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---0.1424- - ;)( 00l0864)(1-0.3)
k -0.003) .
- -0.1021
Then,
NL = c8 - &Cj ),_
- 0.4021
H,{ = - &~. )_
-. 0.1021
Example 3.4
A light aircraft has a wing loading of 1450 N/m2, wing aspect ratio of 8, and
tail aspect ratio of 4. The aerodynamic center of the wing-fuselage combination
is at 0.24 mac from the wing leading edge. The static margin is -0.05. Using the
following data, determine the tab deflection to trim the stick force at a speed of
160 km/h in level fiight at sea level. What is the stick force gradient at this speed?
a,, -. a, = O.l/deg, croL.u, = /t - /w = 0, 8e = -2 deg, Vi = 0.6, e = 0.5a, r7t =
0.9, q". f = O.ICL, r = 0.5, Se - 1.85 m2,ce = 0.608 m, Chot--0.003ldeg, Ch&= '
- 0.006]deg, Ch.o = 0, Ch8, = -0.003/deg, and Gi :5.0 rad/m.
Solution. This aircraft is statically unstable because it has negative static
margin (Hn - -0.05). We have
1
8uim = --,,,.,(-. . +K2)
where
K"=-K, .C ~(:g )_
K' = ;:pK]
138 PERFORMANCE, STABIUTY, DYNAMICS, AND CONTROL
V
Fig. 2 28 Schematicillustrahon ofcorner \relocit)r turn.
From above relations, we observe that, for a given value of thrust T and aero-
dynamic efficiency Em, the turning performance improves with increase in load
factor n and lift coefficient CL but only to be limited by the aerodynamic limit
CL,max and the structurallimit nmn.
Assuming that the fiight path angle y is small, let us plot the variation of turn
rate to with velocity V for various values ofload factor n as shown in Fig. 2.28.
The curve corresponding to n = nhm represents the structural boundary and that
corresponding to CL,max represents the aerodynamic boundary. The velocity at
the intrersection of these two boundaries is called the comer vclocit)r. This is the
velocity for maximum instantaneous turn rate or MATR. For a typical fighter
aircrafi, the corner velocity is about 300-350 kn (550-650 km/h).vln a classical
tuming dogfight situation, the pilot who gets to his comer velocity first usually
gains an upper hand and has a better chance for first point-and-shoot capability.
In the following, we will consider the turning flight at corner velocity.
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