Page 206 - Theory and Design of Air Cushion Craft

Introduction 189

Fig. 5.1 Picture showing water surface deformation in/off cushion during model tests in towing tank.

1
Fr,=2.50
2
0.25 0.50 0.75 l.(
x=xll c

Fig. 5.2 Wave profile inside a cushion at various Froude numbers.

on early SES in China, for example, the air ingestion into the water cooling pump in
SES model 713 and into the water propulsion system for model 717 and WD-901.
The depth of the wave hollow inside the cushion is equal to four times the cushion
pressure depression, i.e. h = rj [pjv] = -4 where r\ denotes wave hollow depth inside
2
3
the cushion, p c, the cushion pressure (N/m ) and y the weight density of water 7(N/m ,y
2
3
= p w g, where p w is normally taken as 998.4 kg/m at 20°C and g as 9.81 m/s ). Once
the overall craft trim has been estimated at primary hump speed, it may therefore be