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AFDD Weight Models 159<br />
where fP = fQΩother/Ωmain. Based on 28 aircraft, the average error of the drive-shaft equation is 16.0%<br />
(fig. 19-19). Based on 23 aircraft, the average error of the rotor-brake equation is 25.1% (fig. 19-20).<br />
The clutch weight in the weight statement is associated with an auxiliary power unit, and is a fixed input<br />
value. The conventional rotor drive-system clutch and free-wheeling device weights are included in the<br />
gear-box and rotor-shaft weight equations. Parameters are defined in table 19-13, including units as<br />
used in these equations.<br />
Typically fP = fQ = 60% for twin main rotors (tandem, coaxial, and tiltrotor); for a single main<br />
rotor and tail rotor, fQ =3%and fP = 15% (18% for 2-bladed rotors).<br />
Table 19-12. Parameters for drive-system weight.<br />
parameter definition units<br />
PDSlimit drive system rated power hp<br />
Nrotor number of main rotors<br />
number of gear boxes<br />
Ngb<br />
Ωrotor main rotor rotation speed rpm<br />
Ωeng engine output speed rpm<br />
fQ second (main or tail) rotor rated torque %<br />
frs<br />
(fraction of total drive system rated torque)<br />
rotor shaft weight (fraction gear box and rotor shaft)<br />
Table 19-13. Parameters for drive shaft and rotor brake weight.<br />
parameter definition units<br />
QDSlimit PDSlimit/Ωrotor hp/rpm<br />
number of intermediate drive shafts<br />
Nds<br />
xhub length of drive shaft between rotors ft<br />
fP second (main or tail) rotor rated power<br />
(fraction of total drive system rated power)<br />
%<br />
Vtip main rotor tip speed ft/sec<br />
19–8 Flight Controls Group<br />
The flight controls group consists of cockpit controls, automatic flight control system, and system<br />
controls. Wcc and Wafcs weights are fixed (input). System controls consist of fixed-wing flight controls,<br />
rotary-wing flight controls, and conversion (rotor tilt) flight controls. The weight equations model<br />
separately non-boosted controls (which do not see aerodynamic surface or rotor loads), boost mechanisms<br />
(actuators), and boosted controls (which are affected by aerodynamic surface or rotor loads). The load<br />
path goes from pilot, to cockpit controls, to non-boosted controls, to boost mechanisms, to boosted<br />
controls, and finally to the component.<br />
Fixed-wing flight controls consist of non-boosted flight controls and flight-control boost mechanisms.<br />
The weights are:<br />
full controls w =0.91000W 0.6<br />
MTO<br />
only stabilizer controls w =0.01735W 0.64345<br />
MTO S 0.40952<br />
ht