AEROELASTIC ANALYSIS FOR ROTORCRAFT IN FLIGHT OR IN A WIND TUNNEL

( NASA Ames Research Center )

     The testing of rotorcraft, either in flight or in a wind tunnel, re-
quires a consideration of the coupled aeroelastic stability of the rotor
and airframe, or the rotor and support system. Even if the primary purpose
of a test is to measure rotor performance, ignoring the question of dynamic
stability introduces the risk of catastrophic failure of the aircraft.
This computer program was developed to incorporate an analytical model of
the aeroelastic behavior of a wide range of rotorcraft. Such an analyti-
cal model is desirable for both pre-test predictions and post-test corre-
lations. The program is also applicable in investigations of isolated ro-
tor aeroelasticity and helicopter flight dynamics and could be employed as
a basis for more extensive investigations of aeroelastic behavior, such as
automatic control system design.

     The program incorporates an analytical model which is applicable to
a wide range of rotors, helicopters, and operating conditions. The equa-
tions of motion used in the model were derived using an integral Newtonian
method, which provides considerable insight into the blade inertial and
aerodynamic forces. The rotor model includes coupled flap-lag bending and
blade torsion degrees of freedom, and is applicable to articulated, hinge-
less, gimballed, and teetering rotors with an arbitrary number of blades.
The aerodynamic model is valid for both high and low inflow, and for both ax-
ial and nonaxial flight. Rotor rotational speed dynamics, including engine
inertia and damping, and perturbation inflow dynamics are included in the
aerodynamic model.

     For a rotor on a wind-tunnel support, a normal mode representation of
the test module, strut, and balance is used. The aeroelastic analysis for
rotorcraft in flight is applicable to a general two-rotor aircraft, in-
cluding single main-rotor and tandem helicopter configurations, and side-
by-side or tilting proprotor aircraft configurations. The rotor model in-
cludes rotor-rotor aerodynamic interference and ground effect. The air-
craft model includes rotor-fuselage-tail aerodynamic interference, engine
dynamics, and control dynamics. A constant-coefficient approximation is
used for nonaxial flow and a quasistatic approximation is used for the low
frequency dynamics. The coupled system dynamics results is a set of linear
differential equations which are used to determine the stability and aeroe-
lastic response of the system.

     This program is written in FORTRAN IV for batch execution and has been
implemented on an IBM 360 series computer with a central memory requirement
of approximately 624K of 8 bit bytes. This program was developed in 1977.

     COSMIC, and the COSMIC logo are registered trademarks of the National
Aeronautics and Space Administration. All other brands and product names
are the trademarks of their respective holders.



                                        1




LANGUAGE: FORTRAN IV

MACHINE REQUIREMENTS: IBM 360 SERIES

PROGRAM SIZE: APPROXIMATELY 13,793 SOURCE STATEMENTS

DISTRIBUTION MEDIA: 9 Track 1600 BPI EBCDIC Card Image Format Magnetic Tape

PROGRAM NUMBER: ARC-11150

DOMESTIC - DOCUMENTATION PRICE: $55.00    PROGRAM PRICE: $500.00

INTERNATIONAL - DOCUMENTATION PRICE: $110.00   PROGRAM PRICE: $1000.00



                                        2