SEARCH · Search NASA

Results for “L/D”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11

All sources NASA NTRS DOE OSTI

NASA NTRS1980

Selected advanced aerodynamics and active controls technology concepts development on a derivative B-747

The feasibility of applying wing tip extensions, winglets, and active control wing load alleviation to the Boeing 747 is investigated. Winglet aerodynamic design methods and high speed wind tunnel test results of winglets and of symmetrically deflected ailerons are presented. Structural resizing analyses to determine weight and aeroelastic twist increments for all the concepts and flutter model test results for the wing with winglets are included. Control law development, system mechanization/reliability studies, and aileron balance tab trade studies for active wing load alleviation systems are discussed. Results are presented in the form of incremental effects on L/D, structural weight, block fuel savings, stability and control, airplane price, and airline operating economics.

Source record↗

NASA NTRS1981

Acoustic performance of inlet suppressors on an engine generating a single mode

As part of a program to evaluate an inlet suppressor design method based on mode cutoff ratio, three single degree of freedom liners with different open area ratio face sheets were designed for a single spinning mode. This mode was generated by placing 41 rods in front of the 28 blade fan of a JT15D turbofan engine. At the liner design this near cutoff mode has a theoretical maximum attenuation of nearly 200 dB per L/D. The data show even higher attenuations at the design condition than predicted by the theory for dissipation of a single mode within the liner. This additional attenuation is large for high open area ratios and should be accounted for in the theory. The data shows the additional attenuation to be inversely proportional to acoustic resistance. It was thought that the additional attenuation could be caused by reflection and modal scattering at the hard to soft wall interface. A reflection model was developed, and then modified to fit the data. This model was checked against independent (multiple pure tone) data with good agreement.

Heidelberg, L. J.↗

NASA NTRS1982

Space Shuttle entry longitudinal aerodynamic comparisons of flight 2 with preflight predictions

An overview of the aerodynamic performance, longitudinal trim, and control surface effectiveness as developed from the second Shuttle flight is presented, along with comparisons with preflight predictions. The Orbiter enters the atmosphere at Mach 29 and descends through all the Mach speeds until touchdown. Control mechanisms for the Orbiter are outlined, noting the lessening of angle of attack as the terminal configuration is reached. Methods of developing the wind tunnel predictions are reviewed, including performance in different altitudes and speed regimes, and the impetus to decouple the flight control system from aerodynamics with respect to uncertainties. Preflight predictions agreed well with the lift/drag ratio above Mach 1, but higher L/D was exhibited than predicted below Mach 1. A deficiency in the wind tunnel environment was concluded for the inaccuracies in the predictions for hypersonic trim characteristics.

Romere, P. O.↗

NASA NTRS1982

Wind estimation using air data probe measurements to evaluate meteorological measurements made during Space Shuttle entries

Deterministic and weighted least squares methods for obtaining estimates of the horizontal winds encountered during the Shuttle entry phase are described. The estimates are based on in situ Air Data System (ADS) measurements of angle-of-attack, side-slip angle and true airspeed, in conjunction with inertial trajectory parameters obtained from the post flight trajectory reconstruction. Accuracies in the wind estimates obtained from each method are assessed using both theoretical arguments and flight results. Comparisons of derived winds with meteorological measurements taken during the first three Shuttle entries have demonstrated: (1) the usefulness of the wind estimators for evaluating meteorological measurements below 50 kft, and (2) the potential for adequate wind determinations in the absence of independent wind measurements. Comparisons of STS-3 flight-derived L/D versus predicted values from the LaRC aerodynamic data base are presented from 50 kft to touchdown. These results exemplify the importance of such determinations to enhance the ongoing Shuttle aerodynamic and aerothermodynamic research.

Kelly, G. M.↗

NASA NTRS1982

A review of aeroassisted orbit transfer

The development of a theory of aeroassisted orbital plane change maneuvers and necessary equipment is traced and an assessment is made of potential applications. Synergetic plane changes are effected through a combination of aerodynamic and propulsive forces involving the dip of an orbiting vehicle into the atmosphere, performance of an aerodynamic turn using thrust if necessary, then reboosting into a reconfigured orbit. The Orbiter is noted to possess large synergetic plane change capability, and configurations of spacecraft such as the Venus Orbiting Imaging radar for using aeroassist to brake interplanetary velocities before establishing orbits are described. Technology advances necessary to construct effective aerobrake, aerocapture, and orbital transfer vehicles are explored, including fabrication of inflatable ballutes, lighter L/D configurations, and lifting brakes, which are considered to be minor extensions of current capabilities.

Walberg, G. D.↗

NASA NTRS1983

Five-hole pitot probe time-mean velocity measurements in confined swirling flows

Nonswirling and swirling nonreacting flows in an axisymmetric test section with an expansion ratio D/d = 2, which may be equipped with contraction nozzles of area ratios 2 and 4, are investigated. The effects of a number of geometric parameters on the flow-field are investigated, among them side-wall expansion angles of 90 and 45 deg, swirl vane angles of 0, 38, 45, 60, and 70 deg, and contraction nozzle locations L/D = 1 and 2 (if present). Data are acquired by means of a five-hole pitot probe enabling three time-mean velocity components in the axial, radial, and azimuthal directions to be measured. The velocities are extensively plotted and artistic impressions of recirculation zones are set forth. The presence of a swirler is found to shorten the corner recirculation zone and to generate a central recirculation zone followed by a precessing vortex core. A gradual inlet expansion has the effect of encouraging the flow to remain close to the sidewall and shortening the extent of the corner recirculation zone in all cases investigated.

Yoon, H. K.↗

NASA NTRS1983

Flow fields and aerodynamic characteristics for hypersonic missiles with mid-fuselage inlets

A study was made to quantify forebody flow fields and to evaluate aerodynamic performance trends on a matrix of fuselage shapes for the mid-inlet/bolt-on-engine class of hypersonic airbreathing missiles for the Navy's vertical box launcher. The study indicated that inlet mass flow and pressure recovery can be increased by cambering the nose and increasing the width of the fuselage at both Mach 4 acceleration and Mach 6 cruise conditions. Aerodynamic trim predictions show that the drag at zero lift at Mach 4 decreases while the L/D max at Mach 6 increases with the nose camber, although these tendencies reverse with increasing width of maximum fuselage cross section.

Hunt, J. L.↗

NASA NTRS1983

Effect of buoyancy and power design parameters on hybrid airship performance

The effects of several design parameters on the performance of hybrid airships having rotors and propellers were examined with a simple mathematical model. The parameters included buoyancy ratio, Froude number, ratio of rotor power to total power, and rotor shaft tilt. Performance variations resulting from changes in these parameters were calculated, and are presented and discussed. Performance quantities included best climb rate, equivalent vehicle L/D, and maximum speed. Performance at all speeds between hover and maximum speed was found to be sensitive to power distribution between rotors and propellers, and to rotor shaft tilt.

Talbot, P. D.↗

NASA NTRS1983

Subsonic Longitudinal Performance Coefficient Extraction from Shuttle Flight Data: an Accuracy Assessment for Determination of Data Base Updates

Longitudinal performance comparisons between flight derived and predicted values are presented for the first five NASA Space Shuttle Columbia flights. Though subsonic comparisons are emphasized, comparisons during the transonic and low supersonic regions of flight are included. Computed air data information based on the remotely sensed atmospheric measurements as well as in situ Orbiter Air Data System (ADS) measurements were incorporated. Each air data source provides for comparisons versus the predicted values from the LaRC data base. Principally, L/D, C sub L, and C sub D, comparisons are presented, though some pitching moment results are included. Similarities in flight conditions and spacecraft configuration during the first five flights are discussed. Contributions from the various elements of the data base are presented and the overall differences observed between the flight and predicted values are discussed in terms of expected variations. A discussion on potential data base updates is presented based on the results from the five flights to date.

Findlay, J. T.↗

NASA NTRS1984

Mach 6 flow-field and boundary-layer surveys beneath the forebody of an airbreathing missile

A wind tunnel investigation has been conducted to determine the flow characteristics of the shock layer beneath the forebody of a hypersonic, airbreathing missile incorporating an aft-mounted inlet. In the inviscid part of the flow field, the measured parameters were in agreement with those predicted by a three-dimensional Method of Characteristics theory. At test conditions matching full scale Mach and Reynolds numbers at an altitude for maximum L/D cruise, boundary layer transition occurred downstream of the inlet face. While this means that a full size vehicle would have a more easily separated boundary layer, it is noted that the Reynolds number discrepancy between wind tunnel and actual flight conditions may result in a movement of the transition point to somewhere upstream of the inlet.

Johnston, P. J.↗

NASA NTRS1984

Experimental heating distributions for biconics at incidence in Mach 10 air and comparison to prediction

Heating distributions were measured on a 1.9 percent scale model of a generic, aeroassisted vehicle proposed for missions to a number of planets and also a candidate as a moderate L/D earth orbital transfer vehicle. This vehicle is a spherically blunted, 13 deg/7 deg biconic with the fore-cone bent upward 7 deg to provide self-trim capability; also tested was a straight biconic with the same noise radius and half angles. These measurements were made in the Langley 31-Inch Mach 10 Tunnel at values of the free-stream Reynolds number, based on model length, equal to 0.2 and 0.9 million. The angle of attack, referenced to the aft cone, was varied from 0 to 20 deg. Heating distributions predicted with a parabolized Navier Stokes (PNS) code are compared to measurement over the present range of Reynolds number and angle of attack. Windward heating was predicted to within 10 percent by the PNS code. Leeward heating distributions were predicted qualitatively for both values of Reynolds number, but quantitative agreement was poorer than on the windward side.

Miller, C. G.↗

NASA NTRS1984

Design parameters for flow energizers

One of the most significant uses of flow energizers, which are small highly swept strakes mounted immediately above a lifting surface, is in flow control over regions where a lifting surface is joined to another body, such as a fuselage or nacelle. In the presently reported systematic wind tunnel test study of flow energizers, 14 different geometric configurations using a 75-deg sweep flow energizer were tested on a light twin-engine general aviation aircraft model. It is found that cambered flow energizers perform better than their flat counterparts. All but two of the energizer installations developed lower L/D at cruise angles of attack, lower maximum lift coefficients, and lower stall angles of attack than the baseline model.

Ward, D. T.↗

NASA NTRS1985

Study of winglets applied to biplanes

This paper examines, both theoretically and experimentally, the possibility of improving the aerodynamic characteristics of a biplane configuration by adding winglets. Theoretical calculations show good agreement with experiment in predicting inviscid drag due to lift. Theoretical and experimental results indicate that the addition of winglets to an optimized biplane configuration can increase the ideal efficiency factor by up to 13 percent, as well as increasing the lift-curve slope and maximum lift coefficient. A theoretical analysis comparing the biplane with an optimized winglet to an equivalent monoplane indicates that the biplane has the potential for a 6.4-percent increase in L/D(max), and 13-percent increase in C(L) to the 3/2-power/C(D), the classical endurance parameter.

Gall, P. D.↗

NASA NTRS1985

Determination of rarefied-flow aerodynamics of the Shuttle orbiter from flight measurements on STS-6 and STS-7

This report presents the flight data results from the High Resolution Accelerometer Package (HiRAP) experimment on the sixth and seventh Shuttle missions (i.e. STS-6 and STS-7). The data have been reduced to produce aerodynamic force coefficients, principally L/D in the rarefied flow regime. Also, a technique is used to extract approximate body-axis aerodynamic coefficients from the flight data. Comparisons of the rarefied transition flow aerodynamic behavior between the two sets of flight data indicate differences, primarily in the free-molecule flow coefficients; i.e. STS-7 shows a free-molecule flow behavior which correlates with diffuse surface reflection conditions, while STS-6 does not. The data have also been used to estimate the density profiles in the atmosphere. The atmospheric density is generated from 60 to 160 km from each flight. The density profiles produced have a primary wave structure and differences are observed between the two sets of flight data. A new rarefied transitional flow aerodynamic bridging formula has been generated from the flight data. Comparisons with the flight bridging formula and existing Monte Carlo and wind-tunnel data are made.

Blanchard, R. C.↗

NASA NTRS1985

A simplified guidance algorithm for lifting aeroassist orbital transfer vehicles

The derivation, logic, and performance of a simplified atmospheric guidance algorithm for aeroassist orbital-transfer vehicles (AOTVs) are presented. The algorithm was developed to meet the demands for an aerobraking trajectory guidance technique that was uncomplicated, easily integrated into existing trajectory programs, adaptable to a range of vehicle aerodynamic configurations, capable of performance equivalent to currently available guidance programs in compensating for dispersions in entry conditions, atmospheric conditions, and aerodynamic characteristics. The result was a hybrid lifting guidance algorithm combining the method of reference-profile generation with the method of predictor/corrector schemes. The resulting performance is good (less than 3 n.m. error from desired apogee despite uncertainties of + or - 50 percent atmospheric density, + or - 0.2 deg entry flight-path angle, or + or - 50 percent L/D. Combinations of these same dispersions with lesser magnitudes have also been successful, although performance with density 'pockets' within the atmosphere requires more analysis.

Cerimele, C. J.↗

NASA NTRS1986

Towards an advanced vortex flap system: The cavity flap

An extension of the vortex flap concept was explored with the aim of providing high-alpha flight control capability coupled with maneuver drag reduction for highly swept wing configurations. A retractable lower surface flap mounted on a translating hinge is proposed, allowing chordwise extension as well as deflection, the two movements being independently controlled. The frontal cavity formed by the partially extended and deflected flap captures a vortex above a certain angle of attack. The cavity vortex downwash alleviates the effective incidence of the wing leading edge, thus modulating vortex lift; at the same time, the induced suction in the cavity generates thrust. These postulated aerodynamic features of the cavity flap were validated through low speed tunnel pressure and visualization tests on a 65 deg swept oblique wing model, which also provided initial trends of the leading edge vortex alleviation and cavity suction with respect to flap extension, deflection and angle of attack. Force tests on a 60 deg delta model further showed the cavity flap L/D performance to compare favorably with the conventional vortex flap. A two segment flap arrangement with independently control led segments was envisaged for exploiting the vortex modulation capability of the cavity flap for pitch, roll and yaw control, in addition to drag reduction at high angles of attack.

Rao, D. M.↗

NASA NTRS1985

AOTV bluff body flow - Relaxation algorithm

Preliminary investigations have led to the consideration of two classes of energy efficient aeroassisted orbital transfer vehicle (AOTV) concepts, with high and low L/D. The AOTV represent reentry space vehicles which are to fly hypersonically in the continuum upper reaches of the atmosphere. Problems arise in connection with convective and nonequilibrium radiative heating. As the possibilities for obtaining needed information by experimentation are limited, reliance must be placed on computational techniques to simulate testing of design concepts. A new relaxation algorithm for the compressible Navier-Stokes equations has been developed in the context of recent work with a conservative flux difference eigenvector split implicit upwind scheme CSCM (conservative supracharacteristics method). Attention is given to the CSCM implicit method, and early results for axisymmetric bluff body flow including complete forebody and base flow for a free flight range model drag brake AOTV.

Lombard, C. K.↗

NASA NTRS1986

A study of aircraft cruise

The long range aircraft cruise problem is analyzed using a model intermediate in complexity between energy model and point mass model. It is shown that this formulation imbeds the classical steady state cruise as the central member along with several other oscillatory extremals. The oscillatory cruise trajectories are shown to exist if the Hessian of the function QD/VT with respect to altitude and airspeed is positive definite. An expression for predicting the frequency of oscillation is developed. Qualitative effects of increasing the vehicle thrust and improving the L/D are discussed. Numerical results for two fighter aircraft and a transport aircraft are given. While oscillatory cruise mode exists for the two fighter aircraft, steady state cruise at full throttle is found to be optimal for the transport aircraft. A second variation analysis to bring out the reason for fuel savings is developed. It is shown that whenever the Hessian of the function QD/VT is positive definite, the second variation will be zero along the classical steady state cruise arc, indicating that a neighboring extremal is competitive. Comparisons with the previous point mass and energy modeled results are given.

Menon, P. K. A.↗