Rotorcraft Handling Qualities meet Simulation Fidelity

The requirements and criteria for what constitute good and bad rotorcraft handling qualities have developed to the point that new designs and upgrades can be brought to service with a very low risk that any limitations on flight safety or on the capability to perform intended missions will result from deficiencies in flying characteristics. The research base that has elevated the discipline was created over more than two decades of flight and ground-based simulation testing, supported by modelling and simulation, and undertaken by multi-national teams of engineers and pilots.

Alongside these endeavours, the technologies for flight simulators have been developing, but have lacked the benefit of an underpinning research base. The metrics and tolerances in current standards are derived from fixed-wing criteria and shown to be lacking in a number of important aspects. The EPSRC funded research at Liverpool, Lifting Standards (2008-11), has developed a more rational basis for quantifying simulation fidelity, using a handling qualities approach. The research at Liverpool features the 6 degree of freedom motion simulator, HELIFLIGHT-R, alongside close collaboration with the Flight Research Laboratory (NRC, Ottawa). Metrics for predicting fidelity and capturing pilot perceptual fidelity have been derived and used in the development of a new unified approach to qualification. Central to the approach is the need to understand and quantify the level of adaptation that pilots apply as they transition from the simulator to flight. Beyond a certain level of adaptation, the resulting negative training means that safety and operational capability may be compromised. Within the concept of strategy adaptation is the degree of control compensation and hence the link between handling quality and fidelity strengthens. Outstanding questions concern the acceptable tolerances on predicted and perceptual fidelity metrics that a simulator is 'fit for purpose'; what constitutes Level 1 fidelity, and how critical are the handling qualities to this question are continuing research questions.

These questions formed the backdrop to the American Helicopter Society (AHS) workshop on Simulation Fidelity held in Virginia Beach, May 2011. The workshop, chaired by the proposer, was attended by more than 70 delegates and seeds were sown for further collaboration between research laboratories and industry to develop the required evidence base; there is a historical perspective to the development of best practice that needs to be brought into the continuing research. Much has been left poorly documented. In this short research project, the proposer will bring these themes together.

A core activity of the research project will be the preparation of the prestigious AHS Nikolsky paper and lecture, and dissemination at various US Centres, where the opportunity will be taken to reinforce collaboration. Padfield will review the developments of handling qualities criteria since the birth of the practical helicopter 70 years ago. The key innovations that have allowed the industry to break through the barriers to formulating and adopting quality criteria will be identified and described. The critical enabling flight control technologies will also be reviewed and the continuing developments that confer super handling analysed and conjectured. The improvements in rotorcraft handling qualities should have a massive impact on safety and operational capability on the one hand and the technical requirements and training effectiveness of simulators on the other. The author will take the opportunity to strengthen the collaboration on handling qualities and simulation fidelity, setting the stage for the 2012 fidelity workshop in Fort Worth and continuing collaboration into 2013

The proposed research builds on extensive research conducted by the proposer and colleagues, at Liverpool and elsewhere, aimed at making rotorcraft flight safer and more effective. Good flight handling qualities and high fidelity simulators are critical to relieving tension between the twin goals in aviation - safety and operational performance. The handling qualities research pedigree has already led in a step change in design standards and the same is expected to happen in the field of simulator fidelity as a result of the research at Liverpool - fidelity that is vital for qualification of both the aircraft in its physical form and virtual form as a flight simulator.

The impact will thus be twofold. First, rotorcraft flight operations that are safer will facilitate market growth. Second, simulators that are of appropriate fidelity, underpinned by proper scientific evidence, will result in more effective training and safer operations. The simulation industry is expanding, particularly at the lower end of the market and the consequent developments need an engineering science research base to ensure fitness for purpose.

Research of the kind that this small project will bring together aims to inform developments in the qualification processes, e.g. JAR-FSTD-1H, and organisations like EASA (European Aviation Safety Agency) will be encouraged to engage with the work as it matures.