Flight-physical aspects and methods of future military aircraft designs
Modern multirole combat aircraft have to cover a wide scope of performance and manoeuvrability imposing challenging flow-control measures to achieve care-free handling and at the same time to meet range and payload capacities. The longevity of such designs has to be achieved by capability stretching not only via equipment modernization but with the same effort by smart aerodynamic enhancers. The selection of which is assisted by modern flow simulation tools and sophisticated test-facilities, however the design and shaping still is an art when complex flows have to be tamed. Long-range reconnaissance and surveillance tasks materialize into unmanned aircraft of some previously unknown design-space. Fragile, high aspect-ratio configurations – sailplanes only at a first glance -, experience some Reynolds-number effects and become efficient only via the integration of high performance wing technology. The so called asymmetric war-fare will challenge nowadays surveillance and counter-insurgency capabilities with anti-air-systems. Simple missiles, the adaptation of even older combat aircraft or militarized civil general aviation ones may force higher speed and agility into these platforms and these being combined with some signature challenges. More and more influenced by compromises in between flight-physics and signature, the requirements of performance, manoeuvrability and low RCS-signatures must be fulfilled by a common shaping. This may relinquish traditional elements of design in the medium and higher angle-of-attack regime, at sub- and transonic speeds. Constraints are imposed on control-systems. Slats, flaps, roll-devices and classical yaw-controls together with classical flow control via vortex-generators are undesirable. Here the flight-physical properties must be designed into the plan-form, profiles, twist and a continuous blending of these. This can be achieved only with a deeper understanding of the flows complex behaviour to allow for capable and safe designs. Many features of these complex vortex-systems, eventually being combined with transonic effects, especially at the borders of the flight-envelopes, are not yet understood to make the development a straight forward approach. Some aerodynamic problems are presented and modern methods for analysis and design are discussed. Very often numerical flow-simulations help to analyse the task at hand properly. However, many challenges only can be accessed and solved by high-fidelity physical models and the simulation of complex geometries. For these ends, a very detailed validation must be provided by suited experiments also in the transonic regime and even more so at true flight Reynolds-number conditions.