706 PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
D
M
q 130?,:lcr = -0-75
-/ /
┏━━━━━━━━━━━━━┳━━━━━━━━━━┓
┃ LEFT SIDE ┃ RIGHT SIDE ┃
┃ -zls ┃-1-. ┃
┃" ┃-. .o -105 o ┃
┃o 30 ┃-o82O,s 'I5 O ┃
┃ O' l5 (? ~5:3~ ; ┃ ┃
┃ I[l ┃ itl ┃
┗━━━━━━━━━━━━━┻━━━━━━━━━━┛
yls
o
Flg. 8.36 Static vortex locations o'ver 80-deg delta wing at various roll angles for
a = 30 deg.3o
80-deg delta wing. As said earlier, the angle of attack for the onset of wing rock is
below that for vortex asymmetry. Therefore, what actually happensis that, once the
free-to-roll delta wing model starts oscillating because ofloss of roll damping, the
vortex'asymmetry gets established and leads to a sustained,limit-cycle oscillatory
motion.
When the model rolls to the right, the vortex on the right wing (down going)
moves closer to the wing surface, leading to an increase in the lift, whereas that
on the left wing moves away from the wing surface, lcading to a decrease in the
lift. This leads to a stable variation in the static rolling moment with sideslip/roll
angle as observed in Fig. 8.33a The closer the vortex is to the wing upper surface,
the more the lift on that part of the wing is because the suction is higher.
The dynamic vortex positions are presented pictorially in Fig. 8.37a.ltis evident
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