Phần này đề cập đến vấn đề làm thế nào để lựa chọn phân phối áp lực, đặc biệt là trên bề mặt cánh phía trên, để tối đa hóa thang máy. Ngay cả khi một câu trả lời hoàn toàn thỏa mãn yêu cầu được tìm thấy câu hỏi này khá khó khăn, nó vẫn còn để xác định hình dạng thích hợp aerofoil nên giả định để sản xuất phân phối áp lực quy | Propellers and propulsion 537 Calculate the forward speed at which it will absorb 750 kw at 1250 rpm at 3660 m 7 and the thrust under these conditions. Compare the efficiency of the airscrew with that of the ideal actuator disc of the same area giving the same thrust under the same conditions. Power 2imQ Therefore 750000x60 torque e Xo 5730Nm n rps n2 435 rps 2 60 Therefore Q 5730 . ko . . pn2Ds X 435 X 5 X Plotting the given values of kq and TJ against J shows that for kq J and Ĩ . Now J VjnD and therefore V JnD X X Since the efficiency is or the thrust power is 750 X 635 kw Therefore the thrust is m Power 635000 T 6460 N Speed For the ideal actuator disc 1 a . 6460 - -- 2PSV 2 X X 2 X 2 X whence a Thus the ideal efficiency is 771 ẼÕ4Ĩ7 0-958 or 95-8 Thus the efficiency of the practical airscrew is of that of the ideal actuator disc. Therefore the relative efficiency of the practical airscrew is or . Example An aeroplane is powered by a single engine with speed-power characteristic Speed rpm 1800 1900 2000 2100 Power kW 1072 1113 1156 1189 The fixed-pitch airscrew of diameter has the following characteristics J kr kQ 538 Aerodynamics for Engineering Students and is directly coupled to the engine crankshaft. What will be the airscrew thrust and efficiency during the initial climb at sea level when the aircraft speed is 45ms Preliminary calculations required are g kepn2Z 5 kọH1 after using the appropriate values for p and D. J V nD w The power required to drive the airscrew pr is pr ItĩììQ With these expressions the following table may be calculated rpm 1800 1900 2000 2100 Pa kW 1072 1113 1156 1189 rt rps 72 rps 2 900 1003 1115 1225 J kQ
