Defence

Defence Science and Technology Organisation

Keeping military vehicles in the air

The Defence Science and Technology Organisation (DSTO) has provided science and technology (S&T) support to the Australian Defence Force (ADF) aerospace capability over many years. This support encompasses the full capability life cycle for manned and unmanned fixed-winged aircraft and helicopters. Dr David Wyllie explains.

The Air Vehicles Division (AVD) is a Melbourne-based division of DSTO. AVD provides scientific leadership and support for the planning, acquisition, cost-effective operation, safety of flight, simulation modelling and through-life support of air vehicles. This leadership and S&T support includes:

• scientific advice in support of aircraft acquisition decisions
• scientific support to increase aircraft availability and safety
• methodologies to quantify and reduce cost of ownership.

Keeping ADF vehicles flying

From fighter jets to transport aircraft, from helicopters to unmanned aerial vehicles (UAVs), the ADF operates a diverse fleet of aircraft. Making sure that those aircraft are safe to fly is a critical job for ADF airworthiness engineers, who rely heavily on AVD to provide them with the right advice. The safety level to which the ADF operates is governed by airworthiness standards, and AVD provides advice to the ADF on interpretation and implementation of those standards.

Hawk Lead-In Fighter Test

F/A-18 Centre Barrel Test

Structural integrity degrades during the life of an aircraft due to such factors as fatigue, corrosion, disbanding and physical damage. In some cases, degradation can be monitored by inspections, and AVD gives advice to the ADF on where to inspect, inspection techniques and intervals, and repair options. In other cases, it is life limiting, and AVD assesses the life of aircraft. Sometimes the life does not reach that which the ADF wishes, and AVD assists the ADF to extend the life. This can be done by reworking, reinforcing, refurbishing or replacing critical structural parts. The choice between these options is usually based on cost.

A key focus in AVD is to assess the expected service life of an airframe due to fatigue cracking. This life assessment work in AVD is both experimental and analytic. The division has large facilities for testing anything from small material specimens up to whole aircraft structures. The tests can be simple static loading of specimens in a testing machine to verify strength, or they can be a cyclic application of the service load history of an aircraft in a rig to verify its fatigue behaviour. The state of the art is a full-scale fatigue test of a whole aircraft, in which loads are applied by many actuators attached to the structure. The loads represent the aerodynamic and inertia loads due to flight. The actuators are computer-controlled to cycle in synchronization. This generates the required load distributions over the aircraft for all flight manoeuvres and effectively produces a simulation of the actual aircraft flight from takeoff to landing.

F/A-18 Centre Barrel Test

Over the past decade or so, the ADF has been continually improving its management of aircraft engines and mechanical systems, and AVD has been actively contributing to this effort, particularly for the TF-30 engine (the power plant of the F-111) which had to face a contracting Original Equipment Manufacturer support environment.

AVD has significant capabilities in the lifing of critical gas turbine engine components and also serves as a centre of expertise for the ADF on health condition monitoring of propulsion systems. Support and advice is provided on performance monitoring of gas turbine engines, oil wear debris analysis, and system analysis of Health and Usage Monitoring Systems (HUMS). The AVD capabilities have also enabled DSTO to take a lead in the assessment, prediction and development of suppression systems for the control of infrared signatures of air platforms. This role continues to gain importance, as the infrared signature has become a defining characteristic of combat capability for modern air platforms.

Forensic investigations

AVD provides a world-leading capability for forensic examination of defence systems. Urgent operational requests are received on a daily basis to determine why certain material failures have occurred, and the subsequent advice can play a key role in determining if a particular aircraft type should be grounded while further investigations are conducted. This expertise is applied to a wide range of ADF platforms (Air Force, Navy and Army) and underpins the crucial technical role that DSTO provides for aircraft accident investigations. AVD maintains an immediate response capability in the event of an aircraft accident and initially collects physical evidence at the site and then carries out in-depth studies back in Melbourne, so as to provide expert, impartial advice to the Accident Investigation Team and any subsequent board of inquiry.

New aviation force

With the fleet of ageing aircraft, the ADF is slowly migrating to a new aviation force structure that is a mix of militarised commercial aircraft, new-generation military aircraft and uninhabited aircraft. Historic analysis through data mining of past and current ADF aircraft maintenance and operations aims to identify the drivers for platform cost and aircraft serviceability. The research aims to understand the complex and dynamic relationship between these factors and will be used to inform future capability requirements, provide advice on acquisition and optimise ongoing through-life support.

Finite Element Model of the TF-30 Engine

AVD houses and operates national aerodynamic facilities such as the Australian Transonic Wind Tunnel and the Low-Speed Wind Tunnel. These technologies and infrastructure are used to develop aircraft performance models for use in operational analysis studies; to determine aerodynamic loads in support of airframe life extension programs; to predict the aerodynamics of new weapons systems carried and released from ADF aircraft; and the structural dynamics, vibration, aeroelasticity and flutter of aircraft to ensure safety of flight. Emerging flight mechanics research areas include novel aerodynamic control, weapon bay aerodynamic and acoustics, along with optimisation of the aerodynamic design of Unmanned Aerial Systems (UAS) and uninhabited combat aerial vehicles (UCAV). UAS–UCAV is a burgeoning field of vehicle system research as the market place is inundated with new systems—commercial off the shelf and new designs.

Aerosonde UAV model in Low-Speed Wind Tunnel
Photos provided by DSTO

Materials science is an enabling technology and advanced materials and concepts allow improved capability through increased range, speed, load capacity and reduced signature. Advanced composite systems now form the bulk of the structures in aircraft such as the Joint Strike Fighter(JSF), and the Eurocopter Tiger and MRH-90 helicopters. Research is also being undertaken to develop novel composite repairs for the JSF through a JSF Science and Technology Advisory Board sponsored program. Concurrent advances in materials science, electronics and information technology are now making Smart Materials possible in which structures can sense and respond to the initiation of damage (for example corrosion). Such concepts will revolutionise maintenance procedures with potentially large reductions in cost and greater availability of aircraft.

Interactions with industry and academia

DSTO undertakes much of its aerospace research in collaboration with industry and academia. The outcomes are of benefit to the ADF, Australian industry and Australia's research and development community. AVD plays an important role in a number of the alliances DSTO has with key Australian industries and has a number of licensing arrangements in place—for example, vibration-based health monitoring, where some unique advanced algorithms have been patented and licensed to industry for product development. Interactions with universities are facilitated through Centres of Expertise and Cooperative Research Centres.

Dr David Wyllie is the Chief of Air Vehicles Division.

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