How to explain a CS prop to an A&P?

I review how this prop works EVERY TIME I FLY! I review it when I lean it during runup at 1900 rpm 5280' altitude airport) and I review it again when I lean it at cruise.

In both instances, I lean it by drop in rpm. I pull the mixture back until the rpm drops and then push it in a bit. Good to go. I have ONE EGT, and am carbureted, with no fuel flow gauge so cant lean by EGT. Just doesnt run that way. Need injected and probes on all cylinders to do that. This airplane wont even run smoothly on peak EGT because the other cylinders are way past peak into miss firing. So you can even find peak EGT. Only way to lean it is by rpm drop, then enrichen. And we lean the heck out of everything here in Colorado. Lean for takeoff, every time.

Ive flown other airplanes that lean this way in runup.

BTW, there is way to tell if I am at the full flat stops at runup. Pull the prop knob out a bit until the rpm goes down and you KNOW you arent at the stops at 1900rpm now. Lean the same way. It governs but allows just enough rpm drop to be able to lean by rpm.

I bought this Husky from a ATP that was a long time airline pilot. I leaned it and he observed also. He say "yep, I think PIC (he was referring to the training company) had it wrong." Well I dont know about that it may be some planes do it one way and some planes do it the other.

I have flown other constant speed prop planes that worked this way. So its not just Husky. And I have flown other Huskies that work this way, so its not just MY husky.

It appears to me Hartzel does it this way so the pilot can lean by rpm drop.

My leaning technique must be ok. My first Husky engine made 3000 hours without even a top. Never even had the engine taken apart whatsoever.
 
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I love people who don't understand mechanical systems, yet insist they work in a way that is a mechanical impossibility.
 
coloradobluesky said:
I review how this prop works EVERY TIME I FLY! I review it when I lean it during runup at 1900 rpm 5280' altitude airport) and I review it again when I lean it at cruise.

In both instances, I lean it by drop in rpm. I pull the mixture back until the rpm drops and then push it in a bit. Good to go. I have ONE EGT, and am carbureted, with no fuel flow gauge so cant lean by EGT. Just doesnt run that way. Need injected and probes on all cylinders to do that. This airplane wont even run smoothly on peak EGT because the other cylinders are way past peak into miss firing. So you can even find peak EGT. Only way to lean it is by rpm drop, then enrichen. And we lean the heck out of everything here in Colorado. Lean for takeoff, every time.

Ive flown other airplanes that lean this way in runup.

BTW, there is way to tell if I am at the full flat stops at runup. Pull the prop knob out a bit until the rpm goes down and you KNOW you arent at the stops at 1900rpm now. Lean the same way. It governs but allows just enough rpm drop to be able to lean by rpm.

I bought this Husky from a ATP that was a long time airline pilot. I leaned it and he observed also. He say "yep, I think PIC (he was referring to the training company) had it wrong." Well I dont know about that it may be some planes do it one way and some planes do it the other.

I have flown other constant speed prop planes that worked this way. So its not just Husky. And I have flown other Huskies that work this way, so its not just MY husky.

It appears to me Hartzel does it this way so the pilot can lean by rpm drop.

My leaning technique must be ok. My first Husky engine made 3000 hours without even a top. Never even had the engine taken apart whatsoever.
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Why do you pull the prop back to 1900 during run up to lean for best power?

If the rpm changes with mixture then the prop is on a mechanical pitch stop. The governor would keep a constant speed if it's not on a pitch stop. That's why it's called a constant speed prop. Not being a smart ass. Please don't take it that way.

To be clear I'm not saying you are imagining things. I'm just saying if rpm changes with the mixture then you're off the governor and the prop is on a pitch stop.
 
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what's oil pressure doing?
faa_constant_speed_propeller_aspirated_engine.gif



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Sounds to me like he's leaning til it tries to die, then enrichening, and calling that an RPM drop and thinking it has to do with the prop/governor. In reality the drop in RPM is because the engine is ceasing to produce power and if you left the mixture there instead of pushing it in the engine would eventually quit.
 
It doesn't work to lean to peak EGT's unless you have two things:
1. Even air and fuel flow to all cylinders
2. EGT guage on every cylinder

If some cylinders are way lower EGT than others, when you find peak EGT on the hotest cylinder, the other cylinders might actualy be AT PEAK. It just doesnt work if they aren't all about the same

With carbed engines, yoiu dont get even airflow, and with mine, I only have one EGT probe anyway. I just set it to monitor CHT< thats what the manual for the plane says to do . ONe EGT probe doesnt do much.

Ive tried to lean via finding EGT, and no matter how much I lean, the EGT goes up, until the engine starts seriously missing on the other cylinders. So its not possible to lean this plane via EGT.

I lean every time I fly, twice. Once at runup, and at least once when cruise is established.

The reason I posted about doing runup with the prop out a bit, was to PROOVE that the prop is not at the stops when it does this. Normally I dont do runup with the prop out at all, no of course not, Prop in. But doing with the prop out and getting the same rpm drop, prooves the prop is not at the stops at 1900 rpm. Its at the stops at about 1500, Ive checked it.

I've flown other planes with Constant speed props, but dont have access to them for reference. Cessnas 182, Cessna 185, a constant speed prop Cessna RG. Its hard to remember for sure, but on runup I just leaned to rpm drop and then enrichened. So for ME, thats the way they all work. Some however appear to work differently.

Ive had other pilots looking over my shoulder during the lea n process, verifying, yep, rpm drop. Pull the throttle a bit, you get some rpm drop too, maybe 50 rpm then the govenor kicks in.
 
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Im not making statements about how the internals of the prop works. Im just reporting what happens when I pull the mixture knob and look at the tachometer rpms.

I did speculate on why it works this way up in some other post. Its speculation. So disregard it if you want.

I looked in the Hartzell manual that came with the plane and there is, as usual, no discuassion of leaning.
 
Some people like to make fun of others. They are calling those kind of people bullies now. And thats a pretty good description for them. Now I know, we kid people around. Ill take it as a good natured kidding.

Im taking a lot of risk posting this. But this is the way it works, not just for me and my plane either. And Im trying to understand it. Its possible, that ther are two kinds of props. Ones that do it and ones that dont. I really dont know. But there has to be some explanation.

Go out and try it.
Report back with type aircraft, engine and prop.
Im not saying it does on EVERY airplane.
There must be some explanation.
Observe carefully. Try and get rpm drop when you lean. If it doesnt, it doesnt. If it does, it does.

The only thing I can think of is to post a video of me doing it. So until then, Im signing off. End of it for me.
 
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coloradobluesky said:
I've flown other planes with Constant speed props, but dont have access to them for reference. Cessnas 182, Cessna 185, a constant speed prop Cessna RG. Its hard to remember for sure, but on runup I just leaned to rpm drop and then enrichened. So for ME, thats the way they all work. Some however appear to work differently.
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My Cessna 180, two separate 185s, and many 206s, 207s.......didn't work in the manner you report.

Do you have ANY factual references to back up your hallucinations?:no:
 
maybe I'm not doing it right?....which knobs do I turn? :idea:

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Guys please don't be derogatory. We are all here to help each other learn and share our experience. I'm sure it is all in good fun but that can be hard to convey in a post. Just a friendly reminder.
 
I'm kind of losing track here so, if you don't mind, let me recap a bit and also cover couple of points that I have doubts about.

Please correct me if I am wrong.

I would certainly think that the CS prop is on the low pitch stop at run up speeds and the prop is acting as a fixed pitch prop. And will respond to leaning the same way the fixed pitch prop does.

I fly out of Miami and even on the hottest day, I don't think I've ever seen a takeoff DA of even 3000' so I have no experience in leaning for takeoff. But I thought leaning for takeoff was done at full static rpm, not run-up speeds. On a fixed pitch prop, lean for max rpm. It is my understanding that, at static rpm, the CS prop is still on the low pitch stop as the blade AOA is too high to allow the engine to develop redline RPM even at its lowest pitch. Redline rpm cannot be developed until forward motion of the aircraft lowers the blade AOA sometime during the takeoff roll and at that point, the CS prop will come off the low pitch stop. This leads me to believe that if you are leaning a CS prop for high DA, you would do it identically to a fixed pitch?
 
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alfadog said:
I'm kind of losing track here so, if you don't mind, let me recap a bit and also cover couple of points that I have doubts about.

Please correct me if I am wrong.

I would certainly think that the CS prop is on the low pitch stop at run up speeds and the prop is acting as a fixed pitch prop. And will respond to leaning the same way the fixed pitch prop does.

I fly out of Miami and even on the hottest day, I don't think I've ever seen a takeoff DA of even 3000' so I have no experience in leaning for takeoff. But I thought leaning for takeoff was done at full static rpm, not run-up speeds. On a fixed pitch prop, lean for max rpm. It is my understanding that, at static rpm, the CS prop is still on the low pitch stop as the blade AOA is too high to allow the engine to develop redline RPM even at its lowest pitch. Redline rpm cannot be developed until forward motion of the aircraft lowers the blade AOA sometime during the takeoff roll and at that point, the CS prop will come off the low pitch stop. This leads me to believe that if you are leaning a CS prop for high DA, you would do it identically to a fixed pitch?
Click to expand...

You are correct.
 
coloradobluesky said:
Im not making statements about how the internals of the prop works. Im just reporting what happens when I pull the mixture knob and look at the tachometer rpms.

I did speculate on why it works this way up in some other post. Its speculation. So disregard it if you want.

I looked in the Hartzell manual that came with the plane and there is, as usual, no discuassion of leaning.
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Again, it sounds like you're simply leaning past the point where the motor can continue to make power, or even run at all. That has nothing to do with the prop. I'd like to see a video, but I'd also like to see what happens if you lean to this "RPM Drop" and simply leave it there. I bet the engine tries to die.

With a constant speed prop there are only 2 ways the RPM can change (barring malfunction)

1. You don't have enough power to reach the set RPM before the prop hits the stop. This could be because you have a high RPM set with a low throttle setting, such as we normally see on the ground.

2. you have removed enough air or fuel to not make enough power to reach the desired RPM.

What you're describing sounds like #2. Neither of these have anything to do with the constant speed system. This just sounds like a misunderstanding of what's going on.
 
Remember HP and it's "what if?" campaign?

What if? you slowed down the opening and closing of that pilot valve????
 
Here is a way of telling that the prop is NOT at the stops.

Put the prop all the way in and run the plane to the 2100rpm. Now crank the propeller knob out until you get 200 rpm drop, back to 1900 rpm. Now you are certain you are not at the stops. Now run the experiment with the lean knob and see if you get an rpm drop.
 
Of course the throttle can raise and lower the rpm by itself. Prop knob in, run up and down from 1000rpm to 2650rpm with just the throttle.
 
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Reducing power with the mixture doesnt reduce the manifold pressure, retarding the throttle does.
 
Here are some notes from some experiments I ran
Airplane: 1996 Aviat Husky, Carbed Lycoming 0-360, Hartzel Constant Speed Prop.

This was all with the PROP KNOB ALL THE WAY IN:

Experiment 1 (done in the air flying at 100mph indicated, 6000'):
I ran the following experiment. I set it for 20" and 2650rpm. Then I pulled the throttle back to 18" and the RPM went to from 2650rpm to 2600rpm, then climbed back up to 2625rpm.

Experiment 2 (again done in the air)
I ran the following experiment. I set it for 10" and it gave me 2000rpm (this is runup rpm). Then I pulled the throttle back to 9" and the rpm went from 2000 to 1950. Went back up to 1975rpm

Experiment 3 (normal runup done on the ground)
I set it for 2000rpm which is about 15" (static is a bit different you see). I LEANED for an rpm drop and it went to 1900rpm and 13" mainifold. When I pulled the power back to 13" it did the same thing.
 
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What do you mean when you say you "set it 2000RPM"? Set the throttle or the prop control? What position was each one? Without specifying all the facts precisely no one can draw any conclusions from these experiments.
 
Here is the simple answer to my initial question as to why I can lean my constant speed prop by using rpm drop.
At runup rpm:
1. The rpm decreases when the throttle is retarded because this reduces power.
2. The rpm decreases when the engine is leaned past point of most power (75 degrees rich of peak), because this reduces power.

I'm just using 2. above, using the mixture knob to reduce power and the rpm drops and I know I am too lean, so I put 3 half turns back rich and I am good to go!

THAT'S IT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

the the the thats all folks...

Thanks for your patience
 
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coloradobluesky said:
Here are some notes from some experiments I ran
Airplane: 1996 Aviat Husky, Carbed Lycoming 0-360, Hartzel Constant Speed Prop.

This was all with the prop knob all the way in.

Experiment 1 (done in the air flying at 100mph indicated, 6000'):
I ran the following experiment. I set it for 20" and 2650rpm. Then I pulled the throttle back to 18" and the RPM went to from 2650rpm to 2600rpm, then climbed back up to 2625rpm.

Experiment 2 (again done in the air)
I ran the following experiment. I set it for 10" and it gave me 2000rpm (this is runup rpm). Then I pulled the throttle back to 9" and the rpm went from 2000 to 1950. Went back up to 1975rpm

Experiment 3 (normal runup done on the ground)
I set it for 2000rpm which is about 15" (static is a bit different you see). I LEANED for an rpm drop and it went to 1900rpm and 13" mainifold. When I pulled the power back to 13" it did the same thing.
Click to expand...

Prop governors REACT to an underspeed or overspeed condition and are not super instantaneous lighting fast to react...
 
Interesting that it does not climb ALL THE WAY back up to where it was though.
 
coloradobluesky said:
Interesting that it does not climb ALL THE WAY back up to where it was though.
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Sounds like tach error to me, or sticking prop governor issues. I suppose there could be corrosion in the prop and piston assembly or bearings somewhere causing drag in the pitch change mechanism. I would expect it to hunt of that were the case.
 
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The point is, you can use these rpm reductions caused by reducing the power by leaning the mixture even with a Constant Speed Prop both in flight and on the ground.
 
coloradobluesky said:
The point is, you can use these rpm reductions caused by reducing the power by leaning the mixture even with a Constant Speed Prop both in flight and on the ground.
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What leaning technique is recommended by the POH?
 
To paraphrase Winston Churchill ...

"Never before in recorded history have so many known so little about so much."

What a bunch of blow-off about how constant speed props work.

Jim
 
I have some more theory.

The pilot valve opens slowly causing the delay that allows rpms to drop and the governor boost pump produces less pressure (because the rpms have dropped) and this is why the rpms dont come all the way back up to the level they were before the power reduction. Kind of complicated...
 
The only prop airplane I've worked on, the propeller governing range was between 11,000 and 15,000 engine rpm... that was back in the early '80's, I recall just enough to be dangerous, but I do still have training manuals somewhere... I think.
 
BigBadLou said:
How can I politely explain to this A&P that a CS prop should maintain given RPM even with lower manifold pressure at higher altitude/DA?
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ask him to explain how to set a prop governor ??

Yeah I'm back. much reserved.
 
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