# Tag Info

36

Before we get started, I should mention that the most basic constant-speed propellers were driven by balancing air pressure and centrifugal force. The blades were shaped in such a way, or equipped with a counterweight that would cause the blade to intrinsically move to a shallow pitch. However, when air was moved over the blade, it would begin to overpower ...

22

The engine is the same, not simpler. There is one additional level of complication to the system -- the constant speed propeller has a number of extra parts. The pilot needs to handle one more lever, selecting the speed. And needs more training in order to remember to put it at the right setting in various flight conditions -- not to mention how to handle ...

14

The answer to your question is actually really simple: do not exceed the limitations specified in the POH. Really, that's it! Note that LIMITATIONS are not the same as RECOMMENDED PROCEDURES. Recommended procedures are just that: recommendations. Limitations (exclusively from the "limitations" section of the POH) are the hard and fast rules you must ...

12

I recently moved from a fixed pitch propeller (FPP) (cessna 152) to a constant speed propeller (CSP) (Piper Dakota). In the FPP scenario the engine RPM is controlled by the throttle only. High throttle means high RPM and high power/thrust. In the CSP scenario the engine RPM is controlled by the throttle as well as the propeller pitch. One important thing to ...

12

"Dictate" is the wrong word. Within the ranges listed in the POH, the pilot may select rpm/MP settings as he pleases to meet other criteria. Charles Lindbergh instructed many WWII pilots in a technique to extend range, by flying with low rpm and high manifold pressure. This extended range by reducing the "pumping losses" required to maintain low ...

10

The propeller blades indeed have least resistance when aligned with the inflowing airstream, however the inflowing airstream is not the free stream at infinity, but the vector sum of free stream velocity $V$ and rotational velocity of the propeller blade $\omega \cdot r$. In the picture the local Angle of Attack is indicated as $\alpha$. Increasing blade ...

8

The POH has performance tables (random example: http://www.avsim.com/pages/0310/Carenado/Manual5.jpg) showing fuel burn, true air speed, and %hp, for a given altitude, RPM, and manifold pressure. The pilot selects a performance configuration based primarily on what speed they wish to cruise at, which in turn determines how much fuel they're going to use. ...

7

The specific reasons may be specific to each propeller/engine combination, but in general it seems to be related to stresses. According to this King Air POH on page 2-2: Stabilized ground operation between 400 and 1,150 propeller RPM is prohibited. Operation between 0 and 400 propeller RPM is permissible only with propeller feathered. STABILIZED ...

7

Koyovis explained it with maths and cool diagrams, here is my layman's version, if it helps. You're confusing aircraft drag with the drag on the prop. Since the prop is powered, it typically produces thrust not drag with respect to the aircraft. It only produces a net drag if it's windmilling (that is being turned more by the airflow than by the engine) - ...

6

Variable pitch (with feathering) was virtually universal on (at least American) multi-engine fighters, bombers, and transport aircraft even early in the war: the DC-2 had feathering variable pitch, and it entered service in 1934. The P-38 had feathering and variable pitch, and was in service before the US entered the war. Constant speed propellers were ...

6

What happens is when you're on final and you move the prop to MAX RPM, the prop governor moves the blades finer until the RPM is at red line, then governs RPM there by adjusting blade angle as required. As you reduce throttle, the governor moves the blades finer and finer trying to keep the RPM that has been set (maximum or redline RPM in this case). As ...

5

Most of high performance propeller aircraft use constant speed propellers, with variable pitch. The speed remains constant over (most of) the flight regime, while the propeller pitch is varied according to the requirement (by the Constant speed unit or CSU). In case the propeller is stopped in flight (for example, due to engine failure), the propeller pitch ...

5

A propeller has an optimum AoA, where the thrust/drag ratio is highest. A variable prop can maintain this optimum AoA at a wide range of speeds, thereby reducing fuel consumption. That's all it does. Fixed wing propellers have a dilemma that at take-off they require maximum thrust, and in high-speed flight the engine will need to be throttled back to ...

4

What you know about variable pitch propellers is generally correct. If you make a slight change, your flight instructor would not have had any reason to object: They keep propeller blades near their optimum angle of attack across a wide speed range. As the distance from the hub increases, the blade section gains circumferential speed while being in the same ...

3

You can find the full text of the NTSB investigation here and according to that report (bolded for emphasis), Examinations of the left propeller components indicated a propeller blade angle of about 3 degrees at impact. This position was based upon the position of the pitchlock acme screw. The left PCU ballscrew position indicated that the PCU had ...

3

Most WW II era military aircraft had constant speed propellers. People often confuse variable pitch, controllable pitch, and constant speed. In general practice they are all the same thing as all constant speed propellers are just the most common form of a variable pitch propeller. There were very few aircraft where the pilot only had a simple control to ...

3

A pilot requires some additional training and, in most jurisdictions, a formal signoff before being allowed to fly aircraft fitted with a CSU What jurisdiction is that? Who is the formal signoff satisfying? In the US, I went from flying a Cessna 150 with fixed pitch prop and 100 HP to flying a Cessna 177 with constant speed propellor and 180 HP, also fixed ...

3

According to this transcript of the actual mission report from one of the pilots, they did indeed run over square I flew the last 500 miles into Tokyo at altitudes ranging from 1000 feet to 4000 feet in order to fly in the thin overcast and clouds to avoid detection. I used 28 inches of manifold pressure and about 1370 RPM and indicated between 150 ...

3

The purpose of a variable pitch prop is to allow is to allow the pilot to select where on the engine's power curve (s)he wishes to operate the engine. When full power is needed, as for takeoff and initial climb, the throttle is fully opened and the pitch set as shallow as required so as to allow the engine to spool up to the peak of its rated power curve. ...

3

When setting cruise power, if you were to set the manifold pressure first, it would not remain constant as the RPM is reduced. It would have to be re-adjusted after lowering the RPM. When adjusting the RPM lever you are actually controlling a governor which maintains a constant RPM. Any change in manifold pressure will not cause a change in RPM. So ...

3

This is based on another answer I wrote: (Own work) Plane moving forward plus blade moving down gives the prop a new velocity vector, shown above in red. Relative air(speed) is still coming from ahead—but this now no longer concerns the propeller as it has its own velocity vector. As you can see, if the RPM remained constant (down arrow), and the plane ...

3

The advantages of oversquare (MAP > RPM/10) are: less vibration, noise, heat, and wear longer engine life as a result of this much less noise emitted from the engine/propeller more efficient cylinder charging and better combustion, gives lower fuel consumption if leaned properly less power lost to friction inside the engine — Source ...

2

I think acpilot covered most of it. I'd like to add this little tidbit to assist in thinking about how to use your constant speed prop. A constant speed prop is like a continuously variable transmission. The main settings to be concerned with are climb and cruise. In a climb scenario, particularly takeoff, it is desirable to have all power available, ...

2

The general rule of thumb that I am familiar with is 2400RPM set by the governor control lever and 23in-Hg for manifold pressure set by the throttle lever. This is what we do in a Diamond DA-40, for example. I have seen the same settings used in other small aircraft, but I am sure there are variations between models.

2

Most aircraft today either have a fixed pitch propeller, or have constant speed propellers where the RPM is controlled by a governor. Some aircraft have ground adjustable propellers, or manually controllable, variable pitch propellers, but they are pretty rare these days. Cessna 170's were all built with fixed pitch propellers. It is possible to modify ...

2

There is a big difference between "by feel" leaning of a carburated vs fuel injected engine. Carburated engines have less even fuel distribution and when leaning, one cylinder, the already leanest one, will start to misfire quite a bit before the others. So with a carb it's easy to detect one cylinder starting to misfire (the cylinder usually doesn't ...

2

Yes. The prop has a low pitch (fine/high rpm) and high pitch (coarse/low rpm) stop. The low pitch stop sets the blades quite a bit finer than you would have with a fixed pitch propeller, which is usually set at a pitch that will give more or less redline RPM while climbing at wide open throttle. If a constant speed prop failed and the blades went to the ...

2

I believe an Arrow operates the same as my Cardinal. With low manifold pressure, there is not enough oil pressure to drive the prop into anything other than flattest configuration no matter where the prop control is at. If you were take off with prop control not all the way in, then in theory the prop would start getting more twist as engine speed came up, ...

2

An important thing to keep in mind is that the propeller control system has no idea what the blade angle is (except in BETA mode systems which is another topic completely). It's a flyweight governor that just moves the blades coarser, finer, or holds them static based purely on engine speed, and the speed setting from the prop lever is just increasing or ...

2

The description of the accident says the propeller went to a flat pitch of 3°, which is still positive. At such angle, the air is trying to spin the propeller in the same direction as the engine, so the engine running helps the propeller spin. Only if the propeller went all the way to negative pitch would the engine be the air trying to spin it in opposite ...

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