XV-15 litho - NASA's History Office

configurations such as the variable diameter tilt rotors, and terminal area
approach path profiles including nacelle position variations. Bill Decker of Ames
was the principal investigator for the simulation efforts.
As the SHCT Program nears the scheduled 2001 completion date, a new follow-on
research effort is being developed by NASA to apply and evaluate relevant technologies
that emerged during the SHCT activity. One key area of interest is the
feasibility evaluation of Simultaneous Non-Interfering (SNI) terminal area operations.
SNI operations are expected to increase the capacity of existing airports by
allowing VTOL tilt rotor transport aircraft to takeoff and land using terminal area
flight paths separate from that used by the fixed-wing transports. Furthermore, if
short-haul aircraft utilize the SNI operations and are thereby removed from the
runway queue, the larger capacity long-range aircraft would occupy the limited
slots, thereby increasing the number of passengers that can be transported on existing
airport runways. The planned research would identify the technologies and procedures
needed for the aircraft and Air Traffic Management (ATM) system to
obtain maximum aviation system benefits. The evaluations would involve the use
of piloted simulations and flight tests, employing helicopters to represent the tilt
rotor aircraft in near-terminal area operations. A separate program element includes
ATM systems integration work and addresses adverse weather operations (such as
icing conditions). This effort also deals with the automated cockpit and will examine
methods of maintaining safe control during emergencies.
A new element of this follow-on activity is focused on Variable Diameter Tilt
Rotor (VDTR) technology. This tilt rotor variant, being developed by Sikorsky,
employs a proprotor system that provides a larger diameter and lower disc loading
for higher efficiency in hover and low speed helicopter mode flight and, by
the use of a blade retraction mechanism, a smaller diameter “prop” for airplane
mode flight. The lower disc loading also contributes to safety by improving OEI
performance and, if lower tip speeds were employed, would reduce the noise
level. The planned five-year VDTR effort would address full-scale system
design, system integration and reliability and would be conducted with shared
funding by the Government and the contractor.
Additional investigations planned for this initiative address the application of
conformable proprotor blade technology or other advanced proprotor designs to
improve performance and reduce noise. The selected system would be wind tunnel
and flight tested to validate predictions. The last major element deals
with economic viability and passenger comfort issues. These issues include the
improvement of high speed performance by reducing wing thickness while maintaining
the required stability margins, the reduction of proprotor/airframe interaction
losses, and the development of methods to control interior noise and reduce
cabin vibrations.
In a more aggressive effort developed in response to the CTRDAC recommendations,
NASA planners have proposed the advanced technology demonstrator
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