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AFDD Weight Models 163
19–12 Folding Weight
Folding weights are calculated in a number of groups: wing Wfold (including extensions), rotor
Wfold, fuselage Wtfold and Wwfold. These are the total weights for folding and the impact of folding on
the group. A fraction ffoldkit of these weights can be in a kit, hence optionally removable. Thus of the
total folding weight, the fraction ffoldkit is a kit weight in the fixed useful load of the weight statement;
while the remainder is kept in the wing, rotor, or fuselage group weight.
19–13 Parametric Weight Correlation
Figure 19-24 shows the error of the calculated weight for the sum of all parametric weight, accounting
on average for 42% of the empty weight. This sum is composed of the structural group (based on
the AFDD00 equation for rotor blade and hub weights, and the AFDD84 equation for body weight), the
propulsion group (based on the AFDD00 equation for drive system weight), and the flight controls group.
Based on 42 aircraft, the average error of the sum of all parametric weight is 5.3%. The corresponding
average error is 6.1% for the structural group (8.6% for the rotor group alone), 10.9% for the propulsion
group, and 8.7% for the flight controls group.
19–14 References
1) Chappell, D.; and Peyran, R.: Methodology for Estimating Wing Weights for Conceptual Tilt-Rotor
and Tilt-Wing Aircraft. SAWE Paper No. 2107, Category No. 23, May 1992.
2) Chappell, D.P.: Tilt-rotor Aircraft Wing Design. ASRO-PDT-83-1, 1983.
3) Weight Trend Estimation for the Rotor Blade Group, Rotor Hub Group, and Upper Rotor Shaft of the
ABC Aircraft. ASRO-PDT-83-2, 1983.