XV-15 litho - NASA's History Office

lytical models that were being developed in order to validate control systems
designed to meet the handling qualities requirements throughout the flight envelope.
The tests also included flow surveys which revealed the presence of rotor
tip vortices in the vicinity of the tail surfaces. These vortices could influence the
effectiveness of the tail surfaces and produce oscillatory loads and disturbing
vibrations.
Aircraft Design and Simulation
With the tilt rotor technology efforts producing positive results, the managers of
the joint AMRDL and NASA Ames activities could now justify the initiation of
the next step, the development of a new tilt rotor proof-of-concept aircraft. As
part of this plan, in August 1971 Ames awarded contracts to Boeing Vertol and
Bell to conduct preliminary tilt rotor aircraft design studies. These efforts defined
the characteristics and performance of a first generation military or commercial
tilt rotor aircraft using a hingeless (Boeing Vertol) or gimbaled (Bell) rotor system,
provided a preliminary design for a minimum size “proof-of-concept” aircraft,
developed a total program plan and cost estimates for the proof-of-concept
aircraft program, and developed a wind tunnel investigation plan for the aircraft.
In January 1972, with Air Force funding, Ames extended an existing Boeing contract
to produce a preliminary design on an advanced composite wing and to
define a gust and blade load alleviation feedback control system for the tilt rotor
aircraft. This study addressed the concern that the low-disc-loading proprotor
may experience significant thrust, torque, and blade load excursions due to a
high sensitivity to gusts and turbulence.
Work under the Boeing and Bell contracts also included the development of a mathematical
model for simulation and for participation by each contractor in a piloted
flight simulation investigation. These models allowed the test pilots to evaluate the
workload and the handling qualities of the basic aircraft, both without automatic control-enhancing
systems and with various control configurations, employing Stability
and Control Augmentation System (SCAS) control-enhancing algorithms. The simulation
also enabled the pilots to evaluate the thrust/power management characteristics,
the Force-Feel System (FFS), and failure mode design philosophy and aircraft
behavior. The math models were developed not only as an evaluation tool for a particular
aircraft control system design, but also as a device for the development of
improved generic tilt rotor control law and crew station configuration. Initial piloted
simulations were conducted in the Ames Flight Simulator for Advanced Aircraft
(FSAA) in November and December of 1973. The math model created by P. B.
Harendra and M. J. Joglekar of Bell during this period for the tilt rotor design selected
for the flight program, through extensive development and refinement by Roger
Marr and Sam Ferguson, became the basis for the generic tilt rotor math model used
to evaluate various tilt rotor aircraft designs and related air traffic management issues
in the Ames Vertical Motion Simulator in the late 1990s.
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