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Fig. 2. Theoretically predicted hysteresis behaviour of an inextensible sail
profile of given slackness in inviscid flow, showing changes in sail shape and
the lift coefficient as angle of attack is decreased from a high value (1)
through ideal incidence (2) and beyond, when the sail becomes S-shaped (3) and
finally pops through (broken line), adopting a wholly convex shape with
negative camber (4). A subsequent increase in the angle of attack from this
point causes the profile to become S-shaped again (5) before positive camber
is restored. Profile chord lines are indicated in red.