Ight Test Research Articles

A NEW UNMANNED AERIAL VEHICLE SYNTHETIC APERTURE RADAR FOR ENVIRONMENTAL MONITORING

A new Unmanned Aerial Vehicle (UAV) Synthetic Aperture Radar (SAR) has been developed at Multimedia University, in collaboration with Agency of Remote Sensing Malaysia. The SAR operates at C-band, single V V -polarization, with 5m £ 5m spatial resolution. Its unique features include compact in size, light weight, low power and capable of performing real-time imaging. A series of fleld measurements and ∞ight tests has been conducted and good quality SAR images have been obtained. The system will be used for monitoring and management of earth resources such as paddy flelds, oil palm plantation and soil surface. This paper reports the system design and development, as well as some preliminary results of the UAVSAR.

Aircraft Parameter Estimation Experiment Design Considering Measurement Colored Residuals

This work deals with the optimization of ∞ight test maneuvers for aerodynamic parameter estimation considering that the measurements are contaminated with colored residuals. The colored residuals consideration is important to give the direct and realistic assessment of the parameter estimation uncertainty levels prior to ∞ight tests. The optimization technique is based on the concept of ∞ight test data information content and Cramer-Rao lower bound. The discrete autocorrelation matrix of the measurement noise is used in order to compose the optimization criteria considering colored residuals. Some results of a ∞ight test campaign of the CEA-205 CB.9 Curumim aircraft are discussed. The advantages of the proposed maneuvers optimization technique are presented, stressing the easiness of implementation of the signals and the strong improvement in the estimation procedures made possible with the application of the optimized maneuver signals.

Liquid Fuels and Propellants for Aerospace Propulsion: 1903-2003

Introduction M AJOR increases in liquid-fueled propulsion performance have occurred in the past 100 years.TheWright brothersŽ rst  ew on 14 December 1903 with an engine that generated slightly more than 130 lb of thrust for  ights that ranged from 120 to 850 ft (Ref. 1). Contrast that with current aircraft such as the Boeing 777, which can  y 8000 n miles, equipped with engines from the GE90 and PW4000 series that generate over 100,000 lb of thrust. The Wright brothers probably consumed less than a gallon of gasoline in that Ž rst day of  ight tests. In 1997, airlines consumedan average of 177 million gal/day of jet fuel worldwide.2¤ Robert Goddard’s Ž rst  ight of a liquid rocket on 16March 1926 reachedan altitudeof 41 ft and landed184 ft from the launchpoint (seeRef. 3). Again, the contrast with current vehicles such as the space shuttle, which can lift over 50,000 lb to 200C miles into low Earth orbit, is dramatic. The intent of this paper is to describe the evolution of liquid fuels for aircraft and rockets as the engines and vehicles they fuel have undergone these signiŽ cant increases in performance.

Flight-Test Evaluation of Flutter Prediction Methods

Several methods have been formulated to predict the onset of e utter during e ight testing. These methods have been demonstrated using data from simulations; however, a rigorous evaluation that includes data from e ight testing must be performed. The ability of several methods to predict the onset of e utter by analyzing data from e ight tests of the aerostructures test wing is evaluated. The evaluated methods include data-based approaches that use damping extrapolation, an envelope function, the Zimmerman‐ Weissenburger e utter margin, and a discretetime autoregressive moving-average model. Also, a model-based approach that uses the π-method e utterometer is evaluated. The data-based methods are demonstrated to be unable to predict e utter accurately using data from low-speed test points, but converge to the accurate solution as airspeed is increased. Conversely, the e utterometer isdemonstrated tobeimmediatelyconservativeusing data from low-speed testpoints,butthesepredictionsremain conservative and do not converge to the true e utter speed as the envelope is expanded. The operation of a e ight test should note theproperties of each method to perhaps adjust test points based on the predicted e utter margins.

Effect of Midwing Vortex Generators on V-22 Aircraft Forward-Flight Aerodynamics

The effect of midwing vortex generatorson the V-22 aircraft forward-e ight (airplanemode )aerodynamics using computational e uid dynamics is investigated. The multizone Navier -Stokes method is applied to calculate the e ow over a V-22 wing -fuselage-nacelle cone guration in forward e ight with and without vortex generators. The calculations show that thevortex generatorsreduceseparation and producea favorableeffecton both lift and drag if they are properly designed and placed in the right position. The chordwise location and the incidence angle of the vortex generators are two important design variables in achieving the desired separation alleviation. development. 1i3 Acomprehensive reviewon the V-22 Osprey aero- dynamic development during the past 15 years is given by McVeigh et al. 4 The use of computational e uid dynamics (CFD) has been explored by the present author to analyze the complex aerodynam- ics of the V-22 aircraft. The overall e owe eld about the aircraft in hover 5 andforward-e ightmode 6i8 hasbeensimulatedand analyzed using a multizone, thin-layer Navier- Stokes solution. These anal- yses considered the clean aircraft cone guration, as well as the cone guration with external components. The V-22 employs vortex generators, strakes, and fences to en- hance aerodynamic performance. As a predesign tool, it would be desirable to use the CFD method to evaluate the effect of these de- vicesbefore thee nal evaluation on wind-tunnel or e ight tests. In the presentwork,theeffectofthemidwingfairing(alsocalledoverwing fairing) vortex generators (VGs) on the V-22 forward-e ight aerody- namicsisevaluated.TheuseofVGsisnotstraightforward,however. The effectiveness of VGs depends on how the trailing vortices are generated and used to energize the e ow inside the boundary layer. Theusermighthavetoperformalarge numberoftrial-and-errorex- periments to determine the optimum shape, incidence with respect to the oncoming e ow, and the location of the VGs before e nalizing the design applications. The use of the CFD techniques offers an excellent alternative to the required trial-and-error experiments. The present work is performed in the framework of the steady- state Navier- Stokes solution in a structured grid. A new gridding topology for embedding the VGs in an existing CFD model has been developed. The incorporation of the VGs is performed seam- lessly to allow the effect of VGs to be adequately evaluated. The VGs are not embedded using the chimera-type scheme 9 becauseof inaccuracies due to gridoverlapping and interpolations. The present work addresses the VGs installed on the midwing fairing only, and not the wing-mounted VGs nor the forebody strakes found on the engineering, manufacturing, development (EMD) cone guration of the V-22 aircraft.

Recent Improvements to a Hybrid Method for Rotors in Forward Flight

Ahybrid Navier ‐Stokes/full potential solver has been developed for the efe cient prediction of three-dimensional unsteady viscous e ow phenomena that occur over helicopter rotors in forward e ight. The method combines a Navier‐Stokes analysis near the blade, modeling the viscous e ow and near wake with a potential e ow analysis in the far e eld, modeling inviscid isentropic e ow. A grid motion module has been developed to account for the blade motion and elastic deformations. Free and prescribed wake models have been developed to account for the tip vortex effects once the vortex leaves the viscous e ow region and enters the potential e ow region. Sample results are presented for a two-bladed AH-1G rotor in descent and for a UH-60A rotor in high-speed forward e ight. Comparisons with experiments, e ight test data, and other numerical simulations are given.

Navier-Stokes Analysis of Helicopter Rotor Aerodynamics in Hover and Forward Flight

Reynolds-averaged compressible Navier ‐Stokes computations are presented for the hovering 7A model rotor and a low aspect ratio NACA0012 rotor in nonlifting forward e ight. For enhanced hover performance prediction, aeroelastic effects are taken into account by tightly coupling the e ow solver with a e nite element model of the blade based on Timoshenko beam theory. Good agreement between computed and measured rotor performance is achieved for three collective pitch settings on structured periodic grids featuring noncongruent cell faces along the periodicity planes. Results of a hybrid Navier ‐Stokes/Euler chimera hover computation are presented, in addition to the periodic grid analysis demonstrating the superiority of the overset grid approach with respect to tip vortex conservation. The unsteady Navier ‐Stokes computations for the nonlifting forward e ight test case show more sensitivity relative to time step size than comparable Euler analyses. Overall correlation of computed and experimental near-tip pressure distributions over blade azimuth is considered to be fair, and the strong transonic effects on the advancing blade are adequately captured by the numerical analysis.

Real-Time Identification of Flutter Boundaries Using the Discrete Wavelet Transform

Real-time analysis of an airframe’s eutter boundaries during eight testing can help ensure safety and reduce costs. One method of identiecation is to performcorrelation elteringusing a set of singlet functions. The method is abletoidentifyaccuratelythefrequencyand dampingcoefe cientof thesystemtoexcitation, but the computational time required can be too signiecant to implement in real-time. An alternative method is presented for correlation e ltering that employs amultiple-level discretewavelet transform. The wavelet transform decomposes theresponse signal into a set of subsignals that correspond to different frequency bands. The same operation is applied to each entry in a dictionary of singlet functions. The transform results in a considerable reduction in the data and, thus, to a reduction in the computational time needed to calculate the correlation. We demonstrate that our approach is able to identify accurately frequency and damping characteristics of the impulse response of both a synthetically generated test signal and actual eight-test data. As a result, real-time identie cation of eutter boundaries during e ight testing may be possible with relatively low-cost computational resources.

Streamlining Flight Test with the Design and Analysis of Experiments

Traditionale ight-testmethodologytypicallyresultsinlargetestmatricesusingtheapproachofchangingsettings of one input variable at a time, keeping all others at some nominal level. Although this method is functional, another method exists that can dramatically reducetheamount of testing required, increasethe quality of the data analysis, and provide additional insight into system performance. We propose using the principles of statistically designed experiments; and we provide a process for planning e ight test using these principles. The proposed process complements traditional testing methods and places a greater emphasis on structuring test design to increase the precision and interpretability of the data using statistical analysis. Another enhancement to the test processis recommendingsmalland sequentialtesting sothatinformation learned from earliertestsisincorporated in subsequent phases and unnecessary tests can be avoided. The proposed methodology has three phases: building the strategic e ight-test plan, developing detailed test objectives, and planning e ight testing and analysis. This paper discusses the activities conducted in each phase and illustrates the main points with an example from a recent experience with the CV-22 operational test and evaluation. Although our proposal is directed to e ight test, it can be easily implemented in most test environments.

Fast-Response Cylindrical Air Bearing Balance

The air bearing balance described has been designed to support the dynamic force measurement requirements of virtual e ight testing. This balance is a single-degree-of-freedom air bearing spindle. The bearing gas e lm is instrumented with fast-response pressure sensors that enable the determination of forces and moments. The device thus permits the measurement of unsteady aerodynamic loads on spinning test articles. The balance also incorporates a supply of high-pressure air, delivered to the model without friction, for pneumatic actuators or reaction control jets. Spin at up to 20,000 rpm is made possible with a brushless motor. The focus is on calibration properties of the balance, particularly the ine uence of rotation angle and spin rate on the calibration parameters. Combined linearity and repeatability errors less than 0.5% full scale are achieved at a e xed angle. Spin rate and angle deviations introduce calibration variations as large as 20%, but angle and speed curve e tting are shown to reduce this error to less than 1.5%.

Experimentation, Test, and Evaluation Requirements for Future Airbreathing Hypersonic Systems

Experiences gained in recent airbreathing hypersonic vehicle development programs have ascertained that mastering hypersonic e ight will depend directly on continued ability to experiment, test, and evaluate. Indeed, many of the hypersonic e ight systems being studied will require testing and modeling capabilities that do not currently exist or that may soon be lost if current infrastructures are not maintained. The testing and evaluation of hypersonic systems represents a unique set of challenges. Duplication of the hypersonic e ight environment requires extreme temperatures and pressures coupled with complex physical interactions. Ground-test facilities are limited in their ability to duplicate all salient parameters simultaneously. Data from e ight experimentation are also limited due to range airspace requirements for long distance e ight corridors. These limitations manifest themselvesin rangesafety, data acquisition, and environmental concerns.Computational techniquesarea growing supplement to experiment, but are not a replacement. Despite the improvement in both hardware and algorithms, analytical models and computational techniques are extremely time consuming, fall short of adequate e delity, and requiredata to anchor andvalidatethem.Theconclusion isthat only through a uniquecombination of experiment, e ight testing, analysis, and computation, will hypersonic system risks be reduced and the vision of airbreathing hypersonic e ight be realized.

Russian Research on Experimental Hydrogen-Fueled Dual-Mode Scramjet: Conception and Preflight Tests

Theexperienceofmodeldual-modescramjet (DMSCRAM)creationandthemainresultsofgroundandpree ight tests are analyzed in this paper beginning from the conception choice, goals, and working program implemented for about 15 years, preceding to the e rst e ight test of hypersonic e ight laboratory. Design schemes for plane and axisymmetrical engine concept are examined. The description of experimental test facilities, test instrumentation, and methods of readings treatment used in ground-test procedure of DMSCRAM are given. The test results of ground model engine at Mach-number range M =3.5‐6.5 and ground test-results for e ight type engine at M = 5 were cited and cone rmed the durability and readiness of developed DMSCRAM for e ight tests.

Cavity Flame-Holders for Ignition and Flame Stabilization in Scramjets: An Overview

This paper describes ongoing research efforts in the scramjet community on cavity e ame holders, a concept for e ame holding and stabilization in supersonic combustors. During the last few years, cavities have gained the attention of the scramjet community as a promising e ame-holding device, owing to results obtained in e ight tests and to feasibility demonstrations in laboratory-scale supersonic combustors. However, comprehensive studies are needed to determine the optimal cone guration that will yield the most effective e ame-holding capability with minimum losses. The e owe eld characteristics of cavities and research efforts related to cavities employed in lowand high-speed e ows are summarized. Open questions impacting the effectiveness of the cavities as e ame holders in supersonic combustors are discussed.

Sidejet aerodynamic interaction effects of the missile

The side thruster is a highly responsive means for attitude control of missiles. The sidejet force is ine uenced by the interaction of the sidejet with the external aire ow. The sidejet aerodynamic interaction effects were analyzed from following two viewpoints: 1 ) the pressure e eld in the vicinity of the sidejet and 2 ) the force acting on the missile. Technical data of sidejet aerodynamic interaction effects were obtained by means of e ight tests of missiles that were equipped with four impulse side thrusters that were small-size, rapidly burning solid-propellant rocket motors. The data agree with computational e uid dynamics analyses and wind-tunnel tests.

Flutterometer: An On-Line Tool to Predict Robust Flutter Margins

Robust eutter margins can be computed for an aeroelastic model with respect to an associated uncertainty descriptionthatdescribes modelingerrors. Anon-lineimplementationtocomputetheserobustmarginsisconsidered. The on-line approach generates uncertainty descriptions at test points and can account for time-varying errors in themodel.A eutterometer isintroduced as an on-linetool toindicateameasure ofdistancetoe utterduringaeight e utter test. Suchatool is formulated based on robust euttermargin analysis. A e ight test of an F/A-18 is simulated todemonstrate theperformance ofthee utterometer.Thistool isclearly more informativethantraditional tracking of dampingtrends and provides accurate information about the true eutter margin throughout the e ight test. The simulation demonstrates characteristics of the eutterometer that could improve eight test efe ciency by increasing safety and reducing eight time for envelope expansion.

Ultrasonic Method Applied to Full-Scale Solid Rocket Motors

The solid rocket design engineer requires a multitude of data during the static and e ight test phases of a developmentprogram. Forinstance,a betterknowledgeofthebehavioroftheinternal thermalinsulator, especially in the e ap zones, is useful for determining the margins of safety. This, in addition to the heavy work on the modelizationoftheinsulationdegradation,iswhyameasurementtoolfordeterminingthebehavioroftheinsulators hasbeendeveloped.Thistechniqueisdirect,nonintrusive,andbasedonthepropagationofultrasonicwavesthrough the materials: case, insulator, solid propellant, etc. By following the evolution of the echoes coming back from the regression surface or the degraded zone of the insulator in real time, many times per second during the test, one can deduce thefollowing data: thesequenceofeventsatthemeasurement location, the starting timeof degradation and ablation of the insulator, and, coupled with thermoablative computing code, the pyrolysis rate and the heat e ux evolutionreceivedon theinsulatorsurface.Forsolid propellant,thedisplacementofitscombustionfrontalong the insulator is followed, and of course its burning rate is deduced.

Flight-Test Techniques Employed to Successfully Verify F/A-18E In-Flight Lift and Drag

F/A-18E e ight results successfully cone rmed pree ight aerodynamic and performance predictions. Because this was achieved very early in the e ight-test program, the need to rely heavily on e ight data to characterize aircraft performance capabilities was signie cantly reduced. The original aircraft performance e ight evaluation plan was reduced by 60 e ights with obvious cost benee ts. This was a direct result of early e ight test planning by a working group composed of representatives carefully selected from the involved organizations. Flight-test techniques were developed to determine high-quality, in-e ight lift and drag data and to directly demonstrate aircraft performance capability. These techniques are disscussed and a successful correlation of pree ight predictions and early e ight results is presented.

Effect of External Components on V-22 Aircraft Forward-Flight Aerodynamics

The effects of protuberances, forward-looking infrared, AAR47 sensor fairing, and refueling boom on V-22 forward e ight aerodynamics using computational e uid dynamics are investigated. The multizone Navier ‐Stokes method isapplied to thee ow over a complete V-22 wing ‐fuselage‐nacellecone guration, with and without external components. The angle of attack varies from 0 to 16 deg in forward e ight. A slight increase in drag is found at 0-deg angle of attack for an aircraft cone gured with the external units; this effect decreases as the angle of attack increases from zero to moderate values. However, at high angles of attack, the added e ow disturbances due to attachments seems to worsen tail buffeting and lift-to-drag ratio. The numerical results are in general agreement with recent e ight test data.

Within Homogeneous Turbulence: Crow Instability Large Eddy Simulation of Aircraft Wake Vortices

Ambient atmospheric turbulence effects on aircraft wake vortices are studied using a validated large eddy simulationmodel. Our results conŽ rm that the most ampliŽ ed wavelength of the Crow instability and the lifetime of wake vortices are signiŽ cantly in uenced by ambient turbulence (Crow, S. C., “Stability Theory for a Pair of TrailingVortices,” AIAA Journal, Vol. 8, No. 12, 1970,pp. 2172–2179). The Crow instabilitybecomeswell developed in most atmospheric turbulence levels, but in strong turbulence the vortex pair deforms more irregularly due to turbulence advection. The most ampliŽ ed wavelength of the instability decreases with increasing dimensionless turbulence intensity , although it increases with increasing turbulence integral length scale. The vortex lifespan is controlled primarily by and decreases with increasing , whereas the effect of integral scale of turbulence on vortex lifespan is of minor importance. The lifespan is estimated to be about 40% larger than Crow and Bate’s predicted value (Crow, S. C., and Bate, E. R., “Lifespan of Trailing Vortices on a Turbulent Atmosphere,” Journal of Aircraft, Vol. 13, No. 7, 1976, pp. 476–482) but in agreement with Sarpkaya’s recent modiŽ cation (Sarpkaya, T., “Decay of Wake Vortices of Large Aircraft,” AIAA Journal, Vol. 36, No. 9, 1998, pp. 1671–1679) to Crow and Bate’s theory. This larger lifespan is also supported by data from water tank experiments and direct numerical simulations. There appears to be a possibility that the scatter in vortex lifespans due to ambient turbulence alone decreases with increasing Reynoldsnumber, whereas larger scatter of lifespans in  ight tests may result from other factors such as stratiŽ cation, wind shear, and inhomogeneous ambient turbulence.

Flight Testing an Optimal Trajectory for the Saab J35 Draken

Introduction T HE desire to Ž nd the most efŽ cient  ight path has a long history.The developmentof the Ž rst high-performancejet aircraft made it crucial to  y a close to optimal path to perform a givenmission before the fuel ran out. The earliest methods for Ž nding optimal trajectorieswere based on calculusof variations.Discretization of the optimality conditions and solution using numerical methods made it possible to solve quite complicated problems; see Bryson and Desai for a discussion on early strategies. In recent years, the most common approach is to discretize the differential algebraic equations (DAEs) before stating optimality conditions and applying numericalmethods. This strategywas pioneeredbyHargravesandParis, who used theNPSOL optimization package.Recentdevelopmentsin discretizationofDAEs4 andsparse nonlinearoptimizationmethods i 8 represent the current state of the art in trajectory optimization. Althoughmany papers appear in the open literatureon the development of numerical methods for solving trajectory optimization problems, very few papers are available discussing the difŽ culties involved in trying to follow a numerically computed trajectory in a real  ight test. The purpose of the present paper is to report on a simple  ight test that was performed to demonstrate the difŽ culties that may appear in a  ight test. This paper describes the model and numerical implementation used to calculateoptimal trajectories.The presentationof numerical results then follows with the results obtained in the  ight test for a particular test case.