Please explain propeller rpm vs. altitude vs. ground speed?

Ever see/do Ladder programming? My head about came from together first time I had to work with those legacy based systems...
Or how about developing a nice modern PC based software configurator for a Safety Controller. We let our users draw lines to blocks, very intuitive. Customers love it. Fun software to develop too!!! But then we had to add equivalent ladder logic views to assist those who design/think that way...not my favorite "aside". But hey, now I know Ladder Logic extremely well and could probably hold my own programming a big Allen Bradley PLC.
 
Back on topic, if we can disregard the "Pilot Valve" or "Pilot's Value" part of the discussion for a bit ... is there something to leaning for best power by having the prop out just slightly and watching for the RPM drop?
 
The truth is, when you reduce power, you will see a small rpm drop and then the rpms will try and climb back to where they were. It is least noticeable at high power and most noticeable at lower powers. You often hear the argument that the rpms are dropping because it is "at the stops", but it will do it when not at the stops also. You can prove that it is not at the stops by turning the prop knob out a bit first to make sure you are NOT at the stops.

Notice I said that this rpm drop occurs when you reduce POWER. It will do it when you back off the throttle also (do it at less than full power so you can notice it). Leaning reduces power also. So it does it when you lean also.

Notice that when you lean to reduce power, you do NOT see a drop in manifold pressure.

The pilot valve puts this "lag" in rpm in the system so the pilot can lean the engine properly. Like all mechanical control systems the rpms hunt, lag and maybe overshoot etc. and that can be controlled to some extent. Good thing it does that so we pilots can lean to an rpm drop, then richen slightly so we know we are running at or very near max lean.
 
I just brought up the pilot valve to help people realize that the system is designed to work this way on purpose. Makeing that valve more restrictive causes more rpm drop, less restrictive, less rpm drop. So many pilots have been told that rpms don't drop at all due to power reduction with a constant speed prop--which isn't true. RPMs can and do drop even with constant speed prop and how much they drop is controlled by the size of the pilot valve.

If trying to understand the pilot valve confuses you, just ignore it. The important point is that the rpms drop when you lean and then you richen it back up to max rpm. Now you are running as lean as the engine can run and run smoothly. THAT needs to be understood.
 
Back on topic, if we can disregard the "Pilot Valve" or "Pilot's Value" part of the discussion for a bit ... is there something to leaning for best power by having the prop out just slightly and watching for the RPM drop?

Best power or best efficiency? Are you talking about ground leaning to remove the effects of being too rich on the ground at altitude, or in-flight leaning to remove the effects of being too rich in the air / get the best fuel economy?
 
The proper way to lean is to do so by watching EGT and CHT not some mysterious hiccough that one engine in the entire GA fleet has.
 
Best power or best efficiency? Are you talking about ground leaning to remove the effects of being too rich on the ground at altitude, or in-flight leaning to remove the effects of being too rich in the air / get the best fuel economy?
Density altitude ground leaning.
 
And if you don't truly understand what MP is (and I wouldn't blame you, since the FAA materials on this absolutely suck), go directly to this article and read it (do not pass go, do not collect $200 unless you blow it at the FBO): Manifold Pressure Sucks!

Man, that article was fantastic. Just added it to my CFI folder!
 
Man, that article was fantastic. Just added it to my CFI folder!
Ditto....well, except I'm not anywhere near being a CFI :) I'm only partway through it and feel like I'm learning all over again.
 
Density altitude ground leaning.

There’s no published “correct” method. (Welcome to Denver! Haha...)

For a carb’d 182 I’ll lean it at run-up RPM (1800 on mine) to peak, then turn my vernier mixture 1/2 turn richer. For the vast majority of takeoffs, that’s going to be fine. No need to get too fancy with it.

Because the carb at WOT is going to add more fuel than the mixture setting anyway. And all you’re going for with the half turn in, is protection against pre-ignition.

If I absolutely have to get peak performance, I’m probably up at KLXV and I’ll just set it to peak RPM at run-up power and do a final fine adjustment holding brakes on the runway to find the power drop off point and back rich enough to get peak MP while also watching the EGT. Only takes a second once practiced.

Fuel injected and other engines, different. Carb’d 182 is pretty simple.

But if I have calculated that I really need that close to peak performance, the numbers are really tight and I need to be thinking in terms of performance all the way down the runway with a chosen abort point if we don’t have the airspeed needed by that point.

Better to bail, stand on the brakes, and go fiddle with the mixture again or figure out if the headwind switched to a tailwind, or whatever factor has changed, or isn’t right, that caused the lack of airspeed to be what it should have been by a chosen abort point, than nurse it into the air and find it’s also underperforming aloft.

You’ll know you’re going to struggle when you see where the MP gauge ends up at WOT on a 70F day at KLXV. :)

Above 70F at KLXV is an absolute no-go for me, and CPA also teaches it. I wouldn’t even do it loaded more than about half of my usable load in the 182, and wouldn’t even launch in a Skyhawk.

Those are true peak performance moments. Launching from any of the 5,000’+ runway down in town on a hot day isn’t nearly as critical on the carb’d 182. Not for engine power, anyway. The aircraft climb performance will suck bad, and the CHTs will head for numbers you don’t like to see. Being slightly rich will also help with that.

I’d rather be slightly rich and smooth operation than burn everything up shooting for a perfect peak power configuration unless the circumstances really call for max performance by the numbers already calculated.
 
For a carb’d 182 I’ll lean it at run-up RPM (1800 on mine) to peak, then turn my vernier mixture 1/2 turn richer....
Okay, here comes the dummy questions as I only got like 2 sentences in and have two questions:

Q1.) In the sentence above when you say "to peak" do you mean the highest MP, highest RPM or EGT reading? We don't have a EGT gauge yet so hopefully there is a way to do this with MP/RPM???

Q2.) I don't recall our mixture knob being Vernier-able :confused:
 
Okay, here comes the dummy questions as I only got like 2 sentences in and have two questions:

Q1.) In the sentence above when you say "to peak" do you mean the highest MP, highest RPM or EGT reading? We don't have a EGT gauge yet so hopefully there is a way to do this with MP/RPM???

Q2.) I don't recall our mixture knob being Vernier-able :confused:

At a power setting that gives 1800 RPM you’re not in the governed range so it’ll act just like a non-adjustable prop. Then you just peak it. Personally I want to make sure I’m on the rich side of peak so I twist in after that.

A vernier mixture (or even prop and throttle if so equipped) control is twistable to tweak it in and out, instead of pushing the button and moving it. Twist right, it moves forward/rich, left/rearward/lean. But I think you knew that.

Yours may not be vernier. Then you just have to tweak it a little. For takeoff, a little too rich is better than a little too lean once you get it grossly set at run-up.

You’re not going to hurt it if you stay on the rich side of peak for takeoff.
 
So by "peak it" you mean the peak RPM right?

So it sounds like it goes like this then:

1.) A normal run up like setup (feet on brakes, clear of obtacles, prop full forward, mixture full rich)
2.) Push throttle in to obtain 1800rpm
3.) Pull the mixture out slowly and the RPM should rise (not sure how much?) and eventually fall back down again
4.) Push/Vernier the mixture back in to the location of highest RPM.
5.) Vernier/adjust mixture in just a bit more to be on the rich side.
6.) Keep track of where this setting is when returning to land since the mixture will be leaned even more during cruise.

...BTW, my main goal is to learn this from Miranda and her other instructor when we get to KRAP. But is nice to know what to expect. I do have a couple nice long runway options around here I can use to try out an actual takeoff after practicing this leaning. You can sense this flatlander is rather uncomfortable taking off with anything other than mixture full rich!

I think our 182P (1972) must be a bit different than other models. Our prop knob is black (not blue). And I don't recall the mixture being Verniered. A flight Friday or Saturday will answer that question.
 
So by "peak it" you mean the peak RPM right?

So it sounds like it goes like this then:

1.) A normal run up like setup (feet on brakes, clear of obtacles, prop full forward, mixture full rich)
2.) Push throttle in to obtain 1800rpm
I usually stop around 1700 since I know it's going to climb... it's going to easily come up 100 RPM on mine... YMMV.
3.) Pull the mixture out slowly and the RPM should rise (not sure how much?) and eventually fall back down again
As soon as it starts to fall, I'm done pulling and start pushing to go back to the peak.
4.) Push/Vernier the mixture back in to the location of highest RPM.
5.) Vernier/adjust mixture in just a bit more to be on the rich side.
6.) Keep track of where this setting is when returning to land since the mixture will be leaned even more during cruise.

Yeah, it doesn't change all that much (that you could see or measure easily anyway) from day to day, but it changes a little bit with season and temperature. Maybe 1/4" tops.

I also memorize "about where it was" for taxi, or count vernier turns after run-up but before takeoff if I have a looooooong taxi from the run-up area to the runway, since I want that engine leaned to the point of almost dying during long taxi ops.

...BTW, my main goal is to learn this from Miranda and her other instructor when we get to KRAP. But is nice to know what to expect. I do have a couple nice long runway options around here I can use to try out an actual takeoff after practicing this leaning. You can sense this flatlander is rather uncomfortable taking off with anything other than mixture full rich!

I think our 182P (1972) must be a bit different than other models. Our prop knob is black (not blue). And I don't recall the mixture being Verniered. A flight Friday or Saturday will answer that question.

You could still probably take off full rich... it really doesn't rob you of HUGE amounts of power until you get into hot summer days or really high airports...

You might also find, as we did, that memorizing that "approximate" spot for "peak plus a little rich" is also a great place to START the engine... you can play with it, but full rich on start on ours takes at least two more prop blades before it catches, whereas with the mixture back about 2", it fires much sooner. For start for me it's:
1. Lean about 2" back.
2. Two FULL shots of prime (our primer doesn't always fill completely... probably needs new o-rings) if cold. Nothing if warm/hot.
3. Crank...
4. After it catches, which will be nearly instantaneous when you find the happy mixture place for start, throttle to be around 800-ish. (It'll climb as it warms if it was cold, and also as you lean...)
5. Lean the hell out of it until it almost dies and won't let you add any more throttle without dying.
6. Finish whatever other cockpit junk you had to do on the checklist and it'll warm up a bit and you'll see it rise to 900-1000... if it goes above 1000... pull the throttle back a bit... Continental SB says 800+ for proper oil splash at idle... most carbs are set to allow it to idle much lower, of course... and many people don't know about that SB...
7. Mixture one or two twists in so it doesn't die to start moving and throttle to 1000-1200 max... unless you're on a hill, anything between those will work out to a "just fine" taxi speed, in ours anyway. You can experiment but I see plenty of folks goose the things up to 2000 to start rolling and then back down, and it's just unnecessary in the Skylane... it'll start rolling just fine on level ground with normal taxi power applied.
8. Lean AGAIN after you're rolling so it'll die if you try to go higher than 1200.

This "keep leaning it thing" was beat into my head by a 172RG that I flew A LOT that would immediately foul plugs if you didn't lean it correctly on the ground. I got in the habit and now it's exactly that, a habit... I don't even think about the steps anymore. I just lean the snot out of it on the ground. YMMV. It works for me. :)

The fuel-injected 172s and 182s... you can't (easily) be QUITE this aggressive... they tend to stall completely if you get too aggressive with it, leaving you sitting there coasting in taxi and needing a restart. hahaha... But you can lean decently in them for ground ops still... just don't do it so far or quickly until you know the particular airplane and what it likes.

Other aircraft... some like it, some don't... just depends on the engine and fuel-delivery systems. Turbo Seminole liked to be leaned on the ground, but definitely no leaning for power in that thing for takeoff, of course! Etc.
 
Thanks Nate!!!! Sorry about the confusion regarding RPM/MP/EGT

So I now have some lab work to go along with my home work :)

Actually, until you indicated the RPM rise that you see (eg +100RPM at peak) I wouldn't have had a clue whether it would rise 50rpm, 200rpm or even more. So at least I know what I am looking for. And perhaps down here at 1000msl I might not even see that much.

You also caught something that would have thrown me. I lean pretty aggressively after startup and taxi. So that means I'll learn the optimal mixture setting. Only to leave it while taxing and then restore it again prior to take off.

And your comment about startup is very intriguing. From the description of your engine start vs ours...they seem different. I am in the process of upgrading to a Concorde Battery which will turn it over faster than this Gil battery. Our A&P noted the Gil battery resting voltage is lower than the Concorde and said it will crank over quicker so that will be nice. And when I hot start I have the best luck actually pulling the mixture almost to cutoff and as soon as it starts I advance it to full rich. Maybe knowing this other point will help with cold and hot starts.

Great info!!!
 
Its "peak RPM" for that prop knob setting.

What you do is this. You climb up, now you level out. You use your throttle to select manifold pressure. You use your prop knob to select your rpm. Now you pull the mixture out and watch the tachometer. You will see a slight rpm drop when it goes "too lean". Then you richen slightly. You are now running as lean as possible, which is ok if you are at 65% power or below.

The reason you're seeing a slight drop could be for one of two reasons:

1) Your prop governor is lagging and needs to be overhauled.
2) You're leaning so far that you're dropping out of the governing range momentarily, meaning you're so lean that you're losing a LOT of power.

Best watch the EGT gauge down lower. You leaned it right through peak and so far into the other side it was below the power level needed to spin a very flat prop.

Bingo.

It's NOT because the prop is full flat. A pilot can prove that by having the prop knob out a bit when leaning.

There is NO WAY for the pilot to definitively know whether or not the prop is at the stops other than to drop the power low enough (via either throttle or mixture) that RPM drops, in which case you're at the flat stop.

You can have the prop knob full forward and be off the stops, or you can pull the prop back a little bit and be on the stops. Here are some examples:

1) You're on the runway, ready for takeoff but at idle so you're on the stop. You increase the throttle to full with the brakes on so you don't move, you'll develop just slightly less than full rated RPM in most instances. You're still on the stop. You let go of the brakes, and as the plane starts to move, the RPM will increase to the full value. *As soon as it hits full RPM*, if you keep accelerating, the prop will begin to increase pitch to maintain that full RPM. Your prop knob is still full forward, but the prop is no longer on the stop.

2) Do the same thing as above, except before brake release, pull the prop knob back just far enough that the RPM goes down. You're now off the stops. Pull the throttle back until the RPM drops more. Your prop is now at the flat stop even though your prop knob is not fully in.

(Note: This is a thought experiment... You don't have to actually do this, as you still don't have a "prop pitch gauge" or any other way to see whether you're actually on the stop except for knowing the systems. I take no responsibility for anything you do to your engine.)

What I described is what the propeller does. The valve that makes that happen is called the "pilot valve". If that didn't happen, we wouldnt be able to lean via rpm drop. And pilots can lean to rpm drop, thanks to the "pilot valve". Why do you think they call it the pilot valve?

What you described is your misunderstanding of the constant speed prop system. You can't lean to peak power via RPM drop in a plane with a constant speed prop unless the prop is at the stop, which you only know to be true if the plane is standing still on the ground, the prop knob is full forward, and you are developing less than full rated RPM.

Back on topic, if we can disregard the "Pilot Valve" or "Pilot's Value" part of the discussion for a bit ... is there something to leaning for best power by having the prop out just slightly and watching for the RPM drop?

No.

The truth is, when you reduce power, you will see a small rpm drop and then the rpms will try and climb back to where they were. It is least noticeable at high power and most noticeable at lower powers. You often hear the argument that the rpms are dropping because it is "at the stops", but it will do it when not at the stops also.

If you notice the prop dropping and returning to its previous RPM, either you have a problem with your prop governor, or your engine. The only time I have ever seen that behavior is when an engine started making a lot of metal, to the extent that there wasn't sufficient oil pressure for the prop governor to do its job as quickly as it should.

You can prove that it is not at the stops by turning the prop knob out a bit first to make sure you are NOT at the stops.

As explained above, just because the knob isn't full forward, doesn't mean you're not at the stops.

Notice I said that this rpm drop occurs when you reduce POWER. It will do it when you back off the throttle also (do it at less than full power so you can notice it). Leaning reduces power also. So it does it when you lean also.

And in both cases, you either have a problem with your prop governor (if it returns to the selected RPM without you increasing power or richening mixture), or you're dropping power so low that you're below the governing range (if the RPM stays low when you don't increase power/mixture).

Notice that when you lean to reduce power, you do NOT see a drop in manifold pressure.

Nor should you expect to. That doesn't mean that you're developing the same amount of power.

ALL THREE controls affect the amount of power, as do a number of other things, like mag timing. Reducing MP via the throttle reduces the amount of air coming into the engine, thus limiting power. The mixture does the same thing with the fuel side of the equation. To a much lesser extent, the prop control affects engine power as well via changing airflow and limiting the number of power strokes per minute.

You can't look at a single gauge to determine the amount of power you're making (although some fancy engine monitors show a calculated % power approximation). When you're rich of peak EGT, power is limited by airflow. When you're lean of peak EGT, power is limited by fuel flow. When you're near peak EGT, you may have some cylinders ROP and some LOP.

The pilot valve puts this "lag" in rpm in the system so the pilot can lean the engine properly. Like all mechanical control systems the rpms hunt, lag and maybe overshoot etc. and that can be controlled to some extent. Good thing it does that so we pilots can lean to an rpm drop, then richen slightly so we know we are running at or very near max lean.

The only thing that is true about that paragraph is that if you run just slightly rich of where you see an RPM drop, you are definitely "running at or very near max lean." You're also leaving a lot of potential power on the table, as you're running at a similar power setting to if you pulled the throttle back until the RPM dropped and then pushed it in just slightly. That's significantly less than 50% power on my plane, and I'd prefer to be closer to 65%.
 
Nate, why are you using Kent's account to post? Or did Kent just overserve himself with coffee?
 
Nate, why are you using Kent's account to post? Or did Kent just overserve himself with coffee?

Ummm... Well, I've been pretty busy and not on PoA for a couple of days, and I was the guy who posted the ??????...

I do have a mostly-empty cup of coffee next to me, though...
 
You know you are in governing range if you turn the prop knob out and you get an rpm drop.

And if you get an rpm drop you know you are now NOT at the stops.
 
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You know you are in governing range if you turn the prop knob out and you get an rpm drop.

And if you get an rpm drop you know you are now NOT at the stops.

Correct. That was not the mistake Kent was correcting. If your “pilot valve” is so laggy you can set mixture via RPM drop while at the stops, something is wrong.

Or as you said, some mechanical systems have a built in hysteresis.

I’ve been looking for a few days to see if any systems do it on purpose but haven’t found any evidence that they’re set up to be that slow on purpose.

It doesn’t take most governors that long to react.

Most governors have a needle valve that has a set of flyweights working against an adjustable spring. The tension of the spring is adjusted by the propellor control in the cockpit. It’s a stretch to call this a pilot valve.

A pilot valve is used in reference to a high pressure valve upstream of control valves that turns the flow of fluid on and off prior to the control valves being changed. Operated by “the pilot” but it has absolutely nothing to do with aircraft prop governors. Usually in reference to things like hydraulic steering of industrial equipment.

What you’re seeing in lag in a prop governor is a combination of slow reaction time of the flyweights moving out or in to coil or uncoil the spring which opens or closes the needle valve which then moves the blades fairly quickly once the valve moves. There’s very little restriction between the needle valve output and the prop hub. (Blow a deal on a constant speed prop and the engine oil is going overboard very fast.)

Then there’s another delay while the pressure in the hub compresses or decompresses the larger spring in the hub itself.

But it shouldn’t be taking as long as your description was giving the impression it would.

If you can provide a diagram showing this “pilot valve”, I’d be interested in seeing it. The spring tension controlled needle valve with a cable to adjust spring tension, isn’t really a “pilot valve” in hydraulic/engineering terms as commonly used.
 
If you can provide a diagram showing this “pilot valve”, I’d be interested in seeing it. The spring tension controlled needle valve with a cable to adjust spring tension, isn’t really a “pilot valve” in hydraulic/engineering terms as commonly used.

It's in the last diagram on the page he linked before:

http://www.thaitechnics.com/propeller/prop_control.html

It says absolutely nothing about this mystery usage for leaning the mixture...
 
It's in the last diagram on the page he linked before:

http://www.thaitechnics.com/propeller/prop_control.html

It says absolutely nothing about this mystery usage for leaning the mixture...

Ahh. Ok. Pilot valve or needle valve (and yes I understand that all valves aren’t needle valves) may just be semantics here, but you’re correct on the leaning part.

There’s no design intention (that I can find anyway) for that valve to be slow enough to allow for leaning with it. At higher RPM the valve will operate faster since the forces involved in the flyweights vs the speeder spring will be larger and vice-versa. But if it’s noticeably lagging, something else is wrong.
 
Correct. That was not the mistake Kent was correcting. If your “pilot valve” is so laggy you can set mixture via RPM drop while at the stops, something is wrong.

Or as you said, some mechanical systems have a built in hysteresis.

I’ve been looking for a few days to see if any systems do it on purpose but haven’t found any evidence that they’re set up to be that slow on purpose.

It doesn’t take most governors that long to react.

Most governors have a needle valve that has a set of flyweights working against an adjustable spring. The tension of the spring is adjusted by the propellor control in the cockpit. It’s a stretch to call this a pilot valve.

A pilot valve is used in reference to a high pressure valve upstream of control valves that turns the flow of fluid on and off prior to the control valves being changed. Operated by “the pilot” but it has absolutely nothing to do with aircraft prop governors. Usually in reference to things like hydraulic steering of industrial equipment.

What you’re seeing in lag in a prop governor is a combination of slow reaction time of the flyweights moving out or in to coil or uncoil the spring which opens or closes the needle valve which then moves the blades fairly quickly once the valve moves. There’s very little restriction between the needle valve output and the prop hub. (Blow a deal on a constant speed prop and the engine oil is going overboard very fast.)

Then there’s another delay while the pressure in the hub compresses or decompresses the larger spring in the hub itself.

But it shouldn’t be taking as long as your description was giving the impression it would.

If you can provide a diagram showing this “pilot valve”, I’d be interested in seeing it. The spring tension controlled needle valve with a cable to adjust spring tension, isn’t really a “pilot valve” in hydraulic/engineering terms as commonly used.
Pilot operated valve on the constant speed prop just means the oil pressure in the prop dome is controlled by a valve which is in turn controlled by the mechanical governor. Pilot operated in this case just means there isn’t a direct mechanical link from the engine controls in the cockpit that positions the valve.

Doing anything with the mixture control is just going to confuse the pilot if they are attempting to lean the engine by observing small rpm changes while in the governing range. The worst part is that the pilot will have no clue about what the actual engine operating condition actually is.

I’ve got a digital tach and an engine monitor on the ‘kota and have run the GAMI test enough times to know that engine rpm does not change while leaning until the engine gets too lean to run.
 
There is NO WAY for the pilot to definitively know whether or not the prop is at the stops other than to drop the power low enough (via either throttle or mixture) that RPM drops, in which case you're at the flat stop.

Yes there is:
You know you are in governing range if you turn the prop knob out and you get an rpm drop.
And if you get an rpm drop, when you pulled the prop knob out, you know you are now NOT at the stops.
 
There’s no design intention (that I can find anyway) for that valve to be slow enough to allow for leaning with it. At higher RPM the valve will operate faster since the forces involved in the flyweights vs the speeder spring will be larger and vice-versa. But if it’s noticeably lagging, something else is wrong.

The fact that it is NOTICEABLE is why it works! The pilot leans by pulling the mixture, then he NOTICES an rpm drop and he knows to richen it slightly.

Stop thinking you know the answer to this puzzle (that it is on the stops and there can't be any lag in governing rpm), open your mind, sharpen your senses, and just go out and do a runup with the prop knob pulled a bit so you KNOW you arent on the stops, and OBSERVE what happens to the rpms when you lean. Try it at higher power also. Then try it by pulling the throttle back a little. There is LESS rpm drop at higher power. (Almost none at full throttle) It will all make sense.
 
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The fact that it is NOTICEABLE is why it works! The pilot leans by pulling the mixture, then he NOTICES an rpm drop and he knows to richen it slightly.

Stop thinking you know the answer to this puzzle (that it is on the stops and there can't be any lag in governing rpm), open your mind, sharpen your senses, and just go out and do a runup with the prop knob pulled a bit so you KNOW you arent on the stops, and OBSERVE what happens to the rpms when you lean. Try it at higher power also. Then try it by pulling the throttle back a little. There is LESS rpm drop at higher power. (Almost none at full throttle) It will all make sense.

Oh I was planning to try it, but I’m pretty sure from experience that my governor is not that slow and it would start to adjust before one could truly find a peak.

I think you’ve been flying something with a VERY slow governor if you can find a peak before it adjusts downward and ruins your ability to find the actual peak.

Bigger prop systems with more mass and at lower power settings with lower oil pressure would take longer, but ours really isn’t that slow. You’d be twisting the mixture out and the governor would be increasing the pitch to slow the prop back down nearly simultaneously.

It’s definitely not the correct way to find a peak.
 
The fact that it is NOTICEABLE is why it works! The pilot leans by pulling the mixture, then he NOTICES an rpm drop and he knows to richen it slightly.

Stop thinking you know the answer to this puzzle (that it is on the stops and there can't be any lag in governing rpm), open your mind, sharpen your senses, and just go out and do a runup with the prop knob pulled a bit so you KNOW you arent on the stops, and OBSERVE what happens to the rpms when you lean. Try it at higher power also. Then try it by pulling the throttle back a little. There is LESS rpm drop at higher power. (Almost none at full throttle) It will all make sense.

Please cite a published source that the purpose of the pilot valve is to assist leaning and/or a source that recommends leaning an engine with a constant-speed prop by finding peak RPM.
 
The fact that it is NOTICEABLE is why it works! The pilot leans by pulling the mixture, then he NOTICES an rpm drop and he knows to richen it slightly.

Stop thinking you know the answer to this puzzle (that it is on the stops and there can't be any lag in governing rpm), open your mind, sharpen your senses, and just go out and do a runup with the prop knob pulled a bit so you KNOW you arent on the stops, and OBSERVE what happens to the rpms when you lean. Try it at higher power also. Then try it by pulling the throttle back a little. There is LESS rpm drop at higher power. (Almost none at full throttle) It will all make sense.
What you describe is not an appropriate way to lean the engine. The system is not designed to work the way you describe. If yours does there is something wrong with it.
 
What people have a misunderstanding of if they think at runup, 1800-1900 rpm or so, is they think if the prop knob is all the way in that the prop is at the stops, fully flat. And that this is the reason they get an rpm drop. Well, you DO get an rpm drop, but its because of the lag in response of the prop to the decrease in power when you lean.

You can proove you are NOT on the stops by backing the prop knob off a bit, seeing an rpm drop, so you know you are in governing range, and doing the runup from that configuration. Because the prop knob has reduced rpm, you KNOW that the prop is not full flat from there.

And if you get an rpm drop from the lag at runup, you get it in the air at cruise power, though it is less noticable at higher power. This technique gives pilots a way to lean without having full instrumentation and balanced fuel injectors. It also gives the pilot a way to lean at runup when you need it at high altitudes.

I know there is nothing wrong with my prop or governor. Its a Lycoming 0-360 with a Marvel Schebler carburetor and a Hartzel constant speed prop. And other aircraft exhibit the same behavior.

Im not saying its wrong to lean with other techniques, they may work fine. But this is how pilots leaned before engines had balanced fuel injection and full instrumentation. And it still works! I know it works because I've done it thousands of times.

Cheers!
 
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Lycomings recommendations

For 5,000 feet density altitude and above, or high ambient temperatures, roughness or reduction of power may occur at full rich mixture. The mixture may be adjusted to obtain smooth engine operation. For fixed-pitch propellers, lean to maximum RPM at full throttle prior to takeoff where airports are at 5,000-feet density altitude or higher. Limit operation at full throttle on the ground to a minimum. For direct-drive and for normally aspirated engines with a prop governor, but without fuel flow or EGT, set throttle at full power and lean mixture at maximum RPM with smooth operation of the
 
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What people have a misunderstanding of if they think at runup, 1800-1900 rpm or so, is they think if the prop knob is all the way in that the prop is at the stops, fully flat. And that this is the reason they get an rpm drop. Well, you DO get an rpm drop, but its because of the lag in response of the prop to the decrease in power when you lean.

So why doesn't it come back up again then? Nothing you are writing makes any sense. The propeller control selects RPM. Fully forward means selecting redline RPM. As 1800RPM < Redline on every engine relevant to the current audience, the governor will keep the prop at the flat pitch stop in an effort to raise the RPM. If it's not at the stop something is very wrong.
 
What people have a misunderstanding of if they think at runup, 1800-1900 rpm or so, is they think if the prop knob is all the way in that the prop is at the stops, fully flat. And that this is the reason they get an rpm drop. Well, you DO get an rpm drop, but its because of the lag in response of the prop to the decrease in power when you lean.

You can proove you are NOT on the stops by backing the prop knob off a bit, seeing an rpm drop, so you know you are in governing range, and doing the runup from that configuration. Because the prop knob has reduced rpm, you KNOW that the prop is not full flat from there.

And if you get an rpm drop from the lag at runup, you get it in the air at cruise power, though it is less noticable at higher power. This technique gives pilots a way to lean without having full instrumentation and balanced fuel injectors. It also gives the pilot a way to lean at runup when you need it at high altitudes.

I know there is nothing wrong with my prop or governor. Its a Lycoming 0-360 with a Marvel Schebler carburetor and a Hartzel constant speed prop. And other aircraft exhibit the same behavior.

Im not saying its wrong to lean with other techniques, they may work fine. But this is how pilots leaned before engines had balanced fuel injection and full instrumentation. And it still works! I know it works because I've done it thousands of times.

Cheers!
Nah you’re still not understanding what’s happening.
 
Lycomings recommendations

For 5,000 feet density altitude and above, or high ambient temperatures, roughness or reduction of power may occur at full rich mixture. The mixture may be adjusted to obtain smooth engine operation. For fixed-pitch propellers, lean to maximum RPM at full throttle prior to takeoff where airports are at 5,000-feet density altitude or higher. Limit operation at full throttle on the ground to a minimum. For direct-drive and for normally aspirated engines with a prop governor, but without fuel flow or EGT, set throttle at full power and lean mixture at maximum RPM with smooth operation of the

The underlined agrees with me, and I agree with it. Maximum RPM means the RPMs change when you change the mixture!!! And the change is observable on the tach. Constant speed within a range yes, but you can still get 50 or 100 RPM difference from the change in power that the mixture causes.
 
The underlined agrees with me, and I agree with it. Maximum RPM means the RPMs change when you change the mixture!!! And the change is observable on the tach. Constant speed within a range yes, but you can still get 50 or 100 RPM difference from the change in power that the mixture causes.
Yeah and that’s the same thing that’s occurring on the ground during a mag check. It also only occurs when the prop is on a pitch stop. If you’re within the governing range you will not see any RPM change for peak EGT. Also what you quoted is for finding best power for takeoff not in flight leaning.
 
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The underlined agrees with me, and I agree with it. Maximum RPM means the RPMs change when you change the mixture!!! And the change is observable on the tach. Constant speed within a range yes, but you can still get 50 or 100 RPM difference from the change in power that the mixture causes.

No, it doesn't, as that's not what it says. Not sure why the quoter cut off the reset of the sentence.

It says, "set throttle at full power and lean mixture at maximum RPM with smooth operation of the engine as a deciding factor."
 
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