Leaning in High DA

[bstratt]

Question on leaning when you have a fuel injected engine with CS prop. During the ground run up in order to set take off mixture, if you have the prop control full forward, would you lean to max RPM as if you had a fixed pitch? If not is there another way or is it just by guess and ear?

 

[bbchien]

There's no science to this, really. Best RPM plus a smidge rich. You can't hurt the engine much at ABQ, it's topped out at about 80% power in WINTER. FLG is 70%. Tusayan is about 70%. And on and on.

Remember to fly it by the ASI.

 

[Dave Krall CFII]

Question on leaning when you have a fuel injected engine with CS prop. During the ground run up in order to set take off mixture, if you have the prop control full forward, would you lean to max RPM as if you had a fixed pitch? If not is there another way or is it just by guess and ear?

Assuming your TACH is accurate, what could be better than running it up to MAX rpm at the run-up area at a small angle to the runway (or on it) with full climb prop and takeoff configuration, then enrichen just a tad, and let it roll right into the takeoff roll with the best it's got already cranking?

 

[poadeleted20]

CS prop, folks -- can't "lean to best RPM." Lycoming has very specific recommendations for takeoff with a FI/CS/high DA combination:

"[For a] direct drive normally aspirated engine with a prop governor but without a fuel flow gage, set throttle at full power and lean mixture at maximum RPM with smooth operation of the engine as a deciding factor. ... With fuel injection, if the powerplant has a marked fuel flow gage, then set mixture in accordance with instructions on the fuel flow gage and/or in accordance with the airplane Pilot’s Operating Handbook."

See this article for details.

 

[gismo]

CS prop, folks -- can't "lean to best RPM."

But many aircraft with CS props cannot achieve full RPM statically at least at low DA. If this is also true at higher DA, then leaning to peak RPM (and maybe enrichening a bit for cyl temps) while holding on the ground should work. Does anyone know if NA engines get higher or lower static RPM at high DA? I'd think the static RPM would be lower in thinner air, but that would depend on whether the effect of air density on the prop's load exceeds the effect on the engine's performance.

 

[bstratt]

CS prop, folks -- can't "lean to best RPM." Lycoming has very specific recommendations for takeoff with a FI/CS/high DA combination:

"[For a] direct drive normally aspirated engine with a prop governor but without a fuel flow gage, set throttle at full power and lean mixture at maximum RPM with smooth operation of the engine as a deciding factor. ... With fuel injection, if the powerplant has a marked fuel flow gage, then set mixture in accordance with instructions on the fuel flow gage and/or in accordance with the airplane Pilot’s Operating Handbook."

See this article for details.

I'll have to go over to the hangar and check the manual in the plane. My owner's handbook just says to lean as necessary. I do have a fuel flow meter and it is marked, at least in GPH. I know the "book" fuel flows for the various power ratings, e.g. 75% -10.2gph, 65% - 9.2gph, 55% - 8.2 gph. So, would I work backwards by going full throttle, reading the manifold pressure, backing into an estimation of % power and then setting the mixture for a slightly richer fuel flow?

 

[poadeleted20]

But many aircraft with CS props cannot achieve full RPM statically at least at low DA.

Except in cases of old mechanical tachs that are reading low, I've never seen this. Yes, it's not a good idea to do full throttle static runs as you tend to pick up stuff and nick props and bellies, but I've never seen a CS prop plane that wouldn't turn rated RPM on a static run-up (whether the tach properly indicated it or not).

 

[poadeleted20]

I'll have to go over to the hangar and check the manual in the plane. My owner's handbook just says to lean as necessary. I do have a fuel flow meter and it is marked, at least in GPH. I know the "book" fuel flows for the various power ratings, e.g. 75% -10.2gph, 65% - 9.2gph, 55% - 8.2 gph. So, would I work backwards by going full throttle, reading the manifold pressure, backing into an estimation of % power and then setting the mixture for a slightly richer fuel flow?

Better yet, contact Lycoming and get the Operator's Manual for your engine (same book for all O-360-series including your IO-360-C1C6 and my O-360-A4K, which is why I have the right one), and consult the graph on page 3-37 to get power output at full throttle at altitude, and then the graph on page 3-22 to get fuel flow for the power output (use the "best power" lines). Going through that, I get:

5000 - 25"/2700 - 169 HP - 81 pph/13.5 gph
6000 - 24"/2700 - 160 HP - 78 pph/13 gph
7000 - 23"/2700 - 151 HP - 75 pph/12.5 gph
8000 - 22"/2700 - 142 HP - 72 pph/12 gph

Note that these are all "standard day" -- for non-standard temperature, you'd have to go back in the book and recalculate, but it won't change a whole lot.

 

[Dave Siciliano]

Well, my P-Baron won't get full rpm until running down the runway. Confirmed that this is normal with two different shops. I get 2650 static, then, another 50 or so within a couple hundred feet when heading down the runway. I've also chatted about this with a couple owners who confirmed that's how theirs runs.

Best,

Dave

 

[Tom-D]

Any one ever consider that the VSI is your best power meter while wide open throttle in a climb.

why not lean IAW best climb rate?

 

[bstratt]

Better yet, contact Lycoming and get the Operator's Manual for your engine (same book for all O-360-series including your IO-360-C1C6 and my O-360-A4K, which is why I have the right one), and consult the graph on page 3-37 to get power output at full throttle at altitude, and then the graph on page 3-22 to get fuel flow for the power output (use the "best power" lines). Going through that, I get:

5000 - 25"/2700 - 169 HP - 81 pph/13.5 gph
6000 - 24"/2700 - 160 HP - 78 pph/13 gph
7000 - 23"/2700 - 151 HP - 75 pph/12.5 gph
8000 - 22"/2700 - 142 HP - 72 pph/12 gph

Note that these are all "standard day" -- for non-standard temperature, you'd have to go back in the book and recalculate, but it won't change a whole lot.

Don't know why I didn't think of that. Talk about overlooking the obvious!

Thanks. I just ordered one.

 

[jesse]

Any one ever consider that the VSI is your best power meter while wide open throttle in a climb.

why not lean IAW best climb rate?

Not sure how well that would work considering the several second delay of the VSI along with updrafts and downdrafts constantly causing it to fluctuate

 

[Dave Krall CFII]

Any one ever consider that the VSI is your best power meter while wide open throttle in a climb.

why not lean IAW best climb rate?

Maybe in stable conditions, after runway/departure obstacles have been safely cleared, and with patience?

 

[gismo]

Any one ever consider that the VSI is your best power meter while wide open throttle in a climb.

why not lean IAW best climb rate?

Cause a properly adjusted VSI reads zero while you are rolling down the runway hoping for enought speed to take off. The whole idea of leaning for takeoff is to give you max power from the start of the takeoff roll.

BTW one method that works pretty well is to lean to best power (airspeed) at pattern altitude before landing and going back there (plus a smidgen more towards rich) for takeoff. This is assuming you arrive and depart under similar conditions.

 

[Tom-D]

If you are going to lean for take off and are running a constant speed prop, you best employ a EGT gauge.

But if you have a fixed pitch prop you can see best power by leaning to highest RPM. Highest RPM is the maximum horse power you can get, and it will show on the VSI while climbing at wide open throttle.

this is how the Fairchild with 165 horses can cross the rockies at 14,300'

 

[poadeleted20]

If you are going to lean for take off and are running a constant speed prop, you best employ a EGT gauge.

EGT is not your best idea unless you have a perfectly tuned GAMijected engine, because different cylinders will hit best power at different mixture control knob positions, and you don't know what combination of sub-optimal cylinder settings will provide the best power. I strongly recommend sticking with the Lycoming recommendation (which is equally valid for Continental engines) for non-turbo'd CS prop/FI installations unless you have one of the few airplanes where you can't get full RPM on a static run-up, in which case leaning to max RPM is your best course for a high DA takeoff.

 

[Let'sgoflying!]

Does anyone know if NA engines get higher or lower static RPM at high DA?

I am routinely at 7000'da and when I wind it up (IO520K) (almost at static, its just starting to roll) I get 2800rpm, then when breaking ground it gets to rated 2850rpm. I don't think it has been more than 25rpm different if at all, near sea level.

PS I have been leaning to approximately 200-250 ROP; I guess 'P' based on altitude and past experiences with "all forward leaning", adjust during the roll and takeoff and watch CHTs stay below 380-390. If CHTs get to 390, I pitch over slightly and enrichen 50 EGT degrees. I think this was an Ada recommendation that I picked up and I think it is one of the best.

 

[Tom-D]

EGT is not your best idea unless you have a perfectly tuned GAMijected engine, because different cylinders will hit best power at different mixture control knob positions, and you don't know what combination of sub-optimal cylinder settings will provide the best power. I strongly recommend sticking with the Lycoming recommendation (which is equally valid for Continental engines) for non-turbo'd CS prop/FI installations unless you have one of the few airplanes where you can't get full RPM on a static run-up, in which case leaning to max RPM is your best course for a high DA takeoff.

One would assume that who ever installed the EGT would have placed the probe in the leanest cylinder, in fact the installation instructions will tell you what cylinder in your engine will be the leanest.

based upon that, the leanest cylinder will peak first, and you end up with the rest of the set on the rich side of that setting, and it will require a torquemeter to squeek that last bit of horse power out of any engine..

With GAMI's the theory is they all peak at once, That's what they advertise anyway.

 

[Tom-D]

Cessna has for many years placed the instructions for leaning their engines in the POH, it basically said pull the mixture knob to lean untill the engine skips/runs rough. then richen until it runs smooth again.

What does this really do?

In the 0-320 series runing the MA3 SPA carb it simply restricts the fuel flow from the float bowl to the venturi until the engine does not recieve enough fuel to fire the leanest cylinder. This is known as a lean misfire not detonation and that is what you feel as a vibration, that one cylinder misfiring.

At this position all cylinders in the engine are way lean of peak. When you richen the mixture just enough to make it run smooth you are still lean of peak. and that is how we have been running the Cessnas for years with no problems.

In fact when we think we have a fouled spark plug we lean until we loose RPM and wait until it clears. What have we just done?

We have run lean of peak to clean up the combustion chamber and burn off the lead fouling the plug.

Remember, peak is the mixture that will create the hottest flame in the combustion process, thus when we run lean of peak we can not harm the engine by removing more fuel, it'll simply cool until it quits firing the cylinders, but when we run rich of peak we can harm the engine by reducing the RPM by loading the engine with prop pitch which slows the piston speed to the point we will cause detonation by high cylinder pressures.

That is what we termed OVER SQUARE, to a point that will cause harm to your engine.

and to add,

nowhere in the POH will it say get out your ink marker and mark the mixture knob.

 

[midlifeflyer]

Question on leaning when you have a fuel injected engine with CS prop. During the ground run up in order to set take off mixture, if you have the prop control full forward, would you lean to max RPM as if you had a fixed pitch? If not is there another way or is it just by guess and ear?

Depends. What leaning method are you using? If you are leaning at run-up RPM rather than full power, then yes, the method is the same. At run-up power, you don't have enough MP to let the prop maintain RPM and it will act, for leaning purposes, the same as a fixed pitch prop. (BTW, that assumes you use and understand the run-up power leaning method; it's =not= a recomendationto lean for best RPM at runup and leave it there)

But for leaning at full power (or verifying what your run-up leaning told you), you will need to use another method. In the absence of fuel flow targets or the like, you go back to the same method you probably used in a primary trainer with no EGT for leaning at altitude - lead not engine roughness and enrichen to smooth it out.

 

[poadeleted20]

One would assume that who ever installed the EGT would have placed the probe in the leanest cylinder, in fact the installation instructions will tell you what cylinder in your engine will be the leanest.

Since the leanest cylinder varies with atmospheric conditions and power settings, that's not a sure thing. In addition, experience has demonstrated that even for the same aircraft type, the leanest cylinder may vary between airplanes (e.g., not all Tigers have the same leanest cylinder under the same conditions). For those reasons, I'll stick with the Lycoming recommendations and lean using the best available indication of actual power production, which EGT (especially on a single cylinder) is not.

 

[Dave Siciliano]

I have a graphic engine monitor and down load historic data to review on my plane. As Ron said, with different power settings, I have different cylinders peak at different times; therefore, when I did my GAMI lean test, I performed it at the power setting I would use most often.

Using the lean of lean feature on the JPI, I can watch each cylinder peak as I pull back the mixture.

I sure wouldn't rely on putting the EGT probe at what someone states should be the leanest cylinder without measurement.

The P-Baron POH says to lean using TIT, which was great before the graphic engine monitors were available; there are much more precise measurements now. TIT in my plane can be used to lean on the ground, but if you run that power setting long, you'll be frying cylinders in my plane.

Best,

Dave

 

[gismo]

One would assume that who ever installed the EGT would have placed the probe in the leanest cylinder, in fact the installation instructions will tell you what cylinder in your engine will be the leanest.

based upon that, the leanest cylinder will peak first, and you end up with the rest of the set on the rich side of that setting, and it will require a torquemeter to squeek that last bit of horse power out of any engine..

With GAMI's the theory is they all peak at once, That's what they advertise anyway.

Trouble is the first cylinder to peak usually varries with conditions. But if they are all reasonably close to each other, running 200 ROP ought to be plenty rich on the leanest cylinder above 6000-7000 DA. And given that the power vs mixture curve is pretty flat between 50 ROP and 200 ROP, the power will be close enough to max that any further adjustment would be a waste of time.

 

[Tom-D]

Trouble is the first cylinder to peak usually varries with conditions. But if they are all reasonably close to each other, running 200 ROP ought to be plenty rich on the leanest cylinder above 6000-7000 DA. And given that the power vs mixture curve is pretty flat between 50 ROP and 200 ROP, the power will be close enough to max that any further adjustment would be a waste of time.

the engine that runs so even as to switch leanest by conditions will be running so close it will not make a difference any way. I believe that the EGT instrument companies have completed enough testing to know what cylinder to place the prob in.

and your right get it within a couple hundred degrees of peak, you'll do fine.

Bimetalic probes are not pyrometers, but they will show the highest needle reading, and that is good enough. the gauges that are calibrated in 25 degree increments are a laugh, at least a pilot confidence thing, because when you think the instruments have no calibration requirements while installed, and the rusty old probes have been in the exhaust pipe since shep was a pup. how accurate can they be?

pull the mixture back until the highest read is found, push it in a little and release the brakes.

 

[Tom-D]

I sure wouldn't rely on putting the EGT probe at what someone states should be the leanest cylinder without measurement.

Dave

Do you belive JPI didn't do a lot of testing before they knew where to place the probe?

We don't just knock a hole and sticker in there.

 

[Tom-D]

Since the leanest cylinder varies with atmospheric conditions and power settings, that's not a sure thing. In addition, experience has demonstrated that even for the same aircraft type, the leanest cylinder may vary between airplanes (e.g., not all Tigers have the same leanest cylinder under the same conditions). For those reasons, I'll stick with the Lycoming recommendations and lean using the best available indication of actual power production, which EGT (especially on a single cylinder) is not.

The highest power setting you can get from any engine is wide open throttle, at sea level at temps off set to standard day. As I read the installation instructions for all the EGT gauges I have installed that is how the location of the probe is selected for single prob systems. Like it or not, accurate or not, we follow installation instructions, because the gauge manufacturer should know from testing where to place the probe.

""not all Tigers have the same leanest cylinder under the same conditions).""

Is that another reason for not liking Grumman? (unpredictable)

 

[Tom-D]

I would be interested to know from all who have engine monitoring systems how wide the temp. split is across their engines at full throttle. or how much the split is when advancing the power settings from one cylinder to another.

 

[poadeleted20]

the engine that runs so even as to switch leanest by conditions will be running so close it will not make a difference any way.

That is not my experience with instrumented engines.

I believe that the EGT instrument companies have completed enough testing to know what cylinder to place the prob in.

Unless they've tested every engine in every different airplane, that isn't likely.

and your right get it within a couple hundred degrees of peak, you'll do fine.

A couple of hundred degrees one way or the other can change power output dramatically.

pull the mixture back until the highest read is found, push it in a little and release the brakes.

That won't even get you close to best power, which is well on the rich side of peak.

I say again, stick with the engine manufacturer's recommendations, as I really do believe they know best how to get the most power out of their engines.

 

[poadeleted20]

I would be interested to know from all who have engine monitoring systems how wide the temp. split is across their engines at full throttle. or how much the split is when advancing the power settings from one cylinder to another.

I routinely see splits of 150 degrees at full throttle with full rich mixture. The splits usually close as you lean, to somewhere in the 40-80 degree range.

 

[Tom-D]

I routinely see splits of 150 degrees at full throttle with full rich mixture. The splits usually close as you lean, to somewhere in the 40-80 degree range.

Your split is why GAMIs were invented, but 40-80 degrees is a trifle at 1400+- EGT

To get the presice power setting you think you are getting, you would need a calibrated Torquemeter which I doubt you have.

If you really believe that best power is way rich of peak, you and Deakins need to have a talk.

 

[Tom-D]

That is not my experience with instrumented engines..

The testcell that I use with a dyno would prove you wrong, but that is why we don't test engine in the aircraft. too much variation in exhausts and intake filtering and baffeling.

Unless they've tested every engine in every different airplane, that isn't likely..

I bet they came close enought to that to know which cylinder is the leanest. and how far from the exhaust port to place the probe.

A couple of hundred degrees one way or the other can change power output dramatically..

From full rich to full lean on my test cell running the 0-300-A with a MA3SPA carb, fixed load, at full throttle I'll see a horse power change of about 4-6 horse power.

When I place a Too rich main jet (too rich to run with out leaning) from full rich stuttering engine, to best power I'll see a big change. but same engine, same run, best power to 50 lean of peak, I can't read the change on my gauge.

That won't even get you close to best power, which is well on the rich side of peak..

That is less true than you believe, try the airspeed test during flight and see how much you really gain.

I say again, stick with the engine manufacturer's recommendations, as I really do believe they know best how to get the most power out of their engines.

They have a cya thing to consider, we don't.

 

[poadeleted20]

If you really believe that best power is way rich of peak, you and Deakins need to have a talk.

If I'm wrong about that, so is Lycoming. See the chart attached.

 

[Tom-D]

If I'm wrong about that, so is Lycoming. See the chart attached.

Remember, Lycoming does not agree with Deakins on running lean of peak, with their engines. but the cessna POHs have been running the 0-320- 0-360 series lean of peak for decades.

I still contend that pulling the mixture back to gain best RPM as in the Cessna method, for fixed pitch props.

and the leaning to slightly rich of peak by the EGT is proper and prudent method of compensating for density altutude. and to get it any closer you will require instrumentation most PPL flyers don't have in their aircraft rented or owned.

 

[bstratt]

Hi Ron, the Lycoming manual came on the weekend and so I spent some time reading it - I don't know how you came up with those numbers you did from that chart. I think you'd have to be an engineer to figure out what you're supposed to do - I still can't figure out how to place 'A'!

Anyway, despite all those high tech charts, I found it interesting that the manuals instructions for taking off in high DA say that "if you experience roughness pull the mixture back until the engine smooths out". Very unscientific!

 

[Anthony]

Anyway, despite all those high tech charts, I found it interesting that the manuals instructions for taking off in high DA say that "if you experience roughness pull the mixture back until the engine smooths out". Very unscientific!

Being based at a field with an elevation of 5,500 ft. and going up from there, we can see very high DA's in the summer. I lean for best RPM when I do my runup and leave it there. The best RPM at full power is very close to the setting for runup, so with an 8,000 ft runway I'll just enrichen a bit. If its really high DA or at Leadville or shorter runway, I will do a full power lean. I want every potential HP I can get.