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Wing 115
The wing interference at the tail produces an angle-of-attack change ɛ = E(CL/CLα), where
E = dɛ/dα is an input factor determined by the aircraft geometry. Then from the velocity vB of the
wing,
v F int = C FB
⎛
⎝ −ɛvB z
0
ɛvB ⎞
⎠
x
is the interference velocity at the tail.
13–4 Wing Extensions
The wing can have extensions, defined as wing portions of span bX at each wing tip. For the
tiltrotor configuration in particular, the wing weight depends on the distribution of wing area outboard
(the extension) and inboard of the rotor and nacelle location. Wing extensions are defined as a set of
wing panels at the tip. The extension span and area are the sum of the panel quantities, bX =
ext bp
and SX =
ext Sp. The inboard span and area are then bI = b − 2bX, SI = S − SX. Optionally the wing
extensions can be considered a kit, hence the extensions can be absent for designated flight conditions
or missions. As a kit, the wing-extension weight is considered fixed useful load. With wing extensions
removed, the aerodynamic analysis considers only the remaining wing panels. For the induced drag
and interference, the effective aspect ratio is then reduced by the factor (bI/b) 2 , since the lift and drag
coefficients are still based on total wing area S.
13–5 Weights
The wing group consists of: basic structure (primary structure, consisting of torque box and spars,
plus extensions); fairings (leading edge and trailing edge); fittings (non-structural); fold/tilt structure;
and control surfaces (flaps, ailerons, flaperons, spoilers). There are separate models for a tiltrotor or
tiltwing configuration and for other configurations (including compound helicopter).
The AFDD wing-weight models are based on parameters for the basic wing plus the wing tip
extensions (not the total wing and extensions). The tiltrotor-wing model requires the weight on the wing
tips (both sides), consisting of: rotor group, engine system, drive system (except drive shaft), engine
section or nacelle group, air induction group, rotary-wing and conversion flight controls, hydraulic
group, trapped fluids, and wing extensions.