NRFRAME TESTS J.X. Appleford Engineering Systems Division Aeroplane & Armament Evaluation Establisbment Boscombe Down, Salisbury, Wilts SP4 OJF UX 17.0 INTRODUCTION This Section outlines the flight testing required to demonstrate that each of the systems installed in an aircraft is suitable for its operational role(s). It is primarily written from the perspective of a military Flight Test Engineer (FTE) but most of the contents are applicable to civil aircraft. Reflecting the introductory nature of this Volume, its scope is limited to systems normally found in a11 aircraft, e.g., fuel, hydraulic, electrical, etc., systems. Tbe tests described below are usually made under the prevailing ambient conditions and, to assess behaviour under climatic extremes and in a11 weathers, further testing is conducted as described in Section 18. Tests of the propulsion system are covered separately in Section 23, but for systems associated with specific roles the reader should consult appropriate specialized sources (e.g., references 17-l and 17-2 for Airdrop and Arresting Systems, respectively). While the scope of the tests required in any particular case Will depend on the details of the aircraft's design, and on the intended operational usage, the aim is to offer sufficient guidance to enable the reader to appreciate and apply the general principles involved. Chapter 17.1 describes (in suitably broad terms) those aspects which are conunon to the testing of any aircraft system, the subsequent Chapters caver aspects relevant to particular systems, namely: 11.2 Anti/De-icing 17.3 Electrical 17.4 Engine Installation 17.5 Environmental Control 17.6 Escape 17.7 Flying Control 17.8 Fuel 17.9 Hydraulic 17.10 oxygen 17.11 Secondary Power 17.12 Undercarriage, Wheels, and Brakes and some concluding remarks are offered in Chapter 17.13. TO assist the reader with limited knowledge of aircraft systems, these latter Chapters each commence with a brief generic description of the system covered. Depending on the topic involved the format of subsequent paragraphs differ slightly but, typically, each Chapter covers the following aspects: - Paragraph 1 Description of System . Paragraph 2 Test Instrumentation Parameters . Paragraph 3 Preliminary Rig and Ground Tests . Paragraph 4 Flight Tests 17.1 QENERAL CONSIDERATIONS 17.1.1 Test Objectivea In broad terms, the main objective of aircraft system testing is to determine whether or not each system is likely to prove satisfactory when the aircraft is operated in its intended role(s). The term 'satisfactory" implies that, with the aircraft being operated anywhere within its required environmental Paper published by AGARD as part of AGARDograph 3W Flight Tes: Techniques Series - Volume 14, Seprember 1995, entiried “Introduction ro Flight Tes: Engineering”. 17-2 and flight envelopes, the system fully meets its design requirements and Will not: * Hazard the aircraft . Prevent it from fulfilling any aspect of its missions . Require undue maintenance effort, either in terms of "turn-round" time between sorties or long-term "cost of ownership". Important secondary objectives are to define the capabilities of each system, in both normal and emergency (system failed) operation, to identify any need for modification action and to provide appropriate systems operating procedures for inclusion in the Aircrew Manual. Civil and military aircraft are subject to forma1 general airworthiness requirements (which also define the acceptable means of demonstrating compliance with them), as exemplified in the UK by references 17-3 and 17-4, respectively. The FTE should therefore always consult the applicable requirements as an essential preliminary step in planning the test programme. HOWeVer, it should be noted that civil (and many military) design and test requirements are concerned only with airworthiness (or "safety") aspect*, and it Will often be necessary for the FTE (particularly one working for a military "certifying agency") to ensure that appropriate additional testing is conducted to assess the aircraft's "effectiveness" (i.e., its ability to fulfil a11 aspects of its missions without incurring an unacceptable sircrew workload or maintenance effort, etc.). 17.1.1 Overall Test Programme This volume is concerned specifically with flight testing, but it should be appreciated that, as far as aircraft systems testing is concerned, flight testing is usually the last link in a long chain. Typically, each individuel system is subjected to extensive preliminary ground testing on the bench (component tests) and on a suitable rig (sub-system and complete system tests), categorised in the UK as "Stage A" testing. Wben a11 the various systems bave been installed in the aircraft, ground tests of each are conducted using ground power ("Stage B" tests) and then with power provided by the aircraft's agine ("Stage C" tests). As the individual systems then form part of the complete aircraft, the interactions between them should be fully representative. It should be noted that the ground tests (particularly the Stage A tests) offer the opportunity to undertake testing of a type or depth which would be too difficult, risky or expensive to conduct in flight. For example, the effects of jamming of a non-return valve in a fluid control circuit cari,, sensibly, only be studied via grand tests on a bench or rig. For this reason, much of the detailed evidence required to establish confidence in system design and performance is, in fact, derived from ground rather than flight tests. c~nce each system has successfully completed the Stage C tests, the aircraft is cleared for flight testing. c1ear1y. as flight involves simultaneous use of most, if not ail, systems it is sensible (and cost-effective) to SO structure tbe flight test programme that data relevant to several systems (and/or to the aircraft performance and handling qualities tests of Sections 13 and 15, respectively) is obtained from the same test points. While *orne pointer6 are offered in the following paragraphs. the flight test engineer should always consider this aspect when constructing his flight test programme. 17.1.3 Te& Aircraft The *ystern* installed in the test aircraft should be fully representative, in a11 material respect*, of the production standard. In this context it should 17-3 be noted that the performance of one system cari be affected by the performance of another with which it interacts, so that it is important that a11 systems, and their interfaces be of the production standard. If one cl+ more system(s) is/are immature (as is often the case), the need for "repeat" testing must be given careful consideration. Where malfunction or failure degradation of a system cari bave an adverse effect on the aircraft's flying qualities or performance, it may be necessary to simulate such failures in flight via special test equipments (e.g., autopilot "runaway box", non-standard fuel tut-off valve, etc.). Where such equipments are installed, their interfaces with the normal aircraft systems must be such that there is no risk of unwanted interactions with the latter. 17.1.4 Te& Instrumentation In general, most of the flight testing described in this Section Will be conducted in conjunction with that in respect of Performance (Section 13) and Handling Qualities (Section 15). and many of the parameters of interest (such as flight conditions, aircraft configuration and pilot inputs) Will be common. As advice in respect of those parameters is readily available (e.g., reference 17-5 identifies parameter types, ranges, accuracy and sampling rates), Paragraph 2 of each chapter below lists only those parameters (such as temperatures, pressures, flow rates, etc.) which are typically needed to quantify the performance of the particular system under consideration. HOWeVer, it is emphasised that, in practice, the choice of parameters and sensor locations (and of ranges and sampling rates, etc.) must be based on intimate knowledge of the architecture of each system, its mode of operation, and the results obtained during the preliminary bench, rig and ground tests. More general advice on test instrumentation topics may be found in reference 17-6. 17.1.5 Natur. and Scope of Ta&6 Wbile the ergonomies of system operation must be considered, aircraft systems testing is less dependent on aircrew subjective judgement than is, say, the assessment of flying qualities. In cases where assessment cari be based solely on analysis of quantitative data, the manufacturer's development programme may well satisfy many of the certifying agency's needs provided that, where matters of "engineering judgement" are involved, the latter's FTEs bave adequate first-hand access to it. In meeting the overall objectives outlined in paragraph 17.1.1 above, both "normal" and "abnormal" operation of the system must be considered. "Normal" operation implies that the system is fully serviceable and being operated in accordance with the specified procedures. The nature of the flight tests undertaken Will depend on the system under investigation, and the results of the preliminary ground tests. The case of operating the system should be assessed in the context of the workload imposed by other mission- related tasks, and system performance should be monitored via the appropriate flight test instrumentation. In accordance with the guidance on flight test safety given in Section 10, the approach to potentially demanding conditions should be progressive to permit any deterioration in system performance to be identified before it constitutes a flight safety hazard. If any significant shortfalls become apparent before the design operating conditions are reached, modification action should be considered (and, if taken, the bench and/or rig tests repeated as necessary before resuming the flight triais). "Abnormal" operation includes any system malfunction or failure whose probability of occurrence is insufficiently remote for it to be discounted, the "se of any stand-by or emergency systems that are provided to caver such eventualities, and the effects of aircrew errer in operating the (serviceable) systems.