Piezoelectric-Bender Acutated Flaps

The AGRC was known as the Center for Rotorcraft Education and Research (CRER) until 1997, when it was named for Alfred Gessow, Professor Emeritus and director of the Rotorcraft Center from its founding in 1982 to 1991. Gessow has been an almost legendary figure in rotorcraft aerodynamics for the past 50 years, having originally written the "classic textbook on the subject" in 1951!

Over the past 18 years, the Center has developed over a dozen unique experimental facilities and systems, including various rotor rigs for the university’s Glenn L. Martin wind tunnel, a vacuum spin chamber, a hover test stand, an acoustic chamber, composite fabrication and testing laboratories, a 3D laser Doppler velocimeter, and a state-of-the-art data acquisition system, as well as smart structures laboratories, which were funded largely by an ARO MURI grant. "We have an excellent experimental facility, so our program is very balanced between theory and experiment," says Chopra.

These facilities were an important part of winning such a substantial portion of the RCOE funds. "We have built facilities to test rotors that you wouldn’t find at any other university in the world," says Gessow. "And the reason that we’ve done this is that carrying out experiments is much more costly and time consuming than sitting down at a computer and generating new programs, but we are firmly committed to the idea that you have to do both analysis and experiment. You don’t do one without the other – you have to do experiments to try to validate a theory or an analysis."

Many of the contributions of the Center have had an important influence on rotorcraft now under development. This includes areas such as the analysis of the dynamics and aerodynamics of bearingless rotors, rotor wake aerodynamics, and smart structures. Professor Gordon Leishman, who has just published a textbook on helicopter aerodynamics (see Vertiflite Fall/Winter 2000), developed key insights into complex aerodynamic rotor phenomena, particularly unsteady aerodynamics and the characteristics and effects of rotor wakes.

UMD is also the leader in the development and application of smart structures technologies for rotorcraft, funded under the MURI grant. Smart structures are composed of materials that can determine their present state, decide what is the most desirable state, and carry out an appropriate response in a controlled manner. Maryland began research in the area in 1985, and its smart structures program is now larger than the rotorcraft program itself. UMD also has a direct RITA task for about $250K per year entitled the "Quadrotor Computational Fluid Mechanics Program."

One area receiving significant funding under the new grant is Blade-Vortex Interaction, which is caused as each individual rotor blade passes through the wakes of the previous blades. It is one of the prime sources of noise, particularly in descending flight. With the advent of more powerful computers and CFD, it is becoming possible to examine the aerodynamics and acoustic coupling of the BVI process and investigate new means of reducing BVI noise. One effort will investigate innovative new blade designs, such as serrated and scalloped leading edges, as well as tailored blade sweep; the Center will also investigate porosity and acoustic cavities to soften impulsive events on the blades and therefore BVI noise. Other efforts will investigate additional BVI noise reduction concepts and look at the effects of maneuvering flight on noise radiation. These theoretical efforts will be validated and the most promising designs tested in the university’s specialized facilities, using newly developed experimental methods.

Other areas of the RCOE grant are even more revolutionary. If you can shrink a rotorcraft to the size of a child’s toy, and still use them to conduct a variety of missions such as surveillance, communications relay, air sampling, or even weapons targeting designation, you could build a Micro air vehicles at a fraction of the cost of a manned rotorcraft. The Center’s proof-of-concept Micro-COaxial Rotorcraft (MICOR) was developed with off-the-shelf powerplant components and made its first tethered flight in November 1999. The total system weighed only 88 grams (3.1 oz), including the video camera! Under the NRTC grant, additional research will be conducted to develop the necessary analytical, computational and experimental tools for assessing the performance of advanced miniature rotorcraft designs. Key technologies include advanced rotor blade designs for the "miniaturized aerodynamics", flight stability and control, performance, miniaturized power systems, system integration, and flight testing. Several different designs will be built and flight tested. A number of companies are already demonstrating micro air vehicles for the Defense Advanced Research Projects Agency (DARPA). Maryland expects to be able to help DARPA because the demonstrators aren’t being done by rotorcraft companies and the tight schedules means the researchers don’t have the time to do the analysis and understand the basic physics of miniature rotorcraft themselves.

In addition to these efforts with industry and other government agencies, UMD’s commitment to the AGRC was another important consideration by the NRTC. The NRTC grant will be matched by an additional $2.9M from the university and the aerospace department appointed three new tenured-track faculty. Through major contributions in 1997 by Gessow’s son, Jody, the university also established the endowed Alfred Gessow Chair in Rotorcraft Education (held by Chopra) and the Elaine Gessow Fund for rotorcraft education and scholarships, named for Professor Gessow’s wife, who has been affiliated with the university since the 1960s.

Director: Inderjit Chopra

Acoustics: James Baeder, J. Gordon Leishman, Fred Schmitz, Ben Sim

Aerodynamics: Al Gessow, J. Gordon Leishman

Air Traffic: Ella Atkins

CFD: James Baeder, Hong Hu (Hampton U)

Control: Ben Shapiro

Design: V.T. Nagaraj

Dynamics: Inderjit Chopra, V.T. Nagaraj, Norman Wereley

Flight Mechanics: Roberto Celi

Smart Structures: Amr Baz, Norman Wereley

Transmissions and Health Monitoring: Darryll Pines

2000 NRTC Grant Tasks

Efficient Low Noise Rotors

BVI Noise Measurement and Validation For Maneuvering Flight

This effort will measure the rotor blade noise of a helicopter in maneuvering, accelerating and decelerating flight, and then develop an acoustic model that can predict rotor noise.

Rotor Aeroacoustics During Maneuvers

This research will define the fundamental connections between rotor aeroacoustics and rotor dynamics, flight dynamics and pilot behavior.

Minimum Noise Radiation Design Through Blade-Controlled Disturbance-Interaction (B-CD-I) Theory/Experiments

A new experimental model and facility will be developed to assess the influence of rotor blade design on the unsteady aerodynamic response and acoustics of rotors. Unique design concepts will be studied as a means to reduce BVI noise. The complex BVI problem will be assessed using the simplified B-CD-I approach.

Passive Noise Reduction Blade Design Using CFD

CFD analysis will be used to examine innovative concepts to reduce BVI noise.

Active Fluidic Control of Blade-Vortex Interaction Noise

For this project, CFD analysis will evaluate the feasibility of using various micro-fluidic devices near the leading edge of the rotor blade to control the flow over the blade and thereby reduce BVI noise. The most promising fluidic devices will then be evaluated in wind tunnel tests.

Modeling of Non-Linear Unsteady Aerodynamics

This task will develop a non-linear unsteady aerodynamic model for airfoils and rotors that can be used to minimize noise radiation, loads, and vibration levels.

Experimental and Numerical Research on Rotor Wakes and Tip Vortices

This program will measure tip vortices, then develop more accurate analytic models of the vortices and the overall wake structure generated by the rotating blades in hover and forward flight. This improved understanding will help to design rotors with better performance and lower noise levels.

Affordability

Innovative Design, Fundamental Analyses, and Integration of Micro Rotorcraft

This research into improved miniature rotorcraft will result in a fundamental understanding of the physics, system scaling, and integration issues involved. Advanced micro rotorcraft will be developed and demonstrated, including autonomous flights.

Low-Vibration Dynamic Systems

Fundamental Understanding of Vibration Mechanisms in Level and Maneuvering Flight

This effort will enhance the Maryland’s analysis capability and advance the state-of-the-art of predicting vibrations and loads in level and maneuvering flight for current and advanced rotors.

High-Fidelity CFD Loads for Structural Coupling

This research should result in significant advances in the ability to predict aerodynamic loads and vibrations, using CFD to analyze the induced velocity field and blade dynamics. The use of trailing-edge flaps will also be modeled to determine their suitability for low-vibration rotor systems.

Advanced Drivetrains

Adaptive Driveshafts/Struts for Noise and Vibration Reduction, and Damage Mitigation

This project will model transmitted vibrations from helicopter gearbox/drivetrain components and then design, fabricate and test composite drive shafts with embedded shape memory inserts to reduce noise and vibration from the transmission and drivetrain.

Transmission Design for Robust Diagnostics and Prognostics

This task will explore the effects of advanced transmission gear designs and geometries to enhance incipient damage and fault detection.

Smart and Composite Structures

Semi-Active Damping Control of Rotor Systems

For this effort, the AGRC will investigate semi-active actuators based on smart materials to augment the aeromechanical stability of bearingless rotor systems.

Digital-Optical Integrated Flight Controls

Advanced Rotorcraft Flight Control Systems

This is a study of flight control systems and rotor control systems and the relevant effects on flight dynamics and rotor dynamics.

VTOL Air Traffic Control Systems

Airspace Integration and Flight Path Management to Maximize Throughput and Minimize Noise Exposure Surrounding Vertiports

Airport throughput could be greatly increased by using vertical take-off and landing (VTOL) aircraft for flights of less than 450 miles. This project will design an intelligent software architecture to maximize overall throughput and minimize noise at congested airports. System performance and airport-specific VTOL impact will also be characterized.

Active Vibration Suppression
with Smart Actuators