Page 75 - Theory and Design of Air Cushion Craft

Practical formulae for predicting air cushion performance 59

£=1500 900

Fig. 2.9 Dimensions of typical bag and finger type skirt on the large skirt test rig.

Table 2.4 Test sample data for big skirt test rig
Items xlB S/B b
1 0.512 0.0203
2 0.512 0.0289
3 0.512 0.0424
4 0.512 0.0610
5 0.512 0.0289
6 0.333 0.0289
7 0.700 0.0289

Analysis methods

The cushion pressure can be expressed by the following relations:
p c=f{h,H,,H 2,b,t,v },R ei,...} (2.17)
where the geometrical parameters are as shown in Fig. 2.9 and h is the hover height,
t the average nozzle thickness, t = Sib, } the jet velocity, Re^ the Reynold's number for
v
the jet nozzle, Re^ = v^t/u, and v the kinematic viscosity coefficient. According to the
theory of dimensionless analysis, this equation can be written as
PC = pjq-i = /, (hit, H }/H 2, S/B b, x/B, Re }) (2.18)
Bag pressure can also be written as follows:

A = PC /Pi = /2 (hit, H,IH 2, SlB b, x/B, Re }) (2.19)
2
where/7 t is the skirt bag pressure and q- } = 0.5p av }.