Indian Light Combat Aircraft Research Articles

Designer Solid Shims for Assembly of Advanced Carbon Composite Pre-preg based Aircraft Structures

A modern combat aircraft uses considerable amount of advanced composite material in structure build for better flight performance, stealth requirement and higher payload. Combat aircrafts made using composite structure require large numbers of custom shims of various thickness and shapes throughout interface surface, which are presently prepared by suit on assembly process to fill gaps measured between sub-structure parts and skin. The scope of study is four plus generation combat aircraft like Indian Light combat aircraft. These gaps arise due to composite raw material characteristics, mould tool and manufacturing process which results in geometry variation. This research has focussed the delta wing integral fuel tank composite structure. However, these research findings can be applied in other wing shapes made by composite part within the scope. The shims, whether liquid or solid, are necessary to eliminate gaps, maintain structural performance and minimize pull-down forces required to bring the aircraft into engineering nominal configuration for aerodynamic efficiency. Customized shims amount to significant delays in production with much of the time being spent in the critical path of the aircraft assembly. In this research work, we present an alternative strategy for the use of designer solid shim, based on redesign of lay-up moulding tool (female type) and shims manufacturing with change in existing manufacturing value stream. The experimented method has reduced the manufacturing cost of wing assembly, shorten the shimming process cycle and improve the assembly efficiency, product quality and performance.

Structural Life Management in a Combat Aircraft

The paper briefly describes some of the underlying concepts, issues and strategies for ensuring efficient management of structural integrity of an airframe throughout the useful life of an aircraft—especially that of a military combat aircraft. Much of the discussion in the paper is based on the experience of the authors during the design and development phase of the Indian light combat aircraft, namely, LCA Mk-I Tejas, and the information available about the LCA in the open literature or public domain. Even though not an ageing aircraft, LCA is taken as an example to facilitate bringing out various issues and strategies to resolve them, particularly with relevance to the Indian aeronautical scenario. The use of both metallic and composite materials in modern combat aircraft structures necessitates different design strategies to be adopted for their structural integrity throughout their lifetime. In this respect too, the LCA serves as a good example. Within the limited scope of the paper, the description and discussions are primarily limited to some of the important aspects, such as the fatigue degradation in metallic materials and impact damage in composites—which do form the bulk of the effort of life management of airframe structures. Other issues such as corrosion in metals and environmental degradation in composites are also briefly mentioned. A brief description of the aircraft and its structure is given initially. Major steps in designing for structural life management, such as, estimation of static loads, derivation of fatigue spectra for the intended usage, degradation through fatigue or impact damage, lifing philosophies, estimation of life and monitoring of health and usage of individual aircraft are described. A brief mention is also made about structural health monitoring (SHM) as a future direction in life management. It is expected that the exposition in the paper will help understand issues and strategies that would eventually be required as a combat aircraft gets aged in service.

Clearance of Flight-Control-System Software with Hardware-in-Loop Test Platform

The Indian Light Combat Aircraft has flown more than 2000 flights, including trainer and naval variants, without encountering any major faults in the flight safety-critical fly-by-wire control software. This is partly due to the stringent quality control and rigorous testing of the control-law and air-data-system algorithms carried out on various ground platforms before flight. One of these ground test platforms is the hardware-in-loop test platform (Iron Bird). The processing of tolerance bounds to define the pass/fail criteria is an algorithmic development. It guarantees the correctness of the modules, if the set of inputs generates a set of outputs within processed tolerance bounds. This paper presents the philosophy behind the design of test cases and the tools developed to evaluate the control-law and air-data-system modules on the Iron Bird platform, and the procedure to clear the test results. The computation of tolerance bounds and algorithms for their processing have been evolved over a period based on several criteria, testers’ experience, and the experience gained during various levels of testing of air-data-system and control-law algorithms. This process yielded excellent results, and is accepted as a formal clearance methodology for the onboard safety-critical fly-by-wire system software.

Application of System Identification Techniques to Tejas Flight Test Data

Tejas, the Indian Light Combat aircraft, is a fly-by-wire aircraft with relaxed longitudinal stability that provides for enhanced agility, high maneuverability and performance. The aircraft is presently undergoing extensive flight test trails and the flight data gathered is being used by various design groups to evaluate aircraft systems, performance and aerodynamic characteristics. This paper gives an overview of the application of system identification techniques to Tejas flight test data for validation and update of the aircraft aerodynamic database. The aerodynamic characterization is carried out using two different approaches i) point model identification, and ii) coefficient level matching. Typical results are presented from both the approaches along with the time history plots from the flight updated aero database. The main purpose of this paper is show to how system identification techniques can lead to accurate determination of aerodynamic characteristics from flight test data.

Automated Aircraft Sheet Metal Component Production Technologies

This article comprehensively presents an overview of the technological advances in automated aircraft sheet metal component production technology developments due to the initiative by the Aeronautical Development Agency, Ministry of Defense, Government of India, since 1989 in collaboration with the Indian Institute of Technology, Bombay. Commencing with a modest computer-aided flat pattern development software system suitable for a class of sheet metal components, this activity after several stages of development has now resulted in the development of full-fledged, personal-computer-based graphical interactive, three-dimensional application flat pattern development and automated production loft generation system. This research, encompassing the practical methods (exclusively developed for flat pattern software), literature survey, development of key algorithms suitable for designing a system for automated loft generation for a variety of surfaces with complex geometric features characteristic of aircraft sheet metal components with the aid of a wide choice of surface model creations, and testing and validation (carried out through an associated aircraft factory, Hindustan Aeronautics Limited), is now being published through four full-length papers concluding with the present paper. In fact, comprehensive illustrations of production lofts sampled from over thousands of parts used in the factory pertinent to the Indian Light Combat Aircraft (termed as Tejas) and other projects like Advanced Light Helicopter (termed as Dhruv) sheet metal components are included here to provide insight into these developments, and also to provide a glimpse of the success of the mission of indigenous automated aircraft sheet metal component manufacture.