曝光台 注意防骗
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Then, the variation of elevator deflection with equilibrium or trim-lift coefficient
can be expressed as
where
d8e _(dC,)fix
dCL - Cm8
- xcg - No
Cm8
Cm8 = -a, V i r7r r
(3.101)
(3.102)
(3.103)
We observe that, for a statically stable airplane, d8e/dCL < O. The term Cm8 iS
often called the elevator control power.
We can express the variation of the elevator deflection with trim-lift coefficient
as
where
8e.o =
=8e.o- C N C~
(3.104)
(3.105)
(3.106)
C .u,+ CJ .f - ar(cLrw.oL _ iw + it)Vi
(3.107)
-CiuB
Here, a'w.oL is the wing zero-lift angle of attack, which depends on wing camber
and wing twist. Usually, the tail setting angle /, is adjusted to make 8e,o positive.
From Eq. (3.105) or (3.106), we observe that the elevator deflection required
to trim a given lift coefficient directly depends on the level of stick-fixed static
stability. It is through this relation that the pilot gets a feel of the level of stick-
fixed stability of the airplane. This level changes from one trim point to another
if the center of gravity shift or the wing camber manipulation is employed for
longitudinal control. In such cases, the pilot will immediately sense it by observing
differing amounts of elevator deflections needed for trim.
6.
STATIC STABILITY AND CONTROL
+
6to
m
6i.n lr,
L.L
lcg.t No
┏━━━━┳━━━━━━━━┳━━━━━━┓
┃ ┃ ┃ ┃
┣━━━━╋━━━━━━━━╋━━━━━━┫
┃ . ┃"-""'r.--' -- ┃?; -- - ┃
┃ . ┃ ┃-, -.t.-'. ┃
┃-4 ┃ ┃ ┃
┃'\ _t ┃ ┃ ┃
┃ { ┃ ┃ ┃
┃ < ┃ ┃ ┃
┗━━━━┻━━━━━━━━┻━━━━━━┛
lc92 7rcgi
mi
┏━━━━━━━━━━━━━━━━━━━━━━━┓
┃ ---lcg= Ntj ┃
┃ _CLmat Cl ┃
┃ K:~: ┃
┣━━━━━━━━━━━━━━━━━━━━━━━┫
┃ X::, ┃
┣━━━━━━━━━━━━━━━━━━━━━━━┫
┃ ┃
┗━━━━━━━━━━━━━━━━━━━━━━━┛
Fig. 338 Effect of center of gravity locahon on elevator deflection for trim.
213
Typical variations of the elevator deflection with trim-lift coefficient for various
center of gravity locations are shown in Fig. 3.38. For a given center of gravity
location, we observe that a statically stable aircraft needs an upward (negative)
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