Aircraft Weight Reduction Research Articles

Equal-load-bearing joining of alclad AA2024-T4 alloy stringers and skins in aviation via friction stir lap welding

Friction stir lap welding of stringers and skin is of great significance for aircraft weight reduction. A welding tool characterized by the conical threaded pin with triple milling facets was proposed to alleviate hook and cold lap defects in friction stir lap welded joints. Sound joints without weld thinning were achieved in AA2024-T4 alloy joints with the thickness of 1.5 mm and 1.2 mm. The design of the thread and triple facets effectively enhanced the material flow behavior, thereby suppressing the formation of hook and cold lap defects. The lap width was significantly broadened to 5 times of skin thickness towards better load-bearing capacity. The ultimate tensile strength of the joint reached 428.3 MPa, equivalent to that of the base material, which fractured at the base material far away from the welding zone.

HIGH TEMPERATURE OXIDATION OF TI-6AL-4V ALLOY FABRICATED BY ADDITIVE MANUFACTURING. INFLUENCE ON MECHANICAL PROPERTIES

Titanium alloys, such as Ti-6Al-4V alloy, fabricated by additive manufacturing processes is a winning combination in the aeronautic field. Indeed, the high specific mechanical properties of titanium alloys with the optimized design of parts allowed by additive manufacturing should allow aircraft weight reduction. But, the long term use of Ti-6Al-4V alloy is limited to 315 °C due to high oxidation kinetics above this temperature [1]. The formation of an oxygen diffusion zone in the metal and an oxide layer above it may reduce the durability of titanium parts leading to premature failure [2, 3]. In this study, Ti-6Al-4V alloy was fabricated by Electron Beam Melting (EBM). As built microstructure evolutions after Hot Isostatic Pressure (HIP) treatment at 920 °C and 1000 bar for 2h were investigated. As built microstructure of Ti-6Al-4V fabricated by EBM was composed of Ti-α laths in a Ti-β matrix. High temperature oxidation of Ti-6Al-4V alloy at 600 °C of as-built and HIP-ed microstructures was studied. This temperature was chosen to increase oxidation kinetics and to study the influence of oxidation on tensile mechanical properties. In parallel, two other oxidation temperatures, i.e. 500 °C and 550°C allowed to access to the effect of temperature on long-term oxidation.

Experimental and numerical investigations of a 2D aeroelastic airfoil encountering a gust in transonic conditions

In order to make substantial progress in reducing the environmental impact of aircraft, a key technology is the reduction of aircraft weight. This challenge requires the development and the assessment of new technologies and methodologies of load prediction and control. To achieve the investigation of the specific case of gust load, ONERA defined a dedicated research program based on both wind tunnel test campaigns and high-fidelity simulations. To reach the experimental objectives, a set-up was designed, manufactured, and implemented within the ONERA S3Ch transonic wind tunnel facility. The first component, called gust generator, consists of two oscillating airfoils installed upstream of the wind tunnel test section and allows to produce air flow deflections. The second component, the test model, is a two degrees-of-freedom aeroelastic model of a supercritical airfoil. A test campaign has been performed leading to the generation of databases for high-fidelity tools validation. These databases have been used in order to assess the capabilities of the elsA code (ONERA-Airbus-Safran property) using its aeroelastic module and a gust model based on the field velocity method. A validation process has been defined to move from experimental results obtained in the wind tunnel with wall boundaries to industrial modeling computed with farfield boundaries. The full process was applied to a transonic case with sine gust excitation signals.

Biomimetic FAA-certifiable, artificial muscle structures for commercial aircraft wings

This paper is centered on a new form of adaptive material which functions much in the same way as skeletal muscle tissue, is structurally modeled on plant actuator cells and capable of rapidly expanding or shrinking by as much as an order of magnitude in prescribed directions. Rapid changes of plant cell shape and sizes are often initiated via ion-transport driven fluid migration and resulting turgor pressure variation. Certain plant cellular structures like those in Mimosa pudica (sensitive plant), Albizia julibrissin (Mimosa tree), or Dionaea muscipula (Venus Flytrap) all exhibit actuation physiology which employs such turgor pressure manipulation. The paper begins with dynamic micrographs of a sectioned basal articulation joint from A. julibrissin. These figures show large cellular dimensional changes as the structure undergoes foliage articulation. By mimicking such structures in aircraft flight control mechanisms, extremely lightweight pneumatic control surface actuators can be designed. This paper shows several fundamental layouts of such surfaces with actuator elements made exclusively from FAA-certifiable materials, summarizes their structural mechanics and shows actuator power and energy densities that are higher than nearly all classes of conventional adaptive materials available today. A sample flap structure is shown to possess the ability to change its shape and structural stiffness as its cell pressures are manipulated, which in turn changes the surface lift-curve slope when exposed to airflows. Because the structural stiffness can be altered, it is also shown that the commanded section lift-curve slope can be similarly controlled between 1.2 and 6.2 rad−1. Several aircraft weight reduction principles are also shown to come into play as the need to concentrate loads to pass through point actuators is eliminated. The paper concludes with a summary of interrelated performance and airframe-level improvements including enhanced gust rejection, load alleviation, ride quality, fatigue life and flight safety.

Surface Roughness Study of Milled Carbon Fiber Reinforced Polymer (CFRP) Composite Using 4 mm 2-Flute Titanium Aluminum Nitride (TiAlN) Coated Carbide End Mills

As the goal for aircraft weight reduction and low fuel consumption becomes a dire concern in aerospace industries, there is driving desire for the increasing use of advanced exotic materials such as composites, titanium and Inconels in the aerospace industry because of their high strength to weight ratio. Nevertheless the inherent anisotropy, inhomogeneous properties of CFRP and low bonding strength within the laminates make machining of these composite materials results in several undesirable effects such as delamination, micro-cracking, burr, fiber pull out and breakage. This paper discusses an experimental investigation into the influence of machining parameters on surface roughness when milling CFRP using 4 mm-diameter 2-fluted carbide end-mill coated with Titanium Aluminium Nitride (TiAlN). Relationship between the machining variables and the output variables is established and a mathematical model is predicted for the surface roughness produced during the milling process for the machining conditions investigated.

The Electrical Aircraft Network—Benefits and Drawbacks of Modifications

Many design objectives drive airplane development. Often aircraft weight reduction is the focus, with due consideration also given to safety, function, and performance. Aircraft weight reduction directly translates into fuel savings followed by reduced CO2 emission, and thus it supports environmental protection. A set of approaches to optimize the electrical system has been investigated for very large modern civil aircraft. Three of these approaches are presented and their benefits and drawbacks are discussed. Firstly the effects of a 230 VAC supply applied to all alternating current consumers of the electrical system are looked at. Secondly the idea of a central power center located in the middle of the aircraft is reviewed. Thirdly the consequences of a shift of allowed voltage drops from one part in the electrical system to others are considered. The investigations presented are part of the German-Spitzencluster-Wettbewerb-which is funded by the German Bundesministerium fur Bildung und Forschung (Fkz.: 03CL03A).