Question on Constant Speed Propellers

Clip4 said:
It makes no difference. The Minimum Fuel Flow Placard makes the published values an operation limitation and 91.9(a) states no person may operate a civil aircraft without complying with the operating limitations specified in the approved Airplane or Rotorcraft Flight Manual, markings, and placards,
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That says you must comply with Limitations that are placarded. It doesn’t say that a placard makes something a Limitation.
 
MauleSkinner said:
That says you must comply with Limitations that are placarded. It doesn’t say that a placard makes something a Limitation.
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This appears to be the placard in question. Is it a limitation?
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azpilot said:
... I advanced the propeller to full forward while at 17" manifold pressure. My CFI cautioned me against doing this and advised me not to advance the propeller until I was abeam the numbers and had reduced power to 13". I've asked my CFI this same question and I'm waiting to hear back from him as well.
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Sure gets LOUDER when that happens! That's what the CFI is telling you ... probably not too good for the engine revving up that quick ...

Clip4 said:
You will find the prop Governor is no longer effective below -14 MP and you can push the prop control forward with no RPM increase. Above that value the engine speed increases.
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In my RV7A I'm usually running 23 squared and near 160 knots. Approaching the pattern, I pull MP down to 15 initially, then to 12 ending at 10 ... when airspeed decays, I began advancing the prop SLOWLY and eventually end at 10MP approaching base ... even at that I can hear the engine wind up a little when I finally advance the prop to fully in ... If I advanced at 14mp, it'd be screaming ...
 
MauleSkinner said:
Doesn’t appear that way to me. It doesn’t even say what the maximum power is, so how can it be a limitation on maximum power?
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I concur. Section 4 of the POH simply says "For maximum power, the mixture should be set in accordance with the Maximum Power Fuel Flow placard."
 
asicer said:
I concur. Section 4 of the POH simply says "For maximum power, the mixture should be set in accordance with the Maximum Power Fuel Flow placard."
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And Section 4 doesn’t define operating limitations.
 
danhagan said:
Sure gets LOUDER when that happens! That's what the CFI is telling you ... probably not too good for the engine revving up that quick ...
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Yes, I think this is really what he was after. In this circumstance, I just mashed the blue knob all the way in. The prop quickly accelerated. I've been emailing him separately about it, and that was really his concern. Moving forward, when I'm in cruise, if I need to advance the prop, I'll twist it in slowly using the Vernier. If I'm in the pattern, I'll wait until downwind when I reduce power to 13".
 
azpilot said:
Yes, I think this is really what he was after. In this circumstance, I just mashed the blue knob all the way in. The prop quickly accelerated. I've been emailing him separately about it, and that was really his concern. Moving forward, when I'm in cruise, if I need to advance the prop, I'll twist it in slowly using the Vernier. If I'm in the pattern, I'll wait until downwind when I reduce power to 13".
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You have a max prop speed to stay under as well (mine is 140), it still "complains" a little even at 100 (if the MP is still above 11). My max flap speed IS 100 so I "coast" into the pattern, use the vernier SLOWLY below 110, start deploying flaps at 95 slowly and by this time can advance the prop control the rest of the way in as I'm generally at 10-11 MP (which DOES change with elevation - my RWY in El Paso is 4100 MSL in Austin it's about 600 and MP is different usually by about 2-3 inches works for me).
 
Clip4 said:
No red knob increasing power will earn you an exhaust valve as a paper weight.
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Sometimes, but not always. Pilots really need to learn more about how mixture works. Understanding this chart (which applies to all N-A piston engines, not just the O-320) should be part of basic groundschool, but unfortunately, even most instructors don't really have a clue — the red lever remains a holy mystery to them, surrounded by rules of thumb that are sometimes right, but often dangerously wrong.leaning.png
 
iamtheari said:
If I am above 5000 MSL and not actively trying to slow down, I'm at full throttle. I probably move knobs and levers more than I really have to, and I'm trying to learn more about that. But the throttle is the one I touch the least in the air.
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Ditto. In my Piper PA-28-161 (fixed-pitch prop), when I'm cruising at, say, 4,000 ft DA or higher, I advance the throttle to full for takeoff and then don't touch it again until it's time to start my descent.

I set power by pulling back the mixture until I'm at the correct RPM for my desired power setting (e.g. 65% or 75%), which puts me at the leanest physically possible for that power setting, well clear of the red zone around 50° ROP.
 
It may have been Deakin who compared operating at cruise with a partially closed throttle plate to operating with a dirty air filter. IOW, your engine needs air as well as fuel to perform maximally, so why would you choose to voluntarily restrict it?

In the Cirrus world, this translates to running WOTLOP - Wide Open Throttle Lean Of Peak - at cruise.

No doubt this concept is highly oversimplified, and requires fuel injection with reasonably balanced injectors. But the overall concept seems sound.
 
FastEddieB said:
It may have been Deakin who compared operating at cruise with a partially closed throttle plate to operating with a dirty air filter. IOW, your engine needs air as well as fuel to perform maximally, so why would you choose to voluntarily restrict it?

In the Cirrus world, this translates to running WOTLOP - Wide Open Throttle Lean Of Peak - at cruise.

No doubt this concept is highly oversimplified, and requires fuel injection with reasonably balanced injectors. But the overall concept seems sound.
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Does the Cirrus power lever maintain full throttle while you pull back from max RPM to ~2500? I saw a good explanation of that lever's operation one time, but it was a while ago.
 
David Megginson said:
Ditto. In my Piper PA-28-161 (fixed-pitch prop), when I'm cruising at, say, 4,000 ft DA or higher, I advance the throttle to full for takeoff and then don't touch it again until it's time to start my descent.

I set power by pulling back the mixture until I'm at the correct RPM for my desired power setting (e.g. 65% or 75%), which puts me at the leanest physically possible for that power setting, well clear of the red zone around 50° ROP.
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I simply avoid the red box by climbing until it disappears. :)
 
iamtheari said:
Does the Cirrus power lever maintain full throttle while you pull back from max RPM to ~2500?
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Pretty much. The first bit of travel knocks off about 200 rpm, from 2700 to 2500. The throttle plate moves a tiny bit, but remains essentially WOT. From that point on the throttle plate does begin to close.

I saw a good explanation of that lever's operation one time, but it was a while ago.
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Here’s a decent explanation:

 
FastEddieB said:
No doubt this concept is highly oversimplified, and requires fuel injection with reasonably balanced injectors. But the overall concept seems sound.
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Usually, yes, but some carbureted 4-bangers like my O-320-D3G also run smoothly LOP.
 
Lean in the climb?
Full rich on take off. (enough fuel flow for 100 to 125d F ROP for Best power plus 80 - 120d F for adequate cooling. This is a pre-requisite for leaning in the climb)
On climb out, pick any cylinder and watch that EGT number. As you climb, it shall drop.
Slowly and continuously dial your mix out or leaner, to keep that target EGT number the same.
You shall be at Best power and adequate fuel flow for cooling, till you level off and do the "big pull" to LOP.
I hope this is the way the smart guys do it. :)
Sorry, I only now realize the leaning question was directed at the Cirrius flyers.
 
David Megginson said:
Great plan! For a N-A engine, above 7–8,000 ft DA, there ain't no red box.

How do you lean during climb?
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Not only that, but my NA planes, even the RV-14 with its itty bitty wings, absolutely love life between 8000 and 12500. That's where I am for almost any trip over 20 miles. I lean by guesswork during the climb but this thread and a couple other recent threads have inspired me to be a better person and get more scientific about it.
 
mandm said:
Wouldn’t full rich at high altitude cause engine roughness?
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Might be enough to kill the engine altogether. The combustible range of gasoline in air is 8:1 (rich), 8 pounds of air to one pound of fuel, to 18:1 (lean). Full rich is usually going to give you near that 8:1 at sea level on a cool day; take it to 10K, where the air density is only 3/4 that of at sea level, and that full-rich is likely to be too much for that engine.
 
Dan Thomas said:
Might be enough to kill the engine altogether. The combustible range of gasoline in air is 8:1 (rich), 8 pounds of air to one pound of fuel, to 18:1 (lean). Full rich is usually going to give you near that 8:1 at sea level on a cool day; take it to 10K, where the air density is only 3/4 that of at sea level, and that full-rich is likely to be too much for that engine.
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Nobody who flies from a high-elevation airport would take off with the mixture full rich (or at least, Darwin quickly weeds out the ones who do), but I suspect some pilots haven't yet made the connection that (say) 8,000 ft density altitude looks the same to your engine when you've climbed up there all the way from a sea-level airport as it does when you're just lifting off a mountain airstrip and trying to clear the trees at the end.
 
David Megginson said:
Nobody who flies from a high-elevation airport would take off with the mixture full rich (or at least, Darwin quickly weeds out the ones who do), but I suspect some pilots haven't yet made the connection that (say) 8,000 ft density altitude looks the same to your engine when you've climbed up there all the way from a sea-level airport as it does when you're just lifting off a mountain airstrip and trying to clear the trees at the end.
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You know there are exceptions to this, right?
 
Rgbeard said:
You know there are exceptions to this, right?
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Aside from the tiny minority of GA piston aircraft that have altitude-compensating fuel systems (which do the leaning for you), when would you take off from an 8,000 ft density-altitude field with the mixture set to full rich with a normally-aspirated engine? I'm always happy to learn new things.
 
David Megginson said:
Aside from the tiny minority of GA piston aircraft that have altitude-compensating fuel systems (which do the leaning for you), when would you take off from an 8,000 ft density-altitude field with the mixture set to full rich with a normally-aspirated engine? I'm always happy to learn new things.
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ah, you added “normally aspirated”.
 
Altitude-compensating systems only do half the job. They sense pressure, and leave the temperature out of it. Temperature makes a big difference in DA.
 
I’m lazy. If ATC needs me to climb from cruise I leave my cruise settings as is (WOT, 2350, 11-12GPH) and just pitch up for a 500fpm VS. That will net me my typically cruise climb speed of 130KTS. Upon level off I’ll fine tune the mixture, but I never touch the prop or throttle. Not text book but it works for me.
 
I cannot find anything in the cessna 182T POH that describes the order of operations - which the group-wisdom suggests is: left-to-right for descent, right-to-left for climb.
For those who saw it in their POH, which section?
 
Hard to find something that’s not there. It’s like proving a negative.
 
nj-pilot said:
I cannot find anything in the cessna 182T POH that describes the order of operations - which the group-wisdom suggests is: left-to-right for descent, right-to-left for climb.
For those who saw it in their POH, which section?
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Maybe not there specifically. But if you look in the performance section it will show acceptable Manifold and RPM settings and even fuel flow. Pretty safe to stay with those recommended settings in most conditions. Using other settings even momentarily, , I can't say for sure.

Brian
CFIIG/ASEL
 
nj-pilot said:
I cannot find anything in the cessna 182T POH that describes the order of operations - which the group-wisdom suggests is: left-to-right for descent, right-to-left for climb.
For those who saw it in their POH, which section?
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I am not a C182 pilot, and am not representing this to be correct for a C182.

But I do drive-around a turbocharged piston-engine plane and I would use this as my general template for flying about anything unless otherwise indicated by the POH.

Climb.

If it's just a couple of minutes, I won't do a whole lot. Climb, level off, double check things.
If it's a "good" climb, I will speed up the prop first, and the power second. Mixture if/as-needed.​

Cruise.

I set the prop first
Bring in cowl flaps
Adjust MP
Adjust mixture and monitor​

Descent.

Leave prop alone
Reduce MP
Check mixture for good numbers
Verify required descent rate​

Pre-landing.

Finally prop comes forward
Open cowl flaps​
 
Radar Contact said:
I’m sure I’ll get roasted out of here but…

You could just leave the mixture and props set for cruise (mixture slightly enriched depending on what cruise altitude was) and just adjust the throttle for landing. In the event of a go-around (rare if you’re a proficient pilot) you’d smoothly move all forward with a flat hand…it’s going to be there anyway.

This would alleviate dumping extra(not needed) cold fuel in your hot cylinders and the noise for the surrounding community.
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ditto. but there's always the "but....but my CFI said...." crowd.
 
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