Constan Speed Props ... a "Better" way to Teach It

All the current lycomings that I am aware of produce their maximum HP at their maximum rated RPM. There is a reason racers and unlimited aerobatic competitors spin their engines well above max rated RPM. Many go as high as 3500 RPM as HP continues to climb beyond that point but prop issues make 3500 about the max useable. Overhaul interval goes down dramatically as you spin a lycoming above 2800 RPM.
 
CharlieD3 said:
I like to know more... If it's knowledge useful to me.

For what exam am I going to need to draw the thing?

Most of us have little desire to become astronauts and don't need to know the inner workings of a constant speed prop.

Nor do we need so much knowledge that we can reboot HAL to the "Mary had a little lamb" stage.

More and more a/c will have FADEC, autoland, and autonomous flight as the years go by. And the speed of change will be exponential as we go.

Thanks for trying to simplify the subject.
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Dan Thomas and LongRoadBob provided some very good contributions.
Look back through this thread and consider those contributions.
Ok ....2500 rpm... or 2700... this a conversation ... I agree that not all recips reach max power at 2500... float the numbers and the concepts still works

I continued to stress "what I meant" to be the very first portions of the CSP conversation.
Although the references Dan provides are full and rich, I hope that we remember that not all pilots will need all of the info to operate the aircraft well, safely and efficiently.

I do agree that after discussing POWER, certainly efficiency is the second half of the chapter titled "WHY We have CSP"...
And then the third half of the discussion would discuss the components...

I believe that knowing your students and being very aware of their aptitude must control the depth of this material.

Consider these....
1) We can set the prop to high rpm for Engine Power Band, for Take Off, Climb and Go Around ... this should work for almost every student.
2) "For cruise flight we can also "Select a Different Prop Rpm" by changing the prop pitch to help "match Prop Bite to Air Speed ( actually relative wind) " to boost efficiency and cruise performance ..... this should work for almost every student.
3) "We select desired prop rpm by providing an input to a gov that can sense both 1) our request (requested rpm) and 2) actual prop rpm. The prop gov will then (by using engine oil to motivate the prop into a bigger bite or smaller bite) continually make fine adjustments to prop blade angle (Bite) via oil pressure to hold the prop to desired rpm. Engine oil is the hydraulic fluid used9 to control the prop pitch) but there is an additional oil pressure pump just for the gov and prop control system. ..... this should work for most students.

4) Certainly a discussion is required on 'WHAT MANIFOLD PRESSURE MEANS" and then "Why does it go up or down" .... and THEN showing the relationship to prop pitch,prop rpm, engine rpm, throttle plate, ambient air pressure, air pressure on each side of the throttle plate... All necessary.... but taught at a rate respecting student aptitude.

5) But some fire hoses need to be metered...Geometric Slip, and even the inner workings of the gov, and much of the depth of the topic ... We have all had students that would devour those concepts.... but not not every student needs that stuff to consistently perform safely.

So let us return to the lesson plan
Objective - The Student needs to have a familiarity of CSPs and the associated components, a general understanding of CSPs and be able to apply that familiarity and understanding to the practical, efficient and safe use thereof.

Completion Standard - The Student will demonstrate competence:
by
a) describing and explaining the general components of the CSP system,
b) demonstrate normal use and procedures including systems checks, and describe, explain and demonstrate abnormal procedures.

When was the last time a pilot had to explain and draw the inner workings of a brake master cylinder?.... or the wheel cylinder" or compare a floating rotor vs floating caliper?..... Never.... hmmm ...so some instructors think that students students need to draw the innards of a gov... but NOT the innards of an alternator or gen... or carb heat airbox...

Pilots ONLY need.... what they NEED.... not what OUR teachers taught us...
Let's tailor the lessons for each student.... Not to target min standards.... but to assure that each INDIVIDUAL student can do HIS best...
 
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Jeff767 said:
All the current lycomings that I am aware of produce their maximum HP at their maximum rated RPM. There is a reason racers and unlimited aerobatic competitors spin their engines well above max rated RPM. Many go as high as 3500 RPM as HP continues to climb beyond that point but prop issues make 3500 about the max useable. Overhaul interval goes down dramatically as you spin a lycoming above 2800 RPM.
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I met a cropsprayer pilot who had raced small airplanes (F1?) and had flown one with an O-200 that was run up to over 4000 RPM. I asked him what would happen if he lost a prop blade at that speed or if it seized suddenly (I knew it could take the engine right off the airplane) and he said they had a cable (wire rope) all the way around the engine and fastened to the airframe in case of that. Small props, too.
 
James the MEI said:
Pilots ONLY need.... what they NEED.... not what OUR teachers taught us...
Let's tailor the lessons for each student.... Not to target min standards.... but to assure that each INDIVIDUAL student can do HIS best...
Click to expand...
That sounds a lot like current public school policy. No-student-left-behind sort of stuff. And that's why we have flight students now that don't have any frame of reference for understanding anything mechanical and no desire to understand anything. For some, their chief concern is the next text message, not getting an education that actually teaches them something useful. Flight training has been dumbed down enough already and we shouldn't be contributing further to it. I covered a lot of this stuff in my classes and the students that wanted it took it in and went forward with it, and several of them are, like me, both pilot and mechanic and some (unlike me) are flying airliners now. Since you can't force-feed a student, the rest did enough work to get the grade and went on, mostly, to do something other than fly. There is no satisfaction in just barely squeaking past the exams. Or in making uninformed decisions that wreck an airplane.

There's no need for the student to have an intimate knowledge of the inner working sof a governor, but he sure should know what it does and why. If he owns an airplane or flies one for some company, his description of symptoms to a mechanic can save either himelf or the company a LOT of time and money. It shortens up the diagnostic process a lot. Pilots who tell the mechanic that "the airplane doesn't climb too good anymore" are a lot less helpful than the one that says "the prop was slow to respond on the runup and in flight." When it comes to electrical systems, the complaint that "the lights went out" is worth much less than "the ammeter was flickering some until it finally went to discharge and stayed there."

If we don't smarten up we will lose our technological advantages to other nations that do a better job of educating their kids. It's already happening.
 
Hmmmm, instruction of male students only. Interesting concept.
 
Rgbeard said:
Where's the part of this discussion that addresses supersonic blade tip speeds?
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Way back in post #2 I mentioned propeller speeds. I said, However, the propeller is limited in its RPM; too fast and the drag mounts unacceptably as the outer portions of the blades approach the speed of sound."

And the tips don't have to get to supersonic speed to see big drag losses; remember that the propeller blade is an airfoil and that the airflow over its cambered side is going to be faster than the blade's movement through the air.

A Cessna A185F's 86" seaplane prop on the IO-520 at redline of 2850 has its tips going 729 MPH plus a little more depending on forward speed (736 MPH at 100 MPH forward). Under Mach 1.0 (767 MPH) but making a terrific racket due to the shockwaves coming off those tips. One 185 POAer here--I forget who--said he gets just as good takeoff performance by dialing the RPM back some on takeoff. Presumably the lost RPM is being made up for by increased efficiency on the slower blades with their slightly higher pitch.

Are there ANY GA airplanes with supersonic prop tips? Don't think so.
 
EdFred said:
Hmmmm, instruction of male students only. Interesting concept.
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Stop it. Things are crazy enough already.

About 15 or 20% of my students were women, and they learned the stuff as well as the guys and they were more careful with the airplanes. Of the few accidents or incidents we had where any damage occurred, none of them were flown by the girls.
 
Visually diagramming a system such as the constant speed prop and its governor, and all of its associated components, is a learning technique for students and a teaching technique for instructors. Just my opinion: it's often helpful as an aid in understanding.

There are some good resources out there for learning this system to the appropriate certificate level (i.e. private, commercial, ATP.) Why not use those?
 
James the MEI said:
Constant Speed Props - The Intro you never got<Snip>
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Interesting take on it. I think when you say "Power goes up as RPM increases" the cynicism in a student is going to be, "Well, duh, it's really the other way 'round. When you throw more avgas in the fire of course the RPM goes up because of the increase in power." So, instead of explaining, you're inviting having to do another explanation that has nothing to do with a constant speed prop.

The purpose of one is to maintain a propeller speed regardless of changes in airspeed. On takeoff, that would be maximum allowable with maximum manifold pressure. In cruise, it would be set at a fuel or power-efficient engine speed. On short final, it would be set for a go around, i.e., the same as for takeoff.

There's your purpose without raising skepticism, imo.
 
Ryan F. said:
In my opinion, John Deakin set the gold standard on teaching this subject matter.

https://www.avweb.com/features_old/pelicans-perch-16those-marvelous-props/
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Absolutely. Whenever anyone asks, I always tell them to Google "Manifold Pressure Sucks!", read that and follow the link to the next column (which is the one you posted).

And this is one area where the FAA's materials are ridiculously bad, which is a large part of why everyone keeps asking questions about it to begin with. IMO, they should buy Deakin's stuff and incorporate it.
 
It seems to me a picture is worth enough words to get the idea how it works:

VPprop.jpg

One of the best parts of a military ground school is having the actual components available to use as training aids:

governor.jpeg

Hands-on visualization breaks through learning barriers such as language and culture. You don't need to know the name of that thingy, as long as you can explain how it works...
 
BY Far...
Dan Thomas has contributed greatly to this conversation. And other have also provided moderating contributions, while my contributions strayed away from my intent for even starting this thread.

I hope that I can restate my positions.
Lesson Plans (hopefully) describe the Topic, Goals, Chronology of the lesson material and completion standards.
Of course a lesson plan does more.

I do believe that some elements are ( by some teachers) over taught and/or taught in the wrong sequence. Each of these can result in lowered results.

I have seen some CFIs teach prop govs in DEPTH early in the lesson when the student has not yet been provided a "Why do we even have CSPs or govs.

I have seen CFIs teach pendulous vanes and jet doors in depth and then require the student to be able to fully explain the same... rather than simply, " Air Gyros, self erecting, self correcting... have specific limitations such as xxx..... certainly the preceding was oversimplified... but, UNDERSTANDING the system and the ability to use it well and safely should be the principal on which training and testing is based.

In my initial new hire ground school with a regional airline, we were, for written and oral exams required to draw the enviro-pressure control system and the outflow valves with the air lines....why.
The training department also required that we be able to state the AoA of the prop blade at station x when the prop was feathered. why
The answer to both questions above is/was that the training department lost sight of the training goals, and lost the balance between rote memory vs understanding.

I personally trained two Northrop Grumman test pilots that needed to be qualified on a certain aircraft because this aircraft was the "in- flight test platform for other equipment". Their pedigrees were MUCH higher than most of ours.. These two experts spent most of their careers flying aircraft well outside of our experiences, but they had little prop time. They had zero interest nor need to learn about the prop gov on the aircraft I trained them in OTHER than , "We have a prop and a gov, it uses engine oil as the hydraulic fluid for motivation and control, this is how the prop and gov normally operate, these are the prop and prop gov limitations, these are the tests, these are the normal vs abnormal ops and now let's look at the QRH for normal ops, check list procedures, tests and abnormal ops...... done.

Certainly all pilots must be able to Fly Safely and Make Good Decisions. And they must know and understand enough about aircraft systems so that they can make good decisions.

Let's remove the prop and prop gov subtopic from the discussion, for a moment and consider the responsibilities of the CFI ( or any professional trainer).
Let's keep in mind the goals and plan in a lesson plan, the order in which the topics are taught, the depth of each topic and the depth of each topic vs the aptitude of the specific student...
I believe that it is our responsibility to teach to assure that the student can perform safely, and certainly the more incite we can give them the better.
And "Training to satisfy the minimum standard" is NOT the acceptable standard. But "over training" can also be a training error.

I expect that we have all seen under trained pilots. I expect that we all have seen pilots who can recite numbers and regulation chapter and verse and draw the pictures, , but you wouldn't want to fly with them. And many of us know pilots who are natural stick and rudder pilots who fly with smoothness and coordination, comply with the POH and regs but are not interested in the nuts and bolts. And ask a twenty year Delta Captain what his response is when xxx fails. His answer will be , "I refer to the checklist".

As serious professional flight instructors, Our performances need to advocate for safety and find a sweet spot in the middle of all of that.

One definition of learning is, "A change in understanding or behavior as a result of new experiences"
I am re-thinking my presentation.
Thank you all for the help.
James
 
Dan Thomas said:
That sounds a lot like current public school policy. No-student-left-behind sort of stuff. And that's why we have flight students now that don't have any frame of reference for understanding anything mechanical and no desire to understand anything. For some, their chief concern is the next text message, not getting an education that actually teaches them something useful. Flight training has been dumbed down enough already and we shouldn't be contributing further to it. I covered a lot of this stuff in my classes and the students that wanted it took it in and went forward with it, and several of them are, like me, both pilot and mechanic and some (unlike me) are flying airliners now. Since you can't force-feed a student, the rest did enough work to get the grade and went on, mostly, to do something other than fly. There is no satisfaction in just barely squeaking past the exams. Or in making uninformed decisions that wreck an airplane.

There's no need for the student to have an intimate knowledge of the inner working sof a governor, but he sure should know what it does and why. If he owns an airplane or flies one for some company, his description of symptoms to a mechanic can save either himelf or the company a LOT of time and money. It shortens up the diagnostic process a lot. Pilots who tell the mechanic that "the airplane doesn't climb too good anymore" are a lot less helpful than the one that says "the prop was slow to respond on the runup and in flight." When it comes to electrical systems, the complaint that "the lights went out" is worth much less than "the ammeter was flickering some until it finally went to discharge and stayed there."

If we don't smarten up we will lose our technological advantages to other nations that do a better job of educating their kids. It's already happening.
Click to expand...

Actually the schools don’t teach what the students need to know but teach lots of stuff that they likely will never need to know.

How many kids can name off their 10 basic human rights and apply them to daily life, can tell me what jury nullification is and how and when to use it

Can cook a raw chicken

Can build a box out of wood

Can do a P&L list and make a yearly business plan

Shoot a rifle, plant a tree, basic first responder medical aid, drive a car and do basic maintenance, understand democide and recent history beyond memorization.

But they can do lots of math that likely won’t be needed and have been trained to operate by bells, obey without question, etc.

Public schools were doomed from the start, the more people let the gov raise their kids the more useless of a human they become.


Same with this prop stuff, the actual function is hardly taught, this setting for this, this setting for this, it’s just not fluid, but they will teach them details that are trivia night fun to know type stuff, but if little to no use in the air. And don’t even get me started on making acronyms for every damn thing.
 
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James331 said:
Actually the schools don’t teach what the students need to know but teach lots of stuff that they likely will never need to know.

How many kids can name off their 10 basic human rights and apply them to daily life, can tell me what jury nullification is and how and when to use it

Can cook a raw chicken

Can build a box out of wood

Can do a P&L list and make a yearly business plan

Shoot a rifle, plant a tree, basic first responder medical aid, drive a car and do basic maintenance, understand democide and recent history beyond memorization.

But they can do lots of math that likely won’t be needed and have been trained to operate by bells, obey without question, etc.

Public schools were doomed from the start, the more people let the gov raise their kids the more useless of a human they become.


Same with this prop stuff, the actual function is hardly taught, this setting for this, this setting for this, it’s just not fluid, but they will teach them details that are trivia night fun to know type stuff, but if little to no use in the air. And don’t even get me started on making acronyms for every damn thing.
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Actually, it is not just kids, but most adults can't do most of the things you listed here either. In fact, it is the younger ones who think I am cool because I build all sorts of stuff. The older ones think I am wasting time on things that can be easily bought at the store. As a matter of fact, we had that discussion here a few weeks ago, and shockingly even some pilots argued that more time spent in school made a better professional.
 
Rgbeard said:
Hmmm. Wonder if there's a reason for that.

When the Cessna 175 engine developed higher RPMs, the prop was sent thru a gearbox.
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Slower, larger propellers are more efficient. Engines produce more HP per pound at higher revs. These are the reasons homebuilders often use geared or belt redrives on their auto engine conversions, as well as airplanes like the Cessna 175 and the 421, some radial engines, and the big V-12s like the Allison and Rolls Merlins used in WWII. We see gearing now on the Rotax engines like the 912, 914 and so on. And the Thielert diesel was, and Austro diesel is, geared.
 
James the MEI said:
And ask a twenty year Delta Captain what his response is when xxx fails. His answer will be , "I refer to the checklist".
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Yeah, you should see the blank stares I get when the applicant reads the checklist, and I ask how to accomplish that step in the checklist or what result they expect to see.
 
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Since we're talking poop speed. Is there a linear association between poop speed and coffee consumption? Maybe an overlay of the poop/coffee curve with the poop/taco truck burrito curve.

I believe I understand the basics of CS props but, I have learned some from this thread partly from reading about a concept again and/or in slightly different terms. My opinion is that the additional information is most likely to be useful when something goes wrong or isn't working as intended. With the added info, I've got a better shot of a positive outcome from managing the situation. Now back to poop speed...
 
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IK04 said:
One of the best parts of a military ground school is having the actual components available to use as training aids:

View attachment 79645

Hands-on visualization breaks through learning barriers such as language and culture. You don't need to know the name of that thingy, as long as you can explain how it works...
Click to expand...

I used a cutaway just like that in my class. And McCauley used to have a dandy brochure that had all those neat pictures that laid out the system and how the components interacted at various speeds and loads. I had a big stack of them that I handed out to the students. It used to be on their website, too, but I can't seem to find it anymore.
 
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James the MEI said:
And ask a twenty year Delta Captain what his response is when xxx fails. His answer will be , "I refer to the checklist".
Click to expand...

That only goes so far. We had complete checklists in our training airplanes too, but the graduate needs to know, reflexively, much of that stuff. Many times there is no time to go thumbing through a checklist. Action, the right action, is needed right now. So that's why ATPs get periodic checks on those big expensive simulators where the examiners throw multiple horrible emergencies at them.
 
Rgbeard said:
Where's the part of this discussion that addresses supersonic blade tip speeds?
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It's coming ... just before the low wing-high wing discussion and after pitch for speed and power for altitude;)

James331 said:
Public schools were doomed from the start, the more people let the gov raise their kids the more useless of a human they become.
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Can't be a nanny state unless you indoctrinate correctly comrade:confused:
 
The amount of power an engine produces is proportional to the amount of fuel it burns. Assuming we are talking about a spark ignition engine, the amount of fuel it can burn depends on the amount of air it can take in. The amount of air it can take in is determined by two things, its engine speed (RPM) and its throttle opening (manifold pressure), just looking at RPM alone will not tell you how much power the engine is generating.

If you look at a power curve for a spark ignition engine, you'll see there is a torque peak and a power peak. Once you get past the power peak, making the engine run faster will generate less power. Also, these power curves are done at full throttle. If you look at the POH of an airplane that has a constant speed propeller, you can see the percent of power generated at different RPM and manifold pressures.

Engines are (slightly) more fuel efficient at lower RPM and larger manifold pressure, partially because of reduced friction at lower engine speeds and partially because of pumping losses. Propellers have less drag at lower RPM, so there's another reason to run the engine slower in cruise. There is a significant limitation though, as the combination of high manifold pressure and low RPM can cause an abnormal type of combustion knows as detonation, which can destroy an engine in a manner of minutes. So, avoid high manifold pressure/low RPM situations, especially with a lean mixture.

The really important things for a pilot to know about a constant speed propeller are, IMO, pretty simple.
  • The prop control adjusts a governor that attempts to hold the propeller at a constant speed.
  • It has limits, at very low power settings and at very high airspeeds it may not be able to do so.
  • When you make a reduction of power, change the throttle opening first.
  • When you make an increase of power, change the propeller setting first.
  • The engine/propeller system is somewhat more efficient at lower engine speeds/higher manifold pressure than vice versa.
  • The governor runs on oil pressure.
 
James331 said:
Actually the schools don’t teach what the students need to know but teach lots of stuff that they likely will never need to know.

How many kids can name off their 10 basic human rights and apply them to daily life, can tell me what jury nullification is and how and when to use it
Can cook a raw chicken
Can build a box out of wood
Can do a P&L list and make a yearly business plan
Shoot a rifle, plant a tree, basic first responder medical aid, drive a car and do basic maintenance, understand democide and recent history beyond memorization.
But they can do lots of math that likely won’t be needed and have been trained to operate by bells, obey without question, etc.
Public schools were doomed from the start, the more people let the gov raise their kids the more useless of a human they become.
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I call them what they are: Government schools. Lowest common denominator indoctrination camps.
After having to do it myself, I wouldn't wish the P/L, Business Plan on anyone! :no:

Cute word, democide, BTW.
 
NoBShere said:
Since we're talking poop speed. Is there a linear association between poop speed and coffee consumption? Maybe an overlay of the poop/coffee curve with the poop/taco truck burrito curve.
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I hear that a lot about coffee. Weird. Nothing I've ever eaten or drank has ever caused me a mayday call from the South Pole. I guess all that dirt and pond water I consumed as a kid gave me a bullet proof gut!
 
IK04 said:
I hear that a lot about coffee. Weird. Nothing I've ever eaten or drank has ever caused me a mayday call from the South Pole. I guess all that dirt and pond water I consumed as a kid gave me a bullet proof gut!
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I find coffee and eggs together most effective.
 
FormerHangie said:
There is a significant limitation though, as the combination of high manifold pressure and low RPM can cause an abnormal type of combustion knows as detonation, which can destroy an engine in a manner of minutes. So, avoid high manifold pressure/low RPM situations, especially with a lean mixture.
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Ah, but for your statement to be complete, you need to define what you mean by "high manifold pressure" and "low RPM". It's not the old "oversquare" rule. I commonly run at 24" or WOT and 2300 RPM, lean of peak. That gets me 170-175 KTAS on 12 gph... And my engine is now past TBO and still running strong.
 
flyingcheesehead said:
Ah, but for your statement to be complete, you need to define what you mean by "high manifold pressure" and "low RPM". It's not the old "oversquare" rule. I commonly run at 24" or WOT and 2300 RPM, lean of peak. That gets me 170-175 KTAS on 12 gph... And my engine is now past TBO and still running strong.
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I think that would be powerplant dependent.

What I'm really thinking of is after takeoff, when you reduce power, reduce manifold pressure first. My only experience in a constant speed equipped airplane was in an 0-470 powered Skylane, and IIRC initial climbout would be full throttle and 2600 RPM. If we were light, and we usually were, we'd climb the rest of the way at 23 inches and 2300 or 2400 RPM. Don't pull the prop back to 2300 RPM with the throttle wide open, reduce manifold pressure first.
 
Flown most of the planes I owned that had turbos under square, they all surpassed TBO. My current plane is a Bonanza, cruise is usually 24" and 2300 rpm, running lean of peak, and is on condition now after passing TBO.
 
FormerHangie said:
What I'm really thinking of is after takeoff, when you reduce power, reduce manifold pressure first. My only experience in a constant speed equipped airplane was in an 0-470 powered Skylane, and IIRC initial climbout would be full throttle and 2600 RPM. If we were light, and we usually were, we'd climb the rest of the way at 23 inches and 2300 or 2400 RPM. Don't pull the prop back to 2300 RPM with the throttle wide open, reduce manifold pressure first.
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That is the way to do it... If you even need to reduce MP. Often that first reduction is from, say, 2700 RPM to 2500 RPM, and 29"/2500 is a perfectly valid power setting for that engine. I think it's much more common these days to leave the throttle wide open and just bring back the prop to reduce noise and be nice to the neighbors on departure. John Deakin advocated that... But I bet it's also pretty common for people to still make an unnecessary power reduction based on being taught "the old way" (ie no oversquare).
 
flyingcheesehead said:
. But I bet it's also pretty common for people to still make an unnecessary power reduction based on being taught "the old way" (ie no oversquare).
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Yup. There's a lot of evidence in forum discussions that plenty of pilots never consult their airplane's POH/AFM. There's much good info in there that would answer many questions without having to post them. I've come across numerous airplanes in the shop that didn't even have the manual on board as required by FAR 91.9 (US) or CAR 605.04 (Canada).
 
One of the hardest things for me was understanding that the blue lever doesn't directly change the propeller pitch. That it sets the RPM which the prop will maintain by adjusting itself via the flyweights. If someone had pointed that out, I would've understood it much quicker.
 
Trever Oakes said:
One of the hardest things for me was understanding that the blue lever doesn't directly change the propeller pitch. That it sets the RPM which the prop will maintain by adjusting itself via the flyweights. If someone had pointed that out, I would've understood it much quicker.
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Thanks for that! I started out on a constant speed prop airplane, but after about 3-4 flights we went over to a Piper and then C172, so I never got the concept well.
I wondered if what you wrote was correct and googles with some more keywords, found this

”My problem with understanding this concept was that I did not know the pitch would be changing UNLESS I moved the blue lever. In my mind (no matter how much reading I did [including Google] or Youtube videos I watched, I continued to treat the blue knob as a mechanical connection to alter the propeller's pitch. ”
Actually in a flight sim web page which led to this article too which was very informative in this...

https://www.avweb.com/features_old/pelicans-perch-16those-marvelous-props/
 
Constant speed props are a good thing, we do adjust the propeller pitch when we move the "blue lever", but it is also self governing, so can change its own pitch as well " the constant speed " part...which really should be called constant RPM. Take off at 2700 RPM and 30 inches of manifold pressure, and once climbing through 1000' agl adjust to 2500 RPM, and 28 inches, then climb up doing 110 knots in cruise climb, where you want to level off at say 10500 asl. You push the nose over to level and accelerate to 174 knots, but the RPM stays at 2500 because the prop is not remain at the same pitch as it was in climb, its getting to a coarser pitch all on its own. Your now level, doing 174 knots, so pull the " blue lever" back to 2400 RPM and YOU just made the prop pitch courser again, but now you grab the throttle and pull it back to 25 inches, thus the engine is making less power so the prop without you doing anything has to go to a finer pitch on its own, to maintain that 2400 RPM at the reduced power setting. Cruise along at lets say 168 knots and 10500 asl, still at 2400 RPM, and 25 inches of manifold pressure. Getting near your destination you push the nose down some, careful not to exceed VNE or the yellow if very bumpy, the prop all on its own went to a more coarse pitch to still stay at 2400 RPM, despite the fact that you're now descending and doing 180 knots. You reduce power to 22 inches, and the prop just went to a finer pitch again on its own to maintain that 2400 RPM you set it at 90 minutes ago. The big thing is that in your head, think of it as a constant RPM propeller control " that blue lever ". Actually speed has nothing to do with it. You set the engine RPM and it will do its best to keep it there, but it has limitations so I say it will try to. If you set a low power setting, and then pull the nose up for climb at 2400 RPM, once it has gone to as fine of a pitch as it can, the RPM will drop because it simply is not making enough power to keep the RPM up at such a low power setting. So it can't always maintain the RPM you set, but it tries to within its design limitations. My last 7000 plus hours of flying have been about 99% in a constant speed propeller, or propellers type of plane. When talking to someone else I call it a "constant speed prop" so they don't think I sound stupid by being the only pilot they know who calls it a "Constant RPM prop" . But in the back of my head its always been just that, a "Constant RPM prop" to me. I basically send it a signal via the "blue lever" of what I want for my desired RPM, and all on its own it does its very best to try and keep it there. When I ask it to operate outside of its abilities, it lets me know by no longer keeping the RPM where I "asked it " to.
And if you see it starting to act oddly in flight, or leak a little bit on your walk around, you know that beautiful prop is about to inflict serious pain on your Visa card.
 
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