Page 94 - Theory and Design of Air Cushion Craft

78 Air cushion theory

Q,

(a)

•?—7 7"
(b)

(c)

Fig. 2.26 Three conditions for heave motion of ACV: (a) equilibrium; (b) underfed; (c) overfed.
reasonable for a conventional medium pressure bag and finger type skirt for small
perturbations. A responsive skirt with high deformability may have lower effective
damping.
Regarding the effect of hovering performance and fan and air duct characteristics
on the heaving stability and damping, we assume as follows:

1. The hovering performance of the skirt complies with the plenum chamber formula.
2. The flow air in the cushion is incompressible.
3. In order to compare the calculation value with experimental results, the rigid
ground surface is considered to heave vertically, and we keep the craft hard struc-
ture unmovable.
Then, according to the flow continuity equation, we have
dm d dV dp a
— = -rp = p a (2.41)
dt dt dt dt