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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 127 records · Page 7

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NASA NTRS1973

Pulsed electromagnetic acceleration

Direct measurements of the power deposited in the anode of a multimegawatt MPD accelerator using thermocouples attached to a thin shell anode reveal a dramatic decrease in the fractional anode power from 50% at 200 KW input power to less than 10% at 20 MW power. The corresponding local power flux peak at a value of 10,000 W/sq cm at the lip of the anode exhaust orifice, a distribution traced to a corresponding peak in the local current density at the anode. A comparison of voltage-current characteristics and spectral photographs of the MPD discharge using quartz, boron nitride and plexiglas insulators with various mass injection configurations led to the identification of different voltage modes and regions of ablation free operation. The technique of piezoelectric impact pressure measurement in the MPD exhaust flow was refined to account for the effects due to probe yaw angle.

Jahn, R. G.↗

NASA NTRS1973

Preliminary measurements on heat balance in pneumatic tires

A variety of tests was undertaken to determine the nature of heat generation associated with a pneumatic tire operating under various conditions. Tests were conducted to determine the magnitude and distribution of internally generated heat caused by hysteresis in the rubber and ply fabric in an automobile tire operating under conditions of load, pressure, and velocity representative of normal operating conditions. These included tests at various yaw angles and tests with braking applied. In other tests, temperature sensors were mounted on a road to measure the effect of a tire rolling over and an attempt was made to deduce the magnitude and nature of interfacial friction from the resulting information. In addition, tests were performed using the scratch plate technique to determine the nature of the motion between the tire and road. Finally, a model tire was tested on a roadwheel, the surface covering which could be changed, and an optical pyrometer was used to measure rubber surface temperatures.

Nybakken, G. H.↗

NASA NTRS1973

Cornering characteristics of a 40 by 14-16 type 7 aircraft tire and a comparison with characteristics of a C40 by 14-21 cantilever aircraft tire

An investigation was conducted at the Langley aircraft landing loads and traction facility to determine the cornering characteristics of a 40 x 14-16 type VII aircraft tire. These characteristics, which include the cornering-force and drag-force friction coefficients and self-alining torque, were obtained for the tire operating on dry, damp and flooded runway surfaces over a range of yaw angles from 0 deg to 20 deg and at ground speeds from 5 to 100 knots, both with and without braking. The results of this investigation indicated that the cornering capability of the 40 x 14-16 type VII aircraft tire is degraded by high ground speeds, thin-film lubrication and tire hydroplaning effects on the wet surfaces, and brake torque. The cornering capability is greatly diminished when locked-wheel skids are encountered.

Tanner, J. A.↗

NASA NTRS1973

An experimental investigation of three oblique-wing and body combinations at Mach numbers between 0.60 and 1.40

An experimental investigation was conducted in an 11- by 11-foot transonic wind tunnel to determine the aerodynamic characteristics of three oblique high aspect ratio wings in combination with a high fineness-ratio Sears-Haack body. The three wings had the same elliptical planform and base line curvature but had different airfoil sections. One wing had an airfoil section designed to have a lift coefficient of 1.0 at a Mach number of 0.7, another to have shock-free supersonic flow over the upper surface, and the other to have a lift coefficient of 1.3 at a Mach number of 0.6. Longitudinal and lateral-directional stability data were obtained at wing yaw angles of 0 deg, 45 deg, 50 deg, and 60 deg over a test Mach number range from 0.6 to 1.4 for angles of attack between minus 7 deg and 9 deg. Reynolds numbers for the study were 4 and 6 million per foot. Flow-visualization studies were made to examine the nature of the flow on the wing surfaces. Notable differences were found in the aerodynamic characteristics of the three wing-body combinations, particularly in the lateral-directional characteristics.

Graham, L. A.↗

NASA NTRS1972

An experimental investigation of an oblique-wing and body combination at Mach numbers between 0.60 and 1.40

An experimental investigation was conducted in an 11- by 11-foot wind tunnel to determine the aerodynamic characteristics of an oblique high aspect ratio wing in combination with a high fineness-ratio Sears-Haack body. Longitudinal and lateral-directional stability data were obtained at wing yaw angles from 0 deg to 60 deg over a test Mach number range from 0.6 to 1.4 for angles of attack between minus 6 deg and 9 deg. The effects of changes in Reynolds number, dihedral, and trailing-edge angle were studied along with the effects of a roughness strip on the upper and lower surfaces of the wing. Flow-visualization studies were made to determine the nature of the flow on the wing surfaces.

Graham, L. A.↗

NASA NTRS1973

C-5A/orbiter wind tunnel testing and analysis: Piggyback ferry

Wind tunnel testing and analytical studies of the feasibility of ferrying the NASA Shuttle Orbiter on the C-5A in a piggyback mode have been accomplished. Testing was conducted in the 8x12 foot low speed wind tunnel using an existing 0.0399 scale C-5A model in conjunction with a NASA 0.0405 scale Orbiter model. Six component force and moment data were measured over a range of pitch and yaw angles to determine lift and drag characteristics, lateral/directional stability characteristics and longitudinal and directional control powers. A description of the wind tunnel test program with a run schedule and the complete plotted data for all the test runs are presented. Initial emphasis was given to determining the effects of the Orbiter above the C-5A and the optimum location for minimum interference on C-5A characteristics. A comprehensive series of cruise configurations were tested including a range of Orbiter longitudinal and vertical locations, incidences, and afterbody fairings. Subsequently, a series of configurations were devised during the test program to determine means of recovering directional stability degradation due to Orbiter interference.

Tomlin, K. H.↗

NASA NTRS1975

Study of a porous surface microphone sensor in an aerofoil

The porous microphone in an airfoil is described as a directional sensor which rejects flow noise. The airfoil allows the sensor to be rotated in the airflow over a wide range of yaw angles, 0 to 90 degrees, avoiding flow separation over the surface of the sensor and its associated additional flow noise. The microphone is discussed in terms of its acoustic properties, vibration sensitivity, effect of Mach number on the directivity function, and flow noise. Additional information on the acoustic calibration of the microphone, the acceleration sensitivity of the airfoil, stationary source and receiver in a moving gas, acoustic tests in airflow, and flow noise tests of the airfoil porous surface sensor is included.

Noiseux, D. U.↗

NASA NTRS1975

Development, fabrication and calibration of a porous surface microphone in an aerofoil

The development of a porous surface microphone in an airfoil intended to measure acoustic signals in a turbulent airflow and to minimize the flow noise is described. The sensor because of its airfoil operates over a wide range of yaw angles and flow velocities without excessive flow noise. The acoustic properties of the porous materials used in the airfoil sensor and their effects on the frequency response of the sensor were analyzed and tested. An accurate airfoil was selected, having a smaller thickness-to-chord ratio and an airfoil sensor was designed. The sensor was calibrated acoustically and its flow noise evaluated in the quiet BBN wind tunnel at flow velocities up to 70 m/sec. Results are presented.

Noiseux, D. U.↗

NASA NTRS1976

Friction characteristics of 20 x 4.4, type 7, aircraft tires constructed with different tread rubber compounds

A test program was conducted at the Langley aircraft landing loads and traction facility to evaluate the friction characteristics of 20 x 4.4, type, aircraft tires constructed with experimental cut-resistant, tread rubber compounds. These compounds consisted of different blends of natural rubber (NR) and an alfin catalyzed styrene-butadiene copolymer rubber (SBR). One tire having a blend of 30 SBR and 70 NR and another having a blend of 60 SBR and 40 NR in the tread were tested together with a standard production tire with no SBR content in the tread rubber. The results of this investigation indicated that the test tires constructed with the special cut-resistant tread rubber compositions did not suffer any significant degradation in tire friction capability when compared with the standard tire. In general, tire friction capability decreased with increasing speed and surface wetness condition. As yaw angle increased, tire braking capability decreased while tire cornering capability increased. Tread-wear data based on number of brake cycles, however, suggested that the tires with alfin SBR blends experienced significantly greater wear than the standard production tire.

Dreher, R. C.↗

NASA NTRS1977

Calibration of a pitot-static rake

A five-element pitot-static rake was tested to confirm its accuracy and determine its suitability for use at Langley during low-speed tunnel calibration primarily at full-scale tunnel. The rake was tested at one airspeed of 74 miles per hour (33 meters per second) and at pitch and yaw angles of 0 to + or - 20 degrees in 4 deg increments.

Stump, H. P.↗

NASA NTRS1976

Behavior of aircraft antiskid braking systems on dry and wet runway surfaces - A velocity-rate-controlled, pressure-bias-modulated system

During maximum braking the average ratio of drag-force friction coefficient developed by the antiskid system to maximum drag-force friction coefficient available at the tire/runway interface was higher on dry surfaces than on wet surfaces. The gross stopping power generated by the brake system on the dry surface was more than twice that obtained on the wet surfaces. With maximum braking applied, the average ratio of side-force friction coefficient developed by the tire under antiskid control to maximum side-force friction available at the tire/runway interface of a free-rolling yawed tire was shown to decrease with increasing yaw angle. Braking reduced the side-force friction coefficient on a dry surface by 75 percent as the wheel slip ratio was increased to 0.3; on a flooded surface the coefficient dropped to near zero for the same slip ratio. Locked wheel skids were observed when the tire encountered a runway surface transition from dry to flooded, due in part to the response time required for the system to sense abrupt changes in the runway friction; however, the antiskid system quickly responded by reducing brake pressure and cycling normally during the remainder of the run on the flooded surface.

Stubbs, S. M.↗

NASA NTRS1977

Friction characteristics of three 30 by 11.5-14.5, type 8, aircraft tires with various tread groove patterns and rubber compounds

A test program was conducted to evaluate friction performance and wear characteristics on wet runways of three 30 x 11.5-14.5, type, aircraft tires having two different tread patterns and natural rubber contents. All test tires had the standard three circumferential groove tread, but two had molded transverse grooves which extended from shoulder to shoulder. The tread rubber content of the two tires with transverse grooves differed in that one had a 100 percent natural rubber tread and the other had a rubber tread composition that was 30 percent synthetic and 70 percent natural. The third test tire had the conventional 100 percent natural rubber tread. Results indicate that the differences in tire tread design and rubber composition do not significantly affect braking and cornering friction capability on wet or dry surfaces. Braking performance of the tires decreases with increased speed, with increased yaw angle and, at higher speeds, with increased wetness of the surface.

Yager, T. J.↗

NASA NTRS1978

Some alternative dynamic design configurations for large horizontal axis WECS

The present U.S. development effort toward large horizontal axis WECS concentrates on the configuration with two rigid blades with collective pitch variation and a yaw gear drive. Alternative configurations without yaw gear drive were considered where the rotor is either selfcentering or where the yaw angle is controlled by blade cyclic pitch inputs. A preliminary evaluation of the dynamic characteristics for these alternative design configurations is presented.

Hohenemser, K. H.↗

NASA NTRS1978

Space shuttle orbiter reaction control system interactions with the vehicle flow field

Test data on the effect of the interaction between the space shuttle orbiter rear-mounted reaction control system jets and the flow over the vehicle in the atmosphere are analyzed with particular attention to yaw angle effects. Masted tank-plus-orbiter jet interactions resulting from combinations of forward and rear-mounted reaction control jets being fired prior to external tank staging are also documented. The primary correlating parameter used for the mated data is a single-jet momentum ratioed to free-stream momentum. An analytic model for computing reaction control system interactions for all control combinations used for mated vehicle coast is included.

Rausch, J. R.↗

NASA NTRS1977

An optimal Space Shuttle ascent trajectory for the first orbital flight test

An optimal solution of the ascent trajectory of the Space Shuttle for the first orbital flight test is presented; the optimization is a minimum propellant, four-control problem in yaw angle, roll angle, pitch angle and vacuum thrust of each Space Shuttle main engine. Piecewise linear segments with juncture points treated as parameters are employed to model the controls. Equations of motion for a three-dimensional flight with pitch plane moment balance about an oblate are integrated numerically with a fourth-order Runge-Kutta method; two- and one-dimensional cubic spline function curve fits of aerodynamic coefficients are used during the first and second stages, respectively. The constraint minimization problem is solved with the Davidon-Fletcher-Powell function method.

Johnson, I. L., Jr.↗

NASA NTRS1979

Aerodynamic characteristics of sixteen electric, hybrid, and subcompact vehicles

An elementary electric and hybrid vehicle aerodynamic data base was developed using data obtained on sixteen electric, hybrid, and sub-compact production vehicles tested in the Lockheed-Georgia low-speed wind tunnel. Zero-yaw drag coefficients ranged from a high of 0.58 for a boxey delivery van and an open roadster to a low of about 0.34 for a current four-passenger proto-type automobile which was designed with aerodynamics as an integrated parameter. Vehicles were tested at yaw angles up to 40 degrees and a wing weighting analysis is presented which yields a vehicle's effective drag coefficient as a function of wing velocity and driving cycle. Other parameters investigated included the effects of windows open and closed, radiators open and sealed, and pop-up headlights. Complete six-component force and moment data are presented in both tabular and graphical formats. Only limited commentary is offered since, by its very nature, a data base should consist of unrefined reference material. A justification for pursuing efficient aerodynamic design of EHVs is presented.

Kurtz, D. W.↗

NASA NTRS1979

Behavior of aircraft antiskid braking systems on dry and wet runway surfaces. A slip-velocity-controlled, pressure-bias-modulated system

The braking and cornering response of a slip velocity controlled, pressure bias modulated aircraft antiskid braking system is investigated. The investigation, conducted on dry and wet runway surfaces, utilized one main gear wheel, brake, and tire assembly of a McDonnell Douglas DC 9 series 10 airplane. The landing gear strut was replaced by a dynamometer. The parameters, which were varied, included the carriage speed, tire loading, yaw angle, tire tread condition, brake system operating pressure, and runway wetness conditions. The effects of each of these parameters on the behavior of the skid control system is presented. Comparisons between data obtained with the skid control system and data obtained from single cycle braking tests without antiskid protection are examined.

Stubbs, S. M.↗

NASA NTRS1979

Wear, friction, and temperature characteristics of an aircraft tire undergoing braking and cornering

An investigation to evaluate the wear, friction, and temperature characteristics of aircraft tire treads fabricated from different elastomers is presented. The braking and cornering tests performed on aircraft tires retreaded with currently employed and experimental elastomers are described. The tread wear rate is discussed in relation to the slip ratio during braking and yaw angle during cornering. The extent of wear in either operational mode is examined in relation to the runway surface.

Mccarty, J. L.↗