPH (in effect, weight vs weight) for an AFP FM200 on a 390, constant indicated airspeed climb, full rich. Fuel flow does not precisely track rho.

I'd be tickled if you ran the same climb test (full rich, hold 125 KIAS, record fuel flow at each 1000 ft) while keeping an eye on the A/F meter.

Yes, I'd be glad to do so! That is, when I can given Chicago weather and holidays!

But let me say this: I think it's important to not lose sight of what's important here, which is not to dismay at what may be some not perfectly ideal behavior, but rather (IMHO) is the vast advantage of leaning with A/F ratio as opposed to the arcane peak EGT plus offset hunting!

Reinhard

 

[N49ex]

Interesting.

You have an EX-5 servo?

Plot below is density vs GPH (in effect, weight vs weight) for an AFP FM200 on a 390, constant indicated airspeed climb, full rich. Fuel flow does not precisely track rho.

I'd be tickled if you ran the same climb test (full rich, hold 125 KIAS, record fuel flow at each 1000 ft) while keeping an eye on the A/F meter.

Just checked my engine build and I have a Precision Airmotive Silverhawk EX-5V A1 servo.

I can run the suggested test, but at full power there won't be any mixture control and tune to an A/F ratio, and divergence will be relevant only to that condition, not necessarily indicative of what the servo will do at other mixtures and fuel flows. So, in addition I'll do a climb at 75% power and a best power initial A/F ratio setting of 12.5, and see how that goes. Screen shots of the displays and data card should capture all.

Reinhard

 

[DanH]

... but rather (IMHO) is the vast advantage of leaning with A/F ratio as opposed to the arcane peak EGT plus offset hunting!

It's a preference brother. Glad you like it.

I see a significant advantage when leaning at full power per the thread title, but folks really don't do much of that.

 

[N49ex]

A/F ratio monitoring

Interesting.

You have an EX-5 servo?

Plot below is density vs GPH (in effect, weight vs weight) for an AFP FM200 on a 390, constant indicated airspeed climb, full rich. Fuel flow does not precisely track rho.

I'd be tickled if you ran the same climb test (full rich, hold 125 KIAS, record fuel flow at each 1000 ft) while keeping an eye on the A/F meter.

Flew two full rich climbs to 5K feet and a 75% best power and 65% lean of peak descent back down. See data attached. What I see is the fuel flow data follows your data fairly accurately; The A/F ratio does drop slightly in the climbs, but I'm not sure what the relevance is (I was taught full power climb always full rich anyway), except I can imagine at higher altitudes when reaching 75% power to then lean accordingly. I suppose one could make a table of permissible A/F ratios between 100% and 75% power and lean accordingly to get maximum performance while maintaining detonation margin.

The 75% best power and 65% lean of peak descents do show some slight variation in A/F ratio as well, but once again, if you have A/F monitoring it's a simple quick adjustment to one number (best power ratio or lean of peak at =< 65% power), and you are done and operating optimally.

 

[DanH]

Flew two full rich climbs to 5K feet and a 75% best power and 65% lean of peak descent back down. See data attached. What I see is the fuel flow data follows your data fairly accurately.

Good. The AFP and Precision servos should meter in a similar manner, They operate on the same principles, regardless of their physical differences.

The A/F ratio does drop slightly in the climbs, but I'm not sure what the relevance is (I was taught full power climb always full rich anyway), except I can imagine at higher altitudes when reaching 75% power to then lean accordingly.

I start leaning much earlier, and continue to lean at regular intervals all the way to cruise altitude, typically 8 to 11K. Target EGT method, really easy.

I suppose one could make a table of permissible A/F ratios between 100% and 75% power and lean accordingly to get maximum performance while maintaining detonation margin.

See "target EGT method", above. Same level of pilot participation as leaning to a specific A/F value.

 

[Kahuna]

FWIW,
Ive been leaning my 540 rv-8 with a big pull just after rotation for ~20 years and do my entire climbs to altitude LOP. A technique I picked up from the twin turbo Cirrus models. Take off, establish climb, big pull to FF, and continue.

In the turbo models, you need not deal with the mixture after the initial big pull as the wastegate is handling that workload for you. On my normalized 540, I keep leaning in the climb.

I would not have the patience for this in a 360 rv 2 seater as the reduced power in the climb would not sit well with me personally, but on the Super 8, there is enough spare power that reduced climb speeds are not enough to bother me. The reduction in fuel consumption over time is very noticeable. The difference is measured in gallons per fill up. Enough to make a material difference in my experience to be worth the trade off of speed vs FF in the climbs.

The only time I do not big pull on departure is when Im doing a zoom climb or I'm at gross 2300lbs full bag of fuel where I dont have the patience at that weight for the longer climb times so Ill climb at that weight ROP and I just don't look at the FF to keep my spirits up.

 

[lr172]

Flew two full rich climbs to 5K feet and a 75% best power and 65% lean of peak descent back down. See data attached. What I see is the fuel flow data follows your data fairly accurately; The A/F ratio does drop slightly in the climbs, but I'm not sure what the relevance is (I was taught full power climb always full rich anyway), except I can imagine at higher altitudes when reaching 75% power to then lean accordingly. I suppose one could make a table of permissible A/F ratios between 100% and 75% power and lean accordingly to get maximum performance while maintaining detonation margin.

The 75% best power and 65% lean of peak descents do show some slight variation in A/F ratio as well, but once again, if you have A/F monitoring it's a simple quick adjustment to one number (best power ratio or lean of peak at =< 65% power), and you are done and operating optimally.

Given you access to AF data, you should really do some research on fuel required and optimum AF ratio. An AF of 10 is crazy rich. Even guys running 15 PSI of boost don't go that rich. If you lean that to 12 or 12.5, you would save a ton of fuel and actually see your horsepower go up and still have significant detonation margin, assuming your timing is fixed at 25*. My porsche engine is air cooled and remarkably similar to a lyc boxer engine. I run 8 PSI of boost and never go richer than 12, even WOT at torque peak.

 

[N49ex]

A/F ratio monitoring

Good. The AFP and Precision servos should meter in a similar manner, They operate on the same principles, regardless of their physical differences.



I start leaning much earlier, and continue to lean at regular intervals all the way to cruise altitude, typically 8 to 11K. Target EGT method, really easy.



See "target EGT method", above. Same level of pilot participation as leaning to a specific A/F value.

Agree. When I said "full power climb always full rich" I really meant just initial climb, particularly off our field which is only at 700 feet. I also start leaning pretty soon, it's just that I do it with A/F numbers. And if it's going to be a best power flight, it's a single tune to A/F of 12.5, with maybe a single tweak at cruise altitude.

But I still don't agree that the EGT method is just as simple. EGT is a only a proxy for mixture. And it's not necessarily consistent. That's why the generally prescribed leaning method has you first finding the peak, then backing off, or going beyond for lean of peak. More operations - A/F is final (of course you ave to be able to trust it!).

 

[N49ex]

A/F ratio monitoring

Given you access to AF data, you should really do some research on fuel required and optimum AF ratio. An AF of 10 is crazy rich. Even guys running 15 PSI of boost don't go that rich. If you lean that to 12 or 12.5, you would save a ton of fuel and actually see your horsepower go up and still have significant detonation margin, assuming your timing is fixed at 25*. My porsche engine is air cooled and remarkably similar to a lyc boxer engine. I run 8 PSI of boost and never go richer than 12, even WOT at torque peak.

Agree that 10 is really rich. Those numbers were that way because I ran the test that Dan asked for, and at full rich that's what the servo does (and it is set up per the manufacturer's specs). So Yes, I do lean some from the get go, but not much. Maybe I should do more per what you say, but for the time being, the fuel flow numbers are governing and are right on the numbers for the engine per Lyc. for full rich take off, and if the A/F shows 10.x, so be it.

 

[DanH]

But I still don't agree that the EGT method is just as simple.

Adjust the blue knob to set a single number on the panel...same for target EGT or A/F ratio.

EGT is a only a proxy for mixture.

Oui, yes, ja, and si are all the same affirmative response. Here A/F is your preferred language. Another speaker may prefer to express best power mixture as 0.08. He too would be correct.

 

[lr172]

A the fuel flow numbers are governing and are right on the numbers for the engine per Lyc. for full rich take off, and if the A/F shows 10.x, so be it.

Not pushing here, as we each must be comfortable with how we run these engines. However, the Lyc numbers are very conservative because they are a least common denominator approach and designed to avoid damage at all cost and not necessarily the best way to maximize engine performance and 10.5:1 is a good place for that objective, as it can deal with A LOT of issues and not detonate or overheat. You have all sorts of instruments to protect yourself, so in a position to seek optimal without risk. I also tend to run full rich from TO to 1K' AGL, as it is a place I have no desire for issues. However, once at 1K, I go for max power. I have no AFR, so use about 150 ROP, which I speculate is around 12:1. Lyc says best power is around 100 ROP and guess that is 12.5-13:1

 

[N49ex]

A/F ratio monitoring

I also tend to run full rich from TO to 1K' AGL, as it is a place I have no desire for issues. However, once at 1K, I go for max power. I have no AFR, so use about 150 ROP, which I speculate is around 12:1. Lyc says best power is around 100 ROP and guess that is 12.5-13:1

Yes, that's pretty much the same as I do, just with the A/F number 12.5.

Just for curiosity, when you say you use 150 ROP, do you first find peak, or just (always) adjust to a pre-determined (same) EGT number? Dan implies he tunes to a single pre-determined EGT number, and therefore it's as simple as tuning to an A/F number. But that runs contrary to my experience that peak EGT is condition dependant and is not always the same. And then why would Garmin EIS (and others) have the peak find feature?

 

[rv6ejguy]

Peak EGT isn't always the same, many variables here and anything away from peak is a guess as far as a comparison to AFR.

 

[DanH]

Dan implies he tunes to a single pre-determined EGT number, and therefore it's as simple as tuning to an A/F number. But that runs contrary to my experience that peak EGT is condition dependant and is not always the same. And then why would Garmin EIS (and others) have the peak find feature?

The target EGT method of climb leaning does not reference peak. Simply note EGT immediately after liftoff near sea level. Lean in the climb to maintain that value. Is it 12/1, or 12.2/1, or 12.6/1? I don't care. Makes no practical difference. The power curve is very flat in this region.

Arrive at cruise altitude, push over, leave the knobs alone until speed picks up. Stay WOT, adjust RPM to 2400 or maybe 2450, pull FF into the 9's. Let it settle a few minutes.

Fine adjustment only requires knowing which cylinder is typically the richest. Move the knob. Did Mr Rich go up or down? If up, lean a little more. If down, richen a little. If it doesn't move, it was already at peak, and the others are LOP. Done.

 

[lr172]

Yes, that's pretty much the same as I do, just with the A/F number 12.5.

Just for curiosity, when you say you use 150 ROP, do you first find peak, or just (always) adjust to a pre-determined (same) EGT number? Dan implies he tunes to a single pre-determined EGT number, and therefore it's as simple as tuning to an A/F number. But that runs contrary to my experience that peak EGT is condition dependant and is not always the same. And then why would Garmin EIS (and others) have the peak find feature?

I have done a lot of observation over the years and have a pretty solid understanding of where the EGT will go in various cases on my engine. Assuming that advance is kept constant, the EGT absolutes are quite consistent. Therefore I adjust mixture to a combo of fuel flow speed and EGT. If you have an advance table that is shifting, like many EIs do, then more caution must be exercised, as advancing or retarding ignition WILL move the EGT by a meaningful amount.

 

[lr172]

Peak EGT isn't always the same, many variables here and anything away from peak is a guess as far as a comparison to AFR.

I don't disagree with that. However, Lyc tells us that these engines produce max power at 80-100 ROP. Max power is typically in 12.5 range for an avg engine, so just work off the loose assumption that 100 ROP is in the neighborhood of 12.5. Obviously lots of variables in play that keep this from an accurate figure. Best I can do without a dyno.