Page 160 - Theory and Design of Air Cushion Craft

Static transverse stability of SES on cushion 143

Input data
Craft parameters, sidewall dimensions and offsets, lift fan characteristics
T

Series of heeling angles
I

Series of inner sidewall drafts { t
Option 1 Option 2

Find corresponding area Find cushion pressure
of air leakage A^, A J2 from weight equation, p c

Find corresponding cushion pressure
from the energy equation

Find general solution of equations (4.8 and 4.9)
i.e. the cushion pressure p c and equilibrium inner draft of sidewalls t

Determine restoring moment M fl at heeling angle 6

Restoring moment curve

Fig. 4.6 Block diagram for calculating the static transverse stability of SES on cushion.

Model and test facility
The static transverse stability for two SES models on cushion were determined by
direct measurements at MARIC and dynamic transverse stability tests were also car-
ried out for one of these models.
The leading particulars for both models are shown in Table 4.1 and a typical sec-
tion of the sidewall is shown in Fig. 4.7. During the tests, solid ballast was moved to
cause model heeling, then the heeling angle measured by a clinometer.

Experimental results
During heeling of an SES on cushion, the restoring moment of the craft will be due
mainly to the difference in buoyancy of the sidewalls unless the sidewalls are very thin.
Experiments normally include the following:
1. Determining the effect of the fan speed on the static transverse stability.