Mechanics of pressure-adaptive honeycomb and its application to wing morphing**This paper was originally presented at the 2010 ASME SMASIS conference, as paper‘SMASIS 2010-3634’. Despite the substantial changes that have been made to the paper,there are still various figures and text stemming from the original.

Abstract

Current, highly active classes of adaptive materials have been considered for use in manydifferent aerospace applications. From adaptive flight control surfaces to wingsurfaces, shape-memory alloy (SMA), piezoelectric and electrorheological fluids aremaking their way into wings, stabilizers and rotor blades. Despite the benefitswhich can be seen in many classes of aircraft, some profound challenges are everpresent, including low power and energy density, high power consumption, highdevelopment and installation costs and outright programmatic blockages due toa lack of a materials certification database on FAR 23/25 and 27/29 certifiedaircraft. Three years ago, a class of adaptive structure was developed to skirtthese daunting challenges. This pressure-adaptive honeycomb (PAH) is capable ofextremely high performance and is FAA/EASA certifiable because it employs wellcharacterized materials arranged in ways that lend a high level of adaptivityto the structure. This study is centered on laying out the mechanics, analyticalmodels and experimental test data describing this new form of adaptive material. Adirectionally biased PAH system using an external (spring) force acting on the PAHbending structure was examined. The paper discusses the mechanics of pressureadaptive honeycomb and describes a simple reduced order model that can beused to simplify the geometric model in a finite element environment. The modelassumes that a variable stiffness honeycomb results in an overall deformation of thehoneycomb. Strains in excess of 50% can be generated through this mechanism withoutencountering local material (yield) limits. It was also shown that the energy density ofpressure-adaptive honeycomb is akin to that of shape-memory alloy, while exhibitingstrains that are an order of magnitude greater with an energy efficiency close to100%. Excellent correlation between theory and experiment is demonstrated in anumber of tests. A proof-of-concept wing section test was conducted on a 12%thick wing section representative of a modern commercial aircraft winglet orflight control surface with a 35% PAH trailing edge. It was shown that cambervariations in excess of 5% can be generated by a pressure differential of 40 kPa.Results of subsequent wind tunnel test show an increase in lift coefficient of 0.3 at23 m s − 1 through an angleof attack from − 6° to + 20°.