Showing papers in "Journal of Aircraft in 1967"

Possibilities of Drag Reduction by the Use of Flexible Skin

Abstract: A flexible aerodynamic surface is considered as a possible means of delaying transition and reducing skin-friction drag. The results of an extensive analytical study on boundary-layer instability and transition in incompressible Blasius-flow over a flexible surface are presented. A simple flexible skin model consisting of a taut membrane and an elastic base has been considered. The mechanical behavior of such a skin is controlled by the mass, the wave propagation velocity, the stiffness, and the damping. The analysis shows that with proper selection of the surface characteristics, the transition can be significantly delayed through reduced amplification rates, even though the critical Reynolds number for instability is only slightly increased. The extent of transition delay and the required surface properties are delineated. The theoretically possible drag reduction is most significant within the Reynolds number range of 3 to 50 X 10 6. Hence, potential fields of application of flexible skins would be in sailplanes, helicopters, small and medium subsonic airplanes, hydrofoils, torpedoes, speed boats, and miniature submarines. Nomenclature a = amplification factor, imaginary part of the complex wave velocity cr = phase velocity, real part of the complex wave velocity Com = wave propagation velocity in the membrane, (T/M)l/<2 d = damping coefficient, Eq. (21) D = damping constant, lb-sec/ft3 KM = mass parameter, Eq. (13) Ks = stiffness parameter, Eq. (15) KD = damping parameter, Eq. (17) m = mass coefficient, Eq. (18) M = membrane mass per unit area, Ib-sec2/ft3 Rx = Reynolds number based on length, Um x/v Rd = Reynolds number based on boundary-layer thickness S = compression stiff ness of base material, Ib/ft3 T = membrane tension, Ib/ft t/oo = freestream velocity, fps x = distance from leading edge along the plate, ft a. = dimensionless wave number, kd /3r = disturbance frequency, a.cr d = boundary-layer thickness, ft d* = boundary-layer displacement thickness, ft v — kinematic viscosity of fluid, ft2/sec p = density of fluid, Ib-sec2/ft3 coo = dimensionless cutoff frequency, (S/M)ll2d/Uo3 w* = circular frequency of disturbance, sec"1 ior = dimensionless circular frequency, (3r/Rd = co^v/U m2

Pressure Distribution on a Rectangular Wing with a Jet Exhausting Normally into an Airstream

Abstract: The interaction between a jet exhausting normally from a lifting surface into a uniform airstream is explored theoretically and experimentally. A theoretical model of the flow is discussed in which the entrainment of the mainstream fluid by the j et is accounted for directly, without recourse to an empirical equation for the jet centerline. Making use of the observation that the jet deforms from a circular cross section into an elliptical cross section as it progresses downstream, the continuity and momentum equations are solved to provide the jet path. The velocity field induced by the jet is then determined by replacing the jet by a sink-doublet distribution. The distribution of sinks represents the entrainment effect of the jet, and the doublet distribution represents the blockage effect of the jet. Lifting surface theory is used to predict the loading on the adjacent lifting surface. The theory does account for the three-dimensionality of the problem, and there is good agreement between theory and the results of an experiment conducted on a 10% thick straight wing at AR = 3.

Unsteady normal force on an airfoil in a periodically stalled inlet flow.

Abstract: The effect of a circumferential inlet velocity distortion on the. normal force response and stall characteristics of a rotating blade in an axial-flow turbomachine was analytically investigated by considering the response of an airfoil subjected to a periodically varying incidence angle. A hypothetical distortion profile that produced both large and small rates of change of incidence was employed in the analysis; the number of distortions per revolution was varied, and a substantial penetration of the incidence angle into the stall region occurred at maximum distortion. Unsteady flow effects, including dynamic stall behavior, were introduced into the analysis by using an empirical set of unsteady aerodynamic data previously obtained on an NACA 0012 airfoil oscillating in pitch over a wide range of test conditions. Use was also made of the unsteady potential flow theory of Theodorsen. It was found that the severity of the dynamic stall was intimately related to the rate at which the incidence angle decreased from its maximum value; slowly decreasing incidence produced the severest dynamic stall, whereas rapidly decreasing incidence yielded very little dynamic stall.

Computerized aircraft synthesis.

Abstract: A concept and philosophy of computerized aircraft synthesis is discussed, and Computer Program SYNAC (SYNthesis of AirCraft) is examined in some detail by considering examples of both its construction and its application. An aircraft synthesis computer program involves three principal functions: determination of force characteristics, determination of aircraft performance, and configuration control. There are three groups of variables: independent configuration size and shape variables; intermediate weight-, propulsion-, and aerodynamic-force characteristics variables; and dependent performance variables. Program SYNAC is organized in seven major modules: input, configuration control, geometry, weight, propulsion, aerodynamics, and performance. The program yields accuracies comparable with conventional aircraft synthesis techniques. Computer time per problem is currently on the order of 1 min, and ultimate times of y - of a minute are expected. A typical application of Program SYNAC involves the maximum-range optimization (in terms of wing area, wing thickness ratio, wing aspect ratio, wing taper ratio, and engine size) of a variable wing-sweep configuration for an air-to-ground mission.

Limits on minimum speed V/STOL wind-tunnel tests.

Abstract: body of revolution, far from the axis," Proc. Roy. Soc. (London) A201, 89-109 (March 1950). 8 Hubbard, H. H., Maglieri, D. J., Huckel, V., and Hilton, D. A. (with appendix by H. W. Carlson), "Ground measurements of sonic-boom pressures for the altitude range of 10,000 to 75,000 feet," NASA TR R-198 (1964). (Supersedes NASA TM X-633.) 9 Walkden, F., "The shock pattern of a wing-body combination, far from the flight path," Aeronaut. Quart. IX, Pt. 2, 164194 (May 1958). 10 Whitham, G. B.; "The flow pattern of a supersonic projectile," Commun. Pure Appl. Math. V, 301-348 (August 1952). 11 Middle ton, W. D. and Carlson, H. W., "A numerical method for calculating near-field sonic-boom pressure signatures," NASA TND-3082(1965). 12 Carlson, H. W., Mack, R, J., and Morris, O. A., "Sonicboom pressure-field estimation techniques," J. Acoust. Soc. Am. (submitted for publication). 13 McLean, F. E. and Shrout, B. L., "Design methods for minimization of sonic-boom pressure-field disturbances," J. Acoust. Soc. Am. (submitted for publication).

Longitudinal handling qualities criteria - An evaluation.

Abstract: Compliance with current longitudinal handling qualities criteria is not a guaranteed acceptance of vehicle characteristics. Several criteria for satisfactory characteristics resulting from handling qualities investigations in simulators and variable-stability airplanes are reviewed; in comparison, these criteria reveal significant areas of disagreement. Further, much of the large-airplane data available that reflect satisfactory characteristics in flight would be judged unacceptable to unsatisfactory from these criteria. Consideration of the piloting technique involved in flightpath control indicates the significance of the parameters La/ 15 g/rad also yield good agreement when mapped onto the nza/0}n vs f plane. These three parameters—nza, La/

Factors influencing glide path control in carrier landing.

Abstract: The carrier landing process involves the interaction of ship motions, the optical landing system, the pilot/air craft combination, air wake disturbances, and the Landing Signal Officer. Mathematical models for these elements are discussed, and methods are presented for determining operational performance indices from terminal landing error dispersion data. A new concept is described for stabilizing the optical landing system against carrier deck motions, which represent one of the most significant obstacles to safe aircraft recovery. Termed "compensated-meatball stabilization," this technique considers the dynamics of the carrier landing system elements and optimizes the Fresnel lens logic scheme for increased landing performance. Simulator experiments were performed to determine the potential accident rate reduction with this stabilization method, and the major results are presented. A significant interaction exists between an aircraft design parameter, related to the lift curve slope, and the optical landing system stabilization. The fundamental factors limiting terminal landing performance are described and several basic solutions to the problem are presented.

Potential flowfield and added mass of the idealized hemispherical parachute.

Abstract: (p, 0) z) =

Ozone measurement survey in commercial jet aircraft.

Abstract: : A survey was made to (1) measure ozone concentrations in CAR 4b jet aircraft cabins and cockpits on flights above 25,000 ft to obtain a 12-month evaluation with emphasis on seasonal and meteorological correlation and (2) locate and chart ozone-enriched air masses to obtain further correlations and to find any abnormal conditions that result in high ozone concentration. The data obtained by monitoring jets showed: (1) External ozone enters via the pressurization system. (2) Ozone concentration varies with altitude, latitude, and season. (3) Pressurization systems of various aircraft do not differ in ozone-decomposing efficiency. (4) Internal ozone concentration is negligible on flights made below the tropopause.

Evaluation of B-52 structural response to random turbulence with stability augmentation systems.

Abstract: A theoretical evaluation of the structural performance of benefits to be expected after installing a state-of-the-art stability augmentation system (SAS) on the B-52 is presented. The new system is expected to provide additional stability in the airplane rigid body motions and the low-frequency structural vibration modes. The mathematical model used in this study included rigid body motions, a large number of normal vibration modes, control surface rotations, and the SAS transfer functions. The dynamic response of the airplane to random atmospheric turbulence was determined using harmonic analysis techniques with provisions made to include the effects of nonlinearities due to SAS saturation. Quantitative estimates of the changes in airplane structural response indicate that fatigue-damage accumulation rates and peak-load amplitudes, due to atmospheric turbulence, can be significantly reduced without degrading the flutter margin.

Equilibrium configuration and tensions of a flexible cable in a uniform flowfield.

Abstract: Equilibrium configuration and tension of flexible cable in uniform flow field, considering tangential drag force and weight effects

Aerodynamics of powerplant installation on supersonic aircraft.

Abstract: Simple ideas derived from theoretical studies are utilized to explain the action of an engine nacelle upon a wing in supersonic flow. The engine installation is shown to influence both the wave drag due to thickness and the drag due to lift. Available theoretical procedures make it possible to estimate the forces on a wing due to the combined action of several nacelles, and results of theoretical calculations are compared with supersonic wind-tunnel-test data. The effects of the relative location of nacelles and the effects of nacelle shape and size on the lift, drag, and pitch characteristics of wind-tunnel models are presented and discussed. Experimental results are used to demonstrate that the camber and twist of the wing should be designed by taking into account the effects of the flowfield from the nacelles. It is indicated that designing for low drag requires consideration of the lift distribution on the airplane and a knowledge of viscous effects.

A method for in-flight measurement of ground effect on fixed-wing aircraft.

Abstract: Flight test method for evaluating ground effect on fixed-wing aircraft in which pilot flies at constant angle of attack and power setting during landing approach

Hydrodynamics of tire hydroplaning.

Abstract: 1 Losey, D. D., A technique for estimating axial flow compressor potential peak efficiency and related performance," M. S. Thesis, Univ. of Cincinnati (1965). 2 Rains, D. A., "Tip clearance flows in axial flow compressors and pumps," California Institute of Technology, Hydrodynamics and Mechanical Engineering Lab., Rept. 5 (June 1964). 3 Carter, A. D. S., Moss, C. S., Green G. R., and Amnear, G. G., "The effect of Reynolds number on the performance of a single-stage compressor," Ministry of Aviation Aeronautical Research Council, Rept. and Memo. 3184 (1960). * Sheets, H. E., "The slotted blade axial flow blower," Trans. Am. Soc. Mech. Engrs. 78, 1683 (1956). 5 Sandercock, D. M., Kovach, K., and Lieblein, S., "Experimental investigation of a five stage axial flow research compressor with transonic rotors in all stages. I—Compressor design," NACA RME54C26 (1954). 6 Sandercock, D. M. and Kovach, K., "Experimental investigation of a five stage axial flow research compressor with transonic rotors in all stages. II—Compressor over-all performance," NACA RME54G01 (1954). 7 Sandercock, D. M. and Kovach, K., "Experimental investigation of a five stage axial flow research compressor with transonic rotors in all stages. Ill—Interstage data and individual stage performance characteristics," NACA RME56G24 (1956). 8 Wiggins, J. O., "A procedure for determining the off-design characteristics of multistage axial flow compressors," M. S. Thesis, Univ. of Cincinnati (1963).

Concorde structural development.

Abstract: Development of the supersonic transport is involving a wide variety of activities in the structural field. Although Concorde is designed for Mach 2, a speed at which aluminum alloys can continue to be used for the primary structure, evaluation of the chosen alloys under complex temperature-stress histories involves considerable laboratory effort. Although many aircraft have already operated under these conditions, none has previously had to last for 50,000 hr. The most significant new design considerations are creep and thermal fatigue. Creep affects the choice of basic material, the design of joints, and the design of structures through its interaction with fatigue life. Thermal stresses, arising from differential expansions within the structure, have a more important effect on fatigue design than on static strength. While the experimental techniques involved are novel, practical methods of accelerated thermal testing using convective heating and cooling are described.

Minimum swept-wing induced drag with constraints on lift and pitching moment.

Abstract: A = coefficient for span-loading series CD = drag coefficient CL = lift coefficient CM = pitching-moment coefficient ACM = CM contributed by the nonelliptical portion of the span loading N = number of terms in the span-loading series S = reference area for coefficients a = aspect ratio b = span c = chord ci = section lift coefficient Cm = section pitching-moment coefficient m = mean aerodynamic chord x, y = longitudinal and lateral coordinates A = quarter-chord sweep angle 0 = transformed lateral coordinate, cos0 — —2y/b \ = taper ratio

Nozzles for jet-lift V/STOL aircraft.

Abstract: flowfield and that temperatures could be hazardous to the airplane. The test program was therefore extended to investigate changes in JBD design which might improve the environment. The three configurations described previously, selected as requiring minimum modifications to existing deflectors, were tested. The results of these tests are shown in Fig. 18, with results from the standard deflector included for comparison. From Fig. 18 it can be seen that these tests successfully demonstrated a JBD design that will prevent any hot gas from reaching the airplane. It can also be seen that modifications which were beneficial in some locations were detrimental in other locations, and that the momentum balance is not adequate to determine the effects of modifications. The fence was expected to turn the forward flow outboard, and (to an extent) it was successful. However, the temperature at the top of the vertical tail shows that the fence also augmented the upward flow. Similarly, reducing the JBD angle to 45° was expected to lower all temperatures on the airplane, but it increased the temperature at the engine inlet. These test results were valuable in the F-111B program and are generally applicable for situations that duplicate the F-111B nozzle spacing, height above the deck, and nozzle inclination. In any other case, the uncertainties in analysis as demonstrated in this test are such that data from exact models should be obtained.

U. S. Air Force Concepts for Accurate Delivery of Equipment and Supplies

Abstract: For many reasons it is often impractical to land and off-load an aircraft or use conventional parachute delivery techniques to provide logistic support for military troops engaged in combat. This problem of getting supplies and equipment to the point of need involves both resupply and assault phases. Each phase has peculiar characteristics which, in addition to the type and quantity of cargo needed, permit one of a family of aerial delivery systems to provide the necessary support. Descriptions of these systems and their characteristics, which provide a high degree of flexibility in the aerial delivery of cargo, are presented. The impact of new aircraft such as the C-141, C-142, and C-5A on mission versatility and capability are discussed as well as problem areas associated with making more effective use of aircraft capability.

Analysis of Dynamic Stress in an Inflating Parachute

Abstract: Analyses of maximum stresses in parachute canopies have previously associated maximum stress with opening shock. Loads calculated from such analyses are too small to account for many cases of canopy failure. It is proposed that the maximum stress on a canopy is related to the radial velocity parallel to the plane of the skirt with which each concentric ring of the canopy reaches its maximum diameter. At this instant it must decelerate the radial component of the air inflow. This deceleration results in a transient hoop stress imposed on the ring of cloth. An expression is developed for evaluating this stress, designated snap stress, relating it to diameter and filling time. The significance of this relation is discussed and magnitudes are calculated, showing that it can account for otherwise unexplained test failures. Suggestions are made for means of relieving this snap stress, and recommendations are made for further investigation of this source of canopy stress.

Analytic Platforms in Cruising Aircraft

Abstract: An extensive cruise error analysis is presented for a strapdown inertial aircraft navigation system with pulse torqued instruments, in the presence of small amplitude oscillations. The analysis accounts for complex lateral and angular vibration with realistic models of coupled motion. Steady and secularly increasing position uncertainties, with accompanying Schuler oscillations, are expressed directly in terms of familiar system constants and statistical motion parameters.

Vibrations of thin conical shells subjected to sudden heating.

Abstract: Nomenclature A = thermal diffusivity B = parameter defined in Eq. (39) E = Young's modulus MT = nondimensional thermal moment, Eq. (10) R = radius at the smaller end T = temperature gradient h = thickness of shell ra, N = longitudinal mode number = odd integers n = number defined in Eq. (23) r, 0 = surface coordinates I = dimensional time t = nondimensional time = I/unit of time w, u, v, = dimensional displacement components of the middle

Aerodynamic penetration and radius as unifying concepts in flight mechanics.

Abstract: The scale of atmospheric entry processes and of certain other problems in vehicle dynamics may be quantified in terms of a vehicle parameter that has the dimension of length. Two such lengths, the "aerodynamic penetration" 2m/pACD and the "aerodynamic radius" 2m/pACL-> have simple physical interpretations and tend to be constant multiples of the characteristic dimensions of geometrically similar vehicles of constant density. The aerodynamic penetration may be used as a linear scale factor to generalize trajectory studies if aerodynamic drag is important, and the aerodynamic radius may be used if aerodynamic lift is important. Several problems involving the deceleration and flight mechanics of entry vehicles, airplanes, and ballistic projectiles are discussed to show the application of these parameters to wellknown situations.

Wind-tunnel simulation of store jettison with the aid of an artificial gravity generated by magnetic fields.

Abstract: In this paper a set of model scaling equations for wind-tunnel simulation of the trajectory of jettisoned stores from aircraft is presented. This scaling is based upon a scaled gravitational acceleration. It is shown that a suitable scaled gravity can be developed by means of magnetized ferromagnetic spheres in a magnetic field gradient. Preliminary experimental results are presented that illustrate that "gravity can be modified" by this technique.

Initial VGH data on operations of small turbojets in commercial transport service.

Abstract: Initial VGH data on small turbojet operations in commercial transport service relating to accelerations, airspeed operating practices and unusual events

Dynamic Analysis of the Rigid Rotor System

Abstract: A unified dynamic analysis for the rotor motion of the rigid or nonarticulated rotor system in a hovering state is presented. The dynamic behavior of the rigid rotor as well as that of the conventional rotor is expressed in a simple linearized mathematical form by using complex variables. The available control moment and the necessary phase shift for a given cyclic pitch input are obtained in general formulas and charts. Generally, the control and damping moments of the rigid rotor system increase with the increment of the napping stiffness, but there is a critical stiffness at which the aforementioned moments will be maximum. Optimum napping stiffness may be given so as to avoid unfavorable coupling motion between roll and pitch. It is not always necessary to install the control gyro, because similar stabilizing effect may be obtained by using the proper blade configuration without a special gyro system. The necessary control phase advance is also given to avoid cross control of the rigid rotor system.

Subsonic-transonic-drag of supersonic inlets.

Abstract: The subsonic-transonic drag of supersonic inlets appears to be a subject that has been largely neglected in the transition from subsonic to supersonic design-point flight. Now that more emphasis is placed on off-design performance of supersonic aircraft, more information is required on this subject. Accordingly, experimental data were obtained on subsonictransonic drag of two types of supersonic inlets. The types investigated were two-dimensional and axisymmetric plug inlets. The two-dimensional inlets were of the single-ramp mixed compression variety. The axisymmetric inlets had a conical plug and were also of the mixed-compression type. The range of variables studied was as follows: two-dimensional inlet ramp angle, 6°-12°; axisymmetric inlet conical plug half-angle, 10°-18°; two-dimensional inlet throat-capture area ratio, 0.32-0.80; and axisymmetric inlet throat-capture area ratio, 0.13-0.80. It was found that two-dimensional inlets have higher additive drags than axisymmetric inlets of the same area ratio and initial angle. This conclusion is the same as in supersonic flight.