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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 271 records · Page 15

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NASA NTRS1987

A piloted simulation of helicopter air combat to investigate effects of variations in selected performance and control response characteristics

A piloted simulation study investigating handling qualities and flight characteristics required for helicopter air to air combat is presented. The Helicopter Air Combat system was used to investigate this role for Army rotorcraft. Experimental variables were the maneuver envelope size (load factor and sideslip), directional axis handling qualities, and pitch and roll control-response type. Over 450 simulated, low altitude, one-on-one engagements were conducted. Results from the experiment indicate that a well damped directional response, low sideforce caused by sideslip, and some effective dihedral are all desirable for weapon system performance, good handling qualities, and low pilot workload. An angular rate command system was favored over the attitude type pitch and roll response for most applications, and an enhanced maneuver envelope size over that of current generation aircraft was found to be advantageous. Pilot technique, background, and experience are additional factors which had a significant effect on performance in the air combat tasks investigated. The implication of these results on design requirements for future helicopters is presented.

Lewis, Michael S.↗

NASA NTRS1986

Helicopter impulsive noise - Theoretical and experimental status

The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade-vortex interaction impulsive noise. A thorough physical explanation of both generating mechanisms is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanisms of high speed impulsive noise are fairly well understood - theory and experiment compare nicely over Mach number ranges typical of today's helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory/experiment are suggested.

Schmitz, F. H.↗

NASA NTRS1986

System identification techniques for helicopter higher harmonic control

This paper presents and compares several system identification techniques proposed for use with higher harmonic control algorithms designed to alleviate helicopter vibration. All method for actively controlling helicopter vibration require the knowledge of how the vibration outputs are related to the control inputs. Off-line or batch identification methods for obtaining this knowledge are presented first. Then the more advanced, adaptive identification techniques proposed to track the helicopter model parameters in flight are discussed. Considerations regarding system identifiability, identification algorithm stability, and computer implementation are also discussed.

Jacklin, S. A.↗

NASA NTRS1986

Helicopter impulsive noise - Theoretical and experimental status

The theoretical and experimental status of helicopter impulsive noise is reviewed. The two major source mechanisms of helicopter impulsive noise are addressed: high-speed impulsive noise and blade-vortex interaction impulsive noise. A thorough physical explanation of both generating mechanism is presented together with model and full-scale measurements of the phenomena. Current theoretical prediction methods are compared with experimental findings of isolated rotor tests. The noise generating mechanism of high speed impulsive noise are fairly well understood - theory and experiment compare nicely over Mach number ranges typical of today's helicopters. For the case of blade-vortex interaction noise, understanding of noise generating mechanisms and theoretical comparison with experiment are less satisfactory. Several methods for improving theory-experiment are suggested.

Schmitz, F. H.↗

NASA NTRS1987

Application of low-power, high-rate PCM telemetry in a helicopter instrumentation system

The use of low-power, high-rate pulse code modulation (PCM) in a helicopter instrumentation system is examined. A Helicopter Instrumentation and Recording System (HIARS) was developed to obtain main rotor blade measurements and fuselage performance measurements. The HIARS consists of a low-power PCM telemeter, a digital PCM system, an optical rotor position sensor, and a PCM decommutation unit; the components and functions of these subsystems are described. Flight tests were conducted to evaluate the ability of the HIARS to measure aircraft parameters. The test data reveal that the PCM telemetry is applicable to helicopter instrumentation systems.

Thomas, Mitchel E.↗

NASA NTRS1986

Helicopter individual-blade-control research at MIT 1977-1985

A new advanced system for active control of helicopters and its application to the solution of rotor aerodynamic and aeroelastic problems is described. Each blade is individually controlled in the rotating frame over a wide range of frequencies. Application of the system to gust alleviation, attitude stabilization, vibration alleviation, blade lag damping augmentation, stall flutter suppression, blade flapping stabilization, stall alleviation, and performance enhancement is outlined. The effectiveness of the system in achieving most of these applications is demonstrated by experimental results from wind tunnel tests of a model helicopter rotor with individual blade control. The feasibility of achieving many or all of the applications of individual blade control using the conventional helicopter swash plate is demonstrated, and the necessary control laws are presented.

Ham, Norman D.↗

NASA NTRS1987

Community reactions to helicopter noise - Results from an experimental study

Community reactions to low numbers of helicopter noise events (less than 50 per day) are investigated using a new type of study design. Although the effect of maximum noise level and number of noise events on helicopter noise annoyance was found to be similar to that represented by the energy summation principle contained in L(eq)-based noise indices, it is noted that the possibility that the number of noise events has only a small effect on annoyance cannot be rejected at the conventional p of less than 0.05 level. The effect of the duration of noise events was also shown to be consistent with L(eq)-based indices. After removing the effects of differences in duration and noise levels, little difference is found between reactions to impulsive and nonimpulsive types of helicopters.

Fields, James M.↗

NASA NTRS1987

Flight test of a digital controller used in a helicopter autoland system

This paper describes the flight test evaluation of an advanced digital helicopter flight control system. The controller was designed using an optimal control design procedure for a fully coupled lateral and longitudinal vehicle model. Explicit integrals of the guidance error were included to produce a type 1 characteristic. Gain scheduling was used to account for changes in the vehicle dynamics. The digital controller was exercised by combining it with state estimators, a trajectory generator, and a closed-loop guidance algorithm to form a helicopter autoland system. A CH-47 tandem rotor helicopter was equipped with sensors, on-board digital flight computers, and electrohydraulic actuators. The system was exercised by automatically flying straight-in descending decelerating trajectories typcial of VFR manual landing approaches. A description of the test-ground facilities, the flight hardware and software, and the velocity and position tracking performance is included.

Downing, David R.↗

NASA NTRS1988

Research On The CH-47B Helicopter

Report describes equipment added to, and research capabilities of CH-47B helicopter. Programmable symbol generator provides display formats for variety of missions - those of vertical-takeoff-and-landing aircraft and helicopters. Powerful general-purpose flight computer in operation. Computer programmable in high-level languages and supports research more efficiently. Flight-control software developed to improve capability of helicopter to perform simulations in flight.

Hilbert, Kathryn B.↗

NASA NTRS1983

Impact of flying qualities on mission effectiveness for helicopter air combat, volume 1

A computer simulation to investigate the impact of flying qualities on mission effectiveness is described. The objective of the study was to relate the effects of flying qualities, such as precision of flight path control and pilot workload, to the ability of a single Scout helicopter, or helicopter team, to accomplish a specified anti-armor mission successfully. The model of the actual engagement is a Monte Carlo simulation that has the capability to assess the effects of helicopter characteristics, numbers, tactics and weaponization on the force's ability to accomplish a specific mission against a specified threat as a function of realistic tactical factors. A key feature of this program is a simulation of micro-terrain features and their effects on detection, exposure, and masking for nap-of-the-earth (NOE) flight.

Harris, T. M.↗

NASA NTRS1988

Minimum-complexity helicopter simulation math model

An example of a minimal complexity simulation helicopter math model is presented. Motivating factors are the computational delays, cost, and inflexibility of the very sophisticated math models now in common use. A helicopter model form is given which addresses each of these factors and provides better engineering understanding of the specific handling qualities features which are apparent to the simulator pilot. The technical approach begins with specification of features which are to be modeled, followed by a build up of individual vehicle components and definition of equations. Model matching and estimation procedures are given which enable the modeling of specific helicopters from basic data sources such as flight manuals. Checkout procedures are given which provide for total model validation. A number of possible model extensions and refinement are discussed. Math model computer programs are defined and listed.

Heffley, Robert K.↗

NASA NTRS1988

Optimization of helicopter airframe structures for vibration reduction considerations, formulations and applications

Several key issues involved in the application of formal optimization technique to helicopter airframe structures for vibration reduction are addressed. Considerations which are important in the optimization of real airframe structures are discussed. Considerations necessary to establish relevant set of design variables, constraints and objectives which are appropriate to conceptual, preliminary, detailed design, ground and flight test phases of airframe design are discussed. A methodology is suggested for optimization of airframes in various phases of design. Optimization formulations that are unique to helicopter airframes are described and expressions for vibration related functions are derived. Using a recently developed computer code, the optimization of a Bell AH-1G helicopter airframe is demonstrated.

Murthy, T. Sreekanta↗

NASA NTRS1988

Wake model for helicopter rotors in high speed flight

Two alternative approaches are developed to calculate blade-vortex interaction airloads on helicopter rotors: second order lifting-line theory, and a lifting surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second order lifting-line theory also improves the modeling of yawed flow and swept tips. Calculated results are compared with wind tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about 20 percent chord, which is within the range of measured viscous core sizes for helicopter rotors.

Johnson, Wayne R.↗

NASA NTRS1989

Plan, formulate, discuss and correlate a NASTRAN finite element vibrations model of the Boeing Model 360 helicopter airframe

Boeing Helicopter, together with other United States helicopter manufacturers, participated in a finite element applications program to emplace in the United States a superior capability to utilize finite element analysis models in support of helicopter airframe design. The activities relating to planning and creating a finite element vibrations model of the Boeing Model 36-0 composite airframe are summarized, along with the subsequent analytical correlation with ground shake test data.

Gabel, R.↗

NASA NTRS1988

A dissociation of objective and subjective workload measures in assessing the impact of speech controls in advanced helicopters

Among the new technologies that are expected to aid helicopter designers are speech controls. Proponents suggest that speech controls could reduce the potential for manual control overloads and improve time-sharing performance in environments that have heavy demands for manual control. This was tested in a simulation of an advanced single-pilot, scout/attack helicopter. Objective performance indicated that the speech controls were effective in decreasing the interference of discrete responses during moments of heavy flight control activity. However, subjective ratings indicated that the use of speech controls required extra effort to speak precisely and to attend to feedback. Although the operational reliability of speech controls must be improved, the present results indicate that reliable speech controls could enhance the time-sharing efficiency of helicopter pilots. Furthermore, the results demonstrated the importance of using multiple assessment techniques to completely assess a task. Neither the objective nor the subjective measures alone provided complete information. It was the contrast between the measures that was most informative.

Vidulich, Michael A.↗

NASA NTRS1989

Importance of engine as a source of helicopter external noise

A turboshaft engine's importance as a source of helicopter external noise is presently evaluated experimentally and analytically on the basis of test data from an MD500E helicopter, with and without engine muffler, during level flyovers and climbing flight. A strong engine noise component is noted for helicopter positions nearly overhead and beyond observed position, especially in the 200-1000 Hz range; its strong rearward directivity suggests the noise source to be the broadband exhaust or combustion noise radiated from the exhaust duct. The engine muffler furnished estimated perceived noise level reductions of 2-3 dB for the centerline.

Janakiram, R. D.↗

NASA NTRS1989

Calculation of blade-vortex interaction airloads on helicopter rotors

Two alternative approaches area developed to calculate blade-vortex interaction airloads on helicopter rotors, second-order lifting-line theory and a lifting-surface theory correction. The common approach of using a larger vortex core radius to account for lifting-surface effects is quantified. The second-order lifting-line theory also improves the modeling of low aspect-ratio blades yawed flow, and swept tips. Calculated results are compared with wind-tunnel measurements of lateral flapping, and with flight test measurements of blade section lift on SA349/2 and H-34 helicopter rotors. The tip vortex core radius required for good correlation with the flight test data is about a 20-percent chord, which is within the range of measured viscous core sizes for helicopter rotors.

Johnson, Wayne↗

NASA NTRS1990

Assessment of worm gearing for helicopter transmissions

A high-efficiency hydrostatic worm gear drive for helicopter transmissions is assessed. The example given is for a large cargo helicopter with three 4000-kW engines and transmission reduction ratio of 110. Also contained are: an efficiency calculation, a description of the test stand for evaluating the feasibility of worm gear hydrostatic mesh, a weight calculation, and a comparison with conventional helicopter transmissions of the same power and transmission reduction ratio.

Chaiko, Lev↗