Tham khảo tài liệu 'thiết kế kỹ thuật máy bay chiến đấu episode 2 part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | RECIPROCATING ENGINES 295 Fig. Factors affecting engine power output from ref. . Space technology has brought about a range of semiconductors capable of transforming solar energy into power. Silicon is about 15 per cent efficient gallium arsenide 11 per cent and cadmium sulphide 8 per cent ref. . Organic cells might be much more efficient but they are some way off. Typical silicon cells are about in square 2 cmX 2cm thick 10to 12mm and 3lb . They are expensive around 75 to 200 per watt generated at 1974 prices. Bright sunlight in the tropics has an energy equivalent to BHP ft2 1 kW m2 . A power unit with propeller having an efficiency of 80 per cent would be able to produce BHP ft2 kW m2 . This means that about 200 ft2 m2 of wing area covered with silicon cells would be needed to produce 3 BHP kW for a weight of 28 lb kg minus electric motor and propeller. The specific weight of such a bank of cells would be something like lb BHP kg kW . 296 THE DESIGN OF THE AEROPLANE Plate 7-2 Liquid-cooled automotive engine developments considered for Blackburn B-48 replica in chapter 15 example 33. Top Bonner Sapphire V6 200 BHP installed in a De Havilland Chipmunk. Aero-Bonner Company Ltd Shoreham UK Bottom TE495-TC700 700 BHP Thunder Engines Inc USA RECIPROCATING ENGINES 297 Power produced varies linearly with incident sunlight. There is marked degradation with latitude and the amount of cloud. On a cloudless day in a temperate latitude around 53 deg north say we might expect solar input and propulsive output around 75 per cent of the values given. Propellers A propeller consists of a number of wing-like aerofoils designed to convert torque into thrust each one of which is subject to the same aerodynamic laws and influences as any other lifting surface. To generate thrust a propeller blade has to be rotated at an angle of attack to the local airflow. The local airflow is conveniently seen