Flight Loads Research Articles

Structural design and verification of an innovative whole adaptive variable camber wing

A whole adaptive variable camber wing (AVCW) equipped with an innovative double rib sheet (DRS) structure is experimentally and numerically studied in this work. The DRS structure adopts the surface contact mode for the force transmission of changeable camber wing instead of the conventional rigid hinge joint contact. The whole AVCW design allows to adjust the shape of wing in a real-time at various flight conditions, which is of great interest for Unmanned Aerial Vehicle (UAV) applications. The flight-test experiments demonstrate that the total AVCW carrying the developed adaptive control system (ACS) can enhance UAV flight efficiency by 14.1% comparing to a traditional fixed-wing of Talon UAV. In addition, it indicates that employing the whole AVCW structure can sustain a larger flight load, without increasing the weight of entire wing structure except for the actuator device and adhesives, which is promising for future engineering applications.

Additively manufactured Ti-6Al-4V replacement parts for military aircraft

This paper is motivated by the need to better understand the potential of Additively Manufactured (AM) Ti6-Al-4V replacement parts for future use on operational aircraft. Unfortunately, the interaction between surface and near surface (sub-surface) breaking material discontinuities, i.e. porosity due to and lack of fusion or keyholing, and the rough surface that is associated with AM parts complicates the analysis needed for certification. The present paper attempts to cut through this “Gordian knot”.1The Gordian Knot is a legend of Phrygian Gordium that is associated with Alexander the Great. An oracle had declared that any man who could unravel its elaborate knots was destined to become the ruler of all of Asia. Alexander reasoned that it would make no difference how the knot was loosed, so he drew his sword and sliced it in half with a single stroke. This explanation is taken from Wikipedia.1 To this end this paper presents a computational investigation into the fatigue life of AM Ti6-Al-4V parts subjected to two (quite different) representative flight load spectra that does not require the explicit modelling of the surface and subsurface porosity. Given the susceptibility of the “as manufactured” AM Ti6-Al-4V to fatigue crack nucleation and fleet experience from with conventionally manufactured parts, it is assumed that cracks in AM Ti6-Al-4V will initiate and grow from the day that the part enters service. The results of the present analysis suggest that for many parts of F/A-18 Classic Hornet and P3C (Orion) aircraft AM Ti-6Al-4V replacement parts may have an acceptable fatigue life. It also illustrates the potential for using fracture toughness measurements to guide the choice of the AM process and the associated post manufacture treatment.

Thermostructural Response of a Spatially Graded Metal-Ceramic Composite Panel Subjected to High-Speed Flight Loads

AbstractThe response of a thermally and mechanically loaded metal-ceramic spatially graded composite structural panel is considered. The load profiles that are representative of in-flight high-spee...

Scaled sequential threshold least-squares (S2TLS) algorithm for sparse regression modeling and flight load prediction

This paper presents a Scaled Sequential Thresholded Least Squares (S2TLS) algorithm to construct sparse regression models for flight load prediction. The combined use of a sparsification parameter λ and a magnification factor χ is proposed to tune both the model complexity and the regressor complexity. A bumpiness function is introduced to preferentially select simple regressors to improve model prediction. A cost function J consisting of the estimation residual and the bumpiness is then proposed to determine parameters (χ, λ) satisfying balanced performance. Parametric analysis is undertaken to investigate the effect of χ and λ on sparse regression performance. It is found that the optimal solution is hidden within a trench-like region of the (χ, λ) domain. Two methods using different optimization variables and algorithms are then presented to search for optimal combinations of λ and χ. Case studies are performed, and model results are compared against the test and CFD data of flight loads. Excellent agreement is observed, and the data (even with significant complications) is well bounded by the 95% confidence interval. Importantly, the underlying load-driving factors can be successfully identified. The new S2TLS algorithm represents a robust, efficient, and accurate method for flight load modeling and prediction.

Numerical and experimental comparative study of Aluminum and hybrid mounting interfaces of launch vehicle avionics for weight reduction

Weight is a paramount parameter for launch vehicle applications. Avionics are used for command, control and guidance of launch vehicle. Interface brackets are used for mounting of these avionic packages to the launch vehicle chassis. Dynamic loads and vibration responses dominate the design criteria for these interface brackets. The weight sensitivity on range is more prominent for the upper stages of the launch vehicle. To improve the performance of launch vehicle, employment of light weight hybrid (Aluminum honeycomb panel made up of honeycomb core with face sheets at top and bottom) bracket instead of comparatively heavy conventional all metallic aluminum alloy bracket, for a particular case of mounting two of the launch vehicle avionic packages is explored in this study. Comparable vibration responses are obtained along all three axes for the two bracket configurations (aluminium alloy vs hybrid) with packages mounted for the standard random vibration inputs. Sufficient static margin of safety is achieved for high deceleration re-entry flight loads as well. It is concluded that tremendous weight saving on mounting interfaces can be gained without compromising on factor of safety and amplification of vibration responses.

Airline capacity decisions under supply-demand equilibrium of Australia’s domestic aviation market

Australia is especially reliant on air transportation because of the geographical distribution of the urban centers across the country. This paper seeks to identify the antecedents of the capacity decisions of the airlines operating in Australian domestic aviation market. We examine the factors on both sides of the supply-demand equilibrium using monthly data of twenty-one major domestic routes linking eight major cities between January 2004 and December 2015. To investigate the relationship between flight demand and the variables of capacity decisions (flight frequency, aircraft size, load factor, and available seats), the pooled series cross-sectional data are analyzed using a two-stage least-squares method to model the supply-demand interaction. The results statistically differentiate the airlines’ strategies regarding capacity decisions for the short-haul, medium-haul, and long-haul routes. The results suggest that competition would lead to more flights, smaller aircraft size, lower load factors, and more available seats in all markets. Low-cost carriers play a key role in the short-haul market. Higher jet fuel prices scales up aircraft size on all flight routes. Notably, the socio-economic parameters of population and employment rates affect flight demand more strongly on the long-haul routes than other routes.

Study of the Local Strength of the Main Rotor Torsion Bar under the Action of Flight and Test Bench Loads

The stress-strain state for the torsion bar of the helicopter main rotor under the action of flight and test bench loads is analyzed. The technique of estimating the ultimate state by phenomenological strength criteria and maximum stresses is described. The close agreement between calculation results and experimental data is observed.

Analysis on Cracked Commuter Aircraft Wing Under Dynamic Cruise Load By Means of XFEM

In this paper, a new investigation of crack propagation on a commuter aircraft wing is discussed. The aircraft is a 19-seater multi-purpose commuter aircraft designed for a mission on the remote area. The dynamic load acting on the wing is assumed as harmonic load considering aerodynamic lift at a particular excitation frequency. A 3D wingbox CAD model is developed for the numerical simulation. Extended finite element (XFEM) is applied to analyse the crack propagation on the aircraft wing. The crack growth simulation is successfully done, and the results are shown in some details. These results provided a novel insight on the computational simulation of cracked wing structure under dynamic flight load.

For Jet Engine Wing Mounting

The mounting of a jet engine under the wing of an airliner can be a daunting task for turbofan engineers. Thrust forces generated by gas path momentum flow changes in a jet engine are transmitted by pressure (and friction) forces on stators and struts attached to the engine case. Case engine mounts then transmit the thrust forces (as high as 100,000 pounds thrust on the largest engines) to the wing pylons to pull the plane forward. The mounts must also support the engine weight (as high as 20,000 pounds) and carry nacelle flight loads. Engine bypass ratios are increasing (12:1 on the new geared fan engines), with fan sizes ever growing (178 inch diameter fan on the new GE9X). Mounting these new engines under a wing can present new challenges. During the early days of its introduction in the late 1960’s, Boeing’s iconic 747 jumbo jet had engine mount problems. These are examined, together with their solution.

Developing an accelerated flight load spectrum based on the nz-N curves of a fleet

Fatigue load spectra are essential for fatigue analyses and full-scale fatigue testing (FSFT) of aircraft structures. Because of the long test period, an accelerated load spectrum is required to reduce time consumption and cost. This paper presents a new approach for developing an accelerated flight load spectrum. Using the measured nz-N curves per flight for a Fokker F27 fleet, 55 individual load spectra were reconstructed, the damage of which was calculated using the damage curve method, and verification was conducted using fatigue tests on 2024-T3 aluminum alloy centered-hole specimens. A lognormal distribution function was used to model the variation in the load spectrum damage per flight for the fleet. Assuming that the structural property variation follows a lognormal distribution, the fleet life is found to follow a lognormal distribution with the mean equal to that including the load spectrum variation and the variance equal to the sum of the variance in structural properties and load spectra. Then, we obtained the damage severity of the accelerated load spectrum that meets the reliability requirements for fleet life. The nz-N curve of the accelerated spectrum was subsequently determined based on statistical analysis and probability extrapolation of the exceedance number. Finally, an accelerated flight load spectrum was developed based on the nz-N curve, the damage severity of which was determined by fatigue analysis and testing.

A method to evaluate determinant factors on airport check-in level of service

Understanding how operational procedures and demand growth can influence the check-in level of service (LoS) is an important issue for airport operators, but the importance of these factors has never been determined. With the aim of filling this gap, this paper proposes a method to evaluate the main variables that can influence the LoS of an international airport check-in. The methodology used for this study included the collection and processing of data, infrastructure analysis, software simulation of 273 scenarios and non-linear regression. São Paulo–Guarulhos international airport, Brazil, was used as a case study. The main results suggest that, among operational procedures, the processing time at counters is the most important factor, followed by the number of counters per airline, the use of self-service technologies and the opening time of the check-in desks. Airport operators must be aware of increases in flight load factors and the addition of new flights to adjust the need for counters for each airline.

Laboratorio virtual para la interpretación de las cargas en vuelo

La asignatura "Cargas en Vuelo'' enmarcada en el Máster en Ingeniería Aeroespacial se basa en los conceptos vistos en los cursos de Mecánica del Vuelo y Análisis Estructural del Grado en Ingeniería Aeroespacial. Por un lado, las ecuaciones involucradas no pueden resolverse por métodos tradicionales pero por otro necesitamos que nuestros estudiantes adquieran competencias específicas derivadas de la interpretación de dichas ecuaciones. En el presente artículo proponemos una herramienta numérica en forma de laboratorio virtual, sencilla e intuitiva, desarrollada en el entorno del software Mathematica que permite resolver interactivamente las ecuaciones de la Mecánica del Vuelo simétrico de un avión y obtener resultados directamente relacionados con el diseño estructural. Se muestra el funcionamiento del modelo con algunos ejemplos.

Aircraft reliability assessment for an individual mission based on recordable flight parameters

AbstractReliability of aircraft varies with different missions, because load conditions are always diverse. In limited sample size circumstances, convention aircraft mission reliability assessment method can only give an average result for a kind of mission. Motivated by the practical need of reliability assessment for an individual mission, this paper constructs a novel method, which can assess reliability for a specific mission based on flight parameters. The mission reliability model can be established according to the relationship between flight loads, flight parameters, and reliability via adopting fault data and flight parameters synthetically. Statistical inference of aircraft failure rate is proposed, and then, the mission reliability can be assessed according to the fault data of the focused aircraft. It is worth noticing that the proposed method can also assess the reliability for a mission category via conducting an average calculation across all individual missions belonging to the target mission category. An illustrative example shows that the proposed method not only can give reliability assessments with a same precision with existing approaches for a specific mission category but also can reasonably assess the reliability regarding an individual mission.

Single engine turboprop aeroplane class in small air transport

PurposeThis paper aims to present the analysis of introduction of single engine turbo-prop aeroplane class in terms of certification specifications and flight crew licensing regulations.Design/methodology/approachFollowing the results of flight testing and additional performance and sizing calculations, the proposed class was placed among the existing aeroplane taxonomy in terms of performance, flight loads, mass penalty, fuel economy and several other factors. Concerning small air transport initiative, the new class was tried to be placed as a starting point in commercial pilot career.FindingsThe paper points the potential market for single engine turbopropeller aeroplanes and lists today obstacles in wider introduction. Therefore, remarks about required change of regulations and requirements for design process, as well as for crew licensing, are underlined.Practical implicationsThe results of the study would be helpful in preliminary design of a new low-power turboprop aeroplane, as well as during tailoring the certification specifications.Originality/valueThe approach presented in this paper is a detailed extension of an original idea presented by author for the first time during Clean Sky/small air transport workshop.

Equivalence relationship between a three-axis centrifugal test load and flight load

For aircraft flying with high accelerations and high acceleration change rates in three-dimensional space, load simulation tests are usually carried out in a three-axis centrifuge with three degrees of freedom. A triaxial centrifugal test that simulates the actual flight environment must reflect the real effect of the flight load on the structure. An acceleration analysis model of a three-axis centrifuge in body coordinates is established to meet this requirement. The spatial distribution of the acceleration and the effects of kinematic parameters on acceleration are analyzed. Using the acceleration analysis model, the displacement equivalence and strain energy equivalence relations of a beam in a centrifugal environment and actual flight environment are studied. Moreover, equivalence relationships meeting requirements are proposed and validated for a specific example. The distribution of the acceleration and the equivalence relations of the two environments are the basis for the ground simulation of flight loads.

Active Stabilization of Slung Loads in High-Speed Flight Using Cable Angle Feedback

This paper addresses the problem of active stabilization of slung loads up to 130 kt. To demonstrate the method, simulations of a utility helicopter with a dynamic inversion controller (as its automatic flight control system) and a CONEX cargo container were used. An airspeed-scheduled controller utilizing cable angle feedback was designed for the nonlinear-coupled system by the classic root locus technique. Nonlinear simulations of straight and level flight at different airspeeds were used to validate the controller performance in stabilizing the load pendulum motions. Controller performance was also evaluated in complex maneuvers with different levels of turbulence. The results show that using cable angle feedback provides or improves system stability when turbulence is not included in the simulation. When light/moderate turbulence is present, sustained limit cycle oscillations are avoided by the use of the controller. For severe turbulence levels, the controller did not provide any significant improvement.

Flight Load Assessment for Light Aircraft Landing Trajectories in Windy Atmosphere and Near Wind Farms

This work focuses on the wake encounter problem occurring when a light, or very light, aircraft flies through or nearby a wind turbine wake. The dependency of the aircraft normal load factor on the distance from the turbine rotor in various flight and environmental conditions is quantified. For this research, a framework of software applications has been developed for generating and controlling a population of flight simulation scenarios in presence of assigned wind and turbulence fields. The JSBSim flight dynamics model makes use of several autopilot systems for simulating a realistic pilot behavior during navigation. The wind distribution, calculated with OpenFOAM, is a separate input for the dynamic model and is considered frozen during each flight simulation. The aircraft normal load factor during wake encounters is monitored at different distances from the rotor, aircraft speeds, rates of descent and crossing angles. Based on these figures, some preliminary guidelines and recommendations on safe encounter distances are provided for general aviation aircraft, with considerations on pilot comfort and flight safety. These are needed, for instance, when an accident risk assessment study is required for flight in proximity of aeolic parks. A link to the GitHub code repository is provided.

EVALUATION OF THE FORMATION AND VORTEX TRACE INFLUENCE OF LIGHT UNMANNED MULTICOPTERS

The introduction of unmanned aerial vehicles is one of the most dynamic areas of civil aviation development over the last years. The main field of their application is the performance of different aerial works. The most part of the aerial works is characterized by a small distance of flying unmanned vehicles from humans, animals, plants and infrastructure. Thus the influence of inductive velocities of these vehicles on the objects and some processes of aerial works is the topical issue. The article considers the problems of evaluation of vortex trace formation and description of inductive velocities field within the flying area of light unmanned multicopters which are the most popular and promising for the performance of the basic aerial works. The studies have been conducted by a numerical experiment using the software package developed in Delphi. On the bases of the defined multicopter parameters, conditions and flight modes created package provides simulation of the vortex trace formation of multicopter as a set of the mutually influencing П-shaped vortices of the multicopter rotors, graphic visualization of the vortex trace and calculations according to the inductive velocities in the flight area with the construction of the vector diagrams as well as some related problems. The article presents the graphic data on the spatial configuration of vortex trace and distribution of inductive velocities in the transverse planes which are unequally distant from the multicopter; for example, light hexacopter "Odonata agro", for which the proximity of experimental and calculation data of drops sedimentation at aerial spraying, received with the use of the package, confirms indirectly the package adequacy as well as configurations of vortex trace which are comparable in flight weight and load upon rotors of quadcopters and octocopters. According to the calculated data the general regularities and features of the vortex trace formation and configuration, distributions of the inductive velocities within the flying area of the light multicopters are formulated in this paper. The results can be used at the evaluation of the parameters and the vortex trace influence of light unmanned aerial vehicles on the surrounding objects and optimization of rational structural designs and multiсopter flight modes while performing aerial works.

Performance of high mach number scramjets - Tunnel vs flight

While typically analysed through ground-based impulse facilities, scramjets experience significant heating loads in flight, raising engine wall temperatures and the fuel used to cool them beyond standard laboratory conditions. Hence, the present work numerically compares an access-to-space scramjet's performance at both these conditions. The Mach 12 Rectangular-to-Elliptical Shape-Transitioning scramjet flow path is examined via three-dimensional and chemically reacting Reynolds-averaged Navier-Stokes solutions. Flight operation is modelled through 800 K and 1800 K inlet and combustor walls respectively, while fuel is injected at both inlet- and combustor-based stations at 1000 K stagnation temperature. Room temperature walls and fuel plena model shock tunnel conditions. Mixing and combustion performance indicates that while flight conditions promote rapid mixing, high combustor temperatures inhibit the completion of reaction pathways, with reactant dissociation reducing chemical heat release by 16%. However, the heated walls in flight ensured 28% less energy was absorbed by the walls. While inlet fuel injection promotes robust burning of combustor-injected fuel, premature ignition upon the inlet in flight suggests these injectors should be moved further downstream. Coupled with counteracting differences in heat release and loss to the walls, the optimal engine design for flight may differ considerably from that which gives the best performance in the tunnel.

Determination of the critical plane and durability estimation for a multiaxial cyclic loading

An analytical procedure is proposed to determine the critical plane orientation according to the Findley criterion for the multiaxial cyclic loading. The cases of in-phase and anti-phase cyclic loading are considered. Calculations of the stress state are carried out for the system of the gas turbine engine compressor disk and blades for flight loading cycles. The formulas obtained are used for estimations of the fatigue durability of this essential element of structure.