Active Flutter Suppression
Sponsor: Federal Aviation Administration (FAA)
Active Flutter Suppression (AFS) technology has been in development since the late 1960s. Still, it has not seen wide application on actual flight vehicles and there are still significant concerns regarding its safety and reliability. The technology has significant potential, if included from the start of the design process of advanced aircraft, for overall vehicle weight reduction. If aeroelastic stability problems are encountered late in the development of an advanced airplane or when major modifications are made to an existing airplane, the technology can offer solutions that otherwise, if only passive aeroelastic modifications are allowed, would be too costly.
The goals of this proposed research are to study active flutter suppression technology from the perspective of the state of the art of its building blocks today, to develop engineering tools, supported by experiments, that would allow assessment of its safety, to create a standard test case that would allow researchers to develop and compare methods and results, and, in general, provide insights and results that would help the FAA in this area.
This proposal seeks support for a one-year Part 1 effort out of a two-year effort that would require Year II funding. The Part 2 effort proposal will be submitted later, separately.
Free Play FAA Project Extension
Control surface freeplay and the resulting limit cycles oscillations, vibrations, structural fatigue, and, possibly, degradation of ride comfort and flutter safety margins have been of concern to airplane designers and builders, operators, and regulatory agencies for years. Experimental work using simple wind tunnel models done by the military in the 1950s led to control surface freeplay limit requirements for aircraft in MIL standards that were later adopted by the civil regulatory authorities. Some relaxations of the MIL Standard based strict freeplay limits were introduced in the last twenty years or so, based on better analytical / computational prediction capabilities developed and driven by the challenges imposed by the emergence of new structural / configuration concepts. Quite a number of publications have appeared describing various new analysis methods and tests.
The body of research work to date in this area has not been as extensive and thorough as it should have been, and, given the prevalence of nonlinear aeroelastic response problems in design, development, and in service, more research is necessary that would cover areas not covered well enough so far and would contribute better to the design, certification, operation, and maintenance of aircraft. Important aspects of the freeplay induced aeroelastic response problem that have not been researched well enough and that directly affect the performance and safety of active flutter suppression systems include
Low-Speed Flight Characteristics and Noise Design Tools for the Integrated Configuration Shaping of Commercial Supersonic Aircraft
Sponsor: National Aeronautics and Space Administration (NASA)
The behavior at low speeds of supersonic long-range airplane configurations must be taken into account during the design of such aircraft. The research work proposed here will focus on the applied-aerodynamics; flight stability and control; handling qualities; take-off, landing, approach performance; noise; and optimization aspects of the low-speed design challenge for low-boom long-range supersonic configurations to become commercially practical. The work will be an integrated University of Washington, University of Michigan, Stanford University, and Boeing effort, in collaboration with NASA.
Aircraft Design, Optimization, and Scaled Model Test Phase II
Sponsor: M4 Engineering
Aeroelastic constraints have always been extremely important in the development of new flight vehicle configurations, often driving the design. With the growing power of design optimization technology and the emergence of new non-conventional configurations, aeroelastic constraints may become even more critical than in the past. The designers of new configurations have to often struggle with significant uncertainty in the aeroelasticity area. While new aircraft that are based on previous aircraft (also known as derivative designs) can benefit from the experience gained with similar configurations and the confidence in analysis and design tools validated for such known configurations, the appearance of new configurations is always a source of major concern regarding the accuracy and reliability of aeroelastic analysis and design techniques.
Current aeroelastic wind tunnel model design, construction, and test technology as well as flight technology is time consuming and very expensive. However, recent developments in manufacturing and automation as well as multidisciplinary design optimization create opportunities for major advancements in aeroelastic model testing capabilities that would support the flight vehicle designer. This work will advance the state of the art by creating technology for rapid aeroelastic scaling of new designs to model level, rapid manufacturing of aeroelastic models (both wind tunnel and scaled flying models), and richer instrumentation and sensing that would lead to more insight and more useful information for the flight vehicle designer or flight test engineer regarding the aeroelastic characteristics of the new configurations in development.