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Showing papers in "Journal of Aircraft in 1982"


Journal ArticleDOI
TL;DR: In this paper, an analytical design technique for an active fluttersuppression and gust-alleviation control system is presented based on a rational approximation of the unsteady aerodynamic loads in the entire Laplace domain, which yields matrix equations of motion with constant coefficients.
Abstract: An analytical design technique for an active flutter-suppression and gust-alleviation control system is presented. It is based on a rational approximation of the unsteady aerodynamic loads in the entire Laplace domain, which yields matrix equations of motion with constant coefficients. Some existing rational approximation schemes are reviewed, and a new technique which yields a minimal number of augmented states for a desired accuracy is presented. The state-space aeroelastic model is used to design a constant gain, partial-feedback control system, which simultaneously assures stability and optimizes any desired combination of gust response parameters throughout the entire flight envelope.

404 citations


Journal ArticleDOI
TL;DR: In this paper, a low-order panel method is presented for the calculation of subsonic aerodynamic characteristics of general configurations, based on piecewise constant doublet and source singularities.
Abstract: A low-order panel method is presented for the calculation of subsonic aerodynamic characteristics of general configurations. The method is based on piecewise constant doublet and source singularities. Two forms of the internal Dirichlet boundary condition are discussed and the source distribution is determined by the external Neumann boundary condition. Calculations are compared with higher-order solutions for a number of cases. It is demonstrated that for comparable density of control points where the boundary conditions are satisfied, the low-order method gives comparable accuracy to the higher-order solutions. It is also shown that problems associated with some earlier low-order panel methods, e.g., leakage in internal flows and junctions and also poor trailing-edge solutions, do not appear for the present method. Further, the application of the Kutta condition is extremely simple; no extra equation or trailing-edge velocity point is required. The method has very low computing costs and this has made it practical for application to nonlinear problems requiring iterative solutions and to three-dimensional unsteady problems using a time-stepping approach. In addition, the method has been extended to model separated flows in three dimensions, using free vortex sheets to enclose the separated zone.

205 citations



Journal ArticleDOI
TL;DR: In this article, the applicability of results obtained at low Reynolds number in water to higher Reynolds number vortex flow phenomena in air is addressed, where appropriate, correlation of water-tunnel vortex flow behavior is made with trends observed in subsonic windtunnel data.
Abstract: Flow visualization studies have been made at Northrop in a hydrodynamic facility of leading-edge vortex flows. Vortex core trajectory and stability characteristics have been obtained on wing planforms suitable for subsonic-transonic and supersonic cruise fighter designs. The applicability of results obtained at low Reynolds number in water to higher Reynolds number vortex flow phenomena in air is addressed. Comparisons of watertunnel vortex positions and burst locations are made with flow visualization results obtained in air. Where appropriate, correlation of water-tunnel vortex flow behavior is made with trends observed in subsonic windtunnel data.

79 citations


Journal ArticleDOI
TL;DR: In this article, a wing of 8 in. span and 2 in. chord was oscillated in a low-speed wind tunnel and the average thrusting effort of the wing was measured and plotted in coefficient form against reduced frequency, with pitching amplitude and phase angle as parameters.
Abstract: In this experimental study of flapping-wing thrust, a wing of 8 in. span and 2 in. chord was oscillated in a lowspeed wind tunnel. The driving apparatus produced nearly sinusoidal heaving with superimposed pitching of variable amplitude and phase angle. The flapping frequency range of 0-8 Hz produced reduced frequencies for which flow separation was unlikely to occur, based on the measured static characteristics of the test airfoil (NACA 0012) over the Reynolds number range of interest (25,000-40,000). The average thrusting effort of the wing was measured and plotted in coefficient form against reduced frequency, with pitching amplitude and phase angle as parameters. Comparisons of the results with theoretical predictions and previous experimental work were made. In general, the results show approximately linear dependence of thrust on reduced frequency and best performance at phase angles of 90-120 deg of pitching lagging heaving. Although thrusting effort was produced for all pitching amplitudes, including zero, the highest readings were obtained for the maximum pitching amplitude of 12.1 deg.

71 citations


Journal ArticleDOI
TL;DR: In this article, a mn-linear dynamic simulation program for tethered aerostats was developed and applied to the study of aerostat response to turbulence and other disturbances.
Abstract: A mn-linear dynamic simulation quter program for a tethered aerostat has been developed ad applied to the study of aerostat response to turbulence and other disturbances. The theoretical &el includes a dynamic tether, dynamic rmtion of the ballonet air and six degrees of freedm for the aerostat. Static and dynamic coefficients measured in a rotating-arm tow tank are employed and the equations of mtion are written for a reference other than the mss center. A traveling-wave turbulence model has also been developed. In a program verification study the flight of an instnntr=nted amstat is compared with simulated flight with input winds reconstructed fm msweplwts on the amstat.

65 citations


Journal ArticleDOI

59 citations


Journal ArticleDOI
TL;DR: In this paper, an inflow dynamics model was used to account for the influence of the unsteady aerodynamics of a hingeless rotor system on a gimballed support in hover.
Abstract: Calculations of the model frequency and damping for a hingeless rotor on a gimballed support in hover are compared with measured results for two configurations (differing in blade flap stiffness). Good correlation is obtaned when an inflow dynamics model is used to account for the influence of the unsteady aerodynamics. The effect of the unsteady aerodynamics is significant for this rotor system. The inflow dynamics model introduces additional states corresponding to perturbations of the wake-induced velocity at the rotor disk. The calculations confirm the experimental observation that the inflow mode introduced by these additional states is measurable for one configuration but not for the other.

50 citations


Journal ArticleDOI
TL;DR: In this article, a structural weight comparison between a new concept wing design, called a "Joined Wing," and a reference conventional wing-plus-horizontal tail (Boeing 727) was made.
Abstract: A structural weight comparison was made between a new concept wing design, called a "Joined Wing," and a reference conventional wing-plus-horizontal tail (Boeing 727). The joined-wing analysis includes two cases that differ only in minimum gage skin thickness. The comparison was accomplished by constructing finite-element computer models of each wing configuration, analyzing each for optimum skin thickness, then determining the structural weight of each wing. The optimizations were based on a fully stressed design concept using a Von Mises criterion for maximum allowable stress. The joined wing was found to be lighter by 12-22%.

46 citations



Journal ArticleDOI
TL;DR: In this paper, the shape of the trajectory in the vertical plane is treated, and spline fits to the drag and fuel flow functions are described, and a suboptimal trajectory is found using the maximum principle of optimal control and singular perturbation theory.
Abstract: Roughly a quarter of the total fuel savings of the new generation of large jet transports will come from the capability of computing fuel optimal flight trajectories between departure point and destination. The shape of the trajectory in the vertical plane is treated here. A simplified mathematical model is described including spline fits to the drag and fuel flow functions. A suboptimal trajectory is found using the maximum principle of optimal control and singular perturbation theory. The inner or boundary-layer solutions are identified as the climb or descent segments of the flight, while the outer solution corresponds to cruise. The inner solutions are expanded to second order in the vicinity of the outer solution to develop cruise control laws for cost-effective response to altered in-flight conditions.

Journal ArticleDOI
TL;DR: In this paper, a reduced-order energy model was used for analysis of chattering cruise, an idealization of time-shared operation between two Mach-number/altitude points, proceeding along the general lines of a study by Gilbert and Parsons.
Abstract: That steady-state cruise is not, in general, fuel-range optimal has been shown in studies by Speyer and others. The presently reported investigation makes use of a reduced-order ("energy") model for analysis of "chattering" cruise, an idealization of time-shared operation between two Mach-number/altitude points, proceeding along the general lines of a study by Gilbert and Parsons. The characteristic nonconvexity of the hodograph figure, which leads to chattering, is examined and attempts are made to relate the extent of the effect to aerodynamic and propulsion-system parameters. One such is an analytical attack on a highly simplified vehicle model featuring Mach-number and altitude independence. Another is a computational study of several aircraft modeled with the usual altitude dependence, and with and without Mach dependence. The trends noted are examined further in a look at specific-energy dependence of the hodograph figure's shape. Although substantial improvements in fuel economy appear in low-energy situations, the best improvement found in the cruise-energy range is about 5%.

Journal ArticleDOI
TL;DR: In this paper, it is shown that there is a way of using excess power for most efficient cruise, the resulting airspeed coming closest to the Gabrielli-von Karman limit line of vehicular performance.
Abstract: There is a basic mismatch between the amount of power installed in small propeller-driven aircraft and that required for efficient cruising, which results from climb performance requirements. It is shown in this paper that there is a way of using excess power for most efficient cruise, the resulting airspeed coming closest to the Gabrielli-von Karman limit line of vehicular performance. A survey of 111 light aircraft was conducted, and it is found that many are operated at this optimum, while many more are not. A figure of merit is developed that measures cruise performance. Rationale is presented that is directly applicable to design for cruise efficiency.

Journal ArticleDOI
TL;DR: In this paper, the effect of Mach number on transonic flutter speed was studied for several values of four different aeroelastic parameters, including angle of attack, angle of freedom, and CAST 7.
Abstract: Transonic flutter analyses are performed for two conventional airfoils, NACA 64A006 and NACA 64A010, and three supercritical airfoils, MBB A-3, CAST 7, and the NASA TF-8A wing section at 65.3% semispan. Two degrees of freedom, plunging and pitching about the quarter-chord axis, are considered. The aerodynamic data are obtained by using the two transonic aerodynamics codes LTRAN2 (indicial and time integration methods) and STRANS2/UTRANS2 (harmonic analysis method). The unsteady aerodynamic data are computed within the low reduced frequency range. For all airfoils, the effect of Mach number on flutter speed is studied for several values of four different aeroelastic parameters. For the MBB A-3 supercritical airfoil, the effect of angle of attack on flutter speed is studied. For the cases of a flat plate and a NACA 64A006 airfoil, time response results are obtained by LTRAN2. Applicability and limitations of the two transonic codes are evaluated. Results for the transonic flutter characteristics of these airfoils are discussed and some comparisons are made. ah b,c

Journal ArticleDOI
TL;DR: In this paper, a wind-tunnel flutter test on a supercritical wing model is described, where the authors investigate the transonic dip and compare with calculated flutter characteristics in which a quasi-threedimensional transonic theory was used.
Abstract: A wind-tunnel flutter test on a supercritical wing model is described. Objectives of the test were to investigate the transonic dip and to make comparisons with calculated flutter characteristics in which a quasi-threedimensional transonic theory was used. The beginning of a transonic dip was measured and a satisfactory agreement with theory could be found. An additional flutter instability in the bottom of the transonic dip could be correlated with the loss of transition strip effectivity at low Reynolds numbers. Nomenclature a,b = correction factors [Eqs. (2)] c =chord Clo = sectional steady lift coefficient CL - wing lift coefficient / = frequency g = damping coefficient k = reduced frequency (related to semichord) k - sectional unsteady lift coefficient, k2D, k3D m = sectional unsteady moment coefficient (related to quarterchord), m2D, m3D MO, = Mach number P0 = stagnation pressure q = generalized coordinate Rec = Reynolds number related to mean aerodynamic chord xt = position of transition strip a = wing angle of incidence A = (mean) sweep angle

Journal ArticleDOI
TL;DR: In this article, the authors developed a tire model for the prediction of vertical and drag loads in response to large discrete surface obstacles shorter than the tire footprint length, where the tire is modeled as a toroidal membrane with the objective of characterizin g the envelope properties of the tire.
Abstract: The development of a tire model for the prediction of vertical and drag loads in response to large discrete surface obstacles shorter than the tire footprint length is presented. The tire is modeled as a toroidal membrane with the objective of characterizin g the enveloping properties of the tire. An explicit set of equations is used to calculate the tire footprint in contact with a user specified surface profile, the tire volume, the pneumatic pressure, and the resultant vertical and drag loads at the wheel axle. Tire carcass and bottoming loads are also predicted. The model is designed to be computationally efficient for use with aircraft digital taxi simulations. Model predictions are compared with tire test data for low-speed fixed axle excursions over short rectangular bumps and dips. Excellent quantitative correlation is demonstrated.

Journal ArticleDOI
TL;DR: In this article, the effects of various kinds of aeroelastic parameters on flutter speeds for the bending-torsion, bendingaileron, and torsion-ailerons branches are studied.
Abstract: Flutter and time-response analyses are performed for a NACA 64A006 conventional and a MBB A-3 supercritical airfoil, both oscillating with plunge, pitch, and aileron pitch degrees-of-freedom (DOF's) in smalldisturbance transonic flow. The aerodynamic coefficients are calculated using the transonic code LTRAN2NLR. The effects of various kinds of aeroelastic parameters on flutter speeds for the bending-torsion, bendingaileron, and torsion-aileron branches are studied. The flutter speeds associated with the bending-torsion branch are plotted against Mach number for different parameter values and the transonic dip phenomenon is demonstrated. To study the flutter modes, the flutter speed, amplitude ratio, and phase difference at different Mach numbers are plotted against the mass ratio for both a 2DOF and a 3DOF case. Time-response results are obtained for the NACA 64A006 and the MBB A-3 airfoils at M=Q.85 and 0.765, respectively. Based on the same sets of parameter values, the flight speeds used to obtain all the neutrally stable responses are very close to the flutter speeds obtained in the flutter analysis. The principle of linear superposition of airloads is used in the flutter analysis, but not in the response analysis.

Journal ArticleDOI
TL;DR: In this article, an instrumentation system which records the rates of change of electric and magnetic flow density at several locations on an F-1068 aircraft and rate of changes of strike current to the boom is described.
Abstract: Recent in-flight direct-strike lightning research, using an NASA F-1068 aircraft, is reviewed. The instrumentation system which records the rates of change of electric and magnetic flow density at several locations on the aircraft and rate of change of strike current to the boom is described. The measurement parameters are: rate of change of electric flux density over a range of 50 amperes per square meter, rate of change of magnetic flux density over a range of 20,000 tesla per second, and rate of change of strike current over a range of 100 kilo-amperes per microsecond. The isolated and shielded instrumentation system employs high-sample-rate digital transient recorders with augmented memory capacity and a wideband analog recorder for data acquisition and recording. The data obtained during the 1980 flight test program are presented and the data significance is discussed.

Journal ArticleDOI
TL;DR: In this paper, the problem of determining aircraft motions along a trajectory is solved using a variational algorithm that generates unmeasured states and forcing functions, and estimates instrument bias and scale-factor errors.
Abstract: The problem of determining aircraft motions along a trajectory is solved using a variational algorithm that generates unmeasured states and forcing functions, and estimates instrument bias and scale-factor errors. The problem is formulated as a nonlinear fixed-interval smoothing problem, and is solved as a sequence or linear two-point boundary value problems, using a sweep method. The algorithm has been implemented for use in flight-test and accident analysis. Aircraft motions are assumed to be governed by a six-degree-of-freedom kinematic model; forcing functions consist of body accelerations and winds, and the measurement model includes aerodynamic and radar data. Examples of the determination of aircraft motions from typical flight-test and accident data are presented.

Journal ArticleDOI
TL;DR: In this paper, the authors describe a test program to verify the design of the composite inboard aileron for the L-1011 airplane, which is fabricated from graphite/epoxy minisandwich covers which are attached to graphite epoxy front spar and ribs, and to aluminum rear spar with fasteners.
Abstract: The sonic fatigue test program to verify the design of the composite inboard aileron for the L-1011 airplane is described. The composite aileron is fabricated from graphite/epoxy minisandwich covers which are attached to graphite/epoxy front spar and ribs, and to ma aluminum rear spar with fasteners. The program covers the development of random fatigue data by means of coupon testing and modal studies on a representative section of the composite aileron, culminating in the accelerated sonic fatigue proof test. The composite aileron sustained nonlinear panel vibration during the proof test without failure. Viscous damping coefficients as low as 0.4% were measured on the panels. The effects of moisture conditioning and elevated temperature on the random fatigue I;fe of both undamaged and impact damaged coupons were investigated. The combination of impact damage, moisture, and a 180°F temperature could reduce the random fatigue life by 50%.


Journal ArticleDOI
TL;DR: In this article, an in-flight investigation of the effect of pure time delays on low LID space-shuttle-type landing tasks was undertaken, and the results indicate that the sensitivity of the pilot ratings to changes in pure time delay in pitch is strongly affected by the task and only slightly affected by changes in control system augmentation mode.
Abstract: An in-flight investigation of the effect of pure time delays on low LID space-shuttle-type landing tasks was undertaken. The results indicate that the sensitivity of the pilot ratings to changes in pure time delay in pitch is strongly affected by the task and only slightly affected by changes in control system augmentation mode. Low LID spot landings from a lateral offset were twice as sensitive to pure time delay as normal low LID landings. For comparison purposes, formation flying was also investigated and was found to be less sensitive to time delay than the landing tasks.

Journal ArticleDOI
TL;DR: In this paper, the authors compared the stalling characteristics of a single-engine aircraft with flight test results using nonlinear simulation and linear stability and control evaluation, using aerodynamic and thrust characteristics obtained from a full-scale test in the NASA Langley Research Center 30 X 60ft Wind Tunnel as well as subscaie model test data.
Abstract: Analytical and numerical estimates of the stalling characteristics of a small, single-engine aircraft are compared with flight test results. Analyses include nonlinear simulation and linear stability-and-control evaluation, using aerodynamic and thrust characteristics obtained from a full-scale test in the NASA Langley Research Center 30 X 60-ft Wind Tunnel as well as subscaie model test data. Flight tests include prestall calibration runs, symmetric gradual stalls, and mildly accelerated stalls in the vertical plane. These tests tend to confirm predictions based upon wind-tunnel results, and they indicate areas in which special care must be taken in collecting data for aerodynamic parameter identification.

Journal ArticleDOI
TL;DR: In this paper, an improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed that provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle.
Abstract: An improved three-dimensional, nonrecursive model for atmospheric turbulence has been developed that provides for simulation of both instantaneous gusts and gust gradients along the flight path of the Space Shuttle. The one-dimensional gust and gust gradient spectral models, which form the basis for the simulation scheme, are developed from three-dimensional, von Karman spectra, integrated over finite limits based on the characteristic dimensions (length, width, and thickness) of the flight vehicle. By means of the simulation process, nondimensional time series for both gusts and gust gradients have been generated and stored on a series of magnetic tapes for four altitude bands ranging from 0 to 10,000 m. These Shuttle Simulation Turbulence Tapes (SSTT) have been validated by means of spectral and statistical analyses with very satisfactory results. The dimensionless form of the time series, coupled with the use of a von Karman spectral model (as opposed to a Dryden model), distinguish the SSTT from earlier turbulence simulation concepts.

Journal ArticleDOI
TL;DR: In this article, the effect of store aerodynamics on wing/store flutter was analyzed using multivariate analysis techniques, and the results indicated that it may not be possible to develop general guidelines for use with a particular aircraft.
Abstract: Owing to the high cost of doing flutter analysis for aircraft carrying large numbers and types of stores, it is not economically feasible to include store aerodynamics when there will be little change in the flutter results. But store aerodynamics should be included if it will change the results of the flutter analysis. This study represents the first systematic analytical study of the effect of store aerodynamics on wing/store flutter. A large number of wing/store single carriage configurations and parameters were included in the study; multivariate analysis techniques were used for the first time to analyze wing/store configurations, modal data, and flutter results. The results of the multivariate analysis indicate that it may not be possible to develop general guidelines, but it is possible to develop specific guidelines for use with a particular aircraft.

Journal ArticleDOI
TL;DR: In this article, the authors find the equivalent external forces and moments exerted on the fluid [Ref. 7, Eqs. (3.46 and 3.47) and they find that there exist an added inertia tensor, principal axes and a center of added mass.
Abstract: Reference , A., Flight Mechanics, Vol. 1: "Theory of Flight Paths," Pergamon Press, New York, 1962, Chap. 9, pp. 149-189. solid body inertia tensor ([#]), principal axes, and mass center, there exist an added inertia tensor ([>!]), principal axes, and a center of added mass. Referring to Ibrahim, we find the equivalent external forces and moments exerted on the fluid [Ref. 7, Eqs. (3.46) and (3.47)] are

Journal ArticleDOI
TL;DR: In this article, the authors illustrate by experimentation rather than analysis the potential effects of laminate design on wing divergence speed, and show good agreement between a modified Southwell prediction and a test actually run to divergence.
Abstract: The purpose of this paper is to illustrate by experimentation rather than analysis the potential effects of laminate design on wing divergence speed. Eleven flexible composite wing models have been tested for aeroelastic divergence at a number of fore and aft sweep angles. These fixed-root models incorporate sectioned aerodynamic shells mounted to interchangeable internal graphite-epoxy plates. These plates provide wing structural stiffness and simulate various off-axis composite structural configurations. Test results, obtained from subcritical testing using a modified Southwell method, clearly identify basic relationships between wing sweep, composite fiber orientation, and wing divergence speed. In addition, good agreement is shown between a Southwell prediction and a test actually run to divergence.

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional theoretical model of each aerofoil section is used to simulate the three-dimensional characteristics of a sailwing, and a theoretical method is presented for the numerical analysis of two dimensional double and single-membrane sailwing aerodynamics taking into consideration the deflection of the trailing-edge wire and the elongation of the membrane due to the aerodynamic forces.
Abstract: In a previous paper by these Authors (see last Abstract), in which a theoretical method for predicting the aerodynamic characteristics of a sailwing was presented, it was assumed that the trailing-edge position and the slackness in the wing surfaces remained fixed However, when the sailwing is loaded the elasticities of the trailing-edge wire and of the wing surfaces cause the trailing edge to move and the surfaces to elongate In the present paper, a two-dimensional theoretical model of each aerofoil section is used to simulate the three-dimensional characteristics of a sailwing, and a theoretical method is presented for the numerical analysis of two-dimensional double- and single-membrane sailwing aerofoil,s taking into consideration the deflection of the trailing-edge wire and the elongation of the membrane due to the aerodynamic forces Development of the method, and results obtained, are discussed in some detail, and several conclusions are drawn

Journal ArticleDOI
TL;DR: In this article, the authors compared the predicted counts of scheduled and unscheduled aircraft with the recorded counts for the above data for the times, 8 a.m.-6 p.m., on the hour.
Abstract: Comparison of Model Predictions with Field Data On July 13 (Friday), 1979, Cleveland center recorded the number of actively controlled aircraft as a function of time of day. (This recording also included a small number of controlled non-IFR aircraft.) Cleveland center, which controls the airspace over parts of Ohio, Michigan, New York, Pennsylvania, and West Virginia, is one of the busiest centers. The sum of the models' predicted counts of scheduled and unscheduled aircraft was compared with the recorded counts for the above data for the times, 8 a.m.-6 p.m., on the hour. At the time the comparisons were made, unscheduled aircounts could be predicted for any day in April 1978. Therefore seasonal adjustment factors for GA activity based on historical data were applied to these counts, so that they would be representative of counts on a typical Friday in July 1979. Figure 1 shows predicted IFR counts and actual counts over Cleveland center. (Data points are connected by lines as a visual aid.) Similar comparisons were made for Houston, Kansas City, and New York centers (one day for each center in the summer of 1979, although the day of the week was different in each case). All comparisons between predicted and measured aircounts show good agreement in terms of small numerical differences in the amplitudes and also similar harmonic content. The largest difference occurs at the peaks and is about 10%. This agreement is sufficient for system planning purposes. It is planned to extend these comparisons to other centers for additional days and seasons of the year, and to quantify the (statistical) differences between measured and predicted counts.

Journal ArticleDOI
TL;DR: In this article, an analysis for predicting parachute inflation is presented for the complete system, including the canopy, payload, and suspension line masses, with first-order effects only for inviscid, incompressible flow.
Abstract: An analysis is presented for predicting parachute inflation. Equations of motion for the complete system are developed from first principles, and are solved with no experimental inputs. Ballistic equations of motion are derived for the canopy, payload, and suspension line masses. However, the enclosed fluid mass is not lumped with the canopy as an apparent mass term. Instead, the fluid conservation equations for a deforming, accelerating control volume are solved to determine the behavior of the captured fluid and its interaction with the canopy. Only first-order effects are included, and the analysis is limited to inviscid, incompressible flow. Results for both porous and nonporous canopies are compared with experimental data.