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At least 793 records · Page 44

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NASA NTRS2002

Initial Flight Tests of the NASA F-15B Propulsion Flight Test Fixture

Flights of the F-15B/Propulsion Flight Test Fixture (PFTF) with a Cone Drag Experiment (CDE) attached have been accomplished at NASA Dryden Flight Research Center. Mounted underneath the fuselage of an F-15B airplane, the PFTF provides volume for experiment systems and attachment points for propulsion experiments. A unique feature of the PFTF is the incorporation of a six-degree-of-freedom force balance. The force balance mounts between the PFTF and experiment and measures three forces and moments. The CDE has been attached to the force balance for envelope expansion flights. This experiment spatially and inertially simulates a large propulsion test article. This report briefly describes the F-15B airplane, the PFTF, and the force balance. A detailed description of the CDE is provided. Force-balance ground testing and stiffness modifications are described. Flight profiles and selected flight data from the envelope expansion flights are provided and discussed, including force-balance data, the internal PFTF thermal and vibration environment, a handling qualities assessment, and performance capabilities of the F-15B airplane with the PFTF installed.

Palumbo, Nathan↗

NASA NTRS1980

Simulators for Safer Shipping

Each year one ship out of every five afloat collides with another vessel, rams a dock, or runs a ground. CAORF (Computer Aided Operations Research Facility), designed and built by Sperry Rand Corporation, incorporates technology developed in a wide variety of aerospace simulation and technical training programs. CAORF can be set up to duplicate the exact handling qualities of any vessel under various conditions of wind, tide and current. Currently a dozen different ships can be "plugged in." Bridge instrumentation is typical of modern shipboard equipment including radar, internal and external c.ommunications and new collision avoidance systems. From repetitive operation of simulated ships, MarAd is building a valuable data base for improving marine safety.

Source record↗

NASA NTRS2002

Airworthiness Qualification Criteria for Rotorcraft with External Sling Loads

This report presents the results of a study to develop airworthiness requirements for rotorcraft with external sling loads. The report starts with a review of the various phenomena that limit external sling load operations. Specifically discussed are the rotorcraft-load aeroservoelastic stability, load-on handling qualities, effects of automatic flight control system failure, load suspension system failure, and load stability at speed. Based on past experience and treatment of these phenomena, criteria are proposed to form a package for airworthiness qualification. The desired end objective is a set of operational flight envelopes for the rotorcraft with intended loads that can be provided to the user to guide operations in the field. The specific criteria proposed are parts of ADS-33E-PRF; MIL-F-9490D, and MIL-STD-913A all applied in the context of external sling loads. The study was performed for the Directorate of Engineering, U.S. Army Aviation and Missile Command (AMCOM), as part of the contract monitored by the Aerothermodynamics Directorate, U.S. Army AMCOM.

Key, David L.↗

NASA NTRS2000

Initial Flight Evaluation of the Army/NASA RASCAL Variable Stability Helicopter

NASA Ames Research Center and the U.S. Army Aeroflightdynamics Directorate (AFDD) [will] have performed initial flight evaluations of the Research Flight Control System (RFCS) that has been integrated into the Army/NASA Rotorcraft Aircrew Systems Concepts Airborne Laboratory (RASCAL) variable stability helicopter. The RASCAL, a highly modified JUH-60A Black Hawk helicopter, is a variable-stability, in-flight simulator that is designed to support flight research programs that leverage on the flight control and handling qualities design tools developed by the Army and NASA. These tools are used in the flight control design life cycle from initial concept definition, through simulation, and ultimately into flight on-board the RASCAL helicopter. The RASCAL will be used to validate methodologies for reducing design cycle costs for new or modified aircraft, and it will serve as a base for the investigation of new rotorcraft technology.

Moralez, Ernesto, III↗

NASA NTRS1998

Objective Situation Awareness Measurement Based on Performance Self-Evaluation

The research was conducted in support of the NASA Safe All-Weather Flight Operations for Rotorcraft (SAFOR) program. The purpose of the work was to investigate the utility of two measurement tools developed by the British Defense Evaluation Research Agency. These tools were a subjective workload assessment scale, the DRA Workload Scale and a situation awareness measurement tool. The situation awareness tool uses a comparison of the crew's self-evaluation of performance against actual performance in order to determine what information the crew attended to during the performance. These two measurement tools were evaluated in the context of a test of innovative approach to alerting the crew by way of a helmet mounted display. The situation assessment data are reported here. The performance self-evaluation metric of situation awareness was found to be highly effective. It was used to evaluate situation awareness on a tank reconnaissance task, a tactical navigation task, and a stylized task used to evaluated handling qualities. Using the self-evaluation metric, it was possible to evaluate situation awareness, without exact knowledge the relevant information in some cases and to identify information to which the crew attended or failed to attend in others.

DeMaio, Joe↗

NASA NTRS2003

Control Reallocation Strategies for Damage Adaptation in Transport Class Aircraft

This paper examines the feasibility, potential benefits and implementation issues associated with retrofitting a neural-adaptive flight control system (NFCS) to existing transport aircraft, including both cable/hydraulic and fly-by-wire configurations. NFCS uses a neural network based direct adaptive control approach for applying alternate sources of control authority in the presence of damage or failures in order to achieve desired flight control performance. Neural networks are used to provide consistent handling qualities across flight conditions, adapt to changes in aircraft dynamics and to make the controller easy to apply when implemented on different aircraft. Full-motion piloted simulation studies were performed on two different transport models: the Boeing 747-400 and the Boeing C-17. Subjects included NASA, Air Force and commercial airline pilots. Results demonstrate the potential for improving handing qualities and significantly increased survivability rates under various simulated failure conditions.

Gundy-Burlet, Karen↗

NASA NTRS2002

Piloted Evaluation of a UH-60 Mixer Equivalent Turbulence Simulation Model

A simulation study of a recently developed hover/low speed Mixer Equivalent Turbulence Simulation (METS) model for the UH-60 Black Hawk helicopter was conducted in the NASA Ames Research Center Vertical Motion Simulator (VMS). The experiment was a continuation of previous work to develop a simple, but validated, turbulence model for hovering rotorcraft. To validate the METS model, two experienced test pilots replicated precision hover tasks that had been conducted in an instrumented UH-60 helicopter in turbulence. Objective simulation data were collected for comparison with flight test data, and subjective data were collected that included handling qualities ratings and pilot comments for increasing levels of turbulence. Analyses of the simulation results show good analytic agreement between the METS model and flight test data, with favorable pilot perception of the simulated turbulence. Precision hover tasks were also repeated using the more complex rotating-frame SORBET (Simulation Of Rotor Blade Element Turbulence) model to generate turbulence. Comparisons of the empirically derived METS model with the theoretical SORBET model show good agreement providing validation of the more complex blade element method of simulating turbulence.

Lusardi, Jeff A.↗

NASA NTRS2003

A High-Order, Time Invariant, Linearized Model for Application to HHCIAFCS Interaction Studies

This paper describes a methodology for the extraction of a linear time invariant model from a nonlinear helicopter model, and followed by an examination of the interactions of the Higher Harmonic Control (HHC) and the Automatic Flight Control System (AFCS). This new method includes an embedded harmonic analyzer inside a linear time invariant model, which allows the periodicity of the helicopter response to be captured. The: coupled high-order model provides the needed level of dynamic fidelity to permit an analysis and optimization of the AFCS and HHC loops. Results of this study indicate that the closed-loop HHC system has little influence on the AFCS or on the vehicle handling qualities, which indicates that the AFCS does not need modification to work with the HHC system. The results also show that the vibration response to maneuvers must be considered during the HHC design process, which leads to much higher required HHC loop crossover frequencies. This research also demonstrates that the transient vibration response during maneuvers can be reduced by optimizing the closed-loop higher harmonic control laws using conventional control system analyses.

Cheng, Rendy P.↗

NASA NTRS2003

Evaluation of Two Unique Side Stick Controllers in a Fixed-Base Flight Simulator

A handling qualities analysis has been performed on two unique side stick controllers in a fixed-base F-18 flight simulator. Each stick, which uses a larger range of motion than is common for similar controllers, has a moving elbow cup that accommodates movement of the entire arm for control. The sticks are compared to the standard center stick in several typical fighter aircraft tasks. Several trends are visible in the time histories, pilot ratings, and pilot comments. The aggressive pilots preferred the center stick, because the side sticks are underdamped, causing overshoots and oscillations when large motions are executed. The less aggressive pilots preferred the side sticks, because of the smooth motion and low breakout forces. The aggressive pilots collectively gave the worst ratings, probably because of increased sensitivity of the simulator (compared to the actual F-18 aircraft), which can cause pilot-induced oscillations when aggressive inputs are made. Overall, the elbow cup is not a positive feature, because using the entire arm for control inhibits precision. Pilots had difficulty measuring their performance, particularly during the offset landing task, and tended to overestimate.

Mayer, Jann↗

NASA NTRS2003

Launch Condition Deviations of Reusable Launch Vehicle Simulations in Exo-Atmospheric Zoom Climbs

The Defense Advanced Research Projects Agency has proposed a two-stage system to deliver a small payload to orbit. The proposal calls for an airplane to perform an exo-atmospheric zoom climb maneuver, from which a second-stage rocket is launched carrying the payload into orbit. The NASA Dryden Flight Research Center has conducted an in-house generic simulation study to determine how accurately a human-piloted airplane can deliver a second-stage rocket to a desired exo-atmospheric launch condition. A high-performance, fighter-type, fixed-base, real-time, pilot-in-the-loop airplane simulation has been modified to perform exo-atmospheric zoom climb maneuvers. Four research pilots tracked a reference trajectory in the presence of winds, initial offsets, and degraded engine thrust to a second-stage launch condition. These launch conditions have been compared to the reference launch condition to characterize the expected deviation. At each launch condition, a speed change was applied to the second-stage rocket to insert the payload onto a transfer orbit to the desired operational orbit. The most sensitive of the test cases was the degraded thrust case, yielding second-stage launch energies that were too low to achieve the radius of the desired operational orbit. The handling qualities of the airplane, as a first-stage vehicle, have also been investigated.

Urschel, Peter H.↗

NASA NTRS2003

An Assessment of CFD Effectiveness for Vortex Flow Simulation to Meet Preliminary Design Needs

The low-speed flight and transonic maneuvering characteristics of combat air vehicles designed for efficient supersonic flight are significantly affected by the presence of free vortices. At moderate-to-high angles of attack, the flow invariably separates from the leading edges of the swept slender wings, as well as from the forebodies of the air vehicles, and rolls up to form free vortices. The design of military vehicles is heavily driven by the need to simultaneously improve performance and affordability.1 In order to meet this need, increasing emphasis is being placed on using Modeling & Simulation environments employing the Integrated Product & Process Development (IPPD) concept. The primary focus is on expeditiously providing design teams with high-fidelity data needed to make more informed decisions in the preliminary design stage. Extensive aerodynamic data are needed to support combat air vehicle design. Force and moment data are used to evaluate performance and handling qualities; surface pressures provide inputs for structural design; and flow-field data facilitate system integration. Continuing advances in computational fluid dynamics (CFD) provide an attractive means of generating the desired data in a manner that is responsive to the needs of the preliminary design efforts. The responsiveness is readily characterized as timely delivery of quality data at low cost.

Raj, P.↗

NASA NTRS2004

Flight Test Results for the F-16XL With a Digital Flight Control System

In the early 1980s, two F-16 airplanes were modified to extend the fuselage length and incorporate a large area delta wing planform. These two airplanes, designated the F-16XL, were designed by the General Dynamics Corporation (now Lockheed Martin Tactical Aircraft Systems) (Fort Worth, Texas) and were prototypes for a derivative fighter evaluation program conducted by the United States Air Force. Although the concept was never put into production, the F-16XL prototypes provided a unique planform for testing concepts in support of future high-speed supersonic transport aircraft. To extend the capabilities of this testbed vehicle the F-16XL ship 1 aircraft was upgraded with a digital flight control system. The added flexibility of a digital flight control system increases the versatility of this airplane as a testbed for aerodynamic research and investigation of advanced technologies. This report presents the handling qualities flight test results covering the envelope expansion of the F-16XL with the digital flight control system.

Stachowiak, Susan J.↗

NASA NTRS1961

Aerodynamic Characteristics of Propeller-Driven VTOL Aircraft

This paper discusses the two major configurations that are usually considered for achieving VTOL while keeping the fuselage essentially horizontal - that is, the tilt-wing and the deflected-slipstream configurations. Because of the high turning losses incurred by deflected-slipstream configurations in hovering and because of the wing-stalling problem of the pure tilt-wing configurations during the transition, it appears that a combination of the two principles should be used. This tilt-wing and flap configuration should make use of a programmed extensible-chord slotted flap together with a leading-edge high-lift device in order to avoid the performance and handling qualities problems associated with wing stalling during the transition while keeping the wing area as low as possible for efficiency in cruising flight.

Kirby, Robert H.↗

NASA NTRS2003

Human Factors Considerations for Safe Recovery from Faults In Flight Control Systems

It is now possible - and important - to develop systems to help resolve Flight Control System (FCS) faults. From a human factors viewpoint, it is imperative that these systems take on roles, and provide functions, that are the most supportive to the pilot, given the stress, time pressure and workload they may experience following a FCS fault. FCS fault recovery systems may provide several different functions, including alerting, control assistance, and decision aiding. The biggest human factors questions are in the role suitable for the technology, and its specific functioning to achieve that role. Specifically, for these systems to be effective, they must meet the fundamental requirements that (1) they alert pilots to problems early enough that the pilot can reasonably resolve the fault and regain control of the aircraft and that (2) if the aircraft s handling qualities are severely degraded the HMS provide the appropriate stability augmentation to help the pilot stabilize and control the aircraft. This project undertook several research steps to develop such systems, focusing on the capabilities of pilots and on realistically attainable technologies. The ability to estimate which functions are the most valuable will help steer system development in the directions that can establish the highest safety levels.

Pritchett, Amy↗

NASA NTRS2000

NASA/ARMY/BELL XV-15 Tiltrotor Low Noise Terminal Area Operations Flight Research Program

A series of three XV-15 acoustic flight tests have been conducted over a five year period by a NASA/Army/Bell Helicopter team to evaluate the noise reduction potential for tiltrotor aircraft during terminal area operations. Lower hemispherical noise characteristics for a wide range of steady-state terminal area type operating conditions were measured during the phase 1 test and indicated that the takeoff and level flight conditions were not significant contributors to the total noise of tiltrotor operations. Phase 1 results were used to design low noise approach profiles that were tested during the phase 2 and phase 3 tests, which used large area microphone arrays to directly measure the ground noise footprints. Approach profile designs emphasized noise reduction while maintaining handling qualities sufficient for tiltrotor commercial passenger ride comfort and flight safety under Instrument Flight Rules (IFR) conditions. This paper will discuss the weather, aircraft, tracking, guidance, and acoustic instrumentation systems, as well as the approach profile design philosophy, and the overall test program philosophy. Acoustic results are presented documenting the variation in tiltrotor noise due to changes in operating condition, indicating the potential for significant noise reduction using the unique tiltrotor capability of nacelle tilt.

Conner, David A.↗

NASA NTRS2004

Selected Flight Test Results for Online Learning Neural Network-Based Flight Control System

The NASA F-15 Intelligent Flight Control System project team has developed a series of flight control concepts designed to demonstrate the benefits of a neural network-based adaptive controller. The objective of the team is to develop and flight-test control systems that use neural network technology to optimize the performance of the aircraft under nominal conditions as well as stabilize the aircraft under failure conditions. Failure conditions include locked or failed control surfaces as well as unforeseen damage that might occur to the aircraft in flight. This report presents flight-test results for an adaptive controller using stability and control derivative values from an online learning neural network. A dynamic cell structure neural network is used in conjunction with a real-time parameter identification algorithm to estimate aerodynamic stability and control derivative increments to the baseline aerodynamic derivatives in flight. This set of open-loop flight tests was performed in preparation for a future phase of flights in which the learning neural network and parameter identification algorithm output would provide the flight controller with aerodynamic stability and control derivative updates in near real time. Two flight maneuvers are analyzed a pitch frequency sweep and an automated flight-test maneuver designed to optimally excite the parameter identification algorithm in all axes. Frequency responses generated from flight data are compared to those obtained from nonlinear simulation runs. An examination of flight data shows that addition of the flight-identified aerodynamic derivative increments into the simulation improved the pitch handling qualities of the aircraft.

Williams, Peggy S.↗

NASA NTRS1947

Data Obtained in the Flight Measurements to Determine the Stability and Control Characteristics of a C-54D Airplane (AAF No. 42-72713) and a Summary of the Test Program

The flight investigation of the C-54D airplane was initiated to determine the necessity of changes or additions to existing handling-qualities requirements to cove the case of instrument approaches with large airplanes. This paper gives a brief synopsis of the results and presents the measured data of tests to determine the stability and control characteristics. It was found that no new requirements were necessary to cover the problems of instrument approaches. The C-54D airplane tested met the Amy and Navy stability and control requirements except for the following items. The control-system friction with autopilot installed vas double that allowed by the requirements. The amount of friction was found to impair the controllability of the airplane in precision flying. The lateral and directional characteristics were good except that the maximum pb/2V was slightly below the minimum required, and the elevator-control forces to obtain the maximum pb/2V at low speeds were above the Army and Navy requirements. The longitudinal stability and control characteristics were good except that the elevator-control forces exceeded the limits of the Army and Navy requirements in turns and in landings. The stalling characteristics were considered good in all conditions with the stall warning in the form of tail buffeting occurring at speeds approximately 5 miles per hour above the stall.

Talmage, Donald B.↗

NASA NTRS1947

A Time History of Control Operation of a C-54 Airplane in Blind Landing Approaches

Tests were made with a C-54 airplane in which airline pilots made several blind approaches to determine whether any special flying techniques were used in blind landings and whether any special handling-qualities requirements would have to be formulated because of such special techniques. It was found that the airplane was flown at all times in the normal manner; that is, all turns were banked turns that were nearly coordinated by use of the rudder so that the sideslip was held close to zero. The pilot expended considerable physical work in continually moving the controls but this wake was due in part to the large friction in the three control systems. The actual control deflections used were small compared to the maximum deflections available.

Talmage, Donald B.↗