Page 103 - Theory and Design of Air Cushion Craft

Air cushion wave-making drag 87

BJl c=0.25
fi,//,=0.125

channel width
greater than 10/ f
and infinite depth

5.0 2.0 1.0 0.6 0.5 0.4 0.3
Fri=vl-Jgl c

Fig. 3.2 C w plotted against F,\ for constant LJB^.

or

is the pressure/length ratio of hovercraft.
where pjl c
As mentioned above, the wave-making drag is a function of cushion length to beam
ratio, pressure to length ratio and Froude number. The cushion length/beam ratio
therefore plays a significant role in the craft performance.
Reference 19 also offered another similar formula for estimating the wave-making
drag:
= g / c) (3-4)
R W C w(4/? c W)l(p v
/
where c is the equivalent cushion length, i.e. c = S C/B C, S c the cushion area, B c the
/
cushion beam and C w the wave-making drag coefficient as shown in Fig. 3.4.
It should be noted that it is best to use the formula above together with formulae