Page 155 - Theory and Design of Air Cushion Craft

138 Stability

Fig. 4.1 Forces acting on SES due to heeling (sidewall emergence has not occurred).

0, I ' £T t I1It 1 1 t 1 It 1 t I1 ! !If 1 1
H
=C .. Ti -

Fig. 4.2 Forces acting on SES due to heeling (one of the sidewalls has emerged).

displaced volume of the sidewalls, but also to the cushion pressure, air flow, gap
height, vertical CG and bow/stern seal clearance.
Transverse stability on the US SES XR-1 decreased so severely during trials that it
overturned while turning at high speed. This was caused by a combination of adop-
tion of thin sidewalls to decrease water friction drag and the relative positions of the
craft's longitudinal and vertical CGs.
In China, there has also been such experience. Poor transverse stability was
experienced on the SES model 711-3 with thin sidewalls, the craft weight was
increased from 1.825 to 2.2 t and the cushion pressure-length ratio from 19 to
24 kgf/m . The transverse stability decreased to an unacceptable degree so that