曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
= Q2 sy12a- cos X(Iz - Ix)
N, = pq(L - ry)
Q2
= ~ ,os2 a- sin 2X(ly - Ix)
Ba/ance of pitching moments. We have
Mi = (Iz - Ix) r p .
Q2
= l:;- sin 2cr cos X(Iz - Ix)
(7.119)
(7.120)
(7.121)
(7.122)
(7.123)
(7.124)
(7.125)
(7.126)
To have a physical understanding of how the inertia-pitching moment arises,let us
assume that the masses Mi and M2 located at the fuselage extremities represent
inertia in yaw Iz ancl masses M3 and M4 located at the wingtips represent the
inertia in roll Ix as shown in Fig. 7.17. In a right spin, the inertia-induced pitching
couple due to Mi and M2 is nose up so as to fiattert the spin attitude, whereas that
due to M3 and M4 is nose down so as to steepen the spin attitude. The netinertial
pitching couple is the difference between these two opposing contributions.
An altemative way of understanding the inertia-induced pitching moment is to
use the gyroscopic analogy. Let us imagine that the inertias in pitch, roll, and yaw
are represented by three gyroscopes located at the airplane's center of gravity as
shown in Fig. 7.18. The gyroscope with inertia Ix is aligned along the x-body axis
and is assumed to be rotating with an angular velocity p. Similarly, the other two
INERTIA COUPLING AND SPIN
Fig. 7.17 Schematicillustration ofinertia-pitching moment.
657
gyroscopes with Iy and Iz are aligned along y- and z-body axes and are assumed
to be rotating with angular velocities of q and r, respectively.
Now if the gyroscope in Fig. 7.18c is disturbed because of an extemal torque
that imparts it a rolling velocity p, then, according to the gyroscopic principles,
it will precess in a direction perpendicular to a plane containing both the vectors
r and p. Hence, in this case, the angular velocity vector of precession will be
along positive y-axis (Fig. 7.19), which corresponds to a noseup pitching motion.
Similarly, if the gyroscope in Fig. 7.18a is disturbed by a torque that imparts it a
yawing velocity r, it will pitch in a noscdown directio: Thus: the net gyroscopic
action will be the difference between these two induced pitching motions.
Generally, Iz >/ so that the inertia pitching couple is positive or nose up
that tends to flatten the spin attitude. For equilibrium, the aerodynamic pitching
moment must be negative or nose down. At angles of attack well above the stall,
the nosedown aerodynamic pitching moment mainly comes from the horizontal
tail with wing making very little contribution.
Balance of rolkng moments. As we have seen earlier, unswept wings have
a strong autorotative tendency at stall. As a result, for angles of attack beyond
N1
the stalling angle, the aerodynamic rolling moment for airplanes having unswept
wings is generally prospin. Another factor that contributes to the development
658 PERFORMANCE, STABILITY, DYNAMfCS, AND CONTROL
, -.
, I
. .
,
, .
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：
动力机械和机身手册3(115)
