Anyone else ever run LOP with fixed pitch prop?

[Shadrach]

I have had unlimited access to a Decathlon for the last week and have enjoyed taking in the countryside low and slow. It is powered by an AEIO320 with a fixed pitch prop. The owner normally operates the plane full rich because he is either in the pattern or below 2000'. I have no recollection of previously flying an injected engine with a fixed pitch prop.  It has minimal engine instrumentation with no EGT nor CHT gauge.  It's his engine so I pretty much fly it as he does.  However, last week I found myself bumping along at a DA well over 5K and I decided to lean to rough and enrichen to smooth. I was surprised to how smooth this engine remained.  Despite not having the tuned induction, when leaning, power and RPM just steadily drop off until the fire goes out completely. There is no point of roughness. There is little to no hint of cycle to cycle variations in power pulses. It is noticeably smoother than my IO360.  Max RPM with the current prop is about 2600RPM and it will easily operate smoothly between 2000 and 2600 at WOT just by manipulating the mixture. 

I theorize that this situation is mainly due to the fixed pitch prop allowing piston speed (RPM) and combustion event speed to sort of harmonize through out the RPM range as power (fuel) is reduced.  If the mixture control were not so crude, it would be hard to tell the difference between mixture and throttle inputs between 2000 and 2600rpm. Has anyone else encountered this?

[M20F]

Why would you want to run LOP in a Decathalon?

[McMooney]

well if you follow the general instructions of leaning to rough then a turn or two,  you are probably lean of peak

[MikeOH]

1 minute ago, McMooney said:

well if you follow the general instructions of leaning to rough then a turn or two,  you are probably lean of peak

I believe the OP's point was he NEVER felt ANY roughness....right up until the engine quit making power.

[EricJ]

With a fixed-pitch prop you can lean to rpms.  Lycoming guidance for fixed-pitch props is to lean to either max rpm or max IAS, whichever you prefer.   I always leaned to peak rpm.

[Shadrach]

27 minutes ago, M20F said:

Why would you want to run LOP in a Decathalon?

why wouldn’t you? I’ve done several 1hr + XCs. There is no means by which to accurately lean it ROP and it’s an injected Lycoming so LOP is the only mixture setting for which the pilot receives feedback.  There is no “lean to rough and enrichen” with this engine. There is only lean to rpm reduction.

[Shadrach]

21 minutes ago, EricJ said:

With a fixed-pitch prop you can lean to rpms.  Lycoming guidance for fixed-pitch props is to lean to either max rpm or max IAS, whichever you prefer.   I always leaned to peak rpm.

Right. But that is for a given throttle setting. We usually set throttle at 2300, full rich at 1800msl. My point was I can just lean to 2300rpm at full throttle with very smooth operation. 

[MikeOH]

14 minutes ago, EricJ said:

With a fixed-pitch prop you can lean to rpms.  Lycoming guidance for fixed-pitch props is to lean to either max rpm or max IAS, whichever you prefer.   I always leaned to peak rpm.

Hmm, why would there be any difference between max RPM and max IAS?

[Shadrach]

21 minutes ago, McMooney said:

well if you follow the general instructions of leaning to rough then a turn or two,  you are probably lean of peak

With a carbed engine, probably so at least on some of the cylinders. My point was that this particular set up allows me to smoothly lean to any RPM between 2000 and 2600 with the throttle wide open.

[Shadrach]

5 minutes ago, MikeOH said:

Hmm, why would there be any difference between max RPM and max IAS?

There wouldn’t be unless you were running a CS prop. 

[M20F]

8 minutes ago, Shadrach said:

why wouldn’t you? I’ve done several 1hr + XCs. There is no means by which to accurately lean it ROP and it’s an injected Lycoming so LOP is the only mixture setting for which the pilot receives feedback.  There is no “lean to rough and enrichen” with this engine. There is only lean to rpm reduction.

I have more hours upside down in a Decathlon then I suspect most of this forum has right side up.  Pull out till rough and then push in.

For the most part though it is a plane to fly full rich and generally full power doing fun stuff. 
 
LOP has its places I remain to be convinced a Decathlon would one of those places. 

[Shadrach]

Just now, M20F said:

I have more hours upside down in a Decathlon then I suspect most of this forum has right side up.  Pull out till rough and then push in.

For the most part though it is a plane to fly full rich and generally full power doing fun stuff. 
 
LOP has its places I remain to be convinced a Decathlon would one of those places. 

Color me appropriately impressed…

Isn’t he a dreamboat guys!

Perhaps you should RTFP. I’m not talking about upside down ops, nor am I talking about pattern ops. I’m talking about low and slow with your elbow hanging out the window taking in the sights and smells of the countryside. Forget it’s a Decathlon and imagine that it’s a Champ, but with a much stronger(relatively speaking) injected engine.

This engine does not get rough, RPMs just smoothly drop until the fire goes out around 1900 RPM. 

The point of the post was that since I don’t fly around with everything firewalled, wouldn’t it be cleaner and cooler to just lean to 2300 RPM rather than pull the throttle back to 2300 RPM at full rich.

[M20F]

4 minutes ago, Shadrach said:

Color me appropriately impressed…

Isn’t he a dreamboat guys!

Perhaps you should RTFP. I’m not talking about upside down ops, nor am I talking about pattern ops. I’m talking about low and slow with your elbow hanging out the window taking in the sights and smells of the countryside. Forget it’s a Decathlon and imagine that it’s a Champ, but with a much stronger(relatively speaking) injected engine.

This engine does not get rough, RPMs just smoothly drop until the fire goes out around 1900 RPM. 

The point of the post was that since I don’t fly around with everything firewalled, wouldn’t it be cleaner and cooler to just lean to 2300 RPM rather than pull the throttle back to 2300 RPM at full rich.

Unless you are flying at 18000’ then just pulling the throttle back and going will get you the appropriate stoichiometric ratio.

I disagree with your assertion.  Enjoy the flight though. 

[EricJ]

49 minutes ago, Shadrach said:

Right. But that is for a given throttle setting. We usually set throttle at 2300, full rich at 1800msl. My point was I can just lean to 2300rpm at full throttle with very smooth operation. 

It's what I always did in 150 and 172s, whatever I was flying with a fixed-pitch prop and no EGT.   At your desired cruise rpm, lean to peak rpm and leave it there.   Much past that seems like over-thinking to me.

[Shadrach]

18 minutes ago, EricJ said:

It's what I always did in 150 and 172s, whatever I was flying with a fixed-pitch prop and no EGT.   At your desired cruise rpm, lean to peak rpm and leave it there.   Much past that seems like over-thinking to me.

I’m not overthinking it all. What you describe is how I have operated every fix pitched carbureted engine I’ve ever flown. 
 

The question being posed is, why bother reducing the throttle on an injected engine if you can just lean to the desired rpm. One less step. Same HP, less fuel.

[EricJ]

2 minutes ago, Shadrach said:

I’m not overthinking it all. What you describe is how I have operated every fix pitched carbureted engine I’ve ever flown. 
 

The question being posed is, why bother reducing the throttle if you can just lean to desired rpm. One less step. Same HP, less fuel.

Throttle controls the amount of air going in, and the carb/whatever mixes in fuel according to the mixture setting.

The mixture reduces the amount of fuel without adjusting the amount of air.

I know you know this, and that you know the implications of each.

There are some times where it is useful to use the mixture to control power output, some emergency situations come to mind.    Don Maxwell's video on how to hot start a Lycoming includes his mention that you can use the mixture like a throttle, but that's for near-idle operation.

[Pinecone]

Low and slow, and you are below 75%, or even better 65%, power, lean to near cut off and slightly richer and enjoy.  You can't hurt anything at low power settings.

I didn't know that there were any fixed pitch Decathalons.  I had Have flow both the 150HP and 180 HP Super.  I have also flow the 7KCAB, which is  fuel injected and fixed pitch.

But my flying has all been pattern work or filling and flopping, so full rich.

[Shadrach]

2 hours ago, Pinecone said:

Low and slow, and you are below 75%, or even better 65%, power, lean to near cut off and slightly richer and enjoy.  You can't hurt anything at low power settings.

I didn't know that there were any fixed pitch Decathalons.  I had Have flow both the 150HP and 180 HP Super.  I have also flow the 7KCAB, which is  fuel injected and fixed pitch.

But my flying has all been pattern work or filling and flopping, so full rich.

The 150hp decathlons came with both fixed and CS props. Not sure if it was an option or a model year change. The thing about leaning a fixed pitch, injected Lycoming is that leaning to near cut off represents a 300-500rpm drop (depending on where you start) before it gets rough. I had never had this experience before, as all previous fixed pitch time was in carbureted aircraft.

[Shadrach]

14 hours ago, M20F said:

Unless you are flying at 18000’ then just pulling the throttle back and going will get you the appropriate stoichiometric ratio.

I disagree with your assertion.  Enjoy the flight though. 

My apologies for my snark, Mike. It was not meant to be mean spirited.  I fly with all types of operators with various experience levels.  I have grown wary of any statement that starts with "I have 10,000 hours in...and I...", because often the information that follows such a statement is purely an appeal to authority (logical fallacy) with very little in the way of supporting technical information.  It's the dialectic equivalent of saying "In case you didn't know, I am superior to you and therefore, so are my opinions."  When I was a greenhorn more than 25 years ago, I was more receptive to the "I'm the Ace of the base" commentary, but over the years I have heard some pretty ignorant statements follow those kinds of proclamations, especially on the subject of leaning.

[M20F]

1 hour ago, Shadrach said:

My apologies for my snark, Mike.

Haha I have known you long enough, it’s all good.  Like many things we agree to disagree.  You are always the gentleman. 

[EricJ]

6 hours ago, Shadrach said:

The 150hp decathlons came with both fixed and CS props. Not sure if it was an option or a model year change. The thing about leaning a fixed pitch, injected Lycoming is that leaning to near cut off represents a 300-500rpm drop (depending on where you start) before it gets rough. I had never had this experience before, as all previous fixed pitch time was in carbureted aircraft.

C172s have been shipping with fuel-injected IO-360s for quite a while (nearly thirty years) with fixed pitch props, but I think they have EGT in those with G1000.   Regardless, it's not a big deal to adjust power with mixture regardless of whether the prop is fixed pitch or not.   We do it routinely with constant-speed props, the only difference with a fixed pitch is that if you want a particular rpm and FF (or whatever) you may have to adjust both mixture and throttle to get there.