Constant speed propeller

Variable pitch propeller are, in which the pitch of the propeller blades can be varied, whereby the angle of attack of the blades can be adapted to different operating situations. Variable pitch propellers come as and when the ship propeller used.

• 2.1 history
• 2.2 Advantages
• 2.3 disadvantages
• 2.4 Operation

Aviation

The variable pitch propeller aviation is an air screw, the blade pitch (pitch) can be adjusted on the ground or during the flight.

Variable pitch propeller in aviation are due to developments in the 1930s, when due to the increasing velocity range at the fixed pitch propeller aircraft increasingly used in its performance appeared to be limited. The adjustable propeller at the bottom, first used not satisfied, because only an adjustment to the launch site or to the load state was possible. By propellers that were adjustable in flight, it was possible to adapt the propeller to the ambient conditions during startup and also at cruise. The great advantage of the variable-pitch propeller is the possibility of adapting the propeller pitch to the actual speed, comparable to a continuously variable transmission in an automobile ( CVT ). Anyone who has tried to drive away in fifth gear, you know how hard it had propeller aircraft before the era of variable pitch at startup. Therefore one also has rather chosen only the third gear for aircraft and taken the low maximum speed in purchasing.

By introducing the variable pitch propeller, the performance of the aircraft have experienced a major advance: A Boeing 247 with constant speed propeller needed for the same engine power 20 % less off distance, had 22 % better climb performance and by 5.5 % more travel speed. In addition, the increased security in multi-engine airplanes, as with a failed engine, the corresponding propeller in " feathering " ( feathered fashion ) could be brought. This allows the motor turned not forcibly continue ( which could result from the motor housing to break the crankshaft), and the air resistance was much smaller - the remaining engines needed less power to keep the aircraft in the air. Even with touring motor gliders pitch propeller can be used with feathering to achieve less drag in motorless flight.

Basically an automatic or manual adjustment may be considered. Also, the variable pitch can allow a continuous change in the slope or just certain levels. The highest level of development of the variable-pitch propeller is the constant speed propeller ( constant speed propeller ), in which the engine speed remains constant and the shear force is controlled only by the movement of the propeller blades. This offers the advantage immediately to have in case of need the full engine power is available without first masses must be accelerated, as well as a thrust reverser is possible as well as a sailing position which provides the lowest air resistance at engine idle. This goes so far that in model aircraft for 3D flying stopped in the air and can briefly be flown backwards.

Benefits

More thrust at takeoff and climb, reduced load on the engine, as a result, significantly less fuel consumption. The possibility of feathering with faulty machine and the reverse thrust ( for braking on landing and maneuver at the airfield ) make modern flight operations with propeller aircraft possible.

Disadvantages

Additional maintenance and control effort, but ultimately be operated under the propeller aircraft only slow lowercase or training aircraft, and nostalgic machines without propeller. Even higher motorized variants of the standard aircraft Cessna 172 and Piper PA- 28 have variable pitch, and recently even individual Ultralight (eg, Flight Design ).

Shipping

In contrast to the conventional fixed pitch propeller, which today is usually made of a piece, " Controllable Pitch Propeller ", or variable pitch propeller blades are rotatably mounted on the hub while. This allows the slope (English pitch) infinitely adjustable from zero thrust in the direction of advance or withdrawal. Pitch propellers are used in units for use where good maneuverability, generator operation and / or highly variable duration speeds are required, such as ferries, passenger ships, feeder.

History

Variable pitch existed at least since the time around 1850. Their complex mechanical construction was their success but long way. The principle of modern variable-pitch propeller went back to the water turbine with Verstellschaufeln in Kaplan- construction. After the engineer had Englesson the Swedish company KaMeWa laid the foundations for the technical implementation, the company Escher-Wyss in 1934 brought the first Schiffsverstellpropeller modern design out. The circulating on Lake Zürich, Etzel was the first ship equipped with it.

Benefits

The drive can be in running marine engine "forward " to be "back" reversed, which is associated with a considerable saving of time, as the machine does not stop, and also must not be shut down to minimum speed. Hence the maneuverability is much improved.

The engine is started at zero thrust and ramped up to march speed, it is not yet burdened by drive torque at startup. The vehicle does not directly drive when the engine is started. A By rotating the shaft so that the machine by flow (eg passing ships in the harbor ) is prevented by the standing to zero thrust propeller. Ships with controllable pitch propellers do not have a reverse gear, possibly a reduction gear with fast- revving engines. Thus, a major weakness is omitted in the drive system. The efficiency is better at different speeds than in the case of a fixed pitch propeller.

Disadvantages

A variable is mechanically much more complex and expensive to manufacture than a propeller with a fixed arrangement of the propeller blades. The adjustment requires a certain amount of maintenance, and is an additional system that may fail. The power transmission is to some extent weakened by the multi-piece propeller blade and a separate hub. The energetic efficiency of propulsion is via a large part of the adjustment good, but not as optimal as the efficiency of a fixed pitch propeller, which operates in its nominal torque.

Operation

The adjustment is carried out hydraulically in large marine propellers, the necessary cables are axially through the shaft. Small plants can also be adjusted mechanically. The motor is unloaded (wing position zero) run up to its rated speed. When this is reached, the propeller can be used to maneuver. At a constant speed generator operation. In the case of the so-called Kombinatorbetriebs load regulation follows the parallel in the wide range Drehzahl-/Steigungskennlinien.