In January, we looked at FlexFoil; a variable geometry airfoil system that seamlessly integrates into the trailing edge of the wing. During the year the system has made the leap from the test bench to the sky, with NASA conducting tests of the FlexFoil on a modified Gulfstream III business jet.
For all the advances in aircraft design over the last century, the wings of an airplane are still fundamentally clumsy. If airplanes spent all their time flying straight and level, the airfoils would only need to be one shape, but that's not how it works – they need to turn and blank, ascend and descend, stay in the air at different speeds, and go through all that tedious taking off and landing.
In a conventional wing, changing shape is achieved by equipping the wing with flaps that pivot, slide, and generally rely on mechanics that create all sorts of seams and gaps. These not only make the wing less efficient, but also noisier.
NASA’s Environmentally Responsible Aviation (ERA) project aims at making airplanes quieter and more fuel efficient. One aspect of this is the FlexFoil, made by Ann Arbor, Michigan-based FlexSys and developed as part of NASA and the U.S. Air Force Research Laboratory’s (AFRL) Adaptive Compliant Trailing Edge (ACTE) project.
Put simply, FlexFoil is a shape-changing assembly that replaces the flaps on a wing and can alter shape in flight to produce seamless bendable and twistable aerofoil surfaces. This allows the FlexFoil to act like a flap in its various positions while still providing an unbroken air surface. This makes for a more streamlined wing and reduces noise during takeoffs and landings. Importantly, it’s designed not only for new aircraft designs, but for retrofitting to existing ones.
The ACTE flights were carried out at NASA's Armstrong Flight Research Center in Edwards, California, using the Gulfstream III as a testbed with the composite material FlexWing replacing both of the aircraft’s 19-ft (5.7-m) aluminum flaps. The purpose of the test was to take it out of the wind tunnels and determine if its airworthy. The FlexFoil was locked in a series of shapes to allow engineers to collect data on its aerodynamic performance under real-life flight conditions.
NASA says that work continues on commercial applications for the FlexFoil as well as for those beyond aircraft wings. It is hoped that ACTE technology will allow engineers to tailor wings to particular purposes at the best efficiency and using much lighter materials.
"The first flight went as planned – we validated many key elements of the experimental trailing edges," says Thomas Rigney, ACTE Project Manager. "We expect this technology to make future aircraft lighter, more efficient, and quieter. It also has the potential to save hundreds of millions of dollars annually in fuel costs."