A new annular lift fan configuration that has very high lift efficiency is explored by using\na numerical scheme. The inlet lip radius and diffuser angle are maximized by semicircle duct\nwalls and the location of the lift fan is moved from the throat to the diffuser area to maximize the\ndiffusion effect of the ducted fan. The improved lift fan achieves the figure of merit of 0.772 and the\npower loading of 9.03 lbs/hp without ground effect, very close to the theoretical limit. Under the\nground effect, the figure of merit reaches 0.822 with the power loading of 9.62 lbs/hp. The improved\nlift efficiency deteriorates the transition characteristics with higher momentum drag and pitching\nmoment. However, with the aid of jet thrusts directly providing part of the lift during transition,\nthe peak of momentum drag and pitching moment can be lowered. A total thrust to weight ratio of\n0.7 is enough for all of the requirements in transition and in hover and for the maximum speed of\n0.75 Mach in cruise flight.
Loading....