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154 AFDD Weight Models<br />
where Tat is at maximum speed, design gross weight, and SLS conditions, calculated or input. Parameters<br />
are defined in table 19-5, including units as used in these equations.<br />
Table 19-5. Parameters for tail weight.<br />
parameter definition units<br />
Sht horizontal tail planform area ft 2<br />
Svt vertical tail planform area ft 2<br />
Aht horizontal tail aspect ratio<br />
Avt vertical tail aspect ratio<br />
Vdive design dive speed at sea level kts<br />
Rtr tail rotor radius ft<br />
PDSlimit drive system rated power hp<br />
R main rotor radius in hover ft<br />
Vtip main rotor hover tip velocity<br />
number of auxiliary thrusters<br />
ft/sec<br />
Nat<br />
Tat thrust per propeller lb<br />
Aat auxiliary thruster disk area ft2 19–4 Fuselage Group<br />
The fuselage group consists of: basic structure; wing and rotor fold/retraction; tail fold/tilt; and<br />
marinization, pressurization, and crashworthiness structure. The AFDD84 model is a universal bodyweight<br />
equation, used for tiltrotor and tiltwing as well as for helicopter configurations. The AFDD82<br />
model is a helicopter body-weight equation, not used for tiltrotor or tiltwing configuration.<br />
For the AFDD84 (UNIV) model, the basic structure weight is<br />
wbasic =25.41fLGlocfLGretframp<br />
Wbasic = χbasicwbasic<br />
WMTO<br />
1000<br />
0.4879 0.2075 nzWSD<br />
S<br />
1000<br />
0.1676<br />
body ℓ 0.1512<br />
where fLGloc =1.1627 if the landing gear is located on the fuselage, and 1.0 otherwise; fLGret =1.1437<br />
if the landing gear is on the fuselage and retractable, and 1.0 otherwise; framp =1.2749 if there is a cargo<br />
ramp, and 1.0 otherwise. Based on 35 aircraft, the average error of the body equation is 6.5% (fig. 19-9).<br />
The tail fold, wing and rotor fold, marinization, pressurization, and crashworthiness weights are:<br />
wtfold = ftfoldWtail<br />
wwfold = fwfold(Wwing + Wtip)<br />
wmar = fmarWbasic<br />
wpress = fpressWbasic<br />
wcw = fcw(Wbasic + Wtfold + Wwfold + Wmar + Wpress)<br />
Wtfold = χtfoldwtfold<br />
Wwfold = χwfoldwwfold<br />
Wmar = χmarwmar<br />
Wpress = χpresswpress<br />
Wcw = χcwwcw<br />
Typically ftfold =0.30 for a folding tail, and fcw =0.06. For wing folding the weight on the wing tip<br />
(Wtip) is required (calculated as for the wing group). Parameters are defined in table 19-6, including
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