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Tests for leakage identification on Aircraft fluid Mechanical Installations

Periodic Reporting for period 2 - TAMI (Tests for leakage identification on Aircraft fluid Mechanical Installations)

Reporting period: 2018-04-01 to 2019-03-31

Currently, most of leakage tests on aircraft systems are done using the fluid for which this system is designed. Some of these system fluids, like hydraulic fluid and fuel are highly polluting and toxic. Apart from the use of costly fluids which often have to be wasted, there is a need to prevent major loss of time and construction materials used in assembly due to rework. In addition to the hazardous nature of combustible aviation fuel and the acidic nature of Skydrol, they create slip hazard and containment requirements.

The project action will aim to remove the costly and hazardous liquids from the testing regime for aircraft fluid systems and components where possible by substituting the in-service fluid with a test gas. This means replacing aviation fuel, Skydrol and other expensive liquids with either compressed air, hydrogen/nitrogen or helium (balloon gas) test gases. In some instances, the test gas can be recovered to reuse in subsequent test cycles.

Tests for leakage Identification on Aircraft fluid Mechanical Installations (TAMI) will develop and demonstrate modern methods and strategies for leak testing aircraft gas systems, fuel systems and fuel tanks. The overall objective is to deliver more ecological, more efficient, reliable and lower cost means for leak testing of aircraft fluid mechanical systems.

TAMI is part of an over-arching CleansSky 2 project and meets a Call for Proposals from to provide a practical path to leak identification in aircraft. Additionally, TAMI carries out laboratory tests to check models and simulations from a complementary theoretical path coordinated by the Topic Manager. The objective is to ensure that the pass/fail criteria established by the practical tests are underpinned by sound theoretical foundations.
Summary of Activities to M15

In the initial stage of the project the beneficiary (TQC Ltd, UK) established a working relationship with the Topic Manager, and other partners working on the State of Art and theoretical considerations. At the TAMI ‘kick-off’ meeting the Topic Manager gave an overview of the synergies between the theoretical and practical paths of the project. There were presentations by the theoretical path (PASSARO) and by TQC as the sole beneficiary of TAMI.

The main technical effort during this period was to get a more detailed understanding of the nature of the target systems on the aircraft to be tested for leakages. The engineering team at TQC completed a first cut design of the TAMI test bench and concept designs for aircraft representative structures for the practical laboratory tests. An draft version of the specifications for laboratory test was completed, including a template for recording test results. Detailed engineering designs have been completed for the TAMI test bench and the target volumes to be used in laboratory tests. The TAMI test bench will comprise of instrumentation and interfaces for conducting leak tests using tracer gases and pressure decay.

Additionally, TAMI designed and assembled bespoke apparatus to test leakages through pinhole orifices. The objective is to corroborate the leak rates derived by the theoretical path with the aim of establishing the correlation between liquid (fuel) and (test) gas leakages.

Summary of Activities to M27 (end of project)

The TAMI Bench has been fabricated, assembled and factory tested. In brings together in one place the test methods that can be applied to each of aircraft gas fluid systems (WP1), fuel tanks (WP2) and fuel systems (WP3) in order to detect and quantify leakages. It comprises instrumentation to: sequence and control different types of leak test methods; monitor and capture data during the tests; and record the results.

The tests methods supported are tracer gas (Helium) detection, pressure decay, and differential pressure change. The pressure decay method is only sensitive enough for aircraft pipe systems with small to medium volumes, but it is also used with larger volumes to preclude a gross leak in the test cycle for tracer gas detection.

Factory testing was carried out to develop the procedures for the different leak test methods. This is a relatively complex process that requires a deep understanding of fluid mechanics and the leak test cycle. A significant part of the development of test procedures involved calibrating the instrumentation, refining the software control programs, and configuration of the leak test cycle and software to achieve an acceptable level of sensitivity, reliability and repeatability. This process had to be completed for each test method and aircraft system.

The results of the tracer gas method demonstrated that the TAMI bench could be used with a Helium sniffer to detect leaks at proposed sensitivity. An exercise comparing Helium detection with Bubble growth was carried out showing the correlation between them demonstrated the Helium method is more accurate as the leak rate gets smaller.

Finally TQC's own Micro Application Leak Test (MALT) instrument, which is incorporated in the TAMI bench, was used for the (differential) pressure decay method. This is very accurate for small volumes. The MALT unit is best used to ensure components are leak tight before assembly.

The TAMI factory tests at TQC established feasible leak test parameters and control program configuration in preparation for the aircraft systems on the AIR ITD.

Testing on aircraft wing have been completed. The activities in the real environment focused on a leak testing method based on tracer gas (i.e. helium) detection, as this was identified as the most compatible with the aims of the project, i.e. efficient, ecological and sustainable. The results showed that the tests methods were able to detect leakages to at least the required sensitivity. Additional comparative experimentation on specific equipment is required to set precise pass/fail criteria acceptable to the client and industry standards.
This impact of the TAMI this test bench is that it will provide compact and clean leak testing instrumentation that can be moved around an aircraft hanger and connected to the various aircraft systems as required. The operator can select the type of test to be performed and configure the process accordingly.