Aircraft Structures Research Articles

A Novel Individual Aircraft Life Monitoring Method Based on Reliable Life Consumption Assessment

Individual life monitoring is crucial for ensuring aircraft flight safety. Conventional life-consumption-based monitoring methods ignore reliability, thus disjoining them from the aircraft’s reliable life determination and extension, where high confidence and reliability are required. Therefore, this paper proposes a reliable life consumption and individual life monitoring method for aircraft structure fatigue. In the paper, the P-S-N curve, i.e., the relationship between the aircraft structure’s life (N) and fatigue load (S) under a certain probability (P), is established, by which the lower confidence limit of the aircraft structure’s reliable life can be evaluated under any fatigue loads. Based on that and the aircraft’s monitored fatigue loads, the indexes of reliable life consumption and remaining reliable life percentages are proposed and assessed in real time for individual aircraft life monitoring and online life management. Case studies indicate that the proposed method can guarantee high confidence and reliability requirements in individual life monitoring, consistent with the aircraft’s life determination and extension, which are widely accepted nowadays in engineering practice.

Thoughts on the Importance of Similitude and Multi-Axial Loads When Assessing the Durability and Damage Tolerance of Adhesively-Bonded Doublers and Repairs

Adhesively bonded doublers and adhesively bonded repairs are extensively used to extend the operational life of metallic aircraft structures. Consequently, this paper focuses on the tools needed to address sustainment issues associated with both adhesively bonded doublers and adhesively bonded repairs to (metallic) aircraft structures, in a fashion that is consistent with the building-block approach mandated in the United States Air Force (USAF) airworthiness certification standard MIL-STD-1530D and also in the United States (US) Joint Services Structural Guidelines JSSG-2006. In this context, it is shown that the effect of biaxial loads on cohesive crack growth in a bonded doubler under both constant amplitude fatigue loads and operational flight loads can be significant. It is also suggested that as a result, for uniaxial tests to replicate the cohesive crack growth seen in adhesively bonded doublers and adhesively bonded repairs under operational flight loads, the magnitude of the applied load spectrum may need to be continuously modified so as to ensure that the crack tip similitude parameter in the laboratory tests reflects that seen in the full-scale aircraft.

Airworthiness Compliance Verification of Bird Strike on Civil Aircraft Windshield Frame

With the frequent occurrence of bird strikes, minimizing the impact damage effect of birdstrike on flight always is the goal of airworthiness certification. As a large windward component in front of the aircraft, the windshield, and frame have more probability to be suffered from birdstrike. This paper introduces the common connection forms of the windshield frame structure of civil aircraft, and through the interpretation of the airworthiness requirements related to windshield in CCAR-25, puts forward the process and method of compliance verification of windshield frame birdstrike. Based on the SPH method, the dynamic analysis of bird impact on windshield window frame is carried out, the test is carried out to verify that the analysis method is reasonable and conservative, and the results show that the bird impact performance of the windshield frame structure meets the airworthiness requirements.

Additive manufacturing (3D printing): A review of materials, methods, applications and challenges

Several benefits can be gained by using additive Manufacturing (AM) or 3D printing, including design flexibility, mass customization, waste minimization, quickly producing complex structures, and rapid prototyping. The standard methods and materials used in 3D printing, along with their development and use, have been examined. The various applications of AM were discussed, especially in biology, aircraft, building, and defensive structures. Many materials and their stages of evolution, including concrete, ceramics, polymer composites, and metal alloys, were analyzed. We discussed several fundamental processing challenges that arise, including but not limited to void generation, anisotropic behaviors, computer design restrictions, and a layered appearance. This article thoroughly assesses 3D printing, including a survey of its pros and shortcomings, to establish a baseline for future research and development.

Stretch broken carbon fiber for primary wind turbine structure

Stretch broken carbon fiber (SBCF) composites offer significant benefits over conventional continuous fiber composites. These include the greatly enhanced formability of unidirectional tape form products prior to cure without any compromise on the mechanical performance after curing. The recent work performed under the US Army funded Stretch Broken Carbon Fiber for Primary Aircraft Structure program by Montana State University (MSU) is reviewed, along with the results achieved by previous efforts to develop this technology. The achievement of shorter stretch break lengths to improve formability is a principal objective of the work and a successful achievement of the recent efforts. In addition, alternate means of manufacturing SBCF prepregs are discussed, including conventional spooled fiber presentation suitable for running on current prepregging equipment, as well as a newly developed direct to prepreg approach, where the stretch breaking of the fibers is done in-line with the prepregging process. While aerospace primary structure has been the focus of current research efforts, applications in other industries such as wind turbine blades are also obvious areas of applications for SBCF technology.

Design of Dual-tiltable Ducted-Fan Aircraft Based on Cross-coupling Network Control

In recent years, with the rapid development of drone technology, unmanned aerial systems have been widely applied in various fields. Although the flight control and airframe structure of traditional multirotor aircraft are fairly mature, they still face challenges such as low aerodynamic efficiency, low safety, and complex structure. In order to solve these issues, a dual-tiltable-ducted-fan aircraft system is designed. The system is equipped with an STM32F407 processor as the main controller, which receives motion control information from the remote control module. By employing cross-coupling network control methods, it coordinates the output values and tilt angles of the two channeling fans to achieve stable control of the aircraft's flight attitude.

Influence of asymmetrical factors on aircraft ground steering stability

An aircraft taxiing on the ground is affected by several nonlinear forces so that the directional instability may occur during the steering process, and the asymmetric factors could exacerbate this phenomenon. A nonlinear asymmetrical aircraft ground taxiing dynamic model is established in MATLAB/Simulink in this study. Then the numerical continuation method based on the bifurcation theory is used to study the influence of the asymmetrical aircraft structure on the taxiing directional stability by taking the distance between the eccentric mass and the aircraft symmetry plane as the bifurcation parameter. In addition, a dual-parameter bifurcation is conducted to study the influence of the nose-wheel steering angle and the asymmetrical mass eccentric distance on the directional stability. Moreover, the effect of the asymmetrical thrust on the taxiing steering bifurcation characteristics is investigated, and the instability mechanism is revealed by analyzing the aircraft taxiing motion states under five working conditions. Then the dual-parameter bifurcation curves are obtained by introducing the nose wheel steering angle as the additional bifurcation parameter. The Bogdanov-Takens (BT) bifurcation and the Generalized Hopf (GH) bifurcation in the nonlinear ground turning dynamic system are also discussed. The results show that the asymmetrical factors can significantly affect the aircraft ground taxiing directional stability.

Impact analysis of compression preloaded honeycomb sandwich structures

Honeycomb cores made of phenol resin impregnated paper are widely used in sandwich structures of aircraft. Owing to the rather weak core material, this kind of sandwich is prone to a range of damages as a result of impact loading which may accidentally occur during operation. When employed in aircraft these structures have to be damage tolerant. This means barely visible damages have to be considered in the structural design process. In the standard design process for damage tolerant aircraft structures especially the effect of impacts has to be considered but is mostly investigated on unloaded sandwich components. However, aircraft structures are not completely stress free, even when the aircraft is in parking position. At least the structural weight will cause a permanent static preload. In the literature there are only few investigations dealing with the impact behaviour of preloaded honeycomb sandwich structures. In general, studies on composite structures have shown that tension preloads lead to higher structural impact resistance, while prestressing in compression reduces mechanical properties such as impact strength and stiffness of the structure. For this reason, a compression preload is considered as the more critical load case. In order to evaluate the effect of static compression preloads an experimental study on five different honeycomb sandwich configurations was conducted. The experimental investigations showed that even low preloads cause a higher structural damage area, which results in a lower residual strength of the structure. The results indicated that it is recommendable to consider structural compression preloads in the aircraft structural design process.

Polymers as Aerospace Structural Components: How to Reach Sustainability?

AbstractThe aerospace industry has been benefiting from the utilization of polymer materials since fiber‐reinforced polymer composites (FRPC) offer high performances at low densities compared to metals. FRPC facilitated the design of lightweight materials, which is extensively used in aviation today. Since their first integration into structural parts, FRPC has experienced exponential growth over the years and has received a special interest from manufacturing engineering. While FRPC today is a major focus in engineering, the design of polymer matrix relies on polymer chemistry. However, aircraft materials are facing a pressing issue related to sustainability, since their environmental footprint is at an alarming level. In this review, commercial thermosetting polymer composites employed in aircraft structures are exhibited from a chemistry perspective by depicting starting products and curing reactions. The potential of chemistry to help design next‐generation sustainable FRPC for structural parts by means of utilization of sustainable feedstock, energy‐efficient processing, and recycling, is disseminated.

Measuring the spatiotemporal variability in snow depth in subarctic environments using UASs – Part 2: Snow processes and snow–canopy interactions

Abstract. Detailed information on seasonal snow cover and depth is essential to the understanding of snow processes, to operational forecasting, and as input for hydrological models. Recent advances in uncrewed or unmanned aircraft systems (UASs) and structure from motion (SfM) techniques have enabled low-cost monitoring of spatial snow depth distribution in resolutions of up to a few centimeters. Here, we study the spatiotemporal variability in snow depth and interactions between snow and vegetation in different subarctic landscapes consisting of a mosaic of conifer forest, mixed forest, transitional woodland/shrub, and peatland areas. To determine the spatiotemporal variability in snow depth, we used high-resolution (50 cm) snow depth maps generated from repeated UAS–SfM surveys in the winter of 2018/2019 and a snow-free bare-ground survey after snowmelt. Due to poor subcanopy penetration with the UAS–SfM method, tree masks were utilized to remove canopy areas and the area (36 cm) immediately next to the canopy before analysis. Snow depth maps were compared to the in situ snow course and a single-point continuous ultrasonic snow depth measurement. Based on the results, the difference between the UAS–SfM survey median snow depth and single-point measurement increased for all land cover types during the snow season, from +5 cm at the beginning of the accumulation to −16 cm in coniferous forests and −32 cm in peatland during the melt period. This highlights the poor representation of point measurements in selected locations even on the subcatchment scale. The high-resolution snow depth maps agreed well with the snow course measurement, but the spatial extent and resolution of maps were substantially higher. The snow depth range (5th–95th percentiles) within different land cover types increased from 17 to 42 cm in peatlands and from 33 to 49 cm in the coniferous forest from the beginning of the snow accumulation to the melt period. Both the median snow depth and its range were found to increase with canopy density; this increase was greatest in the conifer forest area, followed by mixed forest, transitional woodland/shrub, and open peatlands. Using the high-spatial-resolution data, we found a systematic increase (2–20 cm) and then a decline in snow depth near the canopy with increasing distance (from 1 to 2.5 m) of the peak value through the snow season. This study highlights the applicability of the UAS–SfM in high-resolution monitoring of snow depth in multiple land cover types and snow–vegetation interactions in subarctic and remote areas where field data are not available or where the available data are collected using classic point measurements or snow courses.

The influences of eccentricity on the fastener load and bearing strength of eccentric connection in aircraft structure

Purpose This paper aims to study the influences of eccentricity on the fastener load and bearing strength of the eccentric connection in the aircraft structure. Design/methodology/approach The special experiment is designed for the researches. The fastener loads of the eccentric connection are gained by using the derived formulas and numerical analysis, and the fastener load rules is verified by the experiment. The bearing strength of the eccentric connection is investigated by the experiments under different eccentricities compared with that gained from the experiment. Findings The study results are summarized as follows. Magnitude of the fastener load in the eccentric connection is greatly affected by distance from the fastener to the centroid of the fastener cluster and that from the fastener to the concentrated load. With the increase of eccentricity of the homolateral concentrated load, the fastener load increases, and difference of the fastener loads becomes larger, forming the short plate effect of the bucket. It means that fastener with the maximum load (the shortest plate of the bucket) leads to decrease of the bearing strength of the eccentric connection (the capacity of the bucket). Originality/value The investigation on the influence of eccentricity on the bearing strength of eccentric connection is firstly presented. The vector expression of the fastener load in eccentric connection is firstly derived. And the influencing mechanism of the fastener load on the bearing strengths of the different eccentric connections is demonstrated. The study results can provide guidance for the structure design of the eccentric connection.

Fabrication, characterization, and repair of nanocarbon-loaded aircraft paint-based sensors for real-world SHM: studies at the laboratory scale

There has been considerable interest in piezoresistive nanocarbon-loaded polymer films for structural health monitoring, including damage detection and strain monitoring. While good performance has been demonstrated, issues related to practical implementation have received less attention. Here we present sensors made from exfoliated graphite nanoplatelets (xGnP) incorporated into a commercial paint that is applied to Sikorsky aircraft. A formulation and a fabrication method are developed that deliver high piezoresistive strain sensitivity alongside mechanical integrity. At approximately 7 wt% xGnP, the gauge factor in tension is in the range of 30–55, and the effectiveness of the sensors for damage monitoring is demonstrated by the detection of perforations. To obtain a paintable solution, key considerations in choosing the solvent employed for introducing the nanocarbon are compatibility and the ability to keep the nanocarbon suspended, which is achieved using ethyl acetate. The ability to form sensors in situ on aircraft structures requires an uncomplicated method of making robust electrical connections, which is demonstrated here using embedded copper mesh. The strong, often nonlinear, environmental sensitivity of polymer-nanocarbon materials must also be considered in applications; here, increasing temperature and humidity both raise sensor resistance. This work shows that a second, unstrained reference sensor would work well for automatic compensation. Lastly, a method for effecting a repair that employs standard processes and maintains the high gauge factor is demonstrated. With these advances, the paint-xGnP sensors are ready for in-the-field testing on aircraft.

Development of Fiber Sensors integrated with Aerospace Composites for Structure Health Monitoring

The wide-spread use of composite material in aircraft across the world is expected to create a big need to improve structure health monitoring (SHM). Optical fiber sensors offer more advantages than conventional sensors, such as light weight, small size, immune to electromagnetic interference, easily embedded in composites. Extensive applications have been reported with a few embedded technology details by Boeing and Airbus, etc. In this paper, The methods of improved optical fiber surface-bonded composites by glass cloth and epoxy resin, as well as optical fiber embedded in composites were researched. The installation of fiber and composites, composites assembly pressure adaptability on FBG sensors, influences on structure properties of composite materials due to different fiber diameters and different numbers of optical fibers by the way of microscopic interface analysis and C-san were studied. The adequate fiber embedded technology was found to obtain the most feasibility of SHM. Light intensity and wavelength of FBG sensor surface-bonded by glass cloth are affected by the structural assembly pressure. It can be seen that diameter of embedded optical fiber equal to the thickness of prepreg monolaye, the fiber embedded next to 0 degree layer, less than five fibers within a 25mm width composite unit have little impact on composite structure. Then, 12 FBG sensors were embedded in a typical aircraft structure, a carbon fiber enhanced stiffened composite plate with length 600 mm and width 600 mm, to detect position and energy of external impact load by a mathematical analysis method, cross correlation algorithm. Finally, suggestions on future study are listed from four aspects, co-forming technology of FBG sensor and composite skin, research on the extraction technology of optical fiber, new flexible wing testing technology and advanced fiber optical sensing technology.

Structure design of variable camber wing trailing edge based on multi-block rotating mechanism

The variable camber trailing edge enables the aircraft to maintain the best aerodynamic performance throughout the flight envelope, so as to achieve the ultimate goal of reducing aircraft fuel consumption and air pollutant emissions. It is one of the important characteristics and development direction of the new generation civil aircraft. In order to solve the contradiction between the high load-bearing and the large deformation of the variable camber trailing edge of large aircraft, a structure scheme for variable camber trailing edge based on multi-block rotation was proposed. A parametric optimization method was established for smooth and continuous deformation of multi-block rotating mechanism. The multi-block rotating structure and driving system of variable camber trailing edge were designed, and the deformation function of the variable camber trailing edge demonstrator was preliminarily verified by ground test. The result shows that variable camber wing trailing edge designed by using the present optimization method of multi-block rotating mechanism can realize smooth and continuous morphing. The actual deformation range of the demonstration is 3.9 degrees up to 12.5 degrees down, and the error with the design target is 16.7%. It provides a design reference for solving the engineering application problem of variable camber structure for large aircraft.

Life test result on 4 channel VCELs chip used in 28Gb/s data transfer in space application

For aeronautic applications, in-service Structural Health Monitoring (SHM) is a now established as a key technique to assess the performance and the integrity of composite aircraft structures for real-time in situ monitoring. For space industry, the Assembly Integration and Test including Electrical Ground Support Equipment is an essential tool enabling a satellite or space launcher developer to integrate and validate the electrical functions of its spacecraft before the launching process. In addition, satellite operators and worldwide SatCom manufacturers are willing to improve the on-board processing capacity, functionality and flexibility. In this context, opto-transceiver technology becomes a major building block regarding the highlighted aeronautic, space and ground telecommunication needs.In this context, the paper deals with the robustness evaluation of 850 nm GaAs VCSEL chip on Submount (CoS) used to 4 channel transceivers at 28 Gbit/s. The reliability investigation has been evaluated for two different manufacturers of VCELs and we perform the robustness of the technology regarding the final environment to define the limit usable for space applications. In this paper, we present the first technology of VCSELs. The main failure mechanisms have been defined to establish degradation laws associated. This last action is useful to define the ad equation between technology chosen and mission profile. These results are using for RYTHMS (ReliabilitY of opto-Transceivers for Health Monitoring Systems) Clean sky 2 project.

Исследование динамической устойчивости модели крыла в потоке воздуха

Investigating the aircraft structure elements for compliance with dynamic stability is one of the most important ways to study their dynamic properties. The paper considers possibility of the wing model dynamic loss of stability (flutter type) in the form of a flat rod of variable geometry close to the real wing geometry in the airflow. Internal force factors manifested under the frontal aerodynamic force influence, as well as increment in the lift and aerodynamic moment arising during possible small model oscillations are taken into account from the oncoming airflow side. Due to these external forces increment, the so-called energy pumping from the airflow side occurs, and the problem becomes non-conservative. Behavior of the first three complex eigenvalues of small oscillations was numerically studied, and the critical flow velocities, at which the model could lose dynamic stability, were determined for various parameters of the external aerodynamic forces.

Investigations on electromagnetic scattering characteristics of aircraft rudder considering electromagnetic discontinuities

This work investigates the scattering characteristics of the rudder structure of aircraft considering electromagnetic discontinuities through multi level fast multipole algorithm (MLFMA) of the computational electromagnetics. Firstly, the scattering characteristics of the rudder seam and its influence on the omnidirectional radar cross section (RCS) are performed. Based on the traditional high-frequency analysis theory, the source and spatial contribution distribution of seam scattering are further studied. Numerical results demonstrate that the sidewall of the rudder seam is an important scattering source, and the radar absorbing material (RAM) coated on the sidewall of the seam has a good RCS reduction effect. In addition, this work presents the influence of the rudder deflection on the stealth performance, analyzes the effect of the rudder movement of the ordinary aileron and the split drag rudder on the scattering characteristics of the whole aircraft. The common aileron has little effect on the stealth performance of the aircraft, and it only causes scattering peak in the direction opposite to the control surface. However, the split drag rudder has great damage to the opposite direction stealth performance of the aircraft. When its deflection angle is 45°, the mean value of the opposite direction RCS increases by about two orders of magnitude compared with the deflection angle 0° state. The results indicate that the structure of aircraft rudder has a significant impact on the RCS characteristics of the whole aircraft.

Finding the Weight Difference of a Rectangular Structure with a Parabolic Arc for Mathematical Models Made of Steel and other Composite Materials

The most popular materials for lightweight constructions, including building and aircraft structures, industrial, military, and aerospace technology, are armored composites. Composites made of carbon fiber are typically employed in lightweight applications. The ANSYS program was used to produce four mathematical models. Steel is used in the construction of the first and second versions whereas composite materials are used in the third and fourth variants. To find all the deformations, stresses, and strains that appear on the four models, as well as to calculate the weights of those four structures and compare them, these four models were tested with the ANSYS 15.0 program to obtain equal deformation resistance for all models under the influence of different loads. The results show that the composite models had lower strains, stresses, and deformations than the steel models. Among other results, it was discovered that the weight of the third model made of composite materials decreased by (32.72%) compared to the steel-based first model, and after doing the necessary calculations and assessing the results, the fourth model made of composite materials' weight was reduced by (19.21%) when compared to the second model made of steel.

Experimental investigation on the effect of process variables for the quality characteristics of AA 2024 processed in cold extrusion

Extrusion process has many applications in manufacturing industries due to its ability to produce products of high quality. Extrusion process can be classified into hot extrusion and cold extrusion. The cold forward extrusion is carried out at ambient temperature and has the additional benefit of improved mechanical characteristics. The metarial is compressed under intense pressure through a die orifice with a specific shape during the extrusion process. This process is effected by a few process variables, including die angle, punch speed, and lubrication are in greater extent towards the extrusion force requirement, microstructure and the product quality. Hence, the present experimental work focuses on extrusion of circular billet to produce cylindrical rod. Studying the behaviour of the material and the importance of the input process parameters during the cold extrusion process is the primary goal of this work. The experiments are carried out with AA 2024 alloy because of its wide applications in navy and aircraft structures. The varying die angles (10°, 20° & 30°) as well as punch speed (1.6 mm/min, 3.2 mm/min and 4.8 mm/min) and lubricants (molybdium sulphide (MoS2), zinc stearate and grease) chosen as input parameters. The out put responses of this extrusion process are extrusion force, displacement, time and surface roughness. Extrusion forces are calculated based on flow stress curves at the locations of greatest elastic deformation. The results shows that increasing the punch speed and die angle increases the extrusion force. The microstructure evolutions and grain refinement at different die angles are examined using electron back scatter diffraction analysis. At 30° die angle, the microstructure showed grain refinement. It is also noted that the damage is significant at 30° die angle with a punch speed above 4.8 mm/min.

Development of Low Velocity Bullet Proof Vest

Bulletproof vest is a vest which can protect wearer’s body from the impact of bullet. Soft vests are made of many layers of woven are laminated fibers and can protect the wearer from small caliber, hand gun and shot gun projectiles.Fiber reinforced composite materials have become important engineering materials used such as marine bodies, air craft structures and light weight body armor for ballistic protection in military applications. Composite body armor is an item or piece of clothing that is designed to protect the wearer against a variety of attacks. The most useful properties of composites are high specific strength and specific stiffness, good corrosion resistance and good fatigue resistance. Advanced composite materials, typically consisting of reinforced fibers in a resin matrix.So that we have construct the composite using glass and sisal with resin matrix.