Page 150 - Theory and Design of Air Cushion Craft

Effect of various factors on drag 133

2 3 4 5
v(m/s)

Fig. 3.48 Influence of cushion length/beam ratio on total drag of craft models in different test tanks. 1: tests in
MARIC pj( = 20; 2: same model, thicker skirt, different tank; 3: as 2, pj( = 15.7; 4: as 3, but in MARIC tank.

fl(x9.8N)
r

/
10
A \ //

^ ^^
if
"^
i
• ' Vr~~'' ^-| i i i i i i n i i
_\
\
W n
t t
(mm) (X9.8N) (r/min)
- 60 87.8 10000
/ -— O -— 40 87.8 10000

/ —A--- 20 87.8 10000

Fig. 3.49 Influence of inner draft of sidewalls (on total drag of SES model on still water.

Effect of air flow rate
It is probable that the air flow coefficient Q magnitude will not affect the take-off
performance of hovercraft (except too small values of Q) when the skirt has been
carefully designed, because of the good wave-yielding performance for flexible skirts.
However, craft drag at post-hump speeds will be closely related to Q. Therefore, the