Testing is under way at the U.S. Air Force Arnold Engineering Development Center’s (AEDC) National Full-scale Aerodynamics complex (NFAC) on a full-scale helicopter rotor system for a U.S. DOD customer. This marks the first test at the wind-tunnel complex at Moffett Field, CA, since it was reactivated to full operational capability.
The testing is part of a two-part collaborative effort between the Defense Advanced Research Projects Agency (DARPA), NASA, and the U.S. Army, with DARPA sponsoring the project’s initial phase and NASA and the Army funding the second phase.
A Boeing Smart Material Actuated Rotor Technology (SMART) helicopter rotor is being tested in the NFAC’s 40- x 80-ft wind tunnel to study the system’s forward flight characteristics and to collect data to validate aero-acoustic code analysis.
“DARPA has a program called the helicopter quieting program,” said Jeffrey Johnson, Arnold’s test engineering group lead at NFAC. “Their overall goal is to try and develop codes for predicting the acoustics of helicopters. One component of the program is to take this active flap rotor system and run it at several specific test conditions to get acoustic measurements so they can have that as a database to compare their acoustic prediction codes against.”
Johnson stated that while acoustic prediction codes currently exist, they are empirical and apply only to conventional designs and do not possess sufficient accuracy. The new tools are physics-based and are expected to provide predictions of higher quality and for novel rotor designs.
Testing of the active flap system during the NASA/Army portion of the testing has two primary goals: to reduce vibrations and noise. According to Johnson, the complexity of the test requires a well-coordinated team effort to be successful.
“The biggest challenge is getting the test article installed and then hooking up and verifying all of the systems required to safely operate the motor and rotor system,” he said. “A significant part of that challenge is checking out all the instrumentation and data systems associated with making measurements of the rotors’ health, the research instrumentation and the actuator power associated with making it all work.”
William Warmbrodt, NASA Ames Research Center’s Aeromechanics Branch Chief, said the NFAC is uniquely qualified to conduct testing of the SMART rotor.
“This is the only facility in the world that can test full-scale helicopter rotor systems,” he said. “We are testing rotor systems that have never been operated within simulated forward flight conditions, and to do this safely and still get the kind of quality data out of them is a unique challenge.”
The baseline SMART rotor without a flap was originally designed by McDonnell Douglas 15 years ago for the MD-900, a twin-engine, 7000-lb helicopter. Johnson believes the advanced rotor provides an excellent system to test the prediction codes against.
“We previously tested the baseline rotor to 200 knots,” he said. “For this test, we will simulate level flight in the test section to a velocity of 155 knots. This is the specific test condition DARPA is interested in for their part of the test.”