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Basic Pattern Work Leaning Techniques

iaw4

Well Known Member
This is not about leaning on long cross-country flights (LoP and RoP), but on pattern work.

We are having a bit of an argument here. we have a lycoming 180hp in a vans rv6a. one mag, one elec. ignition.

we fly out of KWHP in SoCal, very dry, typical temperature about 90 degrees Fahrenheit. the runway is 4000' long at 1000' altitude. our airplane has no problem climbing (and outclimbing other airplanes).

our question thus is about what is best for our engine.

A. my son is adamant that the cookbook rule says that we should be full rich on takeoff, climbout, and landing. thus, in the pattern, we barely get off full rich settings. when we fly an hour, we are at full rich about 45 minute of the time.

B. my view was that this seemed not only wasteful but also not so good for the engine (and spark plugs and pocket book). I would fly with half rich only, because the engine to me would seem just as smooth if not smoother than with mixture full rich. I would leave it at half-rich during the entire hour and not even tinker with it.

what's right?

sincerely,

/iaw
 
A is most correct. Lean for taxi, rich for takeoff, and pattern work, as well as landing. Above 3000 - 5000’ leaning is OK.

Lycoming is of the opinion that below 75% power, do whatever you want with the mixture.

B is a bit strange because I honestly don’t know what “half rich” means. Do you mean halfway between full rich and full lean? If so, especially at high power settings, I’d have concerns about detonation.
 
I would suggest a standard operating procedure that best handles as many situations/conditions as possible. Repeating such practices establishes 'muscle memory' which will serve you well when bad things happen. For example, if one were to always use a procedure where take off was performed with the mixture (full) rich you might end up being very surprised during your first high density altitude take-off (and if you've never experienced this, leaning will probably be the last thing you will think of doing).

Of course, such practices require some degree of understanding - you can mess up your engine. There is no doubt that following manufacturer recommendations is good - particularly when one does not understand the reasons behind it. However; it is also useful to understand that many recommendations are for majority of the users (weekend GA pilots (operating near sea level), in this case) and they just want to keep it simple.

I have no data to support this (only observations) but I believe proper leaning at all stages of operation (including taxi) reduces the possibility of stuck valves. This is particularly true for those of us that are based at higher elevations and/or operate a high density altitudes (5,000' MSL and 7,000-10,000' DA, for me).
 
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Leaning is a factor of density altitude. With the information you provided: a standard pressure 29.92, field elevation at 1,000 feet and 90F your density altitude is 3,100 ft. So you’re above 3,000 feet density altitude which Lycoming would recommend leaning the engine. I’d say your son is quoting the CFI that did his primary training of don’t touch the mixture while in the traffic pattern, law of primacy and a safety factor of preventing inadvertent engine shutdown isn’t a bad idea either for those that are not as experienced.

Good luck with the debate!
 
It depends...

In my RV-9A, carbureted O-320, magnetos, I can hear the RPMs increase on downwind when I lean a little. Sometimes the engine is a little rough and leaning it smooths it out. (My carb is adjusted for extra rich for summertime cooling.) And when the mag drop gets high, I know it's because lead fouling is starting to occur, meaning that the mixture has been too rich. I've never heard of leaning as a prevention for stuck valves.

The only reason that I know of for rich on final is in case of a go around, everything is ready. (Carb heat being the exception, except in the UK where carb heat is removed on short final.) On the other hand, when I lived at high altitude, the maximum power setting for takeoff and go around was with mixture leaned a bit, even if this meant that you didn't have the cooling of extra rich that you did at sea level -- a tradeoff between power you probably needed and cooling that you could get with extra airspeed and a shallower climb.

Personally, I tend not to trust generalized instructions that say, "do this!" and don't give any explanation. I've found that sometimes people who lay down absolute edicts are satisfying a need for certainty whereas my nature is to try to understand everything.
 
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This is from the certified world, so take it for what it's worth, but a C172S has a 180 hp Lycoming IO360 and the POH for that airplane says lean for taxi as appropriate, then go full rich for takeoff below 3000' pressure altitude. Above 3000' Pressure Altitude, lean for takeoff.

I have no data to back this up, but my opinion is that Cessna probably put it in the checklist that way so that people don't ballpark it with the red knob and then get fuel starvation on the takeoff roll or spike their CHT's on climb out.

You mentioned leaning for "half rich." I'm assuming means that you pull the mixture knob about 1/2 way out and call it good. The problem I see with this is that if the density alt changes, then what works one day may not work exactly the same the next day.

For example, you may find a mixture knob position that works great today, but tomorrow is 20 degrees cooler and a high pressure area has moved in, that same mixture position will now be quite a bit leaner.

Going back to the Cessna example, The POH for that airplane says if you're going to lean for takeoff, the process is to lean for max power during a full throttle static runup.

If you're set on wanting lean for pattern work, at least that way you won't get any surprises on the takeoff roll and you can leave it there for the duration of your pattern ops as long as CHT's don't get too high.

If that's too much hassle, the short answer is that yeah, you're running rich in pattern ops in the situation you described, but not rich enough to hurt anything.
 
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Good point Terry - I was assuming the very good instrumentation that our RV's tend to have (and know how to use it). However; assumptions... well, you know... :(
 
I'm not sure why there isn't a choice C. I don't really think A and B cover it all that well. I agree with the commenters about muscle memory and keeping procedures. I also want what's best for my engine.

Personally, for me this means:

1) Full power and mixture full rich for takeoff (unless at high density altitudes)
2) Power back when turning crosswind/downwind. Reduce mixture at that time.
3) Prepare for landing/go around. (i.e. Mixture Full Rich, boost pump on, etc)
4) Post-Landing (boost pump off...)

I don't believe it's critical to force every pilot to do these things at precisely the same time. I personally don't go full rich on landing until I turn final. That helps save the plugs, but gives me the rich mixture where it's needed...for go-around.

If you're doing Touch-n-go's then of course, leave the full rich mixture in, but if you're doing full stop, the first thing I do once I'm slowed down is pull the mixture back to absolute minimum fuel flow. You want it so far back that your engine won't even be able to make lots of power.

So there's a balance between saving the plugs and safety of operations. Building the habit is important, but you're not simply being safer if you leave the mixture full rich. You're loading the plugs which may in fact give you more risk. There is a lot of monkey movement during a complete pattern, but I think it's important to just develop it into habit. If you try to cut corners by cutting off steps since you're "only in the pattern" that isn't going to help you out in the long run.

I would also not blindly just leave the mixture back for all ops. That's not building good habit, and depending on your DA, it could give you engine problems. Perhaps if you were flying out of higher elevation airports you may never go "full rich" but other than that, I think this is just plain being lazy.

I know some people will disagree with going full rich after the turn to final, as well, but there is no magic about doing it when abeam the numbers or at any other point. What's important is that you get it done for when you need it, and building good habits so that it becomes reliable.
 
I don’t know much but the problem is too much pattern work without a nice lean and long burn not really full rich. I think regardless of your operations in the pattern too much of it without a nice higher altitude leaned out max operation Is going to result in gunk. JMHO YMMV
 
I'm not sure why there isn't a choice C. I don't really think A and B cover it all that well. I agree with the commenters about muscle memory and keeping procedures. I also want what's best for my engine.

Personally, for me this means:

1) Full power and mixture full rich for takeoff (unless at high density altitudes)
2) Power back when turning crosswind/downwind. Reduce mixture at that time.
3) Prepare for landing/go around. (i.e. Mixture Full Rich, boost pump on, etc)
4) Post-Landing (boost pump off...)

I don't believe it's critical to force every pilot to do these things at precisely the same time. I personally don't go full rich on landing until I turn final. That helps save the plugs, but gives me the rich mixture where it's needed...for go-around.

If you're doing Touch-n-go's then of course, leave the full rich mixture in, but if you're doing full stop, the first thing I do once I'm slowed down is pull the mixture back to absolute minimum fuel flow. You want it so far back that your engine won't even be able to make lots of power.

So there's a balance between saving the plugs and safety of operations. Building the habit is important, but you're not simply being safer if you leave the mixture full rich. You're loading the plugs which may in fact give you more risk. There is a lot of monkey movement during a complete pattern, but I think it's important to just develop it into habit. If you try to cut corners by cutting off steps since you're "only in the pattern" that isn't going to help you out in the long run.

I would also not blindly just leave the mixture back for all ops. That's not building good habit, and depending on your DA, it could give you engine problems. Perhaps if you were flying out of higher elevation airports you may never go "full rich" but other than that, I think this is just plain being lazy.

I know some people will disagree with going full rich after the turn to final, as well, but there is no magic about doing it when abeam the numbers or at any other point. What's important is that you get it done for when you need it, and building good habits so that it becomes reliable.

This is essentially my practice. As I pull power back, mixture comes back also as soon as I hit 65%. This is usually on crosswind leg. Muscle memory tells me how far back to pull the red knob. Mixture stays lean until final when carb heat comes off as well so I am set up for go-around. Mixture gets leaned again as soon as I clear the runway for taxi back.

Chris
 
Leaning in Pattern

This is not about leaning on long cross-country flights (LoP and RoP), but on pattern work.

We are having a bit of an argument here. we have a lycoming 180hp in a vans rv6a. one mag, one elec. ignition.

we fly out of KWHP in SoCal, very dry, typical temperature about 90 degrees Fahrenheit. the runway is 4000' long at 1000' altitude. our airplane has no problem climbing (and outclimbing other airplanes).

our question thus is about what is best for our engine.

A. my son is adamant that the cookbook rule says that we should be full rich on takeoff, climbout, and landing. thus, in the pattern, we barely get off full rich settings. when we fly an hour, we are at full rich about 45 minute of the time.

B. my view was that this seemed not only wasteful but also not so good for the engine (and spark plugs and pocket book). I would fly with half rich only, because the engine to me would seem just as smooth if not smoother than with mixture full rich. I would leave it at half-rich during the entire hour and not even tinker with it.

what's right?

sincerely,

/iaw

I find that in my RV-8 that when I'm doing pattern work I actually spend such little time at full throttle that there really isn't much time or benefit to leaning the engine. For me, it's full power to ~ 900' agl then simultaneously lower the nose and pull lot's of power off (usually combined with beginning the cross wind turn) to level at 1000' agl and keep the speed at 85-90 KIAS. It seems like I practically have to pull the power to idle (10" Hg actually) to keep the speed down while in level flight in the pattern. I don't see much benefit to leaning in this scenario or needlessly adding to the pilots workload when his eyes should be out the window looking for traffic.

Skylor
 
In the pattern (in my Mooney), my practice is to lean aggressively during taxi, take off at full rich (low DA) or leaned rich of peak if DA is >3000'. At pattern altitude the power comes back to whatever I need to maintain my pattern speed (depends on traffic). In general the pattern is so quick leaning is just one more thing to distract me. On landing, I lean for taxi as soon as I exit the runway.

As for the mention above about leaning and valve sticking, it's known that at lower temperatures, the reaction between ethylene dibromide (a reducing agent used as a lead oxide scavenger included in 100LL) and lead oxide (product of combustion of tetraethyl lead) is inhibited, allowing lead oxide deposits to accumulate on spark plugs and the relatively cool exhaust valve stems. These deposits on the valve stems can lead to valve sticking, or corrosion of the stems, which can also cause sticking. citation at Shell

Also, Mike Busch, a strong advocate of lean of peak operations if there ever was one, has been recently discussing the issue of low temperature operation on the lean side of peak and suggesting low CHT limits as well as high limits to help reduce the fouling potential.

On cross country flights (I know you didn't ask :) ) I do not reduce power until I am at the top of climb (the engine is rated for 100% power all day, and it never makes 100% power unless I'm at sea level). On the way up I lean every 1000' of climb, staying on the rich side of peak, until I level off and get to my cruise speed and configuration. Then it's wide open throttle, lean of peak in cruise.
 
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+1 for not leaning in the pattern. I don't normally start leaning until over 3K' after a cruise climb has been started (usually past the Newhall Pass).

Laird
RV6 0-360/CS 1800hrs
KWHP
HH24 (I'm almost always there on weekends. Feel free to stop and chat if you like)
 
I still don't understand why Lycoming regards 3000' as the magic number. When I think of full rich I think of that as a sea level/standard performance requirement.
Maybe I'm wrong though. When I flew at sea level it was always full rich but I was taught to lean as I climb as well. Where I fly now it is always a lean during runup operation.
 
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