Air Force Wright Aeronautical Laboratories Research Articles

Terrain-Aided Navigation Test Results in the AFTI/F-16 Aircraft

Sandia National Laboratories has developed a low-level attack aircraft terrain-aided navigation algorithm for the Air Force Wright Aeronautical Laboratories, Avionics Laboratory. This algorithm is based on the Sandia Inertial Terrain-Aided Navigation (SITAN) approach to terrain-aided navigation that was initially formulated at Sandia in the mid-1970s. Extended Kalman filter theory is used to provide essentially continuous terrain-aided navigation through estimation of inertial navigation system errors from radar altimeter ground clearance measurements and on-board digital terrain elevation data (DTED). The SITAN algorithm is integrated into the Advanced Fighter Technology Integration (AFTI)/ F-16 aircraft, and called AFTI/SITAN to distinguish it from other SITAN designs. AFTI/SITAN performance, as determined by Air Force tracking radar during real-time testing in the AFTI/F-16 aircraft at Edwards Air Force Base from September 1986 through April 1987, is presented. Required performance is less than 100 m median horizontal radial error over 200 nmi trajectories that are flown over gently rolling terrain with available DTED. The flight data support the conclusions that AFTI/SITAN reliably determines aircraft position within an initial 0.5 nmi, CEP horizontal position error, and tracks aircraft horizontal position with an accuracy of 75 m median radial error using DTED supplied by the Defense Mapping Agency. Although accurate estimation of absolute altitude is not required for proper SITAN operation, altitude is estimated with less than 17 m root-mean-square error.

A network of two drive-reinforcement neurons that learns a solution to a realtime dynamic control problem: [formula omitted]. Avionics Laboratory, Air Force Wright Aeronautical Laboratories, AFWAL/AAAT-3, Wright-Patterson Air Force Base, Ohio 45433

Pattern recognition (recognizing a pattern from inputs) and recall (describing or predicting the inputs associated with a recognizable pattern) are essential for neural-symbolic processing and cognitive capacities. Without them the brain cannot interact with the world e.g.: form internal representations and recall memory upon which it can perform logic and reason. Neural networks are efficient, biologically plausible algorithms that can perform large scale recognition. However, most neural network models of recognition perform recognition but not recall: they are sub-symbolic. It remains difficult to connect models of recognition with models of logic and emulate fundamental brain functions, because of the symbolic recall limitation.I introduce a completely symbolic neural network that is similar in function to standard feedforward neural networks but uses feedforward-feedback connections similar to auto-associative networks. However, unlike auto-associative networks, the symmetrical feedback connections are inhibitory not excitatory. Initially it may seem counterintuitive that recognition can even occur because the top-down connections are self-inhibitory. The self-inhibitory configuration is used to implement a gradient descent mechanism that functions during recognition not learning. The purpose of the gradient-descent is not to learn weights (weights are still learned during learning) but to find neuron activation. The advantage of this approach is the weights can now be symbolic (representing prototypes of expected patterns) allowing recall within neural networks. Moreover, considering the costs of both learning and recognition, this approach may be more efficient than feedforward recognition. I show that this model mathematically emulates standard feedforward model equations in single layer networks without hidden units. Comparisons that include more layers are planned in the future.

Development of test facility and optical instrumentation for turbulent combustion research

Practical combustion systems as complex as a gas turbine combustor, a ramjet, or an afterburner pose many design and modeling difficulties. This has created an urgent need for well conceived turbulent combustion experiments to validate the models and to improve their potential design capabilities. With that broad goal in mind, the U.S. Air Force Wright Aeronautical Laboratories, Aero Propulsion Laboratory initiated a major program with the University of Dayton Research Institute to 1) develop a sophisticated combustion test facility, 2) develop state-of-the-art optical instrumentation capable of measurements in nonreactiye and reactive turbulent flows, and 3) carry out well conceived turbulent combustion experiments. This paper describes the development of the combustion test facility and the optical instrumentation. A turbulent flame burner provides low exit turbulence (<0.25%), predictable velocity profile; and it is capable of producing a variety of flame configurations. A two-component LDA system, capable of measuring velocity fluctuations over three orders of magnitude, has been designed. A three-channel laser Raman/Rayleigh spectroscopy (LRS) system, which can simultaneously measure temperature, density, and species concentration, has been constructed. Integration pf the LDA-LRS systems is carried out to measure complex correlations between velocity, temperature, concentration, and density in a turbulent flame. Design and development of auxiliary systems and equipment such as fuel and airflow networks, LDA seeders, and the flow visualization system are described in detail.

The lightning threat to aerospace vehicles

During 1984, the U.S. Air Force Wright Aeronautical Laboratories and the Federal Aviation Administration conducted a lightning measurement program flying a CV-580 aircraft in the vicinity of the Kennedy Space Center, FL. The aircraft was flown in thunderclouds where the regions of precipitation did not exceed 40 dBz between 2000 and 18,000 ft. The aircraft was instrumented to measure the current flow on the wingtips, the displacement and surface current densities on the fuselage and on the wings, the electrostatic field, and the VHF radiation during direct lightning attachment. The transient electromagnetic characteristics of lightning attachments were recorded using six Tektronix 7612D waveform digitizers with sample rates of 5 ns and a Honeywell 101 analog recorder with a 2 MHz frequency response. Data from 21 direct lightning attachments were recorded in the CV-580 aircraft during the program. The maximum displacement and surface current densities measured in the aircraft digital acquisition system during direct lightning attachments were 22 A/m and 2950 T/s, respectively. The maximum charge and action integrals calculated from the analog data collected during direct lightning attachments were about 100 C and 2.9xl0 A-s, respectively. This paper presents the characteristics of the fast transient pulses, the overall characteristics of the lightning flashes, and their relationship with the MIL-STD-1757A test qualification waveform.

A Review of Recent Developments in Iron Aluminides

AbstractThis paper presents a review of recent research conducted at the Air Force Wright Aeronautical Laboratories (AFWAL)/Materials Laboratory to develop iron-aluminides as elevated temperature structural materials. The research consisted of investigations on the microstructure, tensile behavior, deformation, and fracture mechanisms of the DO3 and B2 ironaluminides. Binary Fe-Al alloys with a wide range of Al contents, solidsolution ternary alloys and precipitation- and dispersion-strengthened two-phase alloys have been investigated. It is shown that iron-aluminides have a potential to be structural materials at least up to 650°C.

A Computer-Based System for Workstation Design and Analysis

The Crew Systems Development Branch of the US Air Force Wright Aeronautical Laboratories is pursuing a system of computer-aided design and evaluation techniques (CADETs) for aircraft crew station development. Composed of individual computer-based human factors design tools and analysis methods, the system's key element is a user-interface module (UIM). The UIM serves as the single user-computer interface, through which all CADETs are accessed, eliminating many of the potential disadvantages normally associated with such an approach (e.g. diverse user backgrounds and varying user familiarity with computers). The CADETs are being implemented in a modular architecture to permit easy upgrade, replacement, or addition of any design tool or analysis technique. These features, and others discussed herein, are being combined to produce a system with numerous desirable attributes including user friendliness and software portability. A powerful, effective CADET system will result, employing computer graphic, analytic, and data base technologies for the design of workstation layouts, and the analysis of workstation geometry, man-machine function allocation, and operator workload.

Electromechanical Actuation Technology for the All-Electric Aircraft

Electromechanical actuation is a critical element that must be developed and verified to make the all-electric aircraft a viable concept. For several years the Flight Control Division of the Air Force Wright Aeronautical Laboratories has sponsored activities to demonstrate the credibility of electromechanical actuation systems (EMAS) for primary flight control actuation functions. The foundation for these EMAS activities and several electromechanical actuation development programs are described here. One involves the design, fabrication, and laboratory test of a rotary, hingeline electromechanical actuator. Another involves the development and flight test demonstration of a linear electromechanical actuator for controlling an aileron of a C-141 aircraft. A third involves the design and development of a linear electromechanical actuator for missiles having severe performance, temperature, and volumetric requirements. In addition, a brief summary of the results from two aircraft actuation trade studies compare the baseline (conventional) hydraulic flight control system with an all-electric airplane concept including quantitative comparisons of weight, reliability and maintainability, and life cycle costs.

Effects of spanwise blowing and reverse thrust on fighter low-speed aerodynamics

A brief review of takeoff and landing requirements for the next generation of fighter aircraft indicates that improvement in lift performance and thrust reversing capability will be needed if short takeoff and landing (STOL) operations are to be feasible. A recent joint NASA/Grumman Aerospace Corporation/U.S. Air Force Wright Aeronautical Laboratory wind tunnel investigation was conducted to examine the effects of spanwise blowing on the trailing-edge flap system. This application contrasts with the more familiar method of spanwise blowing near the wing leading edge. Another joint program among NASA/McDonnell Aircraft Company/U.S. Air Force Wright Aeronautical Laboratory investigated the effects of reverse thrust on the low-speed aerodynamics of an F-15 configuration. The F-15 model was fitted with a rotating vane thrust reverser concept which could simulate both in-flight reversing for approach and landing or full reversing for ground roll reduction. The significant results of these two joint programs are reported in this paper. a b c CD CD.O

Evaluation of Sealing Systems For Nonflammable Aircraft Hydraulic Fluids

Efforts within the Materials Laboratory of the Air Force Wright Aeronautical Laboratories to develop seal materials for a nonflammable aircraft hydraulic fluid are discussed. Candidate materials are identified and the laboratory efforts to compound these materials for optimum performance are reported. Candidate seal performance is summarized from dynamic performance tests conducted at temperatures of 135° C and system pressures of 10.35 MPa in the laboratory’s “Chew Tester” and “Rod Seal Tester.” The drastic effect on long term seal performance caused by slight material formulation changes is noted. The value of performance testing of seal materials data to the material compounder is discussed.

A Multifunction Integrated Approach to Providing Aircraft Inertial Data

This paper describes an approach for providing all the inertial information required by an advanced fighter aircraft from a single set of inertial sensors (gyros and accelerometers). Current aircraft have numerous subsystems performing a wide variety of functions, all requiring inertial reference data. The avionics subsystems requiring inertial data include navigation, reference, flight control, autopilot, cockpit displays, mission avionics, and weapon delivery. Each of these functions obtain inertial data from a dedicated set of inertial sensors. This conventional approach has redundancy of inertial sensors and duplication of inertial data, but since there is no communication between the subsystems, there is no advantage in this redundancy and duplication. Duplication can be eliminated and the advantages of redundancy achieved by providing all required inertial data from a common set of inertial sensors. The challenge of this new approach is to produce a cost effective integrated system architecture that can satisfy all inertial requirements and meet aircraft safety-of-flight and survivability constraints. The Air Force Wright Aeronautical Laboratories is conducting the Integrated Inertial Reference Assembly (IIRA) program to validate this new concept of providing all inertial data from a common set of inertial sensors. When demonstrated, the IIRA concept would have direct application to advanced fighter aircraft as well as advanced transports, trainers, cruise missiles, and bombers.

Defense Advanced Research Projects Agency Program – Intelligent Task Automation

The establishment of a science and technology base for many aspects of defense manufacturing and for adapting intelligent systems for complex military operational tasks is a cornerstone effort of advanced research with great national significance. This presentation provides an overview of the efforts of the Defense Advanced Research Projects Agency (DARPA) and the Air Force Wright Aeronautical Laboratories (AFWAL) to plan and fund technology development for a substantial leap in Intelligent Task Automation (ITA). In addressing the needs for high productivity in manufacturing and robust applications to complex military tasks, the ITA program develops and integrates the generic technologies impacting, gripping, sensing, viewing, recognizing and understanding the environment, controlling manipulation, and intelligently providing command of the task.