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Fig.3 56    Typical variation ofstick force with velocity.
v
   Historically, as the flight speed increased, stick forces increased significantly
and exceeded normal pilot capabilities. This led to the development of powered
controls.lnitially, power was supplied only to assist the pilot by means of hydraulic
boosters. With such a system, a proportion of the stick force was still needed to
be applied by the piloL K a booster failed, the system would revert. to full manual
control. Aircraft using such semimanual systems include the Boeing 707 series
and the B-52 Stratofortress Bomber.
    As flight speed increased further, it became more and more difficult to keep
the stick forces within the capability of an average human pilot, and this led to
the development of fully powered control systems. With such systems, the pilot
hardly does anything more than operate a small hydraulic valve, requiring a small
nominal force. The stick force virtually remains constantirrespective of the speed
or the defiection of the control surface. However,.to give the pilot some idea of
 the stick forces involved, an artificial "feel" is introduced to the system. This may
take the form of a simple spring providing an increased resistance with increase
STATIC STABILITY AND CONTROL
235
Fig.3 57   Generic airplane.
of control column movement, or it can be a complex simulator providing forces
proportional to the airspeed or Mach number.
                                       Example 3.1
      For the generic vehicle configuration shown in Fig. 3.57,length of the fuselage =
13.0264 rD,S = 25 ] ~67 r112, Cre = 3l48 m,c = 3.0457 m,/h = 4.287 m.d6]dcr = 0.5,
and CL".WB = 0.047/deg.
   Using the following geometrical data of the fuselage, estimate the slope of the
fuselage pitching-moment-coefficient curve.
   In Table 3.1, Ax is the section length, bf is the section width, and xi is the
distance measured from leading edge of the root chord to the centroid of the
section with one exception for section 6. For section 6, xi  - Ax -. xi.
    So/ution.    The first stepis to determine d6"lda at each body section as shown
in Tables 3.2 and 3.3. Note that ffie va:tues of deu/da in column 3 of Table 3.2 are
obtained from Fig. 3.9b for sections 1-5 and from Fig. 3.9a for section 6. Also
observe that these values are based on xi measured to their centroid for sections
1-5 and 7-14. For section 6, xi is used to estimate d6"/da. Furthermore, these
values obtained from Figs. 3.9a and 3.9b correspond to CLa.WB  =  0.0785. We have
CUr.WB = 0.047. Therefore, we have to apply the correction as follows:
                       (dd ),= (dd ) (000~. 87.5)
 These corrected values are given in column 4 of Table 3.3.
236             PERFORMANCE, STABfLITY, DYNAMICS, AND CONTROL
    Table 3.1   Geometricalfuselage data
==  =   _-_----     ---
Section  Ax,m  bj,m  xi,m
       ~__-___-__--     -
 1     0.6150  0.2057  4.0386
 2     0.5334  0.5258  3.4671
 3     0.5334  0.7849  2.9337
 4     0.5334  1.0211  2.4003
 5     1.0668  1.2268  1.6002
 6     1.0668  1.2802  1.0668
 7     1.0668  1.2802  0.5334
 8     1.0668  1.2268  1.6002
 9     0.5334  1.0744  2.4003
10     0.5334  0.9677  2.9337
11     0.5334  0.8458  3.4671
12     0.5334  0.6248  4.0005
13     0.5334  0.3886  4.5339
14     0.3970  0.1295  4.9987
~~ -: -::=:= = --
Table 3.2   Corrected upwash \ralues
　
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