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1 ASU Propulsion Test Centre Engine Test Bench: major milestone for project team - commissioning of the Dynamometer Control system

The South African Air Force boasts in its arsenal the mighty Hercules that serves as a tactical and strategically cargo air lifter. This popular aircraft is powered by four Allison T56 engines that can each deliver up to 3700 kW. Although the engines are incredibly reliable they still require maintenance and in some cases a complete overhaul.

T56 Engine Test Bed With Dynamometer and Flywheel

After 1 Air Servicing Unit overhauls the engine it is required that the performance of the engines be tested to see if it is functional and strong enough for use on the aircraft. Some people might suggest that the engine be tested on the aircraft wing but this is very dangerous since the engine could malfunction and cause considerable damage to the aircraft itself. For this reason a test bench was built to test the engine before it could be installed and operated on the aircraft.

The fist Engine Test Bench was built at Thaba Tshwane for 1 AD and operated for about 10 years until one of the operators noted substantial cracks in the facility walls. Upon investigation it was found that the facility had developed a sinkhole underneath it and the area was subsequently condemned leaving the SAAF with out a testing facility.

With the C130 fleet still in operation and with no other testing facility in Africa the replacement of the Engine Test Bench became a strategically requirement.
Air Force Base Waterkloof was identified as the location and the drafting process was initiated. With the new facility, additional upgrades were also incorporated. These include the construction of two test cells in the facility as opposed to the one in the condemned facility, the replacement of the old Data Acquisition system and the replacement of the Dynamometer Control System.

Capt C. Versteeg

The two test cells are required because the SAAF does not only require T56 engines two be tested, but also the Pratt and Whitney PT6 range together with the GTCs and APUs used for air start systems and auxiliary power generators respectively. In the old facility a considerable effort was required to “swap” the test cell for the different engines.

The new Engine Test Bench facility was unveiled on 31 August 2006 by Lt Gen C. Gagiano and the reassembly of the old test bench was initiated. This required the reinstallation of the skids that the engines were mounted on, the reinstallation of the 17 ton exhaust, reassembly and servicing of the Froude Hoffmann dynamometer, installing the 5000 m of wiring as part of the sensing and control and adapting the Control Desk to accommodate the upgrade changes.

The new systems that were acquired included the National Instruments Data acquisition Hardware and the Froude Hofmann Texcel VX100 Dynamometer Controller. These new systems provide expandable and extended capabilities as well as an increase in reliability.
One of the major milestones for the project team was the commissioning of the Dynamometer Control system. In order to commission the Controller all systems required to test engines had to be functional since the engine is operated through its full performance profile. This was completed on 19 December 2008 together with the commissioning agent from Froude Hofmann in the United Kingdom. This was the first full performance run since the previous facility was condemned and concluded the most difficult hurdle with regards to the reassembly of the Engine Test Bench.

1 ASU Propulsion Test Center with Air Intakes Top Left

The project team was led by Captain Christo Versteeg a Mechanical Engineer stationed at 1 ASU. The reassembly was managed by SAAF Engineering Services and executed by members from 1 ASU as well as 5 ASU.

The Allison T56 engine is capable of generating 3660 kW (230 rps * 2π * 2576 Nm Turbine Output) with the planetary gearbox reducing the speed to 16.98 rps but increasing the torque to 34 879.04 Nm. The Froude Hoffman F63 dynamometer can absorb up to 6700 kW and has a maximum torque rating of 50 000 Nm. This is the largest dynamometer operating in Africa and is ideal for high torque and quick response applications.

During 2009 the facility will experience further development with regards to the PT6 test cell with the installation of a overhead crane, wiring and an exhaust manifold. The establishment of having a T56 engine testing capability in Africa has sparked a great deal of interest from civilian companies with the prospect of having a local testing facility. The 1 ASU Propulsion Test Centre might quite soon not only serve the South African Air Force but also the whole of Africa.


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