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┃~e,l ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃
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┃8a ┃ ┃ ┃~ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃
┃ ┃ ┃ ┃ ┣━╋━╋━╋━╋━╋━╋━╋━╋━╋━┫
┃ o ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃
┃ ┣━╋━╋━╋━╋━╋━╋━╋━╋━╋━╋━╋━╋━┫
┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃ ┃
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o .4 J LZ 1.6 zo :L4
xl
Crt
b)
Fig. 3.9 Variation of fuselage upwash ahead of the wing.l
STATiC STABILITY AND CONTROL
173
i+aa =/(i-j) (3.10)
'- - / )CNcr.f (3.11)
Cma.f= ,7f lf
where CNa. f iS the normal-force-curve slope given in Fig. 3.10, Xcp iS the center of
pressure location (measured from nose of the body) given in Fig. 3.11, and lf is the
total length of the fuselage. In Figs. 3.10 and 3.ll,lf = In +/A, fA = IAlbf.max,
and fN ~ In/b f.max. Note that the values of CNu g;vlen in Fig. 3.10 are based on
maximum cross-sectional area SB,max of the body and the slope of the pitching-
moment coefficient given by Eq. (3.ll)is based on the product SB*maxlf . Therefore,
we convert this result in terms of the standard reference area S (wing area) and
reference length c (wing mac) as follows:
Cmtr.f =(/ - .)CN..](S St: )
(3.12)
3.3-2 Mng Contribution
The nature of wing contribution depends on the relative distance between the
wing aerodynamic center and the center of gravity .ra (see Fig. 3.4). If the aero-
dynamic center is ahead of the center of gravity, which is generally the case for
Iow-speed general aviation airplanes, the wing contribution is destabilizing. For
modern high-speed airplanes with swept-back wings, the wing aerodynamic center
is usually aft of the center of gravity, and wing contribution is stabilizing.
The wing contribution can be expressed as
Cm.w = Cmac.,n + CL.wXa
where
CL.rju - aLf CtLU
N xa
xa -- _.
c
(3.13)
(3.14)
(3.15)
174 PERFORMANCE, STABILITY, DYNAMICS, AND CONTROL
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