Flight Dynamics and Control Using Folding Wingtips: An Experimental Study

Abstract

This paper presents an experimental investigation on using FOLDing wingtips sERving as cONtrol effectorS (FOLDERONS) for a mini Unmanned Aerial Vehicle (UAV). A representative off-the-shelf mini-UAV with a conventional configuration was selected. The main theme of this paper is to utilise FOLDERONS as a control effector (mainly in roll) to augment the control authority of conventional control surfaces. Furthermore, the impact of actuation rate on the effectiveness of FOLDERONS is assessed. The paper describes the preliminary and detailed design and sizing of the morphing wing. In addition, the manufacturing of the wing system and its integration with the UAV are addressed. Wind-tunnel testing in the RJ Mitchell wind-tunnel at the University of Southampton was performed. Both static (straight and sideslip) and dynamic (straight flight) tests are conducted at a range of airspeeds and Angles Of Attack (AOAs). The impact of folding wingtips on the lateral and directional stability is analysed. The main finding of this paper is that FOLDERONS are effective (especially at large dynamic pressure and AOAs) in controlling the lateral and directional stability. Finally, this study shows that FOLDERONS cannot fully replace conventional ailerons especially at low dynamic pressures, and their strong dependence on the AOA makes them prone to a roll reversal phenomena when the wing (and FOLDERONS) is operating at negative AOAs.

Winglet Geometry Impact on DLR-F4 Aerodynamics and an Analysis of a Hyperbolic Winglet Concept

“…This can be achieved through a cant-morphing winglet. Several studies regarding morphing concepts were performed, see [11][12][13]26] for instance. In this paper, a much simpler and structurally lighter alternative is suggested that does not involve morphing, and therefore, no complex articulation mechanisms are needed: A curved winglet, where local cant angle is different at each section (highly canted root versus nearly vertical tip, with gradual transition in between, see Figure 14 below).…”

“…Due to the largely different flow field nature at the wing tip area at different flight conditions, and the challenge of achieving a winglet shape optimal throughout the whole flight envelope, recent winglet geometry optimization studies in the last decade were mostly focused on cruise as a 'design case' for this wingtip device, resulting in trade-off solutions less optimal for take-off and climb at high angles of attack [3][4][5][6][7][8][9][10]. Few innovative solutions have been suggested including morphing winglets which adapt their cant and/or twist depending on the flow regime [11][12][13], or using an integrated moving device such as a winglet-integrated rudder [14,15] or a gust alleviating conventional aileron [16], as well as active vortex wake control with an oscillating mechanism [14,17,18]. Bio-inspired devices were studied of non-planar wings through a configuration-invariant analytic formulation of the unknown circulation distribution.…”

Identification of In-Flight Wingtip Folding Effects on the Roll Characteristics of a Flexible Aircraft

“…This has also been extensively discussed on the XB-70 aircraft [10][11][12]. Experimental data from wind-tunnel tests of a mini-Unmanned Aerial Vehicle (UAV) equipped with folding wingtips intended for roll control [13,14] have shown significant modifications to both lateral and directional aerodynamic derivatives as a function of flight conditions and fold angles. Additionally, it could be argued that the use of folding wingtip devices could also be used on even smaller scales such as Micro AV (MAV) designs [15] for attitude control and performance augmentation.…”

Electromechanical Actuation for Morphing Winglets

“…Morphing wings have the greatest ambition to significantly alter design and operation of future generations of aircraft [1][2][3][4][5][6]. Their ability to change the wing geometry and reconfigure themselves in multiple shapes in order to match specific flight conditions at the best may dramatically contribute to tackle some of aviation's biggest environmental challenges including fuel efficiency, noise, and emissions.…”