Influence of Forward Speed on Lift Force of Air Cushion Vehicles

The theories and experiments of static peripheral jet in proximity to the ground with application to air cushion vehicles have been investigated in detail for a long time. It is, however, not too much to say that arguments about the influence of forward speed on lift force of A. C. V. (i. e. dynamical theory) have not been made sufficiently.In this paper, the influence of forward speed on lift force of A. C. V. was investigated using a two-dimensional wind tunnel model, and a simple method of theoretical calculation was presented, getting a fairly good agreement with experimental results. The followings are the main conclusions : 1) Total lift force of an A. C. V. is divided into two parts ; lift on upper surface CLu and that on lower surface CLl. They can be considered independently of each other.2) The pressure distribution on the upper surface is independent on the height over the ground and also the type of blowing, CLu is in proportion to jet momentum of blowing air.3) The pressure distribution on the lower surface is regarded as almost uniform except the both ends of the model.4) CLl on lower surface of the model can be calculated by using the simple theory presented in the present paper.5) When jet momentum coefficient Cμ takes small values, both two types of blowing-the A. C. V. type and the jet flap type-give almost same values of CLl. As the value of Cμ is increased, the CLl of A. C. V. type is increased with Cμ, but CLl of the jet flap type reaches the maximum and then it is reduced gradually.6) From the view point of the effective lift for the constant horse power, the jet flap type blowing is considered to have some merits to the A. C. V. type in the case of small Cμ. On the other hand, the A. C. V. type has more merit when the value of Cμ is large. The border line of merit is a straight line passing through the origin proportional to h/D.