Download - NASA

80 Rotor
For a tandem rotor, the rotor longitudinal overlap is o =Δℓ/(2R) =1− ℓ/(2R) (fraction rotor diameter),
or the hub locations are calculated from the input overlap o, and the input location midway between the
hubs:
xhub = xcenter ± R(1 − o)
For a tail rotor, the longitudinal position can be calculated from the main-rotor radius R, tail-rotor radius
Rtr, and tail-otor/main-rotor clearance dtr:
xhubtr = xhubmr − (Rmr + dtr + Rtr)
For a tiltrotor, the lateral position can be calculated from the rotor radius R (cruise value for variablediameter
rotor), fuselage/rotor clearance dfus, and fuselage width wfus:
yhub = ± (fR+ dfus + 1/2wfus)
with the pivot, pylon, and nacelle center-of-gravity lateral positions adjusted to keep the same relative
position to the hub. The calculated clearance between the rotor and fuselage is dfus = |yhub|−(R+ 1/2wfus).
Alternatively for a tiltrotor, the lateral position can be calculated from the wing span, yhub = ± b/2, so
the rotors are at the wing tips; or from a designated wing-panel edge, yhub = ± ηp(b/2).
For twin rotors (tandem, side-by-side, or coaxial), the overlap is o = Δℓ/(2R) = 1 − ℓ/(2R)
(fraction of diameter; 0 for no overlap and 1 for coaxial), where the hub-to-hub separation is ℓ =
[(xhub1 − xhub2) 2 +(yhub1 − yhub2) 2 ] 1/2 (ℓ =2R for no overlap and ℓ =0for coaxial). The overlap area
is mA, with A the area of one rotor disk and
m = 2
π
The vertical separation is s = |zhub1 − zhub2|/(2R).
cos −1 (ℓ/2R) − (ℓ/2R) 1 − (ℓ/2R) 2
The reference areas for the component drag coefficients are the rotor disk area A = πR2 (for
hub drag), pylon wetted area Spylon, and spinner wetted area Sspin. The pylon wetted area is input,
or calculated from the drive system (gear box and rotor shaft) weight, or from the drive-system plus
engine-system (engine, exhaust, and accessories) weight:
Spylon = k 2/3 w/Nrotor
where w = Wgbrs or w = Wgbrs + WES, and the units of k are feet 2 /pound 2/3 or meter 2 /kilogram 2/3 .
The pylon area is included in the aircraft wetted area if the pylon drag coefficient is nonzero. The spinner
wetted area is input, or calculated from the spinner frontal area:
Sspin = f (πR 2 spin)
where Rspin is the spinner radius, which is specified as a fraction of the rotor radius.
The rotor contribution to the aircraft operating length and width is calculated from the locus of
the rotor disk: zdisk = zhub + RC FS (cos ψ sin ψ 0) T . The longitudinal distance from the hub position is
Δx = R(a cos ψ + b sin ψ), so the maximum distance is Δx = ±R √ a 2 + b 2 . The lateral distance from the
hub position is Δy = R(c cos ψ + d sin ψ), so the maximum distance is Δy = ±R √ c 2 + d 2 .
11–3 Control and Loads
The rotor controls consist of collective, lateral cyclic, longitudinal cyclic, and perhaps shaft incidence
(tilt) and cant angles. Rotor cyclic control can be defined in terms of tip-path plane or no-feathering