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Chapter 3
Tasks
The NDARC code performs design and analysis tasks. The design task involves sizing the rotorcraft
to satisfy specified design conditions and missions. The analysis tasks can include mission performance
analysis, flight performance calculation for point operating conditions, and generation of subsystem or
component performance maps.
3–1 Size Aircraft for Design Conditions and Missions
3-1.1 Sizing Method
The sizing task determines the dimensions, power, and weight of a rotorcraft that can perform a
specified set of design conditions and missions. The aircraft size is characterized by parameters such as
design gross weight (WD) or weight empty (WE), rotor radius (R), and engine power available (Peng).
The relationships between dimensions, power, and weight generally require an iterative solution. From
the design flight conditions and missions, the task can determine the total engine power or the rotor
radius (or both power and radius can be fixed), as well as the design gross weight, maximum takeoff
weight, drive-system torque limit, and fuel-tank capacity. For each propulsion group, the engine power
or the rotor radius can be sized.
a) Engine power: Determine Peng, for fixed R. The engine power is the maximum
of the power required for all sizing flight conditions and sizing missions (typically
including vertical flight, forward flight, and one-engine inoperative). Hence the
engine power is changed by the ratio max(PreqPG/PavP G) (excluding flight states for
which zero power margin is calculated, such as maximum gross weight or maximum
effort). This approach is the one most commonly used for the sizing task.
b) Rotor radius: Determine R for input Peng. The maximum power required for
all sizing flight conditions and sizing missions is calculated, and then the rotor
radius determined such that the power required equals the input power available.
The change in radius is estimated as R = Rold PreqPG/PavP G (excluding flight
states for which zero power margin is calculated, such as maximum gross weight or
maximum effort). For multi-rotor aircraft, the radius can be fixed rather than sized
for some rotors.
Alternatively, Peng and R can be input rather than sized. Aircraft parameters can be determined by a
subset of the design conditions and missions.
a) Design gross weight WD: maximum gross weight from designated conditions
and missions (for which gross weight is not fixed).