Jet engine test bench

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A jet engine test bench is a test bench approved to demonstrate the certified thrust of a jet engine . After a new production or overhaul, a jet engine must pass this acceptance before it can be released for flight operations.

Test benches are basically divided into different categories. A distinction is made according to the type of construction:

  • Free field test stands
  • Building test stands

According to the purpose, test stands are divided into

  • MRO test stands, where MRO stands for the English term M aintenance, R epair & O verhaul, in German about maintenance, repair & overhaul;
  • Development test stands.

A test run is essentially about, on the one hand, the mechanical integrity in the form of a leak test and vibration test, and on the other hand, the required performance parameters in the actual performance run, e.g. B. the thrust to demonstrate. Many different parameters are checked for the specifications defined by the engine manufacturer and corrected for standardized conditions, including the so-called ISA conditions, in order to obtain comparability of the performance parameters.

Free field test bench

On a free-field test bench, the engine is fixed to an oversized gallows and can freely suck in air without any limitation and release the exhaust gas jet back into the environment without hindrance. The disadvantage of these test stands is that the noise generated is the same as when an engine works under the wing of an aircraft. Such test stands can therefore only be found in extremely sparsely populated areas.

Building test bench

This variant is the most common form. Until a few years ago it was common for large airlines such as B. Lufthansa overhauled their drives themselves and then carried out appropriate test runs. For example, Lufthansa operates B. in Hamburg and Frankfurt in close proximity to their maintenance station at the airport appropriate test stands. The disadvantage of these test stands is that the geometry, in particular the intake cross-section and the exhaust gas mixing pipe, have a very significant influence on the performance parameters. These values ​​must be determined once for each type of engine using a ring comparison with the engine manufacturer and then remain valid for future test runs. The values ​​are usually stored in computer programs and automatically taken into account in the necessary calculations.

The design of such test stands is diverse. Usually only cross-sectional shapes of a standing "U" are built today, with vertical air intake, horizontal engine positioning and vertical deflection of the exhaust jet by 90 ° into the atmosphere.

MRO test bench

An MRO test stand is usually a normal building test stand, as already mentioned, it can be found at almost every major airport in the world. For a normal test run between 100 and 300 parameters are recorded, the high number being explained by the modern engines and their controllers ( FADEC ).

Development test stands

A development test stand can be both a building and an open field test stand. The main difference to the MRO test stands lies in the requirements placed on the measurement technology. Up to 3000 measuring points are reached, the data of which must be recorded with a high recording rate (up to 2 kHz) and a higher measuring accuracy than with MRO test benches.