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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 577 records · Page 32
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Simulation evaluation of display/FLIR concepts for low-altitude, terrain-following helicopter operations

Trials were run on a six degree of freedom combat helicopter simulator to evaluate head-down displays with integrated FLIR imagery for terrain-following, course-steering, and transition to approach and hover helicopter pilot tasks. Three display formats were tested, providing varying levels of symbology for, e.g., the flight path angle, pitch-attitude data, vertical speed, altitude, etc. The pilots were also furnished flight director guidance, i.e., terrain-following, course steering, airspeed hold, and approach to hover. All the displays permitted the pilots to fly satisfactory mission in the CGI scenarios. The results revealed that the pilots preferred a nonconformal FLIR display superposition.

Swenson, H. N.↗
NASA NTRS1985

Ground effects on V/STOL and STOL aircraft - A survey

The flow fields encountered by jet- and fan-powered Vertical/Short Takeoff and Landing (V/STOL) aircraft operating in ground effect are reviewed and their general effects on the aerodynamic characteristics are discussed. The ground effects considered include (1) the suckdown experienced by a single jet configuration in hover, (2) the fountain flow and additional suckdown experienced by multiple jet configurations in hover, (3) the ground vortex generated by jet and jet flap configurations in Short Takeoff and Landing (STOL) operation and the associated aerodynamic and hot-gas-ingestion effects, and (4) the change in the downwash at the tail due to ground proximity. After over 30 years of research on V/STOL aircraft, the general flow phenomena are well known and, in most areas, the effects of ground proximity can be estimated or can be determined experimentally. However, there are some anomalies in the current data base which are discussed.

Eshlemen, J.↗
NASA NTRS1984

Decennial Specialists' Meeting on Rotorcraft Dynamics, 2nd, Moffett Field, CA, November 7-9, 1984, Proceedings

Various papers on helicopter rotor technology are presented. The subjects considered include: ground resonance analysis using a substructure modelling approach, aerolastic stability of a bearingless rotor, experimentally determined flutter from two and three-bladed model bearingless rotors in hover, lifting surface theory for a helicopter rotor in forward flight, aeroelastic considerations for torsionally soft rotors, and restructuring of a rotor analysis program. Also discussed are: dynamic inflow and its effect on experimental correlations, flap-lag-torsion instability in forward flight, dynamic stability of a bearingless circulation control rotor blade in hover, dynamic response characteristics of a circulation control rotor model pneumatic system, the relations between vibratory loads and airframe vibrations, coupled rotor body vibrations with in-plane degrees of freedom, helicopter vibration reduction concepts.

Source record↗
NASA NTRS1986

Rotor tip vortex geometry measurements using the wide-field shadowgraph technique

Rotor tip vortex geometry data have been acquired using the wide-field shadowgraph technique. Shadowgraphs were taken of the wakes of two model main-rotor systems in hover. These shadowgraphs provided detailed tip vortex trajectories from which axial and radial vortex coordinates were measured. Using these coordinates, prescribed-wake parameters were determined and input into a hover-performance prediction code. The resultant predictions were compared with experimental performance data to help assess the capabilities of this code. Another result of the experimental work was the development of a method to predict the visibility of rotor tip vortices on shadowgraphs. Using this method, the ability of the shadowgraph technique to visualize tip vortices in the rotor wake was quantified.

Norman, T. R.↗
NASA NTRS1987

Comparing Test Data on Scale-Model Helicopter Rotors

Hovering data correlate well, but forward-flight data do not. Report compares acoustics and performance of small-scale helicopter rotor with those of full-scale rotor in both hovering and forward flight.

Kitaplioglu, Cahit↗
NASA NTRS1986

Toward comparing experiment and theory for corroborative research on hingeless rotor stability in forward flight (an experimental and analytical investigation of isolated rotor-flap-lag stability in forward flight)

For flap-lag stability of isolated rotors, experimental and analytical investigations are conducted in hover and forward flight on the adequacy of a linear quasisteady aerodynamics theory with dynamic inflow. Forward flight effects on lag regressing mode are emphasized. Accordingly, a soft inplane hingeless rotor with three blades is tested at advance ratios as high as 0.55 and at shaft angles as high as 20 degrees. The 1.62 m model rotor is untrimmed with an essentially unrestricted tilt of the tip path plane. In combination with lag natural frequencies, collective pitch settings and flap-lag coupling parameters, the data base comprises nearly 1200 test points (damping and frequency) in forward flight and 200 test points in hover. By computerized symbolic manipulation, a linear analytical model is developed in substall to predict stability margins with mode identificaton. To help explain the correlation between theory and data it also predicts substall and stall regions of the rotor disk from equilibrium values. The correlation shows both the strengthts and weaknesses of the theory in substall.

Gaonkar, G.↗
NASA NTRS1984

Helicopter rotor blade aerodynamic optimization by mathematical programming

Formal mathematical programing was applied to the aerodynamic rotor blade design process. The approach is to couple hover and forward flight analysis programs with the general-purpose optimization program CONMIN to determine the blade taper ratio, percent taper, twist distribution, and solidity which minimize the horsepower required at hover while meeting constraints on forward flight performance. Designs obtained using this approach for the blade of a representative Army helicopter compare well with those obtained using a conventional approach involving personnel-intensive parametric studies. Results from the present method can be obtained in 2 days as compared to 5 weeks required by the conventional procedure. Also the systematic manipulation of the design variables by the optimization procedure minimizes the need for the researcher to have a vast body of past experience and data in determining the influence of a design change on the performance.

Walsh, J. L.↗
NASA NTRS1986

Aircraft automatic-flight-control system with inversion of the model in the feed-forward path using a Newton-Raphson technique for the inversion

A new automatic flight control system concept suitable for aircraft with highly nonlinear aerodynamic and propulsion characteristics and which must operate over a wide flight envelope was investigated. This exact model follower inverts a complete nonlinear model of the aircraft as part of the feed-forward path. The inversion is accomplished by a Newton-Raphson trim of the model at each digital computer cycle time of 0.05 seconds. The combination of the inverse model and the actual aircraft in the feed-forward path alloys the translational and rotational regulators in the feedback path to be easily designed by linear methods. An explanation of the model inversion procedure is presented. An extensive set of simulation data for essentially the full flight envelope for a vertical attitude takeoff and landing aircraft (VATOL) is presented. These data demonstrate the successful, smooth, and precise control that can be achieved with this concept. The trajectory includes conventional flight from 200 to 900 ft/sec with path accelerations and decelerations, altitude changes of over 6000 ft and 2g and 3g turns. Vertical attitude maneuvering as a tail sitter along all axes is demonstrated. A transition trajectory from 200 ft/sec in conventional flight to stationary hover in the vertical attitude includes satisfactory operation through lift-cure slope reversal as attitude goes from horizontal to vertical at constant altitude. A vertical attitude takeoff from stationary hover to conventional flight is also demonstrated.

Smith, G. A.↗
NASA NTRS1987

Demonstration of frequency-sweep testing technique using a Bell 214-ST helicopter

A demonstration of frequency-sweep testing using a Bell-214ST single-rotor helicopter was completed in support of the Army's development of an updated MIL-H-8501A, and an LHX (ADS-33) handling-qualities specification. Hover and level-flight (V sub a = 0 knots and V sub a = 90 knots) tests were conducted in 3 flight hours by Army test pilots at the Army Aviation Engineering Flight Activity (AEFA) at Edwards AFB, Calif. Bandwidth and phase-delay parameters were determined from the flight-extracted frequency responses as required by the proposed specifications. Transfer function modeling and verification demonstrates the validity of the frequency-response concept for characterizing closed-loop flight dynamics of single-rotor helicopters -- even in hover. This report documents the frequency-sweep flight-testing technique and data-analysis procedures. Special emphasis is given to piloting and analysis considerations which are important for demonstrating frequency-domain specification compliance.

Tischler, Mark B.↗
NASA NTRS1987

V/STOL and STOL ground effects and testing techniques

The ground effects associated with V/STOL operation were examined and an effort was made to develop the equipment and testing techniques needed for that understanding. Primary emphasis was on future experimental programs in the 40 x 80 and the 80 x 120 foot test sections and in the outdoor static test stand associated with these facilities. The commonly used experimental techniques are reviewed and data obtained by various techniques are compared with each other and with available estimating methods. These reviews and comparisons provide insight into the limitations of past studies and the testing techniques used and identify areas where additional work is needed. The understanding of the flow mechanics involved in hovering and in transition in and out of ground effect is discussed. The basic flow fields associated with hovering, transition and STOL operation of jet powered V/STOL aircraft are depicted.

Kuhn, R. E.↗
NASA NTRS1987

Optimization methods applied to the aerodynamic design of helicopter rotor blades

Described is a formal optimization procedure for helicopter rotor blade design which minimizes hover horsepower while assuring satisfactory forward flight performance. The approach is to couple hover and forward flight analysis programs with a general-purpose optimization procedure. The resulting optimization system provides a systematic evaluation of the rotor blade design variables and their interaction, thus reducing the time and cost of designing advanced rotor blades. The paper discusses the basis for and details of the overall procedure, describes the generation of advanced blade designs for representative Army helicopters, and compares design and design effort with those from the conventional approach which is based on parametric studies and extensive cross-plots.

Walsh, Joanne L.↗
NASA NTRS1987

Wind-tunnel evaluation of an advanced main-rotor blade design for a utility-class helicopter

An investigation was conducted in the Langley Transonic Dynamics Tunnel to evaluate differences between an existing utility-class main-rotor blade and an advanced-design main-rotor blade. The two rotor blade designs were compared with regard to rotor performance oscillatory pitch-link loads, and 4-per-rev vertical fixed-system loads. Tests were conducted in hover and over a range of simulated full-scale gross weights and density altitude conditions at advance ratios from 0.15 to 0.40. Results indicate that the advanced blade design offers performance improvements over the baseline blade in both hover and forward flight. Pitch-link oscillatory loads for the baseline rotor were more sensitive to the test conditions than those of the advanced rotor. The 4-per-rev vertical fixed-system load produced by the advanced blade was larger than that produced by the baseline blade at all test conditions.

Yeager, William T., Jr.↗
NASA NTRS1987

Toward comparing experiment and theory for corroborative research on hingeless rotor stability in forward flight

For flap lag stability of isolated rotors, experimental and analytical investigations were conducted in hover and forward flight on the adequacy of a linear quasisteady aerodynamics theory with dynamic flow. Forward flight effects on lag regressing mode were emphasized. A soft inplane hingeless rotor with three blades was tested at advance ratios as high as 0.55 and at shaft angles as high as 20 deg. The 1.62 m model rotor was untrimmed with an essentially unrestricted tilt of the tip path plane. In combination with lag natural frequencies, collective pitch settings and flap lag coupling parameters, the data base comprises nearly 1200 test points (damping and frequency) in forward flight and 200 test points in hover. By computerized symbolic manipulation, a linear model was developed in substall to predict stability margins with mode identification. To help explain the correlation between theory and data it also predicted substall and stall regions of the rotor disk from equilibrium values. The correlation showed both the strengths and weaknesses of the theory in substall ((angle of attack) equal to or less than 12 deg).

Gaonkar, G.↗
NASA NTRS1986

The development of advanced technology blades for tilt-rotor aircraft

The paper discusses the development and ground testing of blades for the XV-15 tilt-rotor demonstrator aircraft. This work was performed under contract NAS2-11250 with NASA Ames Research Center. These blades, known as the Advanced Technology Blades (ATB), replace the rectangular, steel blades which were part of the XV-15 original design. The materials used in the primary structure of the ATB are fiberglass and high strain graphite epoxy laminates. This facilitates the use of 43 deg of nonlinear twist, a nonuniform tapered planform and thin airfoils required for aerodynamic efficiency. Instrumentation life is extended by encapsulating gages and wiring in the composite structure. Tip shells and cuff fairings are removable to provide access to tip weights and retention hardware; they are also replaceable with alternate research configurations. Extensive laboratory testing has validated predicted strength characteristics. Hover testing has demonstrated performance significantly superior to that predicted by contemporary methodology. Key elements of the test rig used for rotor performance measurement were developed as an ancillary part of the present program. The performance testing included measurement of near- and far-field noise. Induced inflow velocity distributions were also determined and photographs of tip vortex condensation trails were taken. These are providing guidance for modifications to hover peformance codes.

Alexander, Harold R.↗
NASA NTRS1987

A flight investigation of helicopter low-speed response requirements

A flight experiment has been conducted using the Canadian National Aeronautical Establishment's variable-stability airborne simulator to define the dynamic response requirements for operations at hover and low speeds. Fourteen Attitude Command/Attitude Hold, Rate, and Rate Command/Attitude Hold configurations were evaluated by six pilots using both conventional controls and a four-axis integrated sidestick over a low-speed course consisting of precision hover, landing, sidestep, and dash/quickstop tasks. The results indicate that with conventional controls all three response-types were acceptable as long as their response bandwidth was sufficiently high, and higher bandwidths were required in roll than in pitch. With the four-axis sidestick, there was a preference for the Rate systems. The range of acceptable bandwidths was lower, and the spread in pilot ratings smaller, than were found in a similar ground-based simulation.

Mitchell, David G.↗
NASA NTRS1987

A full potential flow analysis with realistic wake influence for helicopter rotor airload prediction

A 3-D, quasi-steady, full potential flow solver was adapted to include realistic wake influence for the aerodynamic analysis of helicopter rotors. The method is based on a finite difference solution of the full potential equation, using an inner and outer domain procedure for the blade flowfield to accommodate wake effects. The nonlinear flow is computed in the inner domain region using a finite difference solution method. The wake is modeled by a vortex lattice using prescribed geometry techniques to allow for the inclusion of realistic rotor wakes. The key feature of the analysis is that vortices contained within the finite difference mesh (inner domain) were treated with a vortex embedding technique while the influence of the remaining portion of the wake (in the outer domain) is impressed as a boundary condition on the outer surface of the finite difference mesh. The solution procedure couples the wake influence with the inner domain solution in a consistent and efficient solution process. The method has been applied to both hover and forward flight conditions. Correlation with subsonic and transonic hover airload data is shown which demonstrates the merits of the approach.

Egolf, T. Alan↗
NASA NTRS1988

Rotorcraft aeroelastic stability

Theoretical and experimental developments in the aeroelastic and aeromechanical stability of helicopters and tilt-rotor aircraft are addressed. Included are the underlying nonlinear structural mechanics of slender rotating beams, necessary for accurate modeling of elastic cantilever rotor blades, and the development of dynamic inflow, an unsteady aerodynamic theory for low-frequency aeroelastic stability applications. Analytical treatment of isolated rotor stability in hover and forward flight, coupled rotor-fuselage stability in hover and forward flight, and analysis of tilt-rotor dynamic stability are considered. Results of parametric investigations of system behavior are presented, and correlation between theoretical results and experimental data from small and large scale wind tunnel and flight testing are discussed.

Ormiston, Robert A.↗
NASA NTRS1988

A flight-test methodology for identification of an aerodynamic model for a V/STOL aircraft

Described is a flight test methodology for developing a data base to be used to identify an aerodynamic model of a vertical and short takeoff and landing (V/STOL) fighter aircraft. The aircraft serves as a test bed at Ames for ongoing research in advanced V/STOL control and display concepts. The flight envelope to be modeled includes hover, transition to conventional flight, and back to hover, STOL operation, and normaL cruise. Although the aerodynamic model is highly nonlinear, it has been formulated to be linear in the parameters to be identified. Motivation for the flight test methodology advocated in this paper is based on the choice of a linear least-squares method for model identification. The paper covers elements of the methodology from maneuver design to the completed data base. Major emphasis is placed on the use of state estimation with tracking data to ensure consistency among maneuver variables prior to their entry into the data base. The design and processing of a typical maneuver is illustrated.

Bach, Ralph E., Jr.↗