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At least 1,387 records · Page 77
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Correlation of full-scale helicopter rotor performance in air with model-scale Freon data

An investigation was conducted in a transonic dynamics tunnel to measure the performance of a 1/5 scale model helicopter rotor in a Freon atmosphere. Comparisons were made between these data and full scale data obtained in air. Both the model and full scale tests were conducted at advance ratios between 0.30 and 0.40 and advancing tip Mach numbers between 0.79 and 0.95. Results show that correlation of model scale rotor performance data obtained in Freon with full scale rotor performance data in air is good with regard to data trends. Mach number effects were found to be essentially the same for the model rotor performance data obtained in Freon and the full scale rotor performance data obtained in air. It was determined that Reynolds number effects may be of the same magnitude or smaller than rotor solidity effects or blade elastic modeling in rotor aerodynamic performance testing.

Yeager, W. T., Jr.↗
NASA NTRS1976

Three-dimensional flow calculation for a transonic compressor rotor

A numerical calculation of the steady, inviscid, three dimensional flow in a isolated transonic compressor rotor has been completed using MacCormack's second order accurate time-marching scheme. This rotor has a tip Mach number of 1.2, an overall diameter of 2 feet, and inlet hub/tip ratio of 0.5. The computed rotor total pressure ratio is 1.82. Comparisons between the numerical solution, measurements of the intra-blade static density field obtained by gas fluorescence, and time resolved exit flow measurements showed that the inviscid computation accurately models transonic rotor aerodynamics and rotor blade pressure distributions in the upstream portions of the blade passages, the viscous effects influencing mainly the downstream flow.

Thompkins, W. T., Jr.↗
NASA NTRS1981

Flag-lag-torsional dynamics of extensional and inextensional rotor blades in hover and in forward flight

The formulation of differential equations of motion for both extensional and inextensional rotor blades, and the effect of cubic nonlinearities was examined. The developed differential equations are reduced to a set of three integro partial differential equations for a hingeless blade by eliminating the extension variable. Aerodynamic forces are modelled using Greenberg's extension of Theodorsen's strip theory. Equations of motion are expanded into polynomial nonlinearities to evaluate the motion of the system.

Crespodasilva, M. R. M.↗
NASA NTRS1981

A theoretical and experimental investigation of shock-associated noise in supersonic jets

This paper examines the fundamental mechanism of broadband shock noise generation in an improperly expanded supersonic jet. The study includes circular convergent-divergent as well as circular convergent nozzles. The main source of shock noise is determined to be the transient interaction between the shock front and the convected vorticity within the jet plume. The discussion of the noise-generation mechanism is based on detailed numerical analysis, theoretical aerodynamic and acoustic modeling, refined measurements of the jet mean flow, shock-cell structure, turbulence, and noise. These results provide a broad-based generalization for the Harper-Bourne and Fisher analysis and prediction method.

Pao, S. P.↗
NASA NTRS1982

Evaluation of a trajectory command concept for manual control of carrier approaches and landings

A novel trajectory control system concept was implemented to provide manual control of a conventional jet aircraft. This concept, called Total Aircraft Flight Control System (TAFCOS), utilizes an inverse model of the aerodynamic and propulsion characteristics and employs feedforward control to provide the required acceleration command. The concept requires on-board digital computations which can easily be handled by a modern airborne computer. The system was studied in a piloted simulation of the carrier approach and landing task with primarily visual flight and guidance cues. The principal modes of vertical flight-path control investigated were vertical velocity command and vertical acceleration command. The study included manual carrier approaches with and without moderate ship motion and associated air disturbances, and tests of the effects of discrete gusts. Manual control of flight path through this new concept was shown to be feasible as an addition to an automatic control system and to have potential as an improved mode of control over conventional control for the carrier approach task.

Mcneill, W. E.↗
NASA NTRS1981

Comparison of wind tunnel and theoretical aeroelastic predictions with flight measured airloads for the B-1 aircraft

An aeroelastic analysis of the B-1 aircraft was generated using the FLEXSTAB computer program. Relatively simple aerodynamic and structural models were employed. Theoretical wing and horizontal stabilizer airloads were compared to wind tunnel predictions and flight data measured during quasi-steady pitch maneuvers at Mach numbers of 0.85 and 1.2 with the wing in the 67.5 degree full aft sweep position. The basic objective was to evaluate the usefulness of the FLEXSTAB program for pre-flight airloads analysis of large flexible aircraft. Significant aeroelastic increments were noted between rigid and flexible vehicle results. FLEXSTAB predicted airloads for the outer wing panel were in good agreement with measured data for both rigid airloads and elastic increments. FLEXSTAB results for the horizontal stabilizer were useful for defining general aeroelastic trends, but absolute load levels were not well predicted due to theoretical limitations and difficulties encountered in modelling the complex B-1 configuration. Overall, the FLEXSTAB program is viewed as a useful integrated tool for static aeroelastic analysis in support of flight programs.

Sims, R. L.↗
NASA NTRS1984

Design of advanced technology maneuvering aircraft models for the National Transonic Facility

The need for a large High-Reynolds-Number Transonic Wind Tunnel which will provide a tool to study phenomena sensitive to Reynolds number is discussed. The National Transonic Facility (NTF), is in the calibration phase and the desired capability. Its usefulness, however, will be influenced by the ability of industry to develop model systems capable of withstanding the severe operating environment of the facility so necessary to achieve full scale Reynolds number, without degradation of accuracy, and at reasonable cost. The feasibility of designing models of advanced aerodynamic technology maneuvering aircraft and to achieve full scale Reynolds number for each configuration in the NTF are determined. It is concluded that the facility does not offer the potential for making tunnel to full scale data correlations for this type of aircraft configuration.

Griffin, S. A.↗
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

The role of airfoil geometry in minimizing the effect of insect contamination of laminar flow sections

A method has been developed to predict the contamination of an airfoil by insects and the resultant performance penalty. Insect aerodynamics have been modeled and the impingement of insects on an airfoil are solved by calculating their trajectories. Upon impact, insect rupture and the resulting height of the debris is determined based on experimental data. A boundary layer analysis is performed to determine which insects cause boundary layer transition and the resultant drag penalty. A contaminated airfoil figure of merit is presented to be used to compare airfoil susceptibility. Results show that the insect contamination effects depend on accretion conditions, airfoil angle of attack and Reynolds number. The importance of the stagnation region to designing airfoils for minimum drag penalties is discussed.

Maresh, J. L.↗
NASA NTRS1986

The optimum hypersonic wind tunnel

The capabilities of existing hypersonic wind tunnels in the U.S. are assessed to form a basis for recommendations for a new, costly facility which would provide data for modeling the hypervelocity aerodynamics envisioned for the new generation of aerospace vehicles now undergoing early studies. Attention is given to the regimes, both entry and aerodynamic, which the new vehicles will encounter, and the shortcomings of data generated for the Orbiter before flight are discussed. The features of foreign-gas, impulse, aeroballistic range, arc-heated and combustion-heated facilities are examined, noting that in any hypersonic wind tunnel the flow must be preheated to prevent liquefaction upon expansion in the test channel. The limitations of the existing facilities and the identification of the regimes which must be studied lead to a description of the characteristics of an optimum hypersonic wind tunnel, including the operations and productivity, the instrumentation, the nozzle design and the flow quality. Three different design approaches are described, each costing at least $100 million to achieve workability.

Trimmer, L. L.↗
NASA NTRS1986

Rarefied flow lift-to-drag measurements of the Shuttle Orbiter

This report presents a discussion of the analysis and the results of sensitive micro-g accelerometry measurements on the Shuttle Orbiter in the rarefied flow flight regime, that is, from altitudes of 60 km to 160 km. A brief description of the experimental apparatus called High Resolution Accelerometer Package (HiRAP) is given along with a description of the ground processing to obtain the lift-to-drag ratio (L/D) from the flight measurements. The flight results of L/D from six missions are presented and discussed. Comparisons are made with preflight wind tunnel data in the near continuum viscous interaction regime and preflight analytical estimates in the rarefied transition regime. Excellent agreement is obtained between flight and wind tunnel data in the viscous regime, but differences are noted between flight and preflight predictions in the transition regime. Free molecule flow F/D data are also obtained on each mission. Comparisons of flight data with classical theory show that complete diffuse reflection is not an appropriate model for rarefied aerodynamic coefficient calculations, and, for the Shuttle, some specular fraction is required. Surface reflection laws are explored to define the sensitivity of the L/D measurements to gas-surface molecule interactions.

Blanchard, R. C.↗
NASA NTRS1988

Progress towards extreme attitude testing with Magnetic Suspension and Balance Systems

Progress is reported in a research effort aimed towards demonstration of the feasibility of suspension and aerodynamic testing of models at high angles of attack in wind tunnel Magnetic Suspension and Balance Systems. Extensive modifications, described in this paper, have been made to the Southampton University suspension system in order to facilitate this work. They include revision of electromagnet configuration, installation of all-new position sensors and expansion of control system programs. An angle of attack range of 0 to 90 deg is expected for axisymmetric models. To date, suspension up to 80 deg angle of attack has been achieved.

Britcher, Colin P.↗
NASA NTRS1988

Hypersonic drone design: A multidisciplinary experience

Efforts were focused on design problems of an unmanned hypersonic vehicle. It is felt that a scaled hypersonic drone is necessary to bridge the gap between present theory on hypersonics and the future reality of the National Aerospace Plane (NASP) for two reasons: to fulfill a need for experimental data in the hypersonic regime, and to provide a testbed for the scramjet engine which is to be the primary mode of propulsion for the NASP. Three areas of great concern to NASP design were examined: propulsion, thermal management, and flight systems. Problem solving in these areas was directed towards design of the drone with the idea that the same design techniques could be applied to the NASP. A seventy degree swept double delta wing configuration, developed in the 70's at NASA Langley, was chosen as the aerodynamic and geometric model for the drone. This vehicle would be air-launched from a B-1 at Mach 0.8 and 48,000 feet, rocket boosted by two internal engines to Mach 10 and 100,000 feet, and allowed to cruise under power of the scramjet engine until burnout. It would then return to base for an unpowered landing. Preliminary energy calculations based upon the flight requirements give the drone a gross launch weight of 134,000 lb. and an overall length of 85 feet.

Source record↗
NASA NTRS1990

Computation Of Flutter In Turbomachinery

"Direct" solution procedure supplants conventional eigenmode analysis. Iterative computational procedure yields critical mach number for onset of flutter and flutter angular frequency, of propfan, turbine with unshrouded blades, or other turbomachinery. Procedure applied to aeroelastic analysis of propfan, in which finite-element model of propfan structure combined with model of unsteady aerodynamics based on three-dimensional subsonic-lifting-surface theory. Particularly suitable for optimization in design because as optimal design evolves, flutter solution expected to change incrementally, so previous solution provides good estimates for start of current solution.

Murthy, Durbha V.↗
NASA NTRS1990

Flight test of a trajectory controller using linearizing transformations with measurement feedback

The design of nonlinear controllers has relied on the use of detailed aerodynamic and engine models that must be associated with the control law in the flight system implementation. Many of these controllers have been applied to vehicle flightpath control problems and have attempted to combine both inner- and outer-loop control functions in a single controller. This paper presents an alternate approach to the design of outer-loop controllers. The approach simplifies the outer-loop design problem by separating the inner-loop (stabilization and control) from the outer-loop (guidance and navigation) functions. Linearizing transformations are applied using measurement feedback to eliminate the need for detailed aircraft models in outer-loop control applications. Also discussed is an implementation of the controller. This implementation was tested on a six-degree-of-freedom F-15 simulation and in flight on an F-15 aircraft. Proof of the concept is provided by flight test data which is presented and discussed.

Antoniewicz, Robert F.↗
NASA NTRS1991

Modeling, simulation, and flight characteristics of an aircraft designed to fly at 100,000 feet

A manned real time simulation of a conceptual vehicle, the stratoplane, was developed to study the problems associated with the flight characteristics of a large, lightweight vehicle. Mathematical models of the aerodynamics, mass properties, and propulsion system were developed in support of the simulation and are presented. The simulation was at first conducted without control augmentation to determine the needs for a control system. The unaugmented flying qualities were dominated by lightly damped dutch roll oscillations. Constant pilot workloads were needed at high altitudes. Control augmentation was studied using basic feedbacks. For the longitudinal axis, flight path angle, and pitch rate feedback were sufficient to damp the phugoid mode and to provide good flying qualities. In the lateral directional axis, bank angle, roll rate, and yaw rate feedbacks were sufficient to provide a safe vehicle with acceptable handling qualities. Intentionally stalling the stratoplane to very high angles of attack (deep stall) was studied as a means of enable safe and rapid descent. It was concluded that the deep stall maneuver is viable for this class of vehicle.

Sim, Alex G.↗
NASA NTRS1987

Typical testing experience in cryogenic wind tunnels

Airfoil testing as a major activity of many wind tunnels is considered, and emphasis is placed on airfoil testing with sidewall boundary-layer removal, oscillating airfoil testing, and three-dimensional wake topology. Buffeting as the structural response of an aircraft or test model to the aerodynamic excitation produced by separated flows is analyzed, as well as flutter problems and testing techniques. Strain-gage balance studies, optical methods and visualization techniques, and fluid mechanics are examined. Focus is placed on a two-spot laser as a boundary-layer probe, hot-film gages, fluctuating-pressure measurements, skin-friction balance, and nonadiabatic airfoil testing. Boattail afterbody pressure tests are covered, and Space Shuttle Orbiter base drag and launch configuration are discussed.

Kilgore, Robert A.↗