Overview of Helicopter HUMS Research in DSTO Air Vehicles Division

Transcription

1 AIAC-12 Twelfth Australian International Aerospace Congress Overview of Helicopter HUMS Research in DSTO Air Vehicles Division Dr Ken Anderson 1 Chief Air Vehicles Division DSTO Australia Abstract: This paper will give an overview of the structure of the DSTO Air Vehicles Division, including listing all activities in this area which are appropriate to the Special Stream on International Collaboration on Helicopter HUMS Research. DSTO has a long history of involvement in both usage and health monitoring for helicopters as well as relevant work on other platforms. This paper will try to place this work in some perspective as well as indicate areas of current interest. 1. INTRODUCTION. Defence Science and Technology Organisation (DSTO) is the prime Science and Technology provider for the Australian Defence sector and is part of the Australian Department of Defence. DSTO is headed by the Chief Defence Scientist who sits with the heads of other Defence agencies on the major Defence Committees. The structure of DSTO (from early 2007) is in the following chart (Fig 1). Figure 1 - Chart of DSTO from early Corporate rather than personal presentation so DSTO reserves right to change presenter. Fifth DSTO International Conference on Health & Usage Monitoring HUMS2007

2 Air Vehicles Division (AVD) of DSTO has a long history commencing as the Mechanical Engineering, Materials, Structures and part (Air Operations Division contains the rest) of the Aerodynamics portion of the original Aeronautical Research Laboratory (ARL) at the old Fishermens Bend airfield, the cradle of Australia s defence aircraft industry. AVD comprises about 200 people and itself has four branches, each headed by a Research Leader, as per the following chart (Fig 2). Most of the work on Health and Usage Monitoring to be described in this paper is performed in the Aircraft Structures and Propulsions Systems Branches. Figure 2 - Chart of AVD Structure USAGE MONITORING. Predominantly, the term usage monitoring is taken to mean the collection of data to determine the fatigue counts seen by critical (or fatigue-limited) components of the helicopter. This may be done at various levels by either counting individual cycles of loading (High Cycle Fatigue since the numbers before failure will be high) or by counting major sequences such as Ground-Air-Ground cycles or engine starts (Low Cycle Fatigue). 2.1 History of usage monitoring involvement. During World War 2, the Fishermens Bend site was also used to manufacture aeroplanes. During the period after the war, Structures Division ARL (now AVD Aircraft Structures Branch) used the completed wings of otherwise incomplete aircraft to empirically determine the equations behind metal fatigue (1). As a result, in 1947 H A (Arthur) Wills published the famous seminal paper which defined, for the first time, the technique used today to determine fatigue lives of aircraft structures. In the 1970 s, two more projects at Fishermens Bend further extended this background - a. The Gust Probe Trial on a Mirage 3 aircraft determined the forcing functions involved in fatigue due to atmospheric turbulence, and b. The Fatigue Life Indicator established the process of converting measured torque (or load) to fatigue counts directly and in-flight. 2

3 In more recent times, full scale fatigue tests [Ref 1] at accelerated count rates have revolutionised fatigue testing of aircraft, first on the F/A-18 and most recently on the LIF Hawk. 2.2 Current usage monitoring directly for helicopters All aircraft and helicopters have some level of usage monitoring ranging from pilot-completed paper forms to automatic data systems. Recent changes show that the level of the usage monitoring desired has increased. The reason can be traced back to the rising capital cost of the engine and airframe. If a simple recording system is used, each component lifed from that data is assumed to see the maximum number of counts in the data. Put simply, if the data for the fleet shows a scatter across a range of usage, simple techniques put a line a safe distance above the top of all that data and apply that conservative line to all components in the fleet. If an individual recording system is used for each engine or airframe, the line needs only be the safe distance above the actual line for that component and every component has a conservative life recorded using the actual counts for that component. In practise, this means the safe lines average a safe distance above the average while in the simple case above it is a safe distance above the worst case. Hence we obtain considerable cost savings (in components not needing replacement) with no reduction in safety. But not at zero cost. The individual recording system implies the need for (i) high data integrity, (ii) mechanisms to allow for any lost data, (iii) comprehensive data management and (iv) the cost of additional equipment and installation. AVD has programs involving usage monitoring of helicopter airframes and of engines (including helicopter engines). Subsequent presentations in this conference will describe these in detail. 2.3 Current usage monitoring which may also be relevant to helicopters AVD also has programs involving usage monitoring of airframes of aircraft other than helicopters and these are not described in this paper. These programs may also produce results relevant to helicopters. 3. HEALTH OR CONDITION MONITORING. Predominantly the phrase health monitoring is taken to mean the collection of data to determine if wear or mechanical failures have endangered the operation of the helicopter or a component of the helicopter. These may be the same components defined as fatigue-limited in the usage monitoring case but may often not be. Interestingly, whereas many of the earliest experiments in usage monitoring involved aircraft structure, health monitoring was born amongst the propulsion bits such as engines, gearboxes, rotors and the like. Two interesting areas of health monitoring development will be mentioned: Transmission Vibration Monitoring. During the later half of the 1970 s and early 1980 s, the Royal Australian Navy routinely recorded vibration signals from helicopter transmissions and forwarded them to DSTO for analysis on a when available basis. Unfortunately, the one recording in December 1983 which needed to be analysed quickly was not because the person doing that analysis was away and a helicopter crashed with the loss of two lives. The counter to that bad result was possession of a sequence of recordings of a fault developing towards failure; a natural fault at that, not one seeded or artificially created. Over the next few years, a number of teams around the world used these series of recordings as validation of their algorithms for transmission health monitoring - by 1986 at least two teams in UK plus a group at DSTO could find hardware faults using vibration signals well before failure and these techniques entered service in the so-called first-generation North Sea HUMS of (2) 3

4 3.1.2 Chinook Engine Monitoring. The early 1980 s also saw development of a monitoring program for the engines in a CH-47C helicopter. This was before digital storage media and most of the technology needed to be developed from scratch. However, once installed and validated, this recorder ran for many months sending back tapes of up to 32 variables across the two engines and flight parameters. Lessons learned from this process included modular data acquisition design, checking data as quickly as possible, data management/storage arrangements and simple maintenance procedures. 3.3 Current health monitoring which may also be relevant to helicopters A wide range of work on fixed wing aircraft and other mechanical systems may also be relevant to helicopters. 3.4 Relevant work in other Divisions Monitoring depends on sensors and data acquisition from those sensors. AVD and another DSTO Division, Maritime Platforms Division (MPD), have worked for some years to produce improved sensor technologies. These fall into a number of classes:- 1. Corrosion sensors; 2. Smart sensors; and 3. Networked data collection. 4. MONITORING SYSTEM ASPECTS The previous two sections have discussed work specifically for usage and health monitoring. However, additional work on the implementation and system aspects of these monitoring processes are essential for these technologies to be useful. AVD work in this area falls into a number of categories. 4.1 Acquisition Advice While DSTO has been occasionally called upon to provide advice relating to projects to fit monitoring systems to existing platforms, the need for advice about optional and included monitoring systems in future acquisitions has become a major component of our work. One aspect of acquisition advice is cost-benefit modelling. Although it is possible to use general purpose software models, or even spreadsheets for such purposes, AVD involvement has included development of the only HUMS-specific Cost Benefit model, HUMSSAVE. Originally targeted at helicopters and used world-wide, HUMSSAVE now has wider application. A separate paper will cover recent work in that area. 4.2 Validation and Certification When a monitoring system has been fitted to an existing platform or a new platform acquired with a system fitted, the monitoring function, data processing and data management must all be validated before items such as the engine or airframe can be certified using the information from these systems. In recent years, most new acquisitions, ranging from land vehicles to aircraft have needed these validation and certification steps. AVD involvement has varied from providing advice to hands-on involvement in the process. 5. CONCLUSION. Air Vehicle Division has a long history in both health and usage monitoring. In many respects, the techniques of health and usage monitoring underlie a large proportion of the work conducted by the Division. 4

5 Following DSTO papers in this conference will look specifically at three areas directly relevant to monitoring helicopters. REFERENCES. 1. The History of Structural Fatigue Testing at Fishermans Bend Australia, Scientific & Technical Report, L. Molent, October 2005, DSTO-TR Helicopter Gear Box Condition Monitoring for Royal Australian Navy, K.F Fraser & C.N. King, proceedings of 41 st Mechanical Failures Prevention Group, Naval Air Station Patuxent River, MD, October