it probably is worth varying the RPM occasionally to keep the governor oil warm and refreshed
Varying the engine power should do the same thing: rotate the blades a bit, because each change of power (torque) needs a pitch change to maintain the rpm constant.
Ok I have to say that I really use the range of the blue lever, that’s what it’s there for! And you should too if the green arc and workload allows.
I typically give it 2000 or less in cruise. A good setting is around 23 inch MP and 2000 RPM, that gives close to 150 knots and around 9 to 9.5 Gal per hour (depending on load and weather) on my plane.
2700 on takeoff, 2500 for climb (climbing on 75%) and 1900-2000 for cruise.
On descent I go down a bit, you really note how it improves glide ratio. Maybe to 1600 on low power settings.
Pax love that! We can fly without headsets at 2000 or below, it’s amazing..
Remark: only do that if terms like “red fin” or “red box” sound some bells, and if you know what power settings actually are ok. If not stick to the book because the wrong handling can harm the engine.
Yes; that is all true, but at 2000rpm you are seriously limiting the max power of your engine. It is probably OK for cruise at FL100 or so.
I once flew EGKA-LEGR at 2200rpm, to squeeze out the most range, but I was at FL120 max. And I was not going fast 
Continental has an SB recommending not to go below 2300 RPM on the IO520 series.
JoeMama_the_Pilot wrote:
Something about CSP simply doesn’t click in my head.
Ok, let’s try to think of RPM in the context of gears in a car. Imagine high RPM as being in 1st gear, while lower RPM settings correlate to the higher gears of the vehicle. When initiating your drive, starting in 1st gear is essential. This is where we generate maximum torque, providing the necessary power to get moving from a standstill. However, it’s crucial to note that operating in this gear is considerably inefficient. The reason behind this is that, while 1st gear offers a significant amount of torque, it does so at the expense of fuel efficiency due to the high engine speed required to maintain this power output.
As you gain momentum, there’s a diminishing need for the intense torque that 1st gear provides. This is when you shift up to higher gears, allowing you to cruise at your acquired speed but at a lower engine speed. Such a shift is advantageous because it reduces fuel consumption. The engine doesn’t have to work as hard to maintain vehicle speed, leading to a more efficient use of fuel.
Translating this analogy to aircraft propeller settings and RPM, the concept mirrors the operation of gears in a car. At a high RPM setting, the propeller is pitched to take smaller bites out of the air, akin to being in 1st gear. It’s relatively “easier” for the propeller to slice through the air in smaller increments, which, under the same throttle setting, causes the engine to rev up faster. This scenario is beneficial when you need quick acceleration or when taking off, as it provides the necessary boost in power.
On the flip side, when you adjust the RPM to a lower setting, the propeller’s pitch changes, allowing it to take much larger bites of the air. This adjustment is akin to shifting into a higher gear in a car, where the demand on the engine becomes “harder,” resulting in a slowdown of the engine speed despite maintaining the same throttle setting. This approach is preferable for cruising phases of flight, where efficiency becomes key, and there’s less need for the high power output required during takeoff or climbing.
And by decreasing the throttle setting first, you reduce the engine’s power output, ensuring that when the propeller pitch is increased to take larger air bites, the engine is not subjected to an abrupt and excessive load. Your POH will tell you the setting that are allowed so that you don’t hurt your engine by putting too much load on its components.
The reason behind this is that, while 1st gear offers a significant amount of torque, it does so at the expense of fuel efficiency due to the high engine speed required to maintain this power output.
Not a valid comparison. It is true that driving in 1st gear produces low mpg but for reasons different to those stated, because the engine torque (MP, en effect, being a proxy for torque) in 1st gear is low.
The purpose of a variable pitch prop is to efficiently absorb the engine torque at different airflow velocities.
Continental has an SB recommending not to go below 2300 RPM on the IO520 series.
Yes this is very true. A lot of engine types have limitations e.g. here you have a hatched area which is not allowed for continuous operation. The reasons vary; on this IO540 type it is believed to be a limit on the crankshaft flange.
What I meant was: what is your operating ceiling at max rpm, and at 2000rpm?
OTOH if you have a turbo then the whole debate shifts anyway.
To the OP, you will probably by now realise that there many more ways to use a CSP than there are pilots… but as some have pointed out, operating a CSP is fairly easy, and dare I say, standardised. But then, there are differences in practical uses.
Following applies to private/pleasure flying only: I still fail to understand the majority of pilots openly stating their love of flight, and then wasting fuel by operating at speeds that will result in incredible fuel flows (and noise) for comparatively little gains in speed, and at the same time reducing air time, e.g. the flying they love so much…
Factors such as total drag, engine efficiency at oversquare operation, overall aircraft specific efficiency, environmental issues, etc, are all set aside " ‘coz this airplane can go fast, so I fly fast", or some "my engine ain’t happy at such and such regime (maybe time to get that prop balanced) or temperature" fairytale.
No mistake here, fast flying can be fun, as in racing, slaloming around obstacles, overtaking slower brethren, etc. But certainly not justified full time if flying for pleasure.
For me, efficiency (and comfort) is the name of the game. A typical example of a flight to the pizza joint, e.g. crossing the Alps N-S. If solo, my take-off settings are 25/25, reducing 23/23 at about 500ft AGL. My field is surrounded by noise sensitive areas, and there’s no need for more. I usually climb at 110KIAS to one of the outbound sectors, and then reduce to cruise settings performing the climb check. Now the aim is Carson speed (the original Fuel Efficiency of Small Aircraft or an easier Mike Busch read What Price Speed?) which calculated for my ship results in 112KIAS. This typically returns about 125KTAS at 4’000ft at 19/19/19 (19", 1900RPM, 19l/h (5.01USG) of preferably Mogas. Further climb at increased FF will make use of the 4" oversquare setting approved by Lyco in the Operator manual. In this example (though on the return flight now, picture below) cruise at FL128 (max FL130 if MIL ON) the MP has dropped to 18.1, the KTAS has increased to 146, the FF (flying 7.5kts above Carson) has increased to 23.9 l/h (6.3USG), and the engine still produces 44% power.
For the descent and approach, the MP will progressively be reduced as to maintain 19 (forgetting and hitting Vne will usually get my attention…), and on finals (usually around 500’AGL) the RPM+Mixture levers will go to full.
In closing, a CSP is not only a tool to get the most performance out of an airplane and efficiency at all speed regimes, but can also be used to lower noise resulting in guaranteed less pilot fatigue.
NCYankee wrote:
it has been at 2500 for most of the flight, except for takeoff and climb to cruise.
That indeed works well for a Vtail, on an IFR flight you basically manage the mixture in climb/ set cruise (2300-2400) and dial in during descent I reduce (power) throttle no to overspeed, I don’t like to be in the yellow arc when going through cloud layers. For me 2700 initial climb, then 2500 cruise 2300. Manifold what I can get mixture stay out of the red box …once passed 6000 the red box starts too vanish ;-). Level changes above 8000 I increase the RPM… During IFR training it feels more like managing a steam boat..;-)….but I love it. I run about 12 GPH on FL100 and true 160Kts
