Skip to main content
Skip to main content

Research Facilities

Skip to main content

Rotor Test Apparatus

The Rotor Test Apparatus (RTA) is one of the rotor test stands available at the National Full-Scale Aerodynamics Complex (NFAC), managed and operated by the U.S. Air Force’s Arnold Engineering Development Center. It is a special-purpose drive and support system for operating helicopter rotors in the 40-by 80- and 80- by 120-Foot Wind Tunnels. The design flexibility of the RTA allows for the accommodation of a variety of rotor diameters and tip speeds.

The RTA houses two tandem-mounted, variable speed electric drive motors, which can provide up to 3000 horsepower at maximum of 437 rpm. The RTA also houses the hydraulic servo-actuators of the primary control-system, and a dynamic control system capable of introducing dynamic perturbations to the non-rotating swashplate (collective and tilt) at frequencies up to 40 Hz. The RTA control system provides collective, longitudinal, and lateral blade pitch control with a direct display of resolved blade-flapping and pitch angles. Using the dynamic control option of the RTA console, time-dependent control motions are entered into the primary control system.

Installed on the RTA is a five-component balance to measure rotor loads at the hub moment center. This balance was designed and fabricated to measure both the steady and vibratory rotor normal, axial and side forces, together with rotor pitch and roll moments to rotor thrust levels of 22,000 lbs. The balance shares a common centerline with the rotor shaft. An instrumented flex-coupling measures rotor torque and residual normal force. The peak load capacities for the rotor balance are as follows:

Normal Force - 22,000 lb
Resultant Shear Force - 4,400 lb
Resultant Moment - 57,800 ft-lb (at the balance moment center)
Torque - 36,000 ft-lb

The maximum resultant hub moment is dependent upon the installed hub height above the balance moment center. The accuracy of the balance at the balance moment center, based on the calibration results for both the single and combined loading sequences was determined to be better than 0.5 percent of the full-scale load capacity.

Various rotor systems can be adapted to use the existing RTA shaft configuration. In some case, a different rotor shaft may need to be designed.