# Tag Info

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

Never say never, but that's not a prop malfunction that I've heard of or that was ever addressed in the turboprops that I've flown. We had various prop malfunctions, but the ways that things could fail that we considered would pretty much leave all blades in the same place. So without claiming that it could not, ever, ever, no way no how, not in all ...

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 ...

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 ...

4

In a well-designed propeller the hinge axis is very close to the line connecting the centers of pressure, so the aerodynamic pitch moment is rather small. The main force is friction; note that the centrifugal pull of the blades at the hub will put a considerable load on the blade bearings, so friction goes up with rotation speed. Regular propellers have ...

3

Control by wire? As in electrically? Many of the small planes like Cessna Cardinal use an engine like Lycoming O-360 (4 cylinder) use a spring to return the blades to a flat pitch, and engine oil pressure to change the blade pitch. The control knob in the cockpit mechanically allows the oil pressure to change the pitch. In other small planes, like a ...

3

I'm afraid that a thorough answer requires the contents of chapters 2 and 3 of Leishman, but here is an outline. The relationship between power and true airspeed from this answer: Power equals torque times angular velocity of the rotor: $P = Q * \Omega$. Most helicopters have constant speed rotors, so the relationship between torque and speed would be ...

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 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

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 ...

2

The flow direction reverses only through the bypass duct pulling by blades with negative pitch. A portion of it will still be sucked by low pressure compressor making 180° turn into the core. Having to counteract the losses in turn will obviously reduce the performance. As stated in research paper by the team funded by Rolls-Royce plc: "the core mass flow ...

1

Yes the prop blades can be mis-indexed on older model turboprop systems. the Hamilton Sundstrand 54H60 system uses a hydro-mechanical prop control and a dome to change pitch. When reinstalling the dome, it is possible to mis-index the blades so that they do not all have the same blade angle. There are however ways to check for this prior to starting the ...

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