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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 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Tiltable-Wing, Tiltable-Rotor Aircraft

New airplane wing tilts 90 degrees, leading edge up, to feather into rotor downwash during hovering, takeoff, or landing. After hovering or takeoff, rotors tilted forward slightly to accelerate airplane into forward flight. As airplane accelerates, wings start to tilt forward. At speeds of 20 to 40 knots (10.3 to 20.6 m/s), wings are in horizontal orientation. In this speed range, rotor power requirements decreased sufficiently to allow wings to assume normal orientation. Tiltable wings movable independently of tiltable rotors. Tilted at whatever pitch schedule yields greatest efficiency.

Stroub, R. H.↗
NASA NTRS1987

The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft

A new design concept in the development of VTOL aircraft with high forward flight speed capability is that of the X-Wing, a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept and two aft-swept wings. Because of the usual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic washin of the forward-swept blades and washout of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.

Gilbert, Michael G.↗
NASA NTRS1987

The effects of aeroelastic deformation on the unaugmented stopped-rotor dynamics of an X-Wing aircraft

A new design concept in the development of vertical takeoff and landing aircraft with high forward flight speed capability is that of the X-Wing. The X-Wing is a stiff, bearingless helicopter rotor system which can be stopped in flight and the blades used as two forward-swept wings and two aft-swept wings. Because of the unusual configuration in the fixed-wing mode, there is a high potential for aeroelastic divergence or flutter and coupling of blade vibration modes with rigid-body modes. An aeroelastic stability analysis of an X-Wing configuration aircraft was undertaken to determine if these problems could exist. This paper reports on the results of dynamic stability analyses in the lateral and longitudinal directions including the vehicle rigid-body and flexible modes. A static aeroelastic analysis using the normal vibration mode equations of motion was performed to determine the cause of a loss of longitudinal static margin with increasing airspeed. This loss of static margin was found to be due to aeroelastic 'washin' of the forward-swept blades and 'washout' of the aft-swept blades moving the aircraft aerodynamic center forward of the center of gravity. This phenomenon is likely to be generic to X-Wing aircraft.

Gilbert, Michael G.↗
NASA NTRS1984

V/STOL maneuverability and control

Maneuverability and control of V/STOL aircraft in powered-lift flight is studied with specific considerations of maneuvering in forward flight. A review of maneuverability for representative operational mission tasks is presented and covers takeoff, transition, hover, and landing flight phases. Maneuverability is described in terms of the ability to rotate and translate the aircraft and is specified in terms of angular and translational accelerations imposed on the aircraft. Characteristics of representative configurations are reviewed, including experience from past programs and expectations for future designs. The review of control covers the characteristics inherent in the basic airframe and propulsion system and the behavior associated with ontrol augmentation systems. Demands for augmented stability and control response to meet certain mission operational requirements are discussed. Experience from ground-based simulation and flight experiments that illustrates the impact of augmented stability and control on aircraft design is related by example.

Franklin, J. 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 NTRS1997

XV-15 Structural-Acoustic Data

Tiltrotor aircraft are a potentially viable means of intercity travel. The tiltrotor is able to transport passengers relatively quickly from the center of a city to destinations within a 300-mile radius. For such vehicles to be commercially viable, the interior noise and vibration levels must be acceptable to the passengers. A review of the literature revealed very little structural-acoustic data related to the tiltrotor. For this reason, structural-acoustic measurements were taken aboard an XV-15 tiltrotor. The six flight conditions included five in level flight, nominally 140-220 knots, for airplane mode (nacelle at 0 degrees) and one out-of-ground-effect (OGE) hover (nacelle at 90 degrees). The flight test measurements included nine exterior surface pressures, five structural accelerations, and two interior pressures. These sensors were located near the tip path plane on the port side of the aircraft. One minute of data was acquired at each condition. The data is presented as time histories, autospectra, coherence functions, and cross-spectra. In general, for level flight, the measured data showed very little effect of forward flight speed except to change the amplitude of the response; however, the character of the response was found to be dependent on spatial location. In contrast, in the hover mode the spatial location had very little effect on the character of the response. Additionally, the report highlights: the coherence between the transducer data and the rotor tach signal; and transfer function calculations between the exterior pressures.

Lyle, Karen H.↗
NASA NTRSDate not supplied

An L1 Adaptive Control Augmentation for a Lift Plus-Cruise Vehicle

This paper presents anL1adaptive control augmentation for a Lift-Plus-Cruise (L+C)vehicle. This class of vehicles operates in three flight modes with different dynamic behavior: vertical, transition, and forward flight. A robust uniform controller is used as a baseline to stabilize the system throughout these flight modes. The uniform controller is a linear control law designed around trim conditions of the aircraft and includes control allocation to achieve the desired forces and moments on the vehicle. TheL1control augmentation is designed for each of these trim conditions to compensate for the nonlinear time- and state-dependent uncertainties in the vehicle dynamics. The augmented control output is then added to the desired force and moment commands on the vehicle. Simulation results demonstrate the effectiveness of control augmentation for reducing the effects of unmodeled dynamics, reduced actuator effectiveness, and time-dependent disturbances. Effectiveness is demonstrated through tracking error metrics.

Andrew Patterson↗
NASA NTRS1977

Load and stability measurements on a soft-inplane rotor system incorporating elastomeric lead-lag dampers

An experimental investigation was conducted of the dynamic response and inplane stability associated with a new soft-inplane helicopter rotor. The unique feature of this rotor was the use of an internal elastomeric damper to restrain the blade inplane motion about the lead-lag hinge. The properties of the elastomer were selected to provide both a nominal first inplane frequency ratio of 0.65 and sufficient damping to eliminate the need for additional external damping sources to prevent ground resonance on a typical fuselage structure. For this investigation a 1/5-scale aeroelastic model was used to represent the rotor. The four-blade model had a diameter of 3.05 m (10 ft) and a solidity of 0.103. The first out-of-plane frequency ratio was 1.06. The model was tested in hover and in forward flight up to an advance ratio of 0.45. At each forward speed the rotor lift was varied up to simulated maneuver conditions. The measured rotor loads and response were within acceptable limits, and no adverse response qualities were observed. Moderate out-of-plane hub moments were measured, even for zero lift, to indicate the beneficial control power available for this design. Blade inplane stability testing indicated that the rotor system damping remained at moderate levels throughout the operating envelope.

Weller, W. H.↗
NASA NTRS1980

A flight investigation of blade section aerodynamics for a helicopter main rotor having NLR-1T airfoil sections

A flight investigation was conducted using a teetering-rotor AH-1G helicopter to obtain data on the aerodynamic behavior of main-rotor blades with the NLR-1T blade section. The data system recorded blade-section aerodynamic pressures at 90 percent rotor radius as well as vehicle flight state, performance, and loads. The test envelope included hover, forward flight, and collective-fixed maneuvers. Data were obtained on apparent blade-vortex interactions, negative lift on the advancing blade in high-speed flight and wake interactions in hover. In many cases, good agreement was achieved between chordwise pressure distributions predicted by airfoil theory and flight data with no apparent indications of blade-vortex interactions.

Morris, C. E. K., Jr.↗
NASA NTRS1982

TF34 Convertible Engine System Technology Program

The ability of the helicopter to function efficiently at zero flight speed is counterbalanced by a limitation to rather low forward flight speeds. An ability to fly efficiently at high speed would provide very significant improvements in rotorcraft productivity and economics. The implementation of such improvements would require the development of a suitable integrated power plant for both the vertical and horizontal flight modes. The engine should be a shaft output engine in the vertical flight mode. In the horizontal mode, the propulsor can be fan or propeller. A description is presented of a program concerned with the demonstration of a convertible turbofan/turboshaft engine. The program is nominally directed toward the demonstration of a propulsion system for an X-wing aircraft. However, the principles being investigated are applicable to any convertible turbofan/turboshaft engine application. At the current early stage of the program, no barrier problems have become apparent, and interesting possibilities for high speed rotorcraft flight are envisaged.

Abdalla, K. L.↗
NASA NTRS1984

An investigation of side-stick-controller/stability and control-augmentation system requirements for helicopter terrain flight under reduced visibility conditions

Simulation of the reduced visibility tasks is effected by providing the pilot with a visually coupled, helmet-mounted display of flight-control symbols superimposed upon terrain-board imagery. Forward-flight, low-speed, and precision-hover control modes are implemented, and a method is developed for the blending of control laws between each control mode. An investigation is made of the variations in the level of integration of primary control functions on a single side-stick controller. For most of the flight tasks investigated, separated controller configurations are preferred to a single, fully integrated side-stick device. Satisfactory handling qualities over all controller configurations are attained only for a precision-hover task conducted with a high level of stability and control augmentation. For most tasks flown with the helmet-mounted display significant degradation in handling qualities occurs relative to the identical tasks flown under visual flight conditions.

Landis, K. H.↗
NASA NTRS1999

Aeroelastic Analysis of the NASA/ARMY/MIT Active Twist Rotor

Aeroelastic modeling procedures used in the design of a piezoelectric controllable twist helicopter rotor wind tunnel model are described. Two aeroelastic analysis methods developed for active twist rotor studies, and used in the design of the model blade, are described in this paper. The first procedure uses a simple flap-torsion dynamic representation of the active twist blade, and is intended for rapid and efficient control law and design optimization studies. The second technique employs a commercially available comprehensive rotor analysis package, and is used for more detailed analytical studies. Analytical predictions of hovering flight twist actuation frequency responses are presented for both techniques. Forward flight fixed system nP vibration suppression capabilities of the model active twist rotor system are also presented. Frequency responses predicted using both analytical procedures agree qualitatively for all design cases considered, with best correlation for cases where uniform blade properties are assumed.

Wilkie, W. Keats↗
NASA NTRS1954

Flight Tests of a 0.13-Scale Model of the Convair XFY-1 Vertically Rising Airplane with the Lower Vertical Tail Removed, TED No.DE 368

An experimental investigation has been conducted to determine the dynamic stability and control characteristics in hovering and transition flight of a 0.13-scale flying model of the Convair XFY-1 vertically rising airplane with the lower vertical tail removed. The purpose of the tests was to obtain a general indication of the behavior of a vertically rising airplane of the same general type as the XFY-1 but without a lower vertical tail in order to simplify power-off belly landings in an emergency. The model was flown satisfactorily in hovering flight and in the transition from hovering to normal unstalled forward flight (angle of attack approximately 30deg). From an angle of attack of about 30 down to the lowest angle of attack covered in the flight tests (approximately 15deg) the model became progressively more difficult to control. These control difficulties were attributed partly to a lightly damped Dutch roll oscillation and partly to the fact that the control deflections required for hovering and transition flight were too great for smooth flight at high speeds. In the low-angle-of-attack range not covered in the flight tests, force tests have indicated very low static directional stability which would probably result in poor flight characteristics. It appears, therefore, that the attainment of satisfactory directional stability, at angles of attack less than 10deg, rather than in the hovering and transition ranges of flight is the critical factor in the design of the vertical tail for such a configuration.

Lovell, Powell M., Jr.↗
NASA NTRS1978

Flight effects on the aerodynamic and acoustic characteristics of inverted profile coannular nozzles

The effect of forward flight on the jet noise of coannular exhaust nozzles, suitable for Variable Stream Control Engines (VSCE), was investigated in a series of wind tunnel tests. The primary stream properties were maintained constant at 300 mps and 394 K. A total of 230 acoustic data points was obtained. Force measurement tests using an unheated air supply covered the same range of tunnel speeds and nozzle pressure ratios on each of the nozzle configurations. A total of 80 points was taken. The coannular nozzle OASPL and PNL noise reductions observed statically relative to synthesized values were basically retained under simulated flight conditions. The effect of fan to primary stream area ratio on flight effects was minor. At take-off speed, the peak jet noise for a VSCE was estimated to be over 6 PNdB lower than the static noise level. High static thrust coefficients were obtained for the basic coannular nozzles, with a decay of 0.75 percent at take-off speeds.

Kozlowski, H.↗
NASA NTRS1989

Sound power spectrum and wave drag of a propeller in flight

Theory is presented for the sound power and sound power spectrum of a single rotation propeller in forward flight. Calculations are based on the linear wave equation with sources distributed over helicoidal surfaces to represent effects of blade thickness and steady loading. Sound power is distributed continuously over frequecy, as would be expected from Doppler effects, rather than in discrete harmonics. The theory is applied to study effects of sweep and Mach number in propfans. An acoustic efficiency is defined as the ratio of radiated sound power to shaft input power. This value is the linear estimate of the effect of wave drag due to the supersonic blade section speeds. It is shown that the acoustic efficiency is somewhat less than 1 percent for a well designed propfan.

Hanson, D. B.↗
NASA NTRS1989

The visually guided control of simulated altitude

Simulated "flights" over three different ground textures were used to examine people's ability to extract optical information useful for active regulation of altitude. The textures were regularly spaced lines as follows: 1) orthogonal to the direction of flight (latitude texture); 2) parallel to the direction of flight (meridian texture); and 3) both parallel and orthogonal (square texture). Visual constant velocity forward flight simulations were displayed on a CRT screen, and subjects asked to maintain one of three initial altitudes using a rate control stick. This task was made difficult by the presence of lateral (irrelevant) and vertical (relevant) "wind gusts." The attitude never varied as winds, forward speed, and vertical rate control resulted in only translational movements. Adjusted root mean square errors (ARMSE) showed altitude regulation was more difficult at higher altitudes and when flying over meridian textures. Refined analysis of a single subject's data showed that this was due both to poorer regulation of the vertical wind disturbance and to a tendency to confuse the lateral wind disturbance for a vertical disturbance.

Vision↗