Research Programs OverView
In April 2012, NASA and the U.S. Army jointly completed a wind tunnel test program examining two notional large tilt rotor designs: the Army's High Efficiency Tilt Rotor (HETR) and NASA's Large Civil Tilt Rotor (LCTR). Testing was carried out in the U.S. Army 7- by 10-ft wind tunnel at NASA Ames Research Center. The data obtained from this test will be used to validate CFD tools and to aid in the development of flight dynamics simulation models.
To provide an expanded database for validation of these predictive tools, NASA and the U.S. Army have recently completed (May 2010) a full-scale wind tunnel test of the UH-60A airloads rotor, including the pressure-instrumented blade. This test, conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel, was designed to produce unique data not available from the flight test.
The objective of this wind tunnel test were to assess the IBC capability to expand the existing flight envelope of the UH-60A rotor.
The SMART rotor is a civilian, full-scale MD 900 Explorer helicopter rotor with on-blade piezoelectric actuators driving trailing edge flaps. The 0.30-chord flaps extend from 0.75 radius to 0.92 radius. It is the only flight-worthy, full-scale, smart material actuated rotor ever designed and built in the United States. The SMART rotor had been successfully whirl tower tested in 2003 prior to this most recent test campaign.
Current flight dynamics and controls research focuses on the handling qualities of large hovering rotorcraft, particularly of a large tiltrotor aircraft such as the Large Civil TiltRotor -2 (LCTR2). The size of these aircraft pose design and operating challenges that begin with the location of the cockpit very far ahead of the aircraft center of gravity.
The UH-60A Airloads Program's, jointly sponsored by NASA and the U.S. Army, objective was to obtain comprehensive, accurate, documented airloads data over the complete operating limits of the UH-60 rotor system that will have long-term value and timely, widespread accessibility so that the rotorcraft community can increase their understanding of rotor behavior, refine and validate their analysis tools, and design improved rotorcraft.
The goal of the LCTR2 design studies is to identify research requirements for future tiltrotors. The LCTR2 is sized to be representative of regional jets (90 passengers), convenient for technology investigations. The focus for near-term research is more realistic assessment of technology requirements and potential benefits.
NASA Ames and the U.S. Army Aeroflightdynamics Directorate researchers are conducting research on the critical problem of helicopter brownout. The work focuses on two main problems; the unsteady external flow of the UH-60 aircraft along the airframe and along the ground during in ground effect hover and the potential external flow differences between a UH-60 and an EH-101 Merlin.
The Aeromechanics Branch of the Flight Vehicle Research and Technology Division has designed and fabricated a suite of radio-controlled aircraft to investigate aerodynamic interaction phenomena between multiple aircraft in formation flight, in ground effect, and in the vicinity of large structures such as buildings or ships. The 1/48th-scale aircraft models are mounted on precision balances and have been tested in the 7- by 10-foot wind tunnel. By matching non-dimensional full-scale aircraft thrust coefficient and advance ratio, wake interactions representative of full-scale events have been successfully captured.
The objectives of the investigation were to quantify the aerodynamic disturbances driving the uncommanded roll response experienced by a ground turning V-22 on the deck of an amphibious ship during recovery operations of upwind rotorcraft.
The objectives of this wind tunnel test were to evaluate the capability of the 80x120 test section as a hover facility; acquire forward flight rotor performance data for comparison with analytical results; and acquire S-76 forward flight rotor performance data in the 80x120 wind tunnel to compare with existing and future 40x80 data for evaluation of differences and similarities between the two full-scale wind tunnel facilities.
Wind tunnel test measurements, flight test measurements, and analytical prediction play a key role in the development of new rotor systems. Tests are typically performed using a range of rotor system sizes and wind tunnel test facilities. To assure the accuracy of wind tunnel testing methodology, a validation study is in progress using test results from model- and full-scale tests in comparison with flight test data.
Wind Tunnel Evaluation of Sikorsky Bearingless Main Rotor Blade Vortex Interaction Research In The 80- By 120-Foot Wind Tunnel
The primary objective of the wind tunnel test was to evaluate the Sikorsky Bearingless Main Rotor in the following five areas: dynamics and stability, rotor structures and loads, handling qualities, aeroperformance and acoustics. A secondary objective of this test was to evaluate the effects of active controls on rotor loads, performance and acoustics.
The objectives of this test were to experimentally simulate the aerodynamics and acoustics of parallel (2-D), unsteady helicopter rotor blade-vortex interactions, in a manner closely matching the simplified computational models frequently used for numerical simulations.
Two tests of an individual blade control (IBC) system for a full-scale helicopter rotor were performed; the first in 1993 and the second in 1994. The objective of the investigations were to evaluate the potential of individual blade control to improve rotor performance, to reduce blade vortex interaction (BVI) noise, and to alleviate helicopter vibrations.
The tilt rotor aircraft holds great promise for improving air travel in the future. It's benefits include vertical take off and landing combined with airspeeds comparable to propeller driven aircraft. However, the noise from a tilt rotor during approach to a landing is potentially a significant barrier to widespread acceptance of these aircraft. The XV-15 Aeroacoustic test will measure the noise from a tilt rotor during descent conditions and demonstrate several possible techniques to reduce the noise.
A key part of NASA's aeronautics research is reducing noise to make helicopters and tiltrotors more acceptable to the public. The objective of the In-Flight Rotorcraft Acoustics Program (IRAP) is to acquire rotorcraft noise data in flight for comparison to wind tunnel data. The type of noise of concern is "blade-vortex-interaction," or BVI, noise.
In an effort to obtain better predictive capabilities and to better understand bearingless rotor dynamics and loading, McDonnell Douglas Helicopter Systems (MDHS) and NASA Ames jointly conducted a wind tunnel test program to study the MDHS advanced bearingless rotor concept.
NASA Ames Research Center and Westland Helicopters Limited (WHL) established a joint research program to document the flight tests of a hingeless Lynx helicopter and perform a correlation study with these data. The flight tests were conducted by WHL in 1985 to evaluate the performance and load characteristics of the Lynx-XZ170 helicopter equipped with rectangular metal blades.
Coupled wing/rotor whirl-mode aeroelastic instability is the major barrier to increasing tiltrotor speeds. This research investigated the unusually simple approach of adjusting the chordwise positions of the rotor blade aerodynamic center and center of gravity to improve the stability boundary of the full aircraft.
The Full-Span Tilt Rotor Aeroacoustic Model is a quarter scale V-22 Osprey being tested in the 40-by 80- Foot Wind Tunnel at Ames Research Center, Moffett Field CA.
Beginning October 2, 2000 the Rotorcraft Aeromechanics Branch will begin testing of Millennium Jet Inc.'s SoloTrek XFV ducted rotor in the 7- by 10-Foot Wind Tunnel at Ames Research Center, Moffett Field CA.