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Aircraft design projects - part 6

Như đã đề cập ở trên, sự khác biệt giữa các lực đẩy và kéo các đường cong, với tốc độ cụ thể, đại diện cho năng lượng có sẵn cho thí điểm để tăng tốc (động năng lượng tăng) hoặc lên cao (tiềm năng năng lượng tăng) máy bay. Lực lượng dư thừa có sẵn (đẩy-kéo) tại tốc độ máy bay khác nhau, và với các máy bay kéo 'g', được hiển thị trên Hình 6.11. | Project study electric-powered racing aircraft 169 Fig. 6.10 Drag and load factor versus aircraft forward speed Fig. 6.11 t-d and load factorversus aircraft forward speed 6.7.2 Climb performance As mentioned above the difference between the thrust and drag curves at a specific speed represents energy that is available for the pilot to either accelerate kinetic energy increase or climb potential energy increase the aircraft. The excess force available thrust-drag at various aircraft speed and with the aircraft pulling g is shown on Figure 6.11. This figure also shows the advantage of fine pitch at low speed and coarse pitch at high speed. Using all the available extra energy to gain height provides the maximum rate of climb. Multiplying T - D by aircraft speed and dividing by aircraft 170 Aircraft Design Projects weight gives the max. climb performance of the aircraft at constant aircraft forward speed i.e. with zero acceleration . The term V T - D W is referred to as the specific excess power SEP . At sea level the maximum rate of climb versus aircraft speed is shown in Figure 6.12. Drag increase in manoeuvring flight as mentioned above has a significant effect on the aircraft SEP. Figures 6.13 and 6.14 illustrate the effect of choice of propeller pitch. Aircraft speed m s Fig. 6.12 Rate of climb versus aircraft forward speed Fig. 6.13 Specific excess power SEP versus aircraft forward speed fine pitch Project study electric-powered racing aircraft 171 Fig. 6.14 Specific excess power SEP versus aircraft forward speed coarse pitch 6.7.3 Turn performance Racing aircraft fly an oval circuit it is therefore necessary to investigate the aircraft turn performance in some detail to establish the optimum racing line. Good turning performance will allow the aircraft to fly a tighter turn and therefore cover less distance in the race. The pilot faces a dilemma. Pulling a tight turn will increase drag and therefore reduce aircraft forward speed. This loss of speed will have to