Flight Testing on Ground - The Laminar Wing Leading Edge Ground Based Demonstrator

Abstract

Economic needs and a growing ecological awareness demand for a cut in aircraft fuel consumption to reduce CO2 emission and operating cost. A long discussed approach is to implement areas of laminar flow on surfaces of transport aircraft. The reduced friction drag of a natural laminar flow (NLF) wing can lead to a reduction in fuel consumption and thus reduction of CO2 emissions of up to 8%. However, laminar flow is sensitive to surface disturbances and requires specific shapes and surface quality, preventing the adaptation of “regular” turbulent wings. Structural features like steps, gaps and surface waviness can cause early laminar/turbulent transition, excluding conventional designs of aircraft wings from laminar flow application. Most of the existing research performed so far was dedicated to verification or determination of aerodynamic parameters. Structures used in these investigations were not representative, like laminar gloves on conventional wing structures. Thus, despite the progress in laminar flow research, there is still a lack in experience of building and especially validating realistic structures designed for the laminar flow environment. Before flight testing of new structures a proof of their operational capabilities on ground is desirable. Under those boundary conditions, a laminar wing leading edge and a suitable test stand design method were developed. A multi-material leading edge concept consisting of CFRP as structural material and an integrally bonded erosion shielding (steel foil) was developed. The leading edge was designed in detail, a manufacturing process developed and a 2.3 m span demonstrator with full-complexity built. The leading edge together with its attachment elements is joined with a wing box to form a ground based demonstrator. To demonstrate compliance with laminar flow requirements under cruise flight conditions and to demonstrate interchangeability of the leading edge under operational on-ground conditions, a novel, smart test stand was designed. For those “wing on ground” and “cruise flight” test cases target geometries were derived in a full wing FE-simulation and used as target shapes for the actuation within the test stand. Wing box spar and ribs as well as actuator attachment positions were optimized to recreate realistic ground based demonstrator surface deformations in a laboratory environment using discrete load introduction.