By Deidre Ortiz, AEDC/PA
ARNOLD AIR FORCE BASE, TENN. — The National Full-Scale Aerodynamics Complex, managed and operated by AEDC, remains the world’s largest aerodynamics test facility and, because of its large size, has a wide range of testing capabilities that are unmatched by any other facility of its kind.
NFAC, a geographically separated unit located at Ames Research Center in Mountain View, Calif., is primarily used for determining the aerodynamic characteristics of large-scale and full-scale fixed wing, rotorcraft and powered-lift vertical and short take-off and landing aircraft. Additionally, it has the capability to perform other non-traditional types of wind tunnel testing on test articles as varied as wind turbines, parachutes and long-haul trucks.
According to Jeffrey Johnson, NFAC Test Operations and Sustainment branch chief, new vertical lift technologies are being readied to undergo testing in the wind tunnel complex. These developments include models supporting the Joint Multi-Role (JMR) technology demonstration and the DARPA Tactically Exploited Reconnaissance Node programs. Both are precursors to the Department of Defense’s Future Vertical Lift program, the plan for which is to develop a family of different sized military lift capabilities to meet various mission profiles.
NFAC has two wind tunnel sections, a 40- by- 80-foot originally built in the 1940s, capable of providing test velocities up to 300 knots and Reynolds numbers up to 3 million per foot. The other tunnel is an 80- by 120-foot test section, capable of testing a full-size Boeing 737 at velocities up to 100 knots at nominal unit Reynolds numbers of 1.1 million per foot. This open-circuit leg was added and a new fan drive system was installed in the 1980s.
Both test sections are lined for acoustic testing.
A system of moveable vanes can be positioned so that air is either drawn through the 80 by 120-foot test section and exhausted into the atmosphere, or driven around the closed circuit through the 40- by 80-foot test section. A passive air exchange system is utilized in the circuit to keep air temperatures below 125 degrees Fahrenheit.
The fan drive system is composed of six variable pitch fans, each 40 feet in diameter, arranged in two rows of three. Each fan has 15 laminated wood blades and is powered by a 22,500 horsepower electric motor. The six fans rotate together at 180 rotations per minute drawing 106 megawatts of electricity at full power while moving more than 60 tons of air per second.
Part of the NFAC capability are two rotor test beds incorporating electric motors and rotor balance systems that are available for testing complete rotor and hub systems independent of the flight vehicle. In addition, the NFAC maintains the expertise to conduct engineering development of new powered models in support of customer needs.
Unique, test-specific requirements are explored with each NFAC test customer to guide the experiment design, and new systems are integrated into the facility as needed. Utility support systems that have been used for testing powered vehicles and components include variable-frequency electrical power, hydraulic power units, cooling water, 150 and 400 hertz (cycles per second) electrical power and jet fuel systems.
Parachutes, helicopters, helicopter blades and wind turbines are only a few projects that have, and continue to be, tested at NFAC. Orion parachute testing was performed in the 80-by-120-foot wind tunnel in late 2014 and early 2015 prior to Exploration Mission-1. NASA researchers, AEDC engineers, NFAC personnel and Airborne Systems worked to help improve the safety and reliability of landing the Orion spacecraft. In all, the team tested 13 parachute configurations.