Level Acceleration Flight Test Methodologies for Helicopter Performance Evaluation

Determining the performance of a helicopter in level flight is of fundamental importance, both strategically and in terms of certification. The most common methodology for testing this is based on implementing an extensive set of precisely stabilised and trimmed measurement points. Measurements are taken across a wide range of helicopter weights, altitudes, and flight speeds. This procedure is highly time-consuming and can significantly impact the total time and cost of flight testing. This paper therefore, proposes an alternative test methodology that aims to increase the efficiency of the performance determination process by using acceleration tests to quickly cover the analysed range of test speeds. To this end, two techniques were considered: acceleration in horizontal flight and quasi-steady acceleration in horizontal flight. Practical research found that the horizontal flight acceleration technique, commonly used for high-performance aeroplanes, does not apply to helicopters due to fundamental differences in control logic. Consequently, a new methodology of quasi-steady horizontal flight acceleration was developed and tested as a potential alternative.
This method involves slow acceleration in horizontal flight, which accurately approximates the sequence of successive steady states required in classical test procedures. The development and optimisation of this methodology were based on extensive flight simulations and specially developed measurement data analysis procedures.
The final validation of the proposed method, as well as a comparison with the results obtained using traditional testing techniques, was confirmed during an actual flight test campaign.