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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 937 records · Page 52

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NASA NTRS1983

AV-8B system identification results from full scale development flight test program

The results presented in this paper demonstrate a methodology for identification of a non-linear model of the AV-88 V/STOL aircraft from flight test data. Conventional aerodynamics, thrust-induced aerodynamic effects and propulsion model correction factors are identified for hover, transitional and low-speed wingborne flight conditions. A special model formulation is adopted which is continuous at zero airspeed. The identified model is validated by prediction of flight test measurements, and by comparison with wind-tunnel results.

Anderson, L. C.↗

NASA NTRS1984

Helicopter rotor performance degradation in natural icing encounter

The analytical model described by Korkan et al. (1982) for predicting the performance degradation of propellers in a natural icing encounter is used to determine the feasibility of predicting helicopter performance degradation in hover during natural icing. The flight condition selected for analysis involves an altitude of 3000 ft and a free-air temperature of 1 F. The values of degradation yielded by the model for rime ice accretion are representative of those experienced in actual flight.

Korkan, K. D.↗

NASA NTRS1984

Experimental study of performance degradation of a model helicopter main rotor with simulated ice shapes

An experimental study utilizing a remote controlled model helicopter has been conducted to measure the performance degradation due to simulated ice accretion on the leading edge of the main rotor for hover and forward flight. The 53.375 inch diameter main rotor incorporates a NACA 0012 airfoil with a generic ice shape corresponding to a specified natural ice condition. Thrust coefficients and torque coefficients about the main rotor were measured as a function of velocity, main rotor RPM, angle-of-incidence of the fuselage, collective pitch angle, and extent of spanwise ice accretion. An experimental airfoil data bank has been determined using a two-dimensional twenty-one inch NACA 0012 airfoil with scaled ice accretion shapes identical to that used on the model helicopter main rotor. The corresponding experimental data are discussed with emphasis on Reynolds number effects and ice accretion scale model testing.

Korkan, K. D.↗

NASA NTRS1982

On-line methods for rotorcraft aeroelastic mode identification

The requirements for the on-line identification of rotorcraft aeroelastic blade modes from random response test data are presented. A recursive maximum likelihood (RML) technique is used in conjunction with a bandpass filter to identify isolated blade mode damping and frequency. The RML technique is demonstrated to have excellent convergence characteristics in random measurement noise and random process noise excitation. The RML identification technique uses an ARMA representation for the aeroelastic stochastic system and requires virtually no user interaction while providing accurate confidence bands on the parameter estimates. Comparisons are made with an off-line Newton type maximum likelihood algorithm which uses a state variable model representation. Results are presented from simulation random response data which quantify the identifed parameter convergence behavior for various levels of random excitation which is typical of wind tunnel turbulence levels. The RML technique is applied to hingless rotor test data from the NASA Langley Research Center Helicopter Hover Facility.

Molusis, J. A.↗

NASA NTRS1983

Handling characteristics of a simulated twin tilt nacelle V/STOL aircraft

The first government-conducted piloted flight simulation of the Grumann-designed twin turbofan-powered tilt-engine V/STOL aircraft (design 698) was conducted at NASA Ames Research Center. The aircraft is discussed with an emphasis on its unique hover characteristics. These chracteristics include the adverse nonminimum phase that occurs in lateral and longitudinal translation, and the large attitude control power available. Both of these features are attributes of the control vanes (a Grumman-patented concept) buried in the fan exhaust flow. The simulation used the following NASA Ames Research Center facilities: the Vertical Motion Simulator with the interchangeable cab, the Sigma 8 computer, and the Computer-Generated Image system with a four-window display.

Wilson, S. B., III↗

NASA NTRS1984

A computational method for helicopter vortex wakes

A method for calculating the wake geometry and blade loads for a hovering helicopter rotor is presented. The approach incorporates a simplified free wake model of the rotor in a finite difference calculation of the flow field. A variation of the 'cloud-in-cell' technique, modified to eliminate self-induced velocity errors for curved vortex filaments, is used. Simple lifting line theory is used to calculate the blade loads. Calculations showing the effect of vortex core size and the number of vortex filaments representing the wake are presented. For large numbers of vortices, it is seen that the wake geometry fails to converge. However, only a few vortices are needed to adequately represent the wake. Comparisons with experimental results are also presented.

Roberts, T. W.↗

NASA NTRS1984

Impact of flying qualities on mission effectiveness for helicopter air combat

Battlefield nap-of-the-earth (NOE) helicopter operations are vital for a use of the helicopter in a high-threat environment. As the pilot's workload in this flight regime is very high, the helicopter's handling qualities become an important factor. The present investigation is concerned with overall mission effectiveness, flying qualities, and their interaction with other parameters. A description is presented of a study which generated a significant amount of date relating the importance of flying qualities to the ability to perform several specific mission tasks. It was found that flying qualities do have a major impact on the ability to perform a specific mission. The impact of flying qualities on Scout helicopter mission effectiveness is mainly related to the probability of being detected. The flying qualities effect most critical to the Scout mission was found to be precision of hover control.

Harris, T. M.↗

NASA NTRS1984

Measured and calculated inplane stability characteristics for an advanced bearingless main rotor

A program of experimental and analytical research has been performed to demonstrate the effects of rotor and fuselage design parameters on rotor in-plane stability, including aeromechanical stability. The experimental data were obtained from hover and wind-tunnel tests of a scaled advanced bearingless main rotor model. Both isolated-rotor and free-hub conditions were tested. Test parameters included blade built-in cone and sweep angles; rotor inplane structural stiffness and damping; pitch link stiffness and location; and fuselage natural frequency, damping, and inertia. The results show that rotor blade structural damping is one of the most influential design parameters in obtaining acceptable aeromechanical stability margins. Other parameters, such as blade cone angle, pitch link location (rotor delta 3) and anisotropic hub damper configurations, may be used to improve stability margins, but their individual effects are subtle.

Weller, W. H.↗

NASA NTRS1984

Optimum design of rotor blades for vibration reduction in forward flight

Modern structural optimization techniques are applied to vibration reduction of helicopter rotor blades in forward flight. The objective function minimized consists of the oscillatory vertical hub shears or the hub rolling moments at one particular advance ratio. The behavior constraints are the frequency placements of the blade and the requirement that aeroelastic stability margins, in hover, remain unaffected by the optimization process. The aeroelastic stability and response analysis is based on a fully coupled flap-lag-torsional analysis of the blade. Numerical results are presented for some typical soft-in-plane hingeless rotor configurations indicating a 15-40 percent reduction in vibration levels, as well as a blade which is 20 percent lighter than the initial design. These results imply that structural optimization techniques can yield substantial practical benefits in the design process of rotor systems.

Friedmann, P. P.↗

NASA NTRS1984

Performance degradation of a model helicopter rotor with a generic ice shape

An experimental program using a commercially available remotely controlled model helicopter in the Texas A&M University (TAMU) subsonic wind tunnel has been conducted to investigate the performance degradation resulting from the simulated formation of ice on the leading edge of the main rotor blades in both hover and forward flight. The rotor blades utilized a NACA 0012 airfoil with a 2.5-in. constant chord. A generic ice shape derived from a predetermined natural ice condition was applied to the 53.375-in.-diameter main rotor, and thrust and torque coefficients were measured for the main rotor as functions of velocity, main rotor rpm, fuselage angle of incidence, collective pitch angle, and spanwise extent of icing. The model helicopter test exhibited significant performance degradation of the main rotor when generic ice was added. An increase of approximately 150 percent in torque coefficient to maintain a constant thrust coefficient was noted when generic ice had been applied to the 85 percent rotor radial location. Also, considerable additional degradation occurred when generic ice was applied to the 100 percent rotor radial location, as compared with the 85 percent simulated ice performance values, indicating the sensitivity of the rotor tip region.

Korkan, K. D.↗

NASA NTRS1984

Transonic flow analysis for rotors. Part 1: Three-dimensional quasi-steady, full-potential calculation

A new computer program is presented for calculating the quasi-steady transonic flow past a helicopter rotor blade in hover as well as in forward flight. The program is based on the full potential equations in a blade attached frame of reference and is capable of treating a very general class of rotor blade geometries. Computed results show good agreement with available experimental data for both straight and swept tip blade geometries.

Chang, I. C.↗

NASA NTRS1984

Operational requirements - system concepts

Nine research areas that are most critical to the issue of cockpits for the single pilot are discussed. Helicopter are addressed in this report. They are as follows: (1) automation priority issues; (2) increased complexity of systems; (3) cockpit workload highest in navigation; (4) auto hover and flight trim controls; (5) voice technology in integrated form; (6) systems must have visual and auditory declutter modes; (7) cockpit should be designed to be NBC resistant; and (8) considerations for spillover to civilian public service.

Voorhees, J. W.↗

NASA NTRS1985

The UH-1H helicopter icing flight test program: An overview

An ongoing joint NASA/Army program to study the effects of ice accretion on unprotected helicopter rotor aerodynamic performance is discussed. This program integrates flight testing, wind tunnel testing, and analytical modeling. Results are discussed for helicopter flight testing in the Canadian NRC hover spray rig facility to measure rotor aero performance degradation and document rotor ice accretion characteristics. The results of dry wind tunnel testing of airfoil sections with artificial ice accretions and predictions of rotor performance degradation using available rotor performance codes and the wind tunnel data are presented. An alternative approach to conducting future helicopter icing flight programs is discussed.

Shaw, R. J.↗

NASA NTRS1984

Assessment of simulation fidelity using measurements of piloting technique in flight

The U.S. Army and NASA joined together on a project to conduct a systematic investigation and validation of a ground based piloted simulation of the Army/Sikorsky UH-60A helicopter. Flight testing was an integral part of the validation effort. Nap-of-the-Earth (NOE) piloting tasks which were investigated included the bob-up, the hover turn, the dash/quickstop, the sidestep, the dolphin, and the slalom. Results from the simulation indicate that the pilot's NOE task performance in the simulator is noticeably and quantifiably degraded when compared with the task performance results generated in flight test. The results of the flight test and ground based simulation experiments support a unique rationale for the assessment of simulation fidelity: flight simulation fidelity should be judged quantitatively by measuring pilot's control strategy and technique as induced by the simulator. A quantitative comparison is offered between the piloting technique observed in a flight simulator and that observed in flight test for the same tasks performed by the same pilots.

Clement, W. F.↗

NASA NTRS1984

Helicopter model rotor-blade vortex interaction impulsive noise: Scalability and parametric variations

Acoustic data taken in the anechoic Deutsch-Niederlaendischer Windkanal (DNW) have documented the blade vortex interaction (BVI) impulsive noise radiated from a 1/7-scale model main rotor of the AH-1 series helicopter. Averaged model scale data were compared with averaged full scale, inflight acoustic data under similar nondimensional test conditions. At low advance ratios (mu = 0.164 to 0.194), the data scale remarkable well in level and waveform shape, and also duplicate the directivity pattern of BVI impulsive noise. At moderate advance ratios (mu = 0.224 to 0.270), the scaling deteriorates, suggesting that the model scale rotor is not adequately simulating the full scale BVI noise; presently, no proved explanation of this discrepancy exists. Carefully performed parametric variations over a complete matrix of testing conditions have shown that all of the four governing nondimensional parameters - tip Mach number at hover, advance ratio, local inflow ratio, and thrust coefficient - are highly sensitive to BVI noise radiation.

Splettstoesser, W. R.↗

NASA NTRS1985

Reconstruction of a 3-dimensional transonic rotor flow field from holographic interferogram data

Holographic interferometry and computer-assisted tomography (CAT) are used to determine the transonic velocity field of a model rotor blade in hover. A pulsed ruby laser recorded 40 interferograms with a 2-ft-diam view field near the model rotor-blade tip operating at a tip Mach number of 0.90. After digitizing the interferograms and extracting fringe-order functions, the data are transferred to a CAT code. The CAT code then calculates the perturbation velocity in seeral planes above the blade surface. The values from the holography-CAT method compare favorably with previously obtained numerical computations in most locations near the blade tip. The results demonstrate the technique's potential for three-dimensional transonic rotor flow studies.

Yu, Y. H.↗

NASA NTRS1985

Finite-difference computations of rotor loads

The current and future potential of finite difference methods for solving real rotor problems which now rely largely on empiricism are demonstrated. The demonstration consists of a simple means of combining existing finite-difference, integral, and comprehensive loads codes to predict real transonic rotor flows. These computations are performed for hover and high-advanced-ratio flight. Comparisons are made with experimental pressure data.

Caradonna, F. X.↗

NASA NTRS1984

Helicopter noise as predicted by three-dimensional monopole and quasi-steady full-potential dipole sources

A three-dimensional quasi-steady full-potential rotor-flow-analysis program, called ROT22 developed at NASA Ames Research Center is run in conjunction with Farassat's (1981) helicopter-noise-prediction code to assess the thickness and loading noises made by a rotor blade. As a model example, the case of a 1/7th UH-1H NACA-0012-profile straight nonlifting rotor blade in hover is studied. Results for tip Mach numbers ranging from .4 to .962 are presented. Also presented is the effect of blade-tip loading on the overall noise and of profile curvature on the thickness noise. The study confirms that the blade volume displacement is a dominant source of helicopter noise and further concludes that the blade tip makes only a small noise contribution that steadily decreases with increasing tip Mach numbers, and that the inclusion of blade profile curvature tends to improve the negative peak amplitudes overpredicted by Schmitz and Yu (1983).

Aggarwal, H. R.↗