Search NASA⌕ Search

SEARCH · Search NASA

Results for “Hover Performance”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Low speed aerodynamic characteristics of a vectored thrust V/STOL transport with two lift/cruise fans

A wind tunnel test was conducted to obtain power on low speed characteristics of a twin fan vectored thrust V/STOL transport aircraft. Longitudinal, as well as some lateral directional data, were analyzed. Hover, STOL, and conventional flight modes were investigated. Determination of STOL characteristics, hover characteristics, roll control effectiveness and aircraft attitude were evaluated. The study also included various means to improve the lifting capability of the aircraft such as by application of fuselage strakes, exhaust vanes capable of shifting the thrust vector aft, and external flap blowing for STOL performance.

Renselaer, D. J.↗
NASA NTRS2014

Engine Power Turbine and Propulsion Pod Arrangement Study

A study has been conducted for NASA Glenn Research Center under contract NNC10BA05B, Task NNC11TA80T to identify beneficial arrangements of the turboshaft engine, transmissions and related systems within the propulsion pod nacelle of NASA's Large Civil Tilt-Rotor 2nd iteration (LCTR2) vehicle. Propulsion pod layouts were used to investigate potential advantages, disadvantages, as well as constraints of various arrangements assuming front or aft shafted engines. Results from previous NASA LCTR2 propulsion system studies and tasks performed by Boeing under NASA contracts are used as the basis for this study. This configuration consists of two Fixed Geometry Variable Speed Power Turbine Engines and related drive and rotor systems (per nacelle) arranged in tilting nacelles near the wing tip. Entry-into-service (EIS) 2035 technology is assumed for both the engine and drive systems. The variable speed rotor system changes from 100 percent speed for hover to 54 percent speed for cruise by the means of a two speed gearbox concept developed under previous NASA contracts. Propulsion and drive system configurations that resulted in minimum vehicle gross weight were identified in previous work and used here. Results reported in this study illustrate that a forward shafted engine has a slight weight benefit over an aft shafted engine for the LCTR2 vehicle. Although the aft shafted engines provide a more controlled and centered CG (between hover and cruise), the length of the long rotor shaft and complicated engine exhaust arrangement outweighed the potential benefits. A Multi-Disciplinary Analysis and Optimization (MDAO) approach for transmission sizing was also explored for this study. This tool offers quick analysis of gear loads, bearing lives, efficiencies, etc., through use of commercially available RomaxDESIGNER software. The goal was to create quick methods to explore various concept models. The output results from RomaxDESIGNER have been successfully linked to Boeing spreadsheets that generate gear tooth geometry in Catia 3D environment. Another initial goal was to link information from RomaxDESIGNER (such as hp, rpm, gear ratio) to populate Boeing's parametric weight spreadsheet and create an automated method to estimate drive system weight. This was only partially achieved due to the variety of weight models, number of manual inputs, and qualitative assessments required. A simplified weight spreadsheet was used with data inputs from RomaxDESIGNER along with manual inputs to perform rough weight calculations.

Robuck, Mark↗
NASA NTRS1987

X-wing potential for Navy applications

The X-wing provides a VTOL aircraft which has a low disc loading hover capability, similar to a conventional helicopter, combined with a high subsonic cruise speed capability. As a result, it hovers with low fuel flow rates which make extended hover duration missions practical. Its low hover power requirements also permit hovering and low speed flight on only one engine in a high speed twin engine aircraft design. The NASA DARPA Sikorsky RSRA X-wing program developed flightworthy X-wing hardware. All design activity and the majority of its component fabrication is completed. A design study was performed on an X-wing concept demonstrator aircraft which is based on the RSRA X-wing components, combined with two MTE engines and a new fuselage.

Linden, Arthur W.↗
NASA NTRS1996

Controls design with crossfeeds for hovering rotorcraft using quantitative feedback theory

A multi-input, multi-output controls design with dynamic crossfeed pre-compensation is presented for rotorcraft in near-hovering flight using Quantitative Feedback Theory (QFT). The resulting closed-loop control system bandwidth allows the rotorcraft to be considered for use as an inflight simulator. The use of dynamic, robust crossfeeds prior to the QFT design reduces the magnitude of required feedback gain and results in performance that meets most handling qualities specifications relative to the decoupling of off-axis responses. Handling qualities are Level 1 for both low-gain tasks and high-gain tasks in the roll, pitch, and yaw axes except for the 10 deg/sec moderate-amplitude yaw command where the rotorcraft exhibits Level 2 handling qualities in the yaw axis caused by phase lag. The combined effect of the QFT feedback design following the implementation of low-order, dynamic crossfeed compensators successfully decouples ten of twelve off-axis channels. For the other two channels it was not possible to find a single, low-order crossfeed that was effective. This is an area to be investigated in future research.

Tischler, Mark B.↗
NASA NTRS2016

Development and Calibration of a Field-Deployable Microphone Phased Array for Propulsion and Airframe Noise Flyover Measurements

A new aeroacoustic measurement capability has been developed consisting of a large channelcount, field-deployable microphone phased array suitable for airframe noise flyover measurements for a range of aircraft types and scales. The array incorporates up to 185 hardened, weather-resistant sensors suitable for outdoor use. A custom 4-mA current loop receiver circuit with temperature compensation was developed to power the sensors over extended cable lengths with minimal degradation of the signal to noise ratio and frequency response. Extensive laboratory calibrations and environmental testing of the sensors were conducted to verify the design's performance specifications. A compact data system combining sensor power, signal conditioning, and digitization was assembled for use with the array. Complementing the data system is a robust analysis system capable of near real-time presentation of beamformed and deconvolved contour plots and integrated spectra obtained from array data acquired during flyover passes. Additional instrumentation systems needed to process the array data were also assembled. These include a commercial weather station and a video monitoring / recording system. A detailed mock-up of the instrumentation suite (phased array, weather station, and data processor) was performed in the NASA Langley Acoustic Development Laboratory to vet the system performance. The first deployment of the system occurred at Finnegan Airfield at Fort A.P. Hill where the array was utilized to measure the vehicle noise from a number of sUAS (small Unmanned Aerial System) aircraft. A unique in-situ calibration method for the array microphones using a hovering aerial sound source was attempted for the first time during the deployment.

Humphreys, William M., Jr.↗
NASA NTRS1979

Noise of a model helicopter rotor due to ingestion of turbulence

A theoretical and experimental investigation of the noise of a model helicoper rotor due to ingestion of turbulence was conducted. Experiments were performed with a 0.76 m dia, articulated model rotor for a range of inflow turbulence and rotor operating conditions. Inflow turbulence levels varied from approximately 2 to 19 percent and tip Mach number was varied from 0.3 to 0.52. Test conditions included ingestion of a atmospheric turbulence in outdoor hover as well as ingestion of grid generated isotropic turbulence in the wind tunnel airstream. In wind tunnel testing, both forward flight and vertical ascent (climb) were simulated. Far field noise spectra and directivity were measured in addition to incident turbulence intensities, length scales, and spectra. Results indicate that ingestion of atmospheric turbulence is the dominant helicopter rotor hover noise mechanism at the moderate to high frequencies which determine perceived noise level.

Paterson, R. W.↗
NASA NTRS2004

Variable Speed CMG Control of a Dual-Spin Stabilized Unconventional VTOL Air Vehicle

This paper describes an approach based on using both bias momentum and multiple control moment gyros for controlling the attitude of statically unstable thrust-levitated vehicles in hover or slow translation. The stabilization approach described in this paper uses these internal angular momentum transfer devices for stability, augmented by thrust vectoring for trim and other outer loop control functions, including CMG stabilization/ desaturation under persistent external disturbances. Simulation results show the feasibility of (1) improved vehicle performance beyond bias momentum assisted vector thrusting control, and (2) using control moment gyros to significantly reduce the external torque required from the vector thrusting machinery.

Lim, Kyong B.↗
NASA NTRS1995

V/STOL systems research aircraft: A tool for cockpit integration

The next generation ASTOVL aircraft will have a complicated propulsion system. The configuration choices include Direct Lift, Lift-Fan and Lift + Lift/Cruise but the aircraft must also have supersonic performance and low-observable characteristics. The propulsion system may have features such as flow blockers, vectoring nozzles and flow transfer schemes. The flight control system will necessarily fully integrate the aerodynamic surfaces and the propulsive elements. With a fully integrated, fly-by-wire flight/propulsion control system, the options for cockpit integration are interesting and varied. It is possible to de-couple longitudinal and vertical responses allowing the pilot to close the loop on flightpath and flightpath acceleration directly. In the hover, the pilot can control the translational rate directly without having to stabilize the inner rate and attitude loops. The benefit of this approach, reduced workload and increased precision, has previously been demonstrated through several motion-based simulations. In order to prove the results in flight, the V/STOL System Research Aircraft (VSRA) was developed at the NASA Ames Research Center. The VSRA is the YAV-8B Prototype modified with a research flight control system using a series-parallel servo configuration in all the longitudinal degrees of freedom (including thrust and thrust vector angle) to provide an integrated flight and propulsion control system in a limited envelope. Development of the system has been completed and flight evaluations of the response types have been performed. In this paper we will discuss the development of the VSRA, the evolution of the flightpath command and translational rate command response types and the Guest Pilot evaluations of the system. Pilot evaluation results are used to draw conclusions regarding the suitability of the system to satisfy V/STOL requirements.

Stortz, Michael W.↗
NASA NTRS1995

V/STOL Systems Research Aircraft: A Tool for Cockpit Integration

The next generation ASTOVL aircraft will have a complicated propulsion System. The configuration choices include Direct Lift, Lift-Fan and Lift+Lift /Cruise but the aircraft must also have supersonic performance and low-observable characteristics. The propulsion system may have features such as flow blockers, vectoring nozzles and flow transfer schemes. The flight control system will necessarily fully integrate the aerodynamic surfaces and the propulsive elements. With a fully integrated, fly-by-wire flight/propulsion control system, the options for cockpit integration are interesting and varied. It is possible to decouple longitudinal and vertical responses allowing the pilot to close the loop on flight path and flight path acceleration directly. In the hover, the pilot can control the translational rate directly without having to stabilize the inner rate and attitude loops. The benefit of this approach, reduced workload and increased precision. has previously been demonstrated through several motion-based simulations. In order to prove the results in flight, the V/STOL System Research Aircraft (VSRA) was developed at the NASA Ames Research Center. The VSRA is the YAV-8B Prototype modified with a research flight control system using a series-parallel servo configuration in all the longitudinal degrees of freedom (including thrust and thrust vector angle) to provide an integrated flight and propulsion control system in a limited envelope. Development of the system has been completed and flight evaluations of the response types have been performed. In this paper we will discuss the development of the VSRA, the evolution of the flight path command and translational rate command response types and the Guest Pilot evaluations of the system. Pilot evaluation results will be used to draw conclusions regarding the suitability of the system to satisfy V/STOL requirements.

Stortz, Michael W.↗
NASA NTRS1996

Guidance of Nonlinear Nonminimum-Phase Dynamic Systems

The research work has advanced the inversion-based guidance theory for: systems with non-hyperbolic internal dynamics; systems with parameter jumps; and systems where a redesign of the output trajectory is desired. A technique to achieve output tracking for nonminimum phase linear systems with non-hyperbolic and near non-hyperbolic internal dynamics was developed. This approach integrated stable inversion techniques, that achieve exact-tracking, with approximation techniques, that modify the internal dynamics to achieve desirable performance. Such modification of the internal dynamics was used (a) to remove non-hyperbolicity which is an obstruction to applying stable inversion techniques and (b) to reduce large preactuation times needed to apply stable inversion for near non-hyperbolic cases. The method was applied to an example helicopter hover control problem with near non-hyperbolic internal dynamics for illustrating the trade-off between exact tracking and reduction of preactuation time. Future work will extend these results to guidance of nonlinear non-hyperbolic systems. The exact output tracking problem for systems with parameter jumps was considered. Necessary and sufficient conditions were derived for the elimination of switching-introduced output transient. While previous works had studied this problem by developing a regulator that maintains exact tracking through parameter jumps (switches), such techniques are, however, only applicable to minimum-phase systems. In contrast, our approach is also applicable to nonminimum-phase systems and leads to bounded but possibly non-causal solutions. In addition, for the case when the reference trajectories are generated by an exosystem, we developed an exact-tracking controller which could be written in a feedback form. As in standard regulator theory, we also obtained a linear map from the states of the exosystem to the desired system state, which was defined via a matrix differential equation.

Devasia, Santosh↗
NASA NTRS2019

Auralization of Unsteady Rotor Noise Using a Solution to the Ffowcs Williams-Hawkings Equation

Auralization of unsteady helicopter flight operations is needed to better understand the impact of maneuvers on community noise. Previous source sound synthesis methods were based on interpolated data, which may lead to artifacts in generating sound for helicopter maneuvers where sound pressure directivity may change rapidly. In this paper, the source sound is synthesized at every time sample using a solution to the Ffowcs Williams-Hawkings Equation along the path of the emission angle between the source and a ground observer. The synthesized sound is then propagated to the ground observer for auralization. Since no interpolation is performed, maneuvers with rapidly changing sound pressure directivities may be more accurately synthesized and auralized. The framework for accomplishing this synthesis and auralization is described, which couples the Fundamental Rotorcraft Acoustic Modeling from Experiments, the second-generation Aircraft NOise Prediction Program, and the NASA Auralization Framework. Synthesis of a hovering rotor is presented to compare with previous synthesis methods. Two examples with a periodic signals are then presented to demonstrate synthesis and auralization of unsteady rotor noise.

Krishnamurthy, Siddhartha↗
NASA NTRS1984

Hovering model helicopter rotor testing

A relatively large test chamber, chosen to minimize room interference effects during helicopter hovering rotor tests, was found in initial operations to exhibit large, random variations of thrust, torque, and blade flapping. The source of these problems, unsteady recirculation of test chamber flow, was addressed by the addition of a 'flow straightener' that reduced these parameter variations to 1.5 percent of mean values. Rotor performance was then measured outside the chamber in calm, free air conditions and compared with chamber results obtained before and after modifications. Attention is given to wake flow visualization conducted in the test chamber, as well as outside.

Piziali, R. A.↗
NASA NTRS1989

A survey of nonuniform inflow models for rotorcraft flight dynamics and control applications

The results of a brief survey of nonuniform inflow models was summarized for the calculation of induced velocities at and near a lifting rotor in and out of ground effect. The survey, conducted from the perspective of flight dynamics and control applications, covers a spectrum of flight conditions including hover, vertical flight, and low-speed and high-speed forward flight, and reviews both static and dynamic aspects of the inflow. A primary emphasis is on the evaluation of various simple first harmonic inflow models developed over the years, in comparison with more sophisticated methods developed for use in performance and airload computations. The results of correlation with several sets of test data obtained at the rotor out of ground effect indicate that the Pitt/Peters first harmonic inflow model works well overall. For inflow near the rotor or in ground effect, it is suggested that charts similar to those of Heyson/Katzoff and Castles/De Leeuw of NACA be produced using modern free-wake methods for use in flight dynamic analyses and simulations.

Chen, Robert T. N.↗
NASA NTRS1990

A survey of nonuniform inflow models for rotorcraft flight dynamics and control applications

The results of a brief survey of nonuniform inflow models was summarized for the calculation of induced velocities at and near a lifting rotor in and out of ground effect. The survey, conducted from the perspective of flight dynamics and control applications, covers a spectrum of flight conditions including hover, vertical flight, and flow-speed and high-speed forward flight, and reviews both static and dynamic aspects of the inflow. A primary emphasis is on the evaluation of various simple first harmonic inflow models developed over the years, in comparison with more sophisticated methods developed for use in performance and airload computations. The results of correlation with several sets of test data obtained at the rotor out of ground effect indicate that the Pitt/Peters first harmonic inflow model works well overall. For inflow near the rotor or in ground effect, it is suggested that charts similar to those of Heyson/Katzoff and Castles/De Leeuw of NACA be produced using modern free-wake methods for use in flight dynamic analyses and simulations.

Chen, Robert T. N.↗
NASA NTRS2016

Handling Qualities Optimization for Rotorcraft Conceptual Design

Over the past decade, NASA, under a succession of rotary-wing programs has been moving towards coupling multiple discipline analyses in a rigorous consistent manner to evaluate rotorcraft conceptual designs. Handling qualities is one of the component analyses to be included in a future NASA Multidisciplinary Analysis and Optimization framework for conceptual design of VTOL aircraft. Similarly, the future vision for the capability of the Concept Design and Assessment Technology Area (CD&A-TA) of the U.S Army Aviation Development Directorate also includes a handling qualities component. SIMPLI-FLYD is a tool jointly developed by NASA and the U.S. Army to perform modeling and analysis for the assessment of flight dynamics and control aspects of the handling qualities of rotorcraft conceptual designs. An exploration of handling qualities analysis has been carried out using SIMPLI-FLYD in illustrative scenarios of a tiltrotor in forward flight and single-main rotor helicopter at hover. Using SIMPLI-FLYD and the conceptual design tool NDARC integrated into a single process, the effects of variations of design parameters such as tail or rotor size were evaluated in the form of margins to fixed- and rotary-wing handling qualities metrics as well as the vehicle empty weight. The handling qualities design margins are shown to vary across the flight envelope due to both changing flight dynamic and control characteristics and changing handling qualities specification requirements. The current SIMPLI-FLYD capability and future developments are discussed in the context of an overall rotorcraft conceptual design process.

Handling Qualities↗
NASA NTRS1981

Experience with high performance V/STOL fighter projects at MBB

Flight control systems and aerodynamic aspects of experimental V/STOL aircraft are discussed. The VJ 101 C featured tilting engines for increased thrust, reheat for takeoff, simple translation, triangular decentralization of the engines for thrust modulation, and moderate ground effects. Two experimental aircraft were built, with and without reheat, capable of Mach 2 and Mach 1.04, respectively. The mechanical flight control system and tests are outlined, both for hover rig and flight configurations. Ground suction, acoustic and thermal loading, sodium silicate coatings to avoid ground corrosion, and recirculation are considered. Results of the follow-on project to the VJ 101 C, the AVS, which was developed by NASA, are reviewed, and it is noted that trends toward thrust-to-weight ratios exceeding one, in concert with low wing loading, favor the development of V/STOL aircraft.

Aulehla, F.↗
NASA NTRS1972

Aerodynamic characteristics of a large scale lift fan transport model with podded fans forward and lift cruise fans mounted above the wing

The aerodynamic characteristics of a large scale V/STOL transport model powered by tip-turbine driven lift fans were investigated. The model had four fans; the forward fans were mounted in pods forward of the wing at midsemispan. The aft fans were placed in cruise nacelles behind and above the wing. A cascade of variable camber exit louvers was placed behind each of the lift-cruise fans to turn the fan flow in the lift direction for hover and transition to wing supported flight. The wing of the model was mounted above the fuselage, had an aspect ratio of 5.8, sweepback of 35 deg at the quarter chord line and a taper ratio of 0.3. Various configurations of the model were tested to explore the transition speed range. Fan performance, turning effectiveness of the variable camber exit louvers, longitudinal and lateral-directional characteristics with fan operation in crossflow are presented.

Kirk, J. V.↗
NASA NTRS1956

Flight Investigation of the Stability and Control Characteristics of Vertically Rising Airplane Research Model with Swept or Unswept Wings and X- or +-tails

The take-off, landing, hovering, and transition flight characteristics of a propeller-driven, fighter-type, vertically rising airplane model were obtained from time histories of the flights and from the pilots' opinions of the flight characteristics. In general, there were no major differences in the behavior of any of the configurations, all of which performed satisfactorily.

CONTROL, LATERAL↗