Testing, testing ...
Lufthansa Technik's engine test facilities in Hamburg and Frankfurt
In order to verify their certified thrust, engines are tested at an authorized test facility. After manufacture or overhaul, the engines must undergo these acceptance tests before they can be approved for flight operations. Lufthansa Technik operates appropriate test facilities for this purpose at its Frankfurt and Hamburg sites. The tests conducted at Frankfurt Airport are primarily specific tests on lease returns, as part of aircraft layovers, within the framerwork of smaller maintenance operations, so-called "B & C work scopes", and production acceptance tests for Rolls-Royce. The Hamburg test facility is used to inspect engines at the finest level of detail after complete overhaul, the "A work scopes".
There are two testing channels in Hamburg: the first channel, now used for APUs, has been in place since 1955; the second was established in 1963. Working two shifts, an average of seven engines are tested here each week. The Frankfurt test facility currently has around half the throughput of the Hamburg facility. Both facilities test CFM 56-5A, 5B, 5C & 7B engines, along with PW 4000 and CF6-80C2. The IAE V2500 is tested exclusively in Frankfurt. The test channels can accommodate engines with a fan diameter of up to 94 inches, around 2.39 meters, without problems. At the APU test facility, air measurements are also carried out, along with measurements of electrical power on APUs from Pratt & Whitney AeroPower (formerly Hamilton Sundstrand) and Honeywell.
A team of 30 personnel, primarily aircraft mechanics and aircraft electronics technicians with appropriate certification, are employed at the Hamburg facilities. When a fault is already known, the engine is first repaired by engine overhaul and then tested. If the fault has not been clearly identified, however, the engine is tested both before and after the repair. In a standard case, the engine only visits the test facility after an overhaul, when it is mounted in the test channel. All relevant values are then measured and the engine is then returned to the customer.
Before the test run, measurement equipent is first attached to the engine: The so-called "Bellmouth" inlet nozzle is mounted at the front to ensure controlled air intake. The cowlings are fitted on the outside to control secondary airflow, and the exhaust nozzles are fitted at the back of the engine. Depending on the engine type, different measuring equipment is used to measure pressure levels, temperatures, vibration, and frequencies. In this way, up to 2,000 engine parameters can be measured in parallel. An adapter is mounted above the engine, to mechanically transfer the generated thrust into the thrust measurement frame. The engine is then accelerated until the speed setpoint of the low-pressure turbine rotor (N1), which drives the fan, is reached. Between 30,000 and 60,000 pounds of thrust is generated, depending on the engine type.
As the tests are conducted within a building, the geometry of the building has a significant effect on performance parameters, as does the geometry of the inlet and outlet nozzles. These values must therefore be individually determined and documented for each engine type, in collaboration with the engine manufacturer. This allows the corrective values to be automatically taken into account for future tests and makes it possible for engine test results to be compared with those produced at any other certified test facility.
The test facilities in Hamburg and Frankfurt are not only used for conventional acceptance testing; special tests are also carried out which go far beyond the level of detail specified in the manual. This makes it possible for Lufthansa Technik to generate manufacturer-independent data and information for its own purposes relating to all current engine types. This can be useful, for example, in analyzing work scopes.
There are further test facilities available within the Lufthansa Technik Group, at the German subsidiaries and holdings N3 Engine Overhaul Services in Arnstadt and Lufthansa Technik Aero Alzey. Whilst Rolls-Royce Trent 500, 700 and 900 engines for widebody, long-haul aircraft are serviced at Arnstadt in Thuringia, the facility at Alzey in the Rhine-Hesse area specializes in engines and APUs for regional airliners.