Methodology for the optimization of the Fly-Away maneuver in case of engine failure during HOGE Operations

Massimo Longo – Flight Test Engineer, AgustaWestland A Finmeccanica Company
Francesco Scorcelletti – Flight Mechanics Specialist, AgustaWestland A Finmeccanica Company

Abstract

Scope
This paper presents the methodology followed to set up and execute a safe and efficient flight test programme to optimize the Fly-Away maneuver technique. The activity has been performed in order to obtain a minimum helicopter height loss after the engine failure starting from helicopter in Hovering-Out-of-Ground-Effect (HOGE) operations.

The flight tests were performed after development of a suitable mathematical model of the helicopter that was validated thanks to the data gathered during a dedicated flight test campaign. The activity was carried out with the NH90-HITN01 Helicopter, the first production Italian Navy Helicopter in the NFH Variant (NATO Frigate Helicopter).

Instrumentation
The Helicopter was instrumented with specific AW Flight Test Instrumentation (FTI) in order to gather data for post-flight analysis and especially for monitoring a limited set of parameters in real-time on board to verify the required safety margin with respect to the limitations.

Test Method
In order to achieve the minimum helicopter height loss, the tests were performed in incremental steps, starting from the “usual” Fly-Away maneuver and changing some parameters in accordance with the preliminary results coming from the mathematical model.

Numerical Simulation
The dynamic simulations were carried out by the flight dynamics code named NFPATH widely used in the AgustaWestland Flight Mechanics department. This program has been tested and validated against flight test data for several AW helicopters such as A109, A119, A129, EH101, AW139, and also the NH90 (GITA version) for the analytical definition of the Height-Velocity envelope.

The NH90 NFH numerical model was initially validated in both steady and dynamic conditions, considering for the latter case the Flight test data gathered for Fly-Away maneuvers. In particular the trajectory resulting from the experimental activity was imposed for the simulations, according to an indirect approach, and several Fly-Away significant variables, such as pitch angle, MR RPM (Revolutions Per Minute), power required, controls, were analyzed and successfully compared to the flight measurements.

After the validation phase, the numerical model was used to predict and extrapolate the Fly-Away capabilities in other test conditions with respect to the ones exploited in the flight test campaign. The compliance with respect to the requirement for Fly-Away was successfully demonstrated. Such analysis was carried out considering the flight procedure defined during the flight test activity and reflects the main characteristics highlighted in order to minimize the height loss.

Conclusion
At the completion of the tests the results obtained were well correlated and in line with the analytical predictions. The main results achieved with the Flight Test activities are the definition of the Fly-Away maneuver technique and its feasibility after the assessment carried out by AW Test Pilot and customer Test Pilots (Army and Navy Pilots).