The evaluation of the Handling and Flying Qualities of an aircraft is an indispensable step on the way to warrant the safe in-service operation.The most important characteristics which need to be verified are controllability, agility, insensitivity to gusts and departure resistance/ spin recovery. In modern aircraft a sophisticated Flight Control System (FCS) assists the pilot in the fulfilment of the mission and stabilizes inherently unstable configurations. Therefore the man-machine-interface is of significant importance. Apart from the evaluation of the Handling Qualities of aircraft by test pilots during dedicated flight tests this discipline strongly relies on mathematical models and simulations. The DLR Institute of Flight Systems has a long tradition in this field of research.
The Handling Qualities characteristics which for classical aircraft are determined by the aerodynamic properties of the airframe are for so called super-augmented aircraft increasingly dominated by the complex structures of digital flightcontrol systems. One key element which needs to be assessed is if pilot commands are translated into appropriate aircraft responses. Unpredictable interactions and coupling events between pilot inputs and the aircraft system may lead to dangerous oscillations, jeopardizing crew and aircraft. Therefore Flight Control Systems need to be designed with appropriate stability margins to ensure the controllability and essentially the safe operation of the aircraft. State-of-the-art modeling and simulation tools allow for a complete assessment of new aircraft designs at the end of the development cycle using PCs. This significantly reduces the likelihood of unpleasant surprises during the first flight.
Methods for the Evaluation of Handling Qualities
Up to the 1920s the subjective assessment of the pilot was the only measure to determine the Handling Qualities of an aircraft. The pilot had to adapt to the peculiarities of the particular vehicle while the engineers had to completely rely on his piloting skill and judgment. Only by comparing various airframes in flight could the Handling Qualities of one specific type be approximated. As the technological developments in aeronautics advanced, more emphasis has been put on economical and safety-related topics. In addition to pilot ratings, mathematical methods, which are predominantly based on data obtained in extensive simulation and in-flight experiments were now being applied using computational tools to determine the Handling Qualities and flight clearance requirements. This had strong implications on the HQ evaluation process.
Today’s HQ analysis uses data obtained from system identification, simulation runs and flight test. The assessment is compiled on the basis of mathematical criteria, specifically tailored to aircraft type, mission, flight condition, etc. Since a new design is extensively tested and evaluated during the design process using piloted and clinical simulations, the Handling Qualities are optimized prior to the service release.