TILT ROTOR AEROACOUSTIC MODEL (TRAM)
AS A NATIONAL RESEARCH FACILITY
Tiltrotor aircraft represent an unique opportunity for the civilian aerospace/aviation industry: the potential introduction of a broad new class of subsonic transport aircraft. The production launch decision of the military's V-22 Osprey, the launch decision for the Bell Boeing 609 small corporate/utility tiltrotor, and the positive findings of the Congressional CTRDAC report (December 1995) as to market potential and enhancement of the U.S. National economic competitiveness that could result from the launch of larger commercial airline carrier tiltrotor transport aircraft all emphasize the importance of development of this technology.
A NASA-sponsored report from Bell-Boeing, 'Civil Tiltrotor -- Phase II Study,' outlined several technology areas that were both 'enabling' or 'enhancing' technologies. The Short Haul (Civil Tiltrotor) SH(CT) program was developed and initiated to address the critical enabling technologies for civilian tiltrotor. However, a key consideration in sustained tiltrotor research in the latter stages of, and after, the SH(CT) program is continued investigations into the 'enhancing' tiltrotor technologies that were not pursued by SH(CT). Additionally, NASA Ames should be prepared to support any follow-on tiltrotor technology demonstrator opportunities resulting from recommendations from the CTRDAC report. Finally, it should further be noted that, undoubtedly, tiltrotor aircraft technology applications for the DOD will not be limited to the V-22 Osprey. New aircraft types including and, perhaps even more importantly, AUAV/UAV versions of tiltrotor technology will start to manifest themselves in the DOD aviation inventory. NASA can be expected to provide its unique contributions to support the DOD in these future military applications of tiltrotor technology.
NASA needs to sustain long-term tiltrotor research programs to meet national requirements for military and civilian tiltrotor aircraft. To accomplish these goals, moderate-to-large scale wind tunnel testing of tiltrotor models is required. This testing will provide the data necessary to confirm aeroacoustic prediction methodologies, and to investigate and demonstrate advanced civil tiltrotor and high-speed rotorcraft technologies.
NASA, and particularly Ames Research Center, is extremely well positioned to fulfill a cornerstone role in experimental tiltrotor aeromechanics research. Three key tiltrotor research test platforms have been, or in the process of being, developed by the Aeromechanics Branch:
- The Rotor Test Apparatus (RTA) upgrade to support ~25 foot diameter proprotors for helicopter-mode research
- The proposed Large Rotor Test Apparatus (LRTA) upgrade for testing ~38 foot diameter proprotors in helicopter-mode
- The Tilt Rotor Aeroacoustic Model (TRAM) for ~9.5 foot diameter, small-scale proprotors for complete tiltrotor operating envelope investigations for isolated rotor and full-span (with dual-rotors and a complete airframe representation) configurations.
With these three test platforms, NASA Ames has, and will continue, to make substantial investments in the technology infrastructure to support tiltrotor research. The majority of this white paper will discuss one such investment: the Tilt Rotor Aeroacoustic Model (TRAM) program. However, as appropriate, the synergy of TRAM experimental lines of investigation with the other tiltrotor research test platforms will be briefly highlighted.
NASA established in 1991 that it had a requirement to gain an improved understanding of the aeroacoustic characteristics of tiltrotor aircraft and, therefore, initiated the development of two hardware-compatible test rigs: an isolated rotor test stand and a full-span model (dual rotors with a complete V-22 airframe representation). These two test stands were inclusively called the Tilt Rotor Aeroacoustic Model (TRAM). The Isolated Rotor is not a stand-alone unit, but is instead intended to be comprised chiefly of major subassemblies of the Full-Span configuration.
The current scope of TRAM experimental investigations is: Acquisition and documentation of a comprehensive isolated proprotor aeroacoustic database including rotor airloads. Acquisition and documentation of a comprehensive full-span tiltrotor aeroacoustic database, including rotor airloads, to enable assessment of key (and largely unexplored) interactional aerodynamic and aeroacoustic effects through correlation of data from the isolated rotor and full-span TRAM wind tunnel data sets. Act as an advanced technology demonstrator test platform for low-noise proprotors developed as a part of the Short Haul (Civil Tiltrotor) program and other major research initiatives.
Young, L. A., "Tilt Rotor Aeroacoustic Model (TRAM): A New Rotorcraft Research Facility," Presented at the AHS International Meeting on Advanced Rotorcraft Technology and Disaster Relief, Gifu, Japan, April 21-23, 1998. Download Paper (PDF Format)