Download - NASA

156 AFDD Weight Models
19–5 Alighting Gear Group
The alighting gear group consists of: basic structure, retraction, and crashworthiness structure.
There are two models, parametric (AFDD82) and fractional. The basic landing gear weight is:
parametric wLG =0.4013W 0.6662
fractional wLG = fLGWMTO
MTO N 0.5360
LG
(W/S) 0.1525
and WLG = χLGwLG. Typically fLG =0.0325 (fractional method). Based on 28 aircraft, the average
error of the parametric equation is 8.4% (fig. 19-11). The retraction and crashworthiness weights are:
wLGret = fLGretWLG
wLGcw = fLGcw(WLG + WLGret)
WLGret = χLGretwLGret
WLGcw = χLGcwwLGcw
Typically fLGret =0.08, and fLGcw =0.14. Parameters are defined in table 19-8, including units as used
in these equations.
Table 19-8. Parameters for landing-gear weight.
parameter definition units
WMTO maximum takeoff weight lb
fLG landing gear weight (fraction maximum takeoff weight)
W/S wing loading (1.0 for helicopter) lb/ft2 NLG number of landing gear assemblies
fLGret retraction weight (fraction basic weight)
crashworthiness weight (fraction basic and retraction weight)
fLGcw
19–6 Engine Section or Nacelle Group and Air Induction Group
The engine section or nacelle group consists of: engine support structure, engine cowling, and
pylon support structure. The weights (AFDD82 model) are:
Wsupt = χsupt0.0412(1 − fairind)(Weng/Neng) 1.1433 N 1.3762
eng
Wcowl = χcowl0.2315S 1.3476
nac
Wpylon = χpylonfpylonWMTO
Based on 12 aircraft, the average error of the engine-support equation is 11.0% (fig. 19-12). Based on
12 aircraft, the average error of the engine-cowling equation is 17.9% (fig. 19-13). The air induction
group weight (AFDD82 model) is:
Wairind = χairind0.0412fairind(Weng/Neng) 1.1433 N 1.3762
eng
Typically fairind =0.3 (range 0.1 to 0.6). Based on 12 aircraft, the average error of the air induction
equation is 11.0% (fig. 19-14). Parameters are defined in table 19-9, including units as used in these
equations.