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At least 415 records · Page 23

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NASA NTRS1978

Three-dimensional canard-wing shape optimization in aircraft cruise and maneuver environments

This paper demonstrates a numerical technique for canard-wing shape optimization at two operating conditions. For purposes of simplicity, a mean surface wing paneling code is employed for the aerodynamic calculations. The optimization procedures are based on the method of feasible directions. The shape functions for describing the thickness, camber, and twist are based on polynomial representations. The primary design requirements imposed restrictions on the canard and wing volumes and on the lift coefficients at the operating conditions. Results indicate that significant improvements in minimum drag and lift-to-drag ratio are possible with reasonable aircraft geometries. Calculations were done for supersonic speeds with Mach numbers ranging from 1 to 6. Planforms were mainly of a delta shape with aspect ratio of 1.

De Silva, B. M. E.↗

NASA NTRS1979

Aerodynamic design and analysis of the AST-200 supersonic transport configuration concept

The design and analysis of a supersonic transport configuration was conducted using linear theory methods in conjunction with appropriate constraints. Wing optimization centered on the determination of the required twist and camber and proper integration of the wing and fuselage. Also included in the design are aerodynamic refinements to the baseline wing thickness distribution and nacelle shape. Analysis to the baseline and revised configurations indicated an improvement in lift-to-drag ratio of 0.36 at the Mach 2.7 cruise condition. Validation of the design is planned through supersonic wing tunnel tests.

Walkley, K. B.↗

NASA NTRS1979

Determination of effective aerodynamic characteristics for entry of External Tank /Space Shuttle/ debris

The effective aerodynamic characteristics for the debris resulting from the Space Shuttle External Tank (ET) are required for estimating the impact points of the debris. The paper develops a methodology that determines the effective values of the aerodynamic parameters required for performing the less complex three-degree-of-freedom (DOF) debris impact analyses. For all of the debris types, 6-DOF mass property and aerodynamic data are computed. From many 6-DOF trajectory simulations, standard deviation range values are calculated. With 3-DOF trajectory matching, these range values are used to determine the effective ballistic coefficient and the range of lift-to-drag ratios for each of the ET debris types defined.

Bonson, S. P.↗

NASA NTRS1979

Inlet design studies for a Mach 2.2 advanced supersonic cruise vehicle

Various inlet-engine combinations have been studied to find a preferred inlet concept for integration with an advanced technology Mach 2.2 cruise vehicle having a cruise lift-to-drag ratio of 9.6. For the purposes of this study, the range capability for a fixed takeoff gross weight was used to assess the various inlet-engine combinations. Inlet concept selection studies are described which indicated that an axisymmetric, mixed compression inlet was preferred. This study considered four inlet and three engine cycle combinations where the engine airflow was tailored to the inlet airflow delivery capability. Detailed design studies of two mixed compression inlet types are discussed. These were a translating centerbody inlet and a collapsing centerbody bicone inlet. The aerodynamic and mechanical design of each inlet is described. These inlets were also matched to different engine cycles tailored to the inlet airflow capability. The range increments favored the bicone inlet concept primarily because of lighter weight, reduced bleed air, and greater transonic airflow/thrust capability.

Shimabukuro, K. M.↗

NASA NTRS1979

Three-dimensional optimum maneuvers of a hypervelocity vehicle

In this paper the optimum three-dimensional maneuver in lift and bank control of a reentry vehicle is investigated. The use of the modified Chapman's variables and a normalized lift coefficient allows a general discussion of the optimum control of an arbitrary vehicle reentering any planetary atmosphere. Several planar problems are solved. Using the condition of equilibrium glide, the maximum cross range and the footprint of a reentry vehicle from circular speed are computed in terms of the maximum lift-to-drag ratio.

Vinh, N. X.↗

NASA NTRS1980

Trajectories optimization in hypersonic flight

Equations of motion were derived for the three dimensional flight of a lifting vehicles, taking into consideration all the main effects of different forces acting on a vehicle at orbital speeds. A set of equations was formulated which are valid for both the flight with lift modulation inside a planetary atmosphere and the Keplerian motion in the vacuum. The equations are independent of the physical characteristics of the vehicle. The only parameters involved are the maximum lift to drag ratio of the vehicle and a constant characterizing the atmosphere. The results obtained can be applied without modifications to any future reentry vehicle, regardless of its size, shape, and mass.

Vinh, N. X.↗

NASA NTRS1980

Aerodynamic design and analysis of the AST-204, AST-205, and AST-206 blended wing-fuse large supersonic transport configuration concepts

The aerodynamic design and analysis of three blended wing-fuselage supersonic cruise configurations providing four, five, and six abreast seating was conducted using a previously designed supersonic cruise configuration as the baseline. The five abreast configuration was optimized for wave drag at a Mach number of 2.7. The four and six abreast configurations were also optimized at Mach 2.7, but with the added constraint that the majority of their structure be common with the five abreast configuration. Analysis of the three configurations indicated an improvement of 6.0, 7.5, and 7.7 percent in cruise lift-to-drag ratio over the baseline configuration for the four, five, and six abreast configurations, respectively.

Martin, G. L.↗

NASA NTRS1980

Effects of atmospheric breakup on crater field formation

This paper investigates the physics of meteoroid breakup in the atmosphere and its implications for the observed features of strewn fields. There are several effects which cause dispersion of the meteoroid fragments: gravity, differential lift of the fragments, bow shock interaction just after breakup, centripetal separation by a rotating meteroid, and possibly a dynamical transverse separation resulting from the crushing deceleration in the atmosphere. Of these, it is shown that gravity alone can produce the common pattern in which the largest crater occurs at the downrange end of the scatter ellipse. The average lift-to-drag ratio of the tumbling fragments must be less than about 0.001, otherwise small fragments would produce small craters downrange of the main crater, and this is not generally observed. The cross-range dispersion is probably due to the combined effects of bow shock interaction, crushing deceleration, and possibly spinning of the meteoroid. A number of terrestrial strewn fields are discussed in the light of these ideas, which are formulated quantitatively for a range of meteoroid velocities, entry angles, and crushing strengths. It is found that when the crater size exceeds about 1 km, the separation between the fragments upon landing is a fraction of their own diameter, so that the crater formed by such a fragmented meteoroid is almost indistinguishable from that formed by a solid body of the same total mass and velocity.

Passey, Q. R.↗

NASA NTRS1980

Bird flight and airplane flight

Research was based on a series of mechanical, electrical, and cinematographic instruments developed to measure various features of air current behavior as well as bird and airplane flight. Investigation of rising obstruction and thermal currents led to a theory of bird flight, especially of the gliding and soaring types. It was shown how a knowledge of bird flight can be applied to glider and ultimately motorized aircraft construction. The instruments and methods used in studying stress in airplanes and in comparing the lift to drag ratios of airplanes and birds are described.

Magnan, A.↗

NASA NTRS1981

Preliminary analysis of STS-1 entry flight data

A preliminary analysis of data acquired during the first shuttle orbiter reentry is presented. Heating levels were higher than predicted. Variations in measured versus predicted lift to drag ratio and trim are discussed, as are plots showing time histories of control surface and jet activity. The confidence felt in the stability and control derivatives is only fair. Confidence in the derivatives extracted for Mach numbers below 3.5 is especially weak, because these derivatives were affected by sideslip data contaminated by wind and turbulence, nonindependent rudder motions, and buffet. The sources of the data used are described. Recommendations are presented for changes to the Aerodynamic Data Book, and for planning future flights.

Source record↗

NASA NTRS1981

Program of Research in Laminar Flow Control in the JIAFS at NASA Langley Research Center

At high Reynolds numbers, the performance of a low drag suction LFC airplane is essentially controlled by the induced drag and the turbulent friction drag of the nonlaminarized area. The question then arises as to how the airplane cruise lift to drag ratio (L/D) sub cruise) cruise increases with increasing extent of laminar flow 0 sub lam./0 sub total (0 = airplane wetted area). In particular, the question arises as to the airplane performance in the optimum case with all laminar flow over the airplane wetted area. Design approaches of all laminar flow LFC airplanes which optimize the airplane range . R = eta sub ov times (L/D) times H times lambda n(W sub 0/W sub E) are considered.

Pfenninger, W.↗

NASA NTRS1981

Numerical optimization of circulation control airfoils

A numerical procedure for optimizing circulation control airfoils, which consists of the coupling of an optimization scheme with a viscous potential flow analysis for blowing jet, is presented. The desired airfoil is defined by a combination of three baseline shapes (cambered ellipse, and cambered ellipse with drooped and spiralled trailing edges). The coefficients of these shapes are used as design variables in the optimization process. Under the constraints of lift augmentation and lift-to-drag ratios, the optimal airfoils are found to lie between those of cambered ellipse and the drooped trailing edge, towards the latter as the angle of attack increases. Results agree qualitatively with available experimental data.

Tai, T. C.↗

NASA NTRS1981

Phugoid oscillations in optimal reentry trajectories

A major problem with operations of lifting reentry vehicle having and aft center-of-gravity location due to large engine mass at the rear is the required hypersonic trim to fight the desired trajectory. This condition is most severe for lifting maneuvers. As a first step toward analyzing this problem, this paper considers the lift requirement for some basic maneuvers in the plane of a great circle. Considerations are given to optimal lift control for achieving the maximization of either the final altitude, speed or range. For the maximum-range problem, phugoid oscillation along an optimal trajectory is less severe as compared to a glide with maximum lift-to-drag ratio. An explicit formula for the number of oscillations for an entry from orbital speed is proposed.

Vinh, N. X.↗

NASA NTRS1981

Effect of sweep angles on aerodynamic performance of double arrow wing - An analytical study

Hybrid wing planforms are studied for adoption on supersonic transport and fighter aircraft. The free vortex sheet method is used to determine effects of the leading-edge sweep angles on the aerodynamic performance of a double arrow wing with a strake. Results show lift and drag increase with the increase of the inboard and outboard leading-edge sweep angles. However, the lift-to-drag ratio is little influenced by the changes in these sweep angles. Spanwise surface pressure distributions on the aft region are influenced by the inboard sweep angle while the outboard sweep angle has no effect on these pressures. Finally, the experimental data and predicted results are compared to show good agreement.

Reddy, C. S.↗

NASA NTRS1983

AOTV Low L/D Preliminary Aeroheating Design Environment

The aerothermal environment to a configuration with a brake face which exhibits a low lift to drag ratio (L/D) of below 0.75 is emphasized. The five times geosynchronous (5 x Geo) orbit entry was selected as the design trajectory. The available data base and math model is discussed. The resulting preliminary design environment is documented. Recommendations as to how the design environment may be improved through technological advances are given.

Engel, C. D.↗

NASA NTRS1981

Flight testing of the Space Shuttle

An account is given of the flight testing development phase of the Space Shuttle Orbiter. Because of its low lift-to-drag ratio, the Orbiter must make its 280-kt landing approach in the lower atmosphere with a steep descent angle of 19 deg, pulling up at 1800 feet altitude to a 1-1.5 deg descent angle, and finally gliding to a landing at 195 kt. The Orbiter has almost neutral aerodynamic static stability in pitch and yaw, requiring the use of electronic stabilization to augment the vehicle's natural stability. Attention is given to the flight test program, which comprised the first four flights of the Space Shuttle, and which substantially relied on preflight analysis to establish confidence in Shuttle flight performance. Also discussed are the solar radiation absorption and aerodynamic heating characteristics

Brand, V. D.↗

NASA NTRS1983

Chemical nonequilibrium effects on flowfields for aeroassist orbital transfer vehicles

Acceptable altitude and velocity ranges for the perigee of aeroassist orbital transfer vehicles (AOTV) have been determined for various values of ballistic coefficient and lift-to-drag ratio. The chemical nonequilibrium effect on the flowfield of a simple but representatively high-drag, blunt configuration was investigated for these perigee conditions, ranging from 73 to 90 km in altitude and 8 to 9.3 km/s in velocity. The analysis was performed using a two-dimensional viscous-shock-layer code which had previously demonstrated good success in predicting nonequilibrium heating on the Space Shuttle. The results indicate lower ratio of nonequilibrium/equilibrium heating for the present AOTV perigee conditions than for the Shuttle flight conditions, due to higher velocity. The trend for the degree of nonequilibrium with the effect of varying wall catalycity and configuration was determined over the altitude range. Some implications to future design consideration are stated.

Shinn, J. L.↗

NASA NTRS1983

Recent studies at NASA-Langley of vortical flows interacting with neighboring surfaces

The importance of leadingedge vortical flows, which occur near and interact with neighboring surfaces, is stressed. Research in this area conducted or sponsored by the NASA Langley Research Center since 1978 is surveyed. Particular attention is given to the cumulative results of a number of theoretical and experimental studies. It is noted that these studies have been carried out in order to understand and use this kind of flow. Much of the work has been devoted to improving the lift-to-drag ratio and pitch characteristics for wings in this flow, although work has also been done on examining the unsteady and lateral characteristics.

Lamar, J. E.↗