Type of propellers螺旋桨类型
**** Hidden Message ***** Type of propellers<BR>In designing propellers, the maximum performance of the airplane for all<BR>condition of operation from takeoff, climb, cruising, and high speed. The<BR>propellers may be classified under eight general types as follows:<BR>1. Fixed pitch: The propeller is made in one piece. Only one pitch<BR>setting is possible and is usually two blades propeller and is often made of<BR>wood or metal.<BR>Wooden Propellers : Wooden propellers were used almost exclusively<BR>on personal and business aircraft prior to World War II .A wood propeller is<BR>not cut from a solid block but is built up of a number of seperate layers of<BR>carefully selected .any types of wood have been used in making propellers,<BR>but the most satisfactory are yellow birch, sugar mable, black cherry, and<BR>black walnut. The use of lamination of wood will reduce the tendency for<BR>propeller to warp. For standard one-piece wood propellers, from five to nine<BR>seperate wood laminations about 3/4 in. thick are used.<BR>Metal Propellers : During 1940 , solid steel propellers were made for<BR>military use. Modern propellers are fabricated from high-strength , heattreated,<BR>aluminum alloy by forging a single bar of aluminum alloy to the<BR>required shape. Metal propellers is now extensively used in the construction<BR>of propellers for all type of aircraft. The general appearance of the metal<BR>propeller is similar to the wood propeller, except that the sections are<BR>generally thinner.<BR>2. Ground adjustable pitch: The pitch setting can be adjusted only<BR>with tools on the ground before the engine is running. This type of<BR>propellers usually has a split hub. The blade angle is specified by the aircraft<BR>specifications. The adjustable - pitch feature permits compensation for the<BR>location of the flying field at various altitudes and also for variations in the<BR>characteristics of airplanes using the same engine. Setting the blade angles<BR>by loosened the clamps and the blade is rotated to the desired angle and then<BR>tighten the clamps.<BR>3. Two-position : A propeller which can have its pitch changed from<BR>one position to one other angle by the pilot while in flight.<BR>4. Controllable pitch: The pilot can change the pitch of the propeller in<BR>flight or while operating the engine by mean of a pitch changing mechanism<BR>that may be operated by hydraulically.<BR>5. Constant speed : The constant speed propeller utilizes a hydraulically<BR>or electrically operated pitch changing mechanism which is controlled by<BR>governor. The setting of the governor is adjusted by the pilot with the rpm<BR>lever in the cockpit. During operation, the constant speed propeller will<BR>automatically changs its blade angle to maintain a constant engine speed. If<BR>engine power is increase, the blade angle is increased to make the propeller<BR>absorb the additional power while the rpm remain constant. At the other<BR>position, if the engine power is decreased, the blade angle will decrease to<BR>make the blades take less bite of air to keep engine rpm remain constant.<BR>The pilot select the engine speed required for any particular type of<BR>operation.<BR>6. Full Feathering : A constant speed propeller which has the ability to<BR>turn edge to the wind and thereby eliminate drag and windmilling in the<BR>event of engine failure. The term Feathering refers to the operation of<BR>rotating the blades of the propeller to the wind position for the purpose of<BR>stopping the rotation of the propeller to reduce drag. Therefore , a Feathered<BR>blade is in an approximate in-line-of-flight position , streamlined with the<BR>line of flight (turned the blades to a very high pitch). Feathering is necessary<BR>when the engine fails or when it is desirable to shutoff an engine in flight.<BR>7. Reversing : A constant speed propeller which has the ability to<BR>assume a negative blade angle and produce a reversing thrust. When<BR>propellers are reversed, their blades are rotated below their positive angle ,<BR>that is, through flat pitch, until a negative blade angle is obtained in order to<BR>produce a thrust acting in the opposite direction to the forward thrust .<BR>Reverse propeller thrust is used where a large aircraft is landed, in reducing<BR>the length of landing run.<BR>8. Beta Control : A propeller which allows the manual repositioning of<BR>the propeller blade angle beyond the normal low pitch stop. Used most often<BR>in taxiing, where thrust is manually controlled by adjusting blade angle with<BR>the power lever. 感谢楼主万分感谢感谢万分
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