5
Air Vehicle Technology

OVERVIEW

The Navy’s air vehicle technology thrust consists of programs in the following areas:

  • Structural life attainment and enhancement,

  • Condition-based maintenance,

  • Reconfigurable rotor blade,

  • Flight controls and dynamics,

  • Abrupt wing stall, and

  • Aerodynamics of advanced Navy air vehicles.

Table 5.1 shows the ONR budget projection for the ATP air vehicle technology area, including transitions to FNCs. Note that condition-based maintenance, which the committee considered as part of this thrust area, has been separated out in this budget listing. Also, the rotary-wing vehicle and concepts areas appearing in this budget listing were not briefed to the committee.

The air vehicle technology thrust includes the traditional areas of aerodynamics, air vehicle structures, flight control, flight mechanics, and the area of air vehicle system health monitoring and maintenance diagnostics. In recent years, funding in this area has been declining. The current work appears to have a strong promise of transitioning useful technology to users in the near to medium term, and it appears to be reasonably well balanced across the technical disciplines.

Some committee members are alarmed that funding is below the critical level needed to keep the Navy a smart buyer in this technical area. Most of the committee is concerned that not enough exploratory development is under way or planned to enable long-term advanced concepts and to prevent technology surprises. Some are concerned that certain programs are marginal S&T activities and should be considered as engineering fixes under the appropriate acquisition program funding.

Areas such as high-speed flight, maneuvering flight, and low-speed flight are not being addressed to the degree that would ensure future capability. The fact that no Navy vision could be articulated that



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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program 5 Air Vehicle Technology OVERVIEW The Navy’s air vehicle technology thrust consists of programs in the following areas: Structural life attainment and enhancement, Condition-based maintenance, Reconfigurable rotor blade, Flight controls and dynamics, Abrupt wing stall, and Aerodynamics of advanced Navy air vehicles. Table 5.1 shows the ONR budget projection for the ATP air vehicle technology area, including transitions to FNCs. Note that condition-based maintenance, which the committee considered as part of this thrust area, has been separated out in this budget listing. Also, the rotary-wing vehicle and concepts areas appearing in this budget listing were not briefed to the committee. The air vehicle technology thrust includes the traditional areas of aerodynamics, air vehicle structures, flight control, flight mechanics, and the area of air vehicle system health monitoring and maintenance diagnostics. In recent years, funding in this area has been declining. The current work appears to have a strong promise of transitioning useful technology to users in the near to medium term, and it appears to be reasonably well balanced across the technical disciplines. Some committee members are alarmed that funding is below the critical level needed to keep the Navy a smart buyer in this technical area. Most of the committee is concerned that not enough exploratory development is under way or planned to enable long-term advanced concepts and to prevent technology surprises. Some are concerned that certain programs are marginal S&T activities and should be considered as engineering fixes under the appropriate acquisition program funding. Areas such as high-speed flight, maneuvering flight, and low-speed flight are not being addressed to the degree that would ensure future capability. The fact that no Navy vision could be articulated that

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program TABLE 5.1 ONR 351 Aircraft Technology Program Budget for Air Vehicles Through FY02 (millions of dollars)   FY99 FY00 FY01 FY02 6.2 Structures 0.7 0.8 0.8 1.6 6.2 AC corrosion (TOCR FNC) 0.0 0.0 0.0 1.8 6.1 Aerodynamics 0.5 0.5 0.3 0.2 6.2 Aerodynamics 1.4 0.8 0.6 0.2 6.2 FC&D 0.7 0.8 0.6 0.6 6.2 RWV 0.1 0.2 1.1 0.1 6.2 Concepts 0.0 0.0 0.0 0.0 6.3 Reconfigurable rotor blade (TOCR FNC) 0.0 0.0 0.0 2.0   Total 3.3 3.0 3.3 6.4 Note: See Appendix C for definitions of acronyms used. includes advanced air vehicles reflects a lack of vision for the potential of aeronautics. From a physics and technology perspective, however, there is no limit to the potential for air vehicle technologies to enable advanced vehicle concepts. What the committee sees missing from the Navy is a call for more performance at affordable costs. Instead the committee sees an assumption that most new vehicle performance technologies would be too costly. Furthermore, there are continuing problem areas that will limit capability but that, if they are understood, can be exploited. One example involves the complex coupling of transonic aerodynamics with an elastic structure, moving control surfaces, and maneuvering flight, most recently found in F/A-18E/F flight tests. Such coupling exemplifies the limits of current technologies, which will continue to surprise us and limit air vehicle capability until they are better understood. Investments are needed to develop the needed understanding in this problem area. Other areas that limit air vehicle capability now—such as high-speed (transonic, supersonic, hypersonic) maneuvering and low-speed flight—require a vision, a plan, and a resource commitment that goes beyond the current one. PROGRAMS REVIEWED Structural Life Attainment and Enhancement The structural life attainment and enhancement (SLAE) program has four components: (1) fatigue-and corrosion-insensitive aircraft (FACIA), (2) maximizing usable service time (MUST), (3) corrosion-assisted fatigue, and (4) bonded composite patches. The FACIA goal is to eliminate corrosion maintenance, corrosion-assisted fatigue, and other fatigue mechanisms (e.g., buffet) associated with current metal control surfaces by developing the following: Analytical capabilities to quantitatively predict corrosion-assisted fatigue life, A three-dimensional architecture for all-composite control surfaces, and A three-dimensional woven composite control-surface hinge. The MUST project aims to increase the life of rotorcraft dynamic components. Technologies being developed under this project are targeted at the H-60 but can be transitioned to other naval rotorcraft,

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program including AH-1 and H-53. The goal of significantly longer service life of rotorcraft dynamic components will be achieved by the following means: Characterization and modeling of the mechanical behavior of highly loaded dynamic components, Analytical tools for predicting failure modes, and Design of engineered soft (i.e., noncatastrophic) slow-growth failure modes. The accomplishment of this goal will be demonstrated through the fabrication and testing of composite dynamic components (bifilar and swashplate). The corrosion-assisted fatigue project is motivated by the accelerated fatigue failures of metallic wing fold lugs and control surface hinges. The objective of this project is to develop strain versus life models that use measured corrosion to predict component structural life with 99 percent reliability and 95 percent confidence. This project will also determine procedures for quantifying corrosion rates. The SLAE program has successfully transitioned the technology of bonded composite patches for repair of primary airframe structures. Demonstrated on the F-5 vertical stabilizer, use of bonded composite patches showed a 75:1 savings compared with full removal and replacement and a 20:1 savings compared with complete reskinning. Findings Bonded composite patches were originally intended for temporary repair but have now been certified for permanent use. This technology transition directly addresses warfighter needs for rapid turnaround of damaged assets, reduced cost of operations, and life extension of legacy aircraft systems. In the FACIA project, the heavily loaded composite control surface hinge and fittings appear to be a unique technology application that warrants continued pursuit. It was unclear what types of failure modes are being evaluated in the MUST project, whether micromechanical considerations are included, or how the life of the engineered failure mode will be quantified and used to derive field-level inspection strategies and metrics. The corrosion-assisted fatigue project directly addresses reduction of operational costs of legacy systems by managing corrosion. The resulting models will enable the definition of corrosion maintenance criteria, including metrics for corrosion with respect to structural integrity. Recommendations While the products of the FACIA and MUST projects are highly relevant and useful to the Navy, ONR should ensure that the activities truly meet the criteria for S&T funding as distinguished from engineering enhancements that should be funded by the appropriate acquisition program. The FACIA project can maximize the effectiveness of its fragile budget by leveraging technology developments from other composite control surface programs. It should continue to pursue the heavily loaded composite control surface hinge and fittings. Long-lasting S&T benefits can also be achieved by leveraging the more accurate analytical predictions of buffet loads that are being developed by other Navy groups and external groups. The MUST project should clarify which types of failure modes are being evaluated, whether micromechanical considerations are included, and how the life of the engineered failure mode will be quantified and used to derive field-level inspection strategies and metrics.

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program Condition-based Maintenance The ONR condition-based maintenance (CBM) program began in FY96 as a 5-year accelerated capabilities initiative to speed delivery of CBM capabilities to the fleet. The CBM program is conducted with the following four thrusts: Corrosion detection sensors, Wireless microelectromechanical systems (MEMS)-based sensors for machinery diagnostics, In situ oil quality monitoring, and Human information/advanced training. Findings An important element of the performance, safety, supportability, and affordability of future weapon systems lies in greatly enhanced self-sufficiency through embedded diagnostics, proactive maintenance and failure avoidance, and rapid restoration of degraded systems. ONR Code 351 efforts under the CBM thrust are making important contributions to this goal. In particular, ONR has had significant inputs to the autonomic logistics area of the JSF program and to the overall emergence of prognostics and health management as a central theme in system development. Specific products like the Total Oil Monitoring System promise near-term payoffs in logistics costs and aircraft availability. Overall, this activity is an important contributor to an evolving concept of aeronautical systems that can sustain high operational tempos under austere operating conditions and with significantly reduced cost of ownership. Technologies from the CBM project have been applied to date only to nonaviation platforms, the advanced amphibious assault vehicle (AAAV), and the drive-up simulated testbed (DUST). The latter includes participation in IMATE DUST, a demonstration of wireless, smart MEMS sensors on an operating aircraft engine. Recommendations ONR should maintain the CBM thrust but should work aggressively to transition the technology to naval aviation systems and to the aviation systems of the other Services. In particular, close liaison with the JSF program is essential to minimize duplication and ensure opportunities to transition CBM results that are identified and realized. The CBM project should take care to address the operability and reliability of wireless sensors in an already electronically dense onboard aircraft environment. Reconfigurable Rotor Blade The goal of this project is to develop a rotor blade that can be optimized in flight for the hover and cruise flight conditions to meet operational improvement goals of aerodynamic cruise efficiency and maximum blade hover loadings. The technology is being specifically developed for application on the V-22 for prop-rotor efficiency. The configuration utilizes component technology that is suitable for the Navy’s severe operating environment. The funding profile includes a mix of 6.2 and 6.3 funds, with DARPA funding to transition the technology to application.

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program Findings This project is an elegant solution to a well-known problem of basic aerodynamics. The utilization of new materials technology in the torsional actuator to solve a Navy operational problem is an excellent example of S&T research. The researchers have blended the technology research with realistic operational requirements by setting the failure mode of the actuator to default for the original V-22 proprotor blade configuration. The mix of funds and leveraging of DARPA funds provides a cost-effective way to meet the Navy’s needs. Recommendations The committee strongly endorses this project and recommends that it be continued as planned. Flight Control and Dynamics This program is focused on naval-unique issues such as control and handling quality in low-speed shipboard approach, automated landing on moving ships with turbulent air wakes, UAV reliability for shipboard operations, and hardware with diagnostics/prognostics for maintenance in a maritime environment. Findings This is an important, relevant, and technically excellent program that is well coordinated with the other Services and NASA. The work in efficient, reliable design (“provably stable"), efficient generation of code, verification and validation (V&V)/testing of nondeterministic software, and prognostics and health management integrated with damage adaptive control, is commendable; however, that work remains restricted in application potential by its focus on traditional flight control functions. The joint Navy/Air Force program in automated/assisted maneuvering is focused on UAVs but appears restricted to gently maneuvering flight. The absence of human-based constraints on maneuvering (instantaneous and steady-state G loading, angular rates and accelerations, and the handling qualities criterion, for example) is not being exploited or studied for potential payoff. Recommendations The program should be kept focused on naval-unique areas, although some consideration should be given to two new directions in order to enable advanced capability systems in the future. The first direction is extending the science and technology of flight control system design (by means of tools that enable flight safety and reliability) to mission-critical functions, such as those required by more autonomous air vehicles. That would address the very critical need for UAVs to have extremely high mission reliability. The second direction involves enabling aggressive maneuvering of UAVs (and some manned air vehicles) for survivability reasons, by seeking out new combinations of propulsion, aerodynamics, structure, and control that purposely exploit elastic structures interacting with thrust vectoring and unsteady flow fields. Such combinations can also yield very-low-speed, short-distance landings.

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program Abrupt Wing Stall This project has the stated objective of developing methodology required to analyze, predict, detect, and prevent uncommanded transonic lateral motions, especially wing drop, for future high-performance aircraft. In particular, it is necessary to understand the aerodynamic phenomena, to develop and validate figures of merit, and to provide guidance on design procedures. The project was instigated by a wing drop problem encountered in the F/A-18E/F, but the knowledge acquired and modeling tools developed in this effort will benefit all future aircraft design. Personnel involved in joint wind tunnel tests with NASA-Langley Research Center and a consortium of computational researchers from government, industry, and academia would form the core team. Findings The committee finds that this is the type of problem and project an S&T group needs to be responsive to. Motivated by new aerodynamic phenomena observed on an existing operational aircraft, the project team has undertaken to understand, characterize, and model the phenomena so that the research results can be applied to future aircraft design. It is noted that this project represents an appropriate leveraging of funds across ONR and technological expertise from other government agencies, industry, and academia. What is more, the principal investigator had expertise in the area, a sign that the project was monitored at the appropriate technological level. Recommendations Steady-state computational fluid dynamics (CFD) results show some promise and should be continued, with the inclusion of critical unsteady aerodynamic effects. In addition, because of the research finding that root moment is important, aeroelastic evaluation of the configuration is recommended. This project is scheduled for completion in FY02. Research should continue until the physical mechanisms that cause abrupt wing stall—for both notched and unnotched wings—are clearly understood. In addition, the basic research premise of the effort could be justified by releasing the wind tunnel data to the U.S. academic community for more accurate turbulence modeling and unsteady aerodynamics algorithm development. ONR, with NASA cooperation, should also consider expanding the wind tunnel experiments to include parameter variations (e.g., dynamic control surface motion, chordwise fences, dynamic angle-of-attack and sideslip inputs and/or responses, and so on) that could lead to a better understanding of significant unsteady and/or nonlinear interactions. This information should include both steady and unsteady data that are suitable for the development and/or modification of theoretical models as well as for the validation of unsteady RANS, LES, and DNS numerical methods for future aircraft development. However, the specific solution of the abrupt wing stall problem on the F/A-18 E/F should be funded by that program office and not by S&T funds. Aerodynamics of Advanced Navy Air Vehicles This program consists of efforts in high-lift aerodynamics, empennage buffet loads prediction, ship-aircraft airwake analysis for enhanced dynamic interface, and VSTOL suckdown, thermal, and acoustic limiting. Although the program was not formally briefed to the committee, the findings and recommendations below are based on the written material that was made available and committee members’ knowledge of the program.

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program Findings This program appears to focus on important maritime-unique technologies that are required by current and future air vehicles. Low-speed, high-lift aerodynamics and other areas mentioned previously are critical to Navy operations. Furthermore, this program appears to have a good record in transitioning those technologies. Recent program transitions also include other areas, such as aeropropulsion integration technology (for the JSF), stores integration technology (for the F/A-18), and VSTOL ground effect technology (for the V-22). The sources of funding for this work have been largely non-ONR; however, only modest ONR 6.2 funding in FY02 and beyond is proposed. Recommendations ONR should ensure that important work in these areas is increased, since it appears to have fallen below a critical level. At a minimum, the Navy needs to recognize some continuing problems—one of which is the lack of robust buffet loads prediction—as well as the potential for future configurations to benefit from technologies that involve tightly coupled, nonlinear aero-structure-controls interactions. The Navy must be a smart buyer in these key areas, and that would require more work in all of them. It is recommended that current aviation platforms and operational programs of interest to the Navy (V-22, F-18E/F, JSF) be reviewed to identify specific historic problems that would require basic S&T research for their solution and then to propose such research for future S&T funding. In particular the committee believes there is an opportunity to expand the performance envelope of advanced aircraft such as the V-22 through an improved understanding of the aerodynamic processes involved and the interactions that occur in operations near the ground for that unique configuration. Such research would have numerous naval-unique operational benefits. ONR should consider the development of better tools and modeling to help realize the full potential of this research. Suggested Topics in Air Vehicle Technology for the Future ATP In addition, the following topics should be considered for the future ATP in this area: Research and development should be conducted on the active reduction of vertical tail buffet by use of wing aerodynamic sources rather than on modification of the resulting structural response to the buffeting forces. Improvements in high-lift aerodynamics could greatly improve naval air operations, especially by reducing the risk and cost of launch and recovery at sea; furthermore, there is an opportunity now to integrate old concepts with new technology. ONR should take a fresh look at improving the performance of lifting airfoils and bodies when influenced by air flows with energy added. Some aircraft, namely the QSRA, YC-14, and AV-8B, have used air flows with energy added, with marked effect on takeoff and landing characteristics. Such technology development (involving basic research and exploratory and advanced development efforts) would be especially important for the design of extremely short takeoff and landing (ESTOL) vehicles, and the technology could be applied to shipboard tactical aircraft, UAVs, and future logistic vehicles. Innovative propulsion system concepts that integrate productively with these added-energy concepts should also be investigated. Since speed of engagement is a key factor in increasing the tempo of combat, and since such speed is limited by aircraft (as well as missile) speed and maneuver capabilities, concepts for

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2001 Assessment of the Office of Naval Research’s Aircraft Technology Program expanding aircraft high-speed capabilities in an affordable manner should be considered. Low-speed performance may be equally critical. ONR should consider extending high speeds to quiet, efficient supersonic cruise and hypersonic flight and low speeds to ESTOL and even routine post-stall flight. Maneuvering performance of aircraft and missiles has always been a key parameter in combat. Trade-offs based on human physiological limits have yielded the current concepts and configurations for air vehicle platforms. But now there is an opportunity to rethink and greatly improve aircraft maneuverablity. New aerodynamic and air vehicle concepts should be explored by ONR to exploit the absence of human-based constraints on maneuvering of UAVs and UCAVs to achieve high maneuverability and greatly improved survivability and lethality.