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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Feedback control laws for highly maneuverable aircraft

During this year, we concentrated our efforts on the design of controllers for lateral/directional control using mu synthesis. This proved to be a more difficult task than we anticipated and we are still working on the designs. In the lateral-directional control problem, the inputs are pilot lateral stick and pedal commands and the outputs are roll rate about the velocity vector and side slip angle. The control effectors are ailerons, rudder deflection, and directional thrust vectoring vane deflection which produces a yawing moment about the body axis. Our math model does not contain any provision for thrust vectoring of rolling moment. This has resulted in limitations of performance at high angles of attack. During 1994-95, the following tasks for the lateral-directional controllers were accomplished: (1) Designed both inner and outer loop dynamic inversion controllers. These controllers are implemented using accelerometer outputs rather than an a priori model of the vehicle aerodynamics; (2) Used classical techniques to design controllers for the system linearized by dynamics inversion. These controllers acted to control roll rate and Dutch roll response; (3) Implemented the inner loop dynamic inversion and classical controllers on the six DOF simulation; (4) Developed a lateral-directional control allocation scheme based on minimizing required control effort among the ailerons, rudder, and directional thrust vectoring; and (5) Developed mu outer loop controllers combined with classical inner loop controllers.

Garrard, William L.↗
NASA NTRS1974

Experimental determination of the principal moments of inertia of the Helios prototype spacecraft

The moment of inertia of the Helios Spacecraft about its spin axis was determined by use of a roll-fixture using two sets of crossed flexure pivots as elastic constraints. The test procedure entailed measurement of a system oscillation period with each of a set of added moment-of-inertia increments. The tare effect of the fixture was determined by a like process and was subtracted from the gross value to yield the spacecraft roll moment of inertia to an estimated accuracy of 0.2%. Lateral moments of inertia (i.e., about each of three axes normal to the spin axis) were determined by a gravity pendulum method that makes use of the fact that any physical pendulum has a minimum period of oscillation determined by a particular distance from the axis of rotation to the system center of gravity.

Gayman, W. H.↗
NASA NTRS1934

Aerodynamic effects of a split flap on the spinning characteristics of a monoplane model

The investigation described in this report was made to determine the change in aerodynamic forces and moments produced by split flaps in a steady spin. The test were made with the spinning balance in the NACA 5-foot vertical wind tunnel. A low-wing monoplane model was tested with and without the split flaps in 12 spinning attitudes chosen to cover the probable spinning range. The changes in coefficients produced by adding the split flaps are given for longitudinal force, normal force, and rolling and yawing moments about body axes. The results obtained indicate that the use of split flaps on an airplane is unlikely, in any case, to have much beneficial effect on a spin, and it might make the spin dangerous. The change in the spin will depend upon the aerodynamic and inertia characteristics of the particular airplane. A dangerous condition is most likely to be attained with airplanes which are statically stable in yaw in the spinning attitude and which have large weights distributed along wings.

Bamber, M J↗
NASA NTRS1995

Resistance to Rolling in the Adhesive Contact of Two Elastic Spheres

For the stability of agglomerates of micron sized particles it is of considerable importance to study the effects of tangential forces on the contact of two particles. If the particles can slide or roll easily over each other, fractal structures of these agglomerates will not be stable. We use the description of contact forces by Johnson, Kendall and Roberts, along with arguments based on the atomic structure of the surfaces in contact, in order to calculate the resistance to rolling in such a contact. It is shown that the contact reacts elastically to torque forces up to a critical bending angle. Beyond that, irreversible rolling occurs. In the elastic regime, the moment opposing the attempt to roll is proportional to the bending angle and to the pull-off force P(sub c). Young's modulus of the involved materials has hardly any influence on the results. We show that agglomerates of sub-micron sized particles will in general be quite rigid and even long chains of particles cannot be bent easily. For very small particles, the contact will rather break than allow for rolling. We further discuss dynamic properties such as the possibility of vibrations in this degree of freedom and the typical amount of rolling during a collision of two particles.

Dominik, C.↗
NASA NTRS1995

Resistance to Rolling in the Adhesive Contact of Two Elastic Spheres

For the stability of agglomerates of micron sized particles it is of considerable importance to study the effects of tangential forces on the contact of two particles. If the particles can slide or roll easily over each other, fractal structures of these agglomerates will not be stable. We use the description of contact forces by Johnson, Kendall and Roberts, along with arguments based on the atomic structure of the surfaces in contact, in order to calculate the resistance to rolling in such a contact. It is shown that the contact reacts elastically to torque forces up to a critical bending angle. Beyond that, irreversible rolling occurs. In the elastic regime, the moment opposing the attempt to roll is proportional to the bending angle and to the pull-off force P(sub c). Young's modulus of the involved materials has hardly any influence on the results. We show that agglomerates of sub-micron sized particles will in general be quite rigid and even long chains of particles cannot be bent easily. For very small particles, the contact will rather break than allow for rolling. We further discuss dynamic properties such as the possibility of vibrations in this degree of freedom and the typical amount of rolling during a collision of two particles.

Dominik, C.↗
NASA NTRS1937

Full-scale Wind-tunnel and Flight Tests of a Fairchild 22 Airplane Equipped with External-airfoil Flaps

Wind-tunnel and flight tests have been made of a Fairchild 22 airplane equipped with a wing having external-airfoil flaps that also perform the function of ailerons. Lift, drag, and pitching-moment coefficients of the airplane with several flap settings, and the rolling- and yawing-moment coefficients with the flaps deflected as ailerons were measured in the full-scale tunnel with the horizontal tail surfaces and propeller removed. The effect of the flaps on the low speed and on the take-off and landing characteristics, the effectiveness of flaps when used as ailerons, and the forces required to operate them as ailerons were determined in flight. The wind-tunnel tests showed that the flaps increased the maximum lift coefficient of the airplane from 1.51 with the flap in the minimum drag position to 2.12 with the flap in the minimum drag position to 2.12 with the flap deflected 30 degrees. In the flight tests the minimum speed decreased from 46.8 miles per hour with the flaps up to 41.3 miles per hour with the flaps deflected. The required take-off run to attain a height of 50 feet was reduced from 820 to 750 feet and the landing run from a height of 50 feet was reduced from 930 to 480 feet. The flaps for this installation gave lateral control that was not entirely satisfactory. Their rolling action was good but the adverse yaw resulting from their use was greater than is considerable, and the stick forces required to operate them increased too rapidly with speed.

Reed, Warren D↗
NASA NTRS1972

Effect of configuration modification on the hypersonic aerodynamic characteristics of a blended delta wing-body entry vehicle

The longitudinal, lateral, and directional aerodynamic characteristics of a delta-wing configuration were obtained experimentally at Mach 20 in helium with Reynolds numbers, based on model length, of 1.5 million and 2.9 million and at a Mach number of 6 in air with a Reynolds number, based on model length, of 4.8 million. The angles of attack varied from 0 deg to 55 deg for two sideslip angles. The effects of the addition of dorsal fins, the removal of wing tip fins, an increase in elevon span, and changes in elevon hinge-line sweep angle are discussed. The unmodified vehicle had a maximum lift-drag ratio of 2.1 at Mach 19 and of 2.4 at Mach 6 with about the same lateral and directional stability level at both Mach numbers. As the Mach number increased from 6 to 20, the longitudinal center of pressure moved forward and more positive elevon deflection was therefore required to maintain a given trim angle. The removal of wing tip fins increased the maximum lift-drag ratio and had a negligible effect on longitudinal stability, but caused directional instability that was not corrected by the dorsal fins examined. The shape of the wing and elevon hinge-line sweep had a large influence on the induced yawing moment due to roll control.

Arrington, J. P.↗
NASA NTRS1977

Effect of wing flexibility on the experimental aerodynamic characteristics of an oblique wing

A solid-aluminum oblique wing was designed to deflect considerably under load so as to relieve the asymmetric spanwise stalling that is characteristic of this type of wing by creating washout on the trailing wing panel and washin on the leading wing panel. Experimental forces, and pitching, rolling and yawing moments were measured with the wing mounted on a body of revolution. In order to vary the dynamic pressure, measurements were made at several unit Reynolds numbers, and at Mach numbers. The wing was investigated when unswept (at subsonic Mach numbers only) and when swept 45 deg, 50 deg, and 60 deg. The wing was straight tapered in planform, had an aspect ratio of 7.9 (based on the unswept span), and a profile with a maximum thickness of 4 percent chord. The results substantiate the concept that an oblique wing designed with the proper amount of flexibility self relieves itself of asymmetric spanwise stalling and the associated nonlinear moment curves.

Hopkins, E. J.↗
NASA NTRS1978

The role of rotor impedance in the vibration analysis of rotorcraft, part 4

A method for a strongly idealized case of vertical excitation and for rolling and pitching moment excitation of a four bladed hingeless rotor on an up-focussing flexible mount is developed. The aeroelastic rotor impedances are computed directly with a finite blade element method that includes aerodynamics. The rotor impedance matrix for three or more blades is determined from the root moment impedance for a single blade by a simple multiblade transformation rule. Force and moment amplitudes transferred from the rotor to support are found to be critically dependent on the support dynamics.

Hohenemser, K. H.↗
NASA NTRS1978

The role of rotor impedance in the vibration analysis of rotorcraft

In an improved method which retains the advantage of separate treatment of rotor and airframe, the rotor impedance is used to correct the input to the airframe. This improved method is illustrated for a strongly idealized case of vertical excitation and then for rolling and pitching moment excitation of a four bladed hingeless rotor on an up-focussing flexible mount. Contrary to the usual approach that represents aeroelastic blade motions by a series of normal blade modes in vacuum, the aeroelastic rotor impedances are computed directly with a finite blade element method that includes aerodynamics. The rotor impedance matrix for three or more blades is determined from the root moment impedance for a single blade by a simple multiblade transformation rule. Force and moment amplitudes transferred from the rotor to the support are found to be critically dependent on the support dynamics.

Hohenemser, K. H.↗
NASA NTRS1987

Exploratory studies of actuated forebody strakes for yaw control at high angles of attack

Wind-tunnel studies have been conducted to evaluate the potential of actuated forebody strakes to provide increased levels of yaw control on fighter aircraft at extremely high angles of attack where conventional aerodynamic controls are ineffective. The studies involved low-speed wind-tunnel tests of actuated forebody strake concepts applied to a generic fighter model and included circumferential pressure and flow visualization surveys on an isolated forebody. Results showed that the actuated forebody strake concept can provide high levels of yaw control over wide ranges of angle-of-attack and sideslip. However, when lifting surfaces were placed in close proximity to the forebody/strake combination, significant interaction effects occurred which reduced the yaw control effectiveness of the strakes and induced coupled rolling and pitching moments.

Murri, Daniel G.↗
NASA NTRS1988

Shape sensitivity analysis of wing static aeroelastic characteristics

A method is presented to calculate analytically the sensitivity derivatives of wing static aeroelastic characteristics with respect to wing shape parameters. The wing aerodynamic response under fixed total load is predicted with Weissinger's L-method; its structural response is obtained with Giles' equivalent plate method. The characteristics of interest include the spanwise distribution of lift, trim angle of attack, rolling and pitching moments, wind induced drag, as well as the divergence dynamic pressure. The shape parameters considered are the wing area, aspect ratio, taper ratio, sweep angle, and tip twist angle. Results of sensitivity studies indicate that: (1) approximations based on analytical sensitivity derivatives can be used over wide ranges of variations of the shape parameters considered, and (2) the analytical calculation of sensitivity derivatives is significantly less expensive than the conventional finite-difference alternative.

Barthelemy, Jean-Francois M.↗
NASA NTRS1988

Shape sensitivity analysis of wing static aeroelastic characteristics

A method is presented to calculate analytically the sensitivity derivatives of wing static aeroelastic characteristics with respect to wing shape parameters. The wing aerodynamic response under fixed total load is predicted using Weissinger's L-method; its structural response is obtained with Giles' equivalent plate method. The characteristics of interest in this study include the spanwise distribution of lift, trim angle of attack, rolling and pitching moments, wing induced drag as well as the divergence dynamic pressure. The shape parameters considered are the wing area, aspect ratio, taper ratio, sweep angle and tip twist angle. Results of sensitivity studies indicate that (1) approximations based on analytical sensitivity derivatives can be used for wide ranges of variations of the shape parameters considered and (2) the analytical calculation of sensitivity derivatives is significantly less expensive than the conventional finite difference alternative.

Barthelemy, Jean-Francois M.↗
NASA NTRS1934

The aerodynamic analysis of the gyroplane rotating-wing system

An aerodynamic analysis of the gyroplane rotating-wing system is presented herein. This system consists of a freely rotating rotor in which opposite blades are rigidly connected and allowed to rotate or feather freely about their span axis. Equations have been derived for the lift, the lift-drag ratio, the angle of attack, the feathering angles, and the rolling and pitching moments of a gyroplane rotor in terms of its basic parameters. Curves of lift-drag ratio against lift coefficient have been calculated for a typical case, showing the effect of varying the pitch angle, the solidarity, and the average blade-section drag coefficient. The analysis expresses satisfactorily the qualitative relations between the rotor characteristics and the rotor parameters. As disclosed by this investigation, the aerodynamic principles of the gyroplane are sound, and further research on this wing system is justified.

Wheatley, John B↗
NASA NTRS1934

Wind-tunnel research comparing lateral control devices, particularly at high angles of attack VI : skewed ailerons on rectangular wings

This report covers the sixth of a series of investigations in which various lateral control devices are compared with particular reference to their effectiveness at high angles of attack. The present report deals with flap-type ailerons hinged about axes having an angle with respect to the leading and trailing edges of the wing. Tests were made on four different skewed ailerons, including two different angles of skew and two sizes of ailerons. At the high angles of attack, all the skewed ailerons tested were slightly inferior with respect to rolling and yawing moments to straight ailerons having the same span and average chord. Computations indicate that the skewed ailerons are also inferior with respect to hinge moments.

Weick, Fred E↗
NASA NTRS1937

The effect of lateral controls in producing motion of an airplane as computed from wind-tunnel data

This report presents the results of an analytical study of the lateral controllability of an airplane in which both the static rolling and yawing moments supplied by the controls and the reactions due to the inherent stability of the airplane have been taken into account. The investigation was undertaken partly for the purpose of coordinating the results of a long series of wind-tunnel investigations with phenomena observed in flight tests; for this reason a hypothetical average airplane, embodying the essential characteristics of both wind-tunnel models and the full-size test airplanes, was assumed for the study.

Weick, Fred E↗
NASA NTRS1941

Wind-tunnel investigation of spoiler, deflector, and slot lateral-control devices on wings with full-span split and slotted flaps

Report presents the results of an extensive investigation made in the NACA 7 by 10-foot wind tunnel of spoiler, deflector, and slot types of lateral-control device on wings with full-span split and slotted flaps. The static rolling and yawing moments were determined for all the devices tested, and the static hinge moments and the time response were determined for a few devices of each type.

Wenzinger, Carl J↗