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160 AFDD Weight Models<br />
and then<br />
WFWnb = χFWnbfFWnbw<br />
WFWmb = χFWmb(1 − fFWnb) w<br />
For a helicopter, the stabilizer-control equation is used. Parameters are defined in table 19-14, including<br />
units as used in these equations.<br />
Table 19-14. Parameters for fixed-wing flight-control weight.<br />
parameter definition units<br />
Sht horizontal tail planform area ft 2<br />
WMTO maximum takeoff weight lb<br />
fFWnb fixed wing non-boosted weight<br />
(fraction total fixed wing flight control weight)<br />
Rotary-wing flight controls consist of non-boosted flight controls, flight-control boost mechanisms,<br />
and boosted flight controls. The non-boosted flight-control weight (AFDD82 model) is:<br />
fraction method WRW nb = χRW nbfRW nb(1 − fRW hyd)wfc<br />
parametric method WRW nb = χRW nb2.1785fnbsvW 0.3999<br />
MTO N 1.3855<br />
rotor<br />
where fnbsv =1.8984 for ballistically survivable (UTTAS/AAH level); 1.0 otherwise. The parametric<br />
method assumes the rotor flight controls are boosted and computes the weight of the non-boosted portion<br />
up to the control actuators. Based on 20 aircraft, the average error of the non-boosted flight controls<br />
equation is 10.4% (fig. 19-21). The flight-control boost-mechanism weight and boosted flight-control<br />
weight (AFDD82 model) are:<br />
wfc =0.2873fmbsv(NrotorNblade) 0.6257 c 1.3286 (0.01Vtip) 2.1129 f 0.8942<br />
RW red<br />
WRW mb = χRW mb(1 − fRW hyd)wfc<br />
WRW b = χRW b0.02324fbsv(NrotorNblade) 1.0042 N 0.1155<br />
rotor c 2.2296 (0.01Vtip) 3.1877<br />
where fmbsv =1.3029 and fbsv =1.1171 for ballistically survivable (UTTAS/AAH level) and 1.0 otherwise;<br />
and fRW red =1.0 to 3.0. Typically fRW nb =0.6 (range 0.3 to 1.8) and fRW hyd =0.4. Based on 21<br />
aircraft, the average error of the boost-mechanisms equation is 6.5% (fig. 19-22). Based on 20 aircraft,<br />
the average error of the boosted flight-controls equation is 9.7% (fig. 19-23). Parameters are defined in<br />
table 19-15, including units as used in these equations.<br />
Table 19-15. Parameters for rotary-wing flight-control weight.<br />
parameter definition units<br />
WMTO maximum takeoff weight lb<br />
Nrotor number of main rotors<br />
Nblade number of blades per rotor<br />
c rotor mean blade chord ft<br />
Vtip rotor hover tip velocity ft/sec<br />
fRW nb rotary wing non-boosted weight (fraction boost mechanisms weight)<br />
fRW hyd rotary wing hydraulics weight<br />
(fraction hydraulics plus boost mechanisms weight)<br />
flight control hydraulic system redundancy factor<br />
fRW red