Flying with constant speed propellers

To keep it simple:
- Fly the setting you want from the afm/poh
- to add power: mixture, prop, throttle
- to reduce power: throttle, prop, mixture

I can understand you. For many of us, it may seem very easy, but that is from a different perspective. When this is all new, and you have nobody competent to really explain it well, it is not that easy. That said:

Im supposed to be at 2000ft and maintain 90kt but due to the weather conditions i have 86kt.What do i change to accelerate back to 90kt? Do i change the throttle? Do i change the pitch? Do i change both the throttle and pitch into an entire different engine setting?

I think this is a poor example. One doesn’t really tweak engine settings to obtain a certain indicated airspeed in cruise flight. You rather set the power setting that you decide on during your preflight planning and the speed is “what you get is what you get”. You then take note if that if the speed is lower than expected and account for that in the planning for your next flight(s).

But apart from that, let’s just say that for some reason you want to increase the cruise power selected. You can generally obtain that EITHER by increasing throttle/MAP (if not yet at full throttle) or by increasing RPM (of not already at the maximum permitted for cruise). You merely HAVE to remain within any operating limitations set out in the limitations section of the POH, and you SHOULD keep a setting that is listed in the performance section of the POH (as only those MAP/RPM combinations will give you a known value for fuel flow and speed). The latter can obviously often be a bit less than book, as book speeds tend to be a bit optimisitic.

For the beginning: learn three MP/RPM settings (climb, two for cruise) and use them. Later you can start to understand things.

Most pilots I know stick to these three settings all their life, by the way.

I concur with boscomantico.

I had similar confusion initially. I spent a lot of time studying how it works, power, MAP, FF, etc lots of great information. But that’s more intellectually interesting than practical and definitely useful to understand while on the ground.

But in practice, what I have been taught that works well for me is to think in term of known power setting for different phases of flight, don’t try to dynamically adjust, just go to pre known settings, which you should learn for your aircraft:

So know settings for example for 75% cruise, 65% cruise, descent, approach, climb, etc and just switch between these settings as you need.

The reason for using a CSP ist to optimize the effectivity of the prop for a given point of operation. High RPM settings are related to a low angle of attack of the blades, good for climb performance, lower RPM settings with a higher AOA of the blades are for better cruise performance.
In general: For a given RPM setting, increase of MAP results in a higher AOA of the blades and otherwise.

For changing the power settings follow the procedures given in the POH to prevent engine damage, especially for engines with manual mixture control.

JoeMama_the_Pilot wrote:

Which do i change if im at 1900ft and i want to climb back to 2000ft? Which do i change in a turn if im slightly too fast and climbing or too slow and descending?

For small corrections change the MAP using the throttle. For cruise climb, descends refer to the settings given in the POH.

oeMama_the_Pilot wrote:

Currently the way i think about it, is that MAP is the engine load and the relationship between MAP and the engine RPM is that im managing how much load the engine outputs per engine rotation.

Depends what you mean by “engine load”, but…

The MAP determines how much power is generated at each power stroke. So the power output is determined by both the MAP and the RPM. That means that the same power output can be obtained by essentially infinitely many combinations of MAP and RPM. The performance section of the POH should give you many choices.

As others have written, you select power settings appropriate for the flight regime and use them. But if you need to fine tune the power setting, I would use the throttle (MAP) and leave the RPM constant.

Generally speaking, you want to have low RPM as that gives less noise, lower engine wear and slightly lower fuel consumption. However (as I’m sure you know from your training), too low RPM with high MAP is bad for the engine. Again, the POH will show you what the safe combinations are. (But the old saying that RPM/100 must not be lower than the MAP is a myth!)

Of course, to get maximum power from the engine you need both max RPM and max MAP.

All good advice. Props forward is great for climb and on a twin (I can’t remember the VP prop approach on a single, stupid I know) on final approach one would put props ppp (pleine petit pas) ie fully forward ready for the go round or re climb if needed.
IIRC 1 inch reduction map would have you descend around 100ft per min if keeping the same trim position. So for most final approaches one can reduce MAP by 5in for a 500ft per min descent.
As already said there is usually a table in the POH where one can set RPM via prop levers and MAP via the throttle and this allows you to choose whether to fly for a particular fuel flow or a chosen speed.

As others have said, memorise power settings for certain configurations and pay less attention to speed – it’s a bit slower and less direct than pitch/power in a 152 that can get you to a speed in seconds. eg in my Arrow

25/25 for climb
24.7/2100 for 65% cruise up to 3000ft and then FT/2100 above
21/21 for final approach

ILS approach maintain cruise power , put the gear down but fly level which gets you into the white arc, and then one stage of flaps. After that make minor adjustments in MP to increase/decrease rate of descent.

I struggled for ages with losing height in the circuit as I’d go gear down, reduce the power and then not adjust the AoA enough and descend like a brick and then have to put power back in and end up in a mess. Now I do gear down, let it settle, then flaps, then to be honest you end up nearly at approach speed without touching the power and can reduce to 21/21 when it’s stabilised.

There is no mixture in this aircraft, but the best way I’ve heard to understand intuitively is this: the throttle is like a foot pedal in a car, while the prop is like the gear shift. Fine pitch → higher RPM = lower gear, so more power available.

Now, operationally, you only need to know the following:

• on the ground, always stay fine pitch, and control RPM using throttle. This is fairly straightforward and behaves like you’ve always been used to
• in the air (rougly) pitch controls RPM and MP controls load (as you’ve said)
• use these predefined settings (you’ll fine tune them later): full low pitch / full throttle for takeoff ; edge of green/yellow arc RPM for initial climb / cruise climb ; 24.7" / 2000 RPM for cruise

Rules for the order of changing:

• increase right to left, decrease left to right: like in a car, if you want to accelerate, you FIRST lower the gear and then press the pedal (doing the opposite runs the risk of overtorquing)
• decrease left to right (for the same reason as above) – especially when switching to cruise

For piloting:

• in a descent, pilot FPM using the stick and speed using the throttle (you can keep cruise RPM or full fine pitch, depending on the situation)
• in a climb, always use climb power (green/yellow edge, full throttle) and pilot speed with the stick
• on final (to prepare for go-around), ALWAYS restore the full fine pitch (this is the most common mistake in CS prop)

It may seem complicated but it’s really not. You just have a few memory items for each situation (switch to climb power after takeoff, start climb in cruise, end climb, full fine pitch on final).

JoeMama_the_Pilot wrote:

Which do i change if im at 1900ft and i want to climb back to 2000ft? Which do i change in a turn if im slightly too fast and climbing or too slow and descending?

For 100ft you don’t have to touch power. You’ll lose maybe 2kt and retrieve them after. Anything above 300ft I would use climb power without thinking too much about specifics.
You don’t change anything in a turn (although you may use climb power if too slow doing 45° turns, but that’s unlikely).
If you’re too fast while climbing, you use the stick (as I said).
Too slow and descending, you use the throttle (like you’ve always done, with caveat to not use full throttle if you’re < 2000RPM).