曝光臺 注意防騙 網(wǎng)曝天貓店富美金盛家居專營店坑蒙拐騙欺詐消費(fèi)者

 that the dynamic vortex positions differ appreciably from the corresponding static
 positions.ln addition, the dynamic vortex position for a given roll angle depends
 on the direction in which the wing is rolling. For example, consider all the vortex
 locations when 4 = +15 deg. The 'vortex locations are quite different depending
 on whether the modelis rolling in the positive or negative direction, i.e., whether
4 > O or 4 < O. A larger vertical displacement occurs when the wing is rolling in
 a direction away from the vortex, and a lower displacement occurs when the wing
 is moving towards the vortex. From Fig. 8.37b, we observe that the time lag exists
  only in the normal direction and not in the spanwise direction.
      To quantify the effects of the normal time lag,let Az - Zr - Zl denote normal
  asymmetry in vortex location as shown in Fig. 8.38. Let us assume that the strength
STABILITY AND CONTROL PROBLEMS AT HIGH ANGLES OF ATTACK   707
  60
  /,o
  20
*o o
    - 20
 -/o
    - 60
  og3oo oaa o~o oo6bo                    
┏━━━━━━━━━━━━━━━━━━━┓
┃oo ao  oo,  r                         ┃
┃_ooooooo                              ┃
┃D   O O  O O  O o Time,               ┃
┣━━━━━━━━━━━━━━━━━━━┫
┃-oooooooo9pooooqooo o1-5o o 2         ┃
┃           .   -    r. i       O  i n ┃
┗━━━━━━━━━━━━━━━━━━━┛
Time History
~  ~~
*= o(-)
t =t7
9= o (+)
t - t,&: to
5o (+)
3
5 (-)
I
t*5'(- )
t = tjo
Fig. 837a    Sketch of vortex trajectories in one cycle of wing rock.30
iso (+)
/ 5o (+)
I.
~
  ~ -. o (-)
t=t7
~/
  += o (*)
  t =to
708           PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
LEFT SIOE                    RIGHT SIDE
                 ,v                    
┏━━━━━━┳━━━━━━━━━━━┓
┃    -z,s    ┃       h-Dynamic hd   ┃
┃            ┃                      ┃
┃            ┃         o-Static Mea ┃
┃            ┃-o /:.,,.. '          ┃
┃       .tt  ┃        IIl           ┃
┗━━━━━━┻━━━━━━━━━━━┛
-1-6   -1-2 .- 0-8  -0-4     O     0-4    0-8    1-2    1-6
        y/s
suremc:nts
tments
Fig. 837b    Static and dynamic vortex Ioc:ations for a = 30 deg, zr/cr = -0.75.3o
of both of the vortices is identical. rlhen, Az > 0 gives rise to a positive rolling
moment and vice versa  Thus, when ~ is increasing or 4  > O,if AzP> O,itleads to
a destabilizing effect. In other word~s, a4la Az  > 0 corresponds to a destabilizing
effect and a#/aAz < 0 to a stable effecL
   In Fig. 8.39, the static and dynamic variations of Az during a wing rock cycle
are presented. We observe that a4/8Az < 0 for 20 deg S 4 < 45 deg during
positive half cycle and for -45 deg <  ~  S  -20 deg during the negative half cycle.
　
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