Like a smile with missing teeth, the jet’s wings have a gappy quality. Their flaps are gone, exposing a tangle of multi-coloured pipes, tubes and wires. It’s not a dignified look for a plane used to ferrying the wealthy and famous around the globe, yet it will have been worth it if new shape-shifting wings can make aviation safer, quieter and more efficient.
The flaps on conventional aircraft wings provide lift, allow safe slow flight and shorten takeoff and landing distances. Unfortunately, they also open up gaps in the wing’s edge, creating turbulent, messy, airflow, which generates noise and makes flight less efficient.
This explains the major surgery underway on a Gulfstream III executive jet in one of the hangars at the newly renamed Nasa Armstrong Flight Research Center (formerly Dryden), about an hour north of Los Angeles, California. In place of the jet’s old flaps, Nasa engineers are fitting a new bendable wing control surface known as an Adaptive Compliant Trailing Edge (ACTE).
The technology’s key advantage is that it eliminates the gaps in wing edges seen in traditional hinged flaps, replacing them with a gently contoured transition. This improves efficiency compared to traditional flaps which are designed for one particular set of flying conditions, according to Craig Stephens, lead engineer for ACTE at Nasa Armstrong. “It’s a continuous flap so you don’t have that break in the wing,” he says. “The structure having that ability allows you to have the aerodynamic efficiency over a wider range of the flight.”
ACTE has been developed by a company named Flexsys. Stephens is reluctant to reveal too many details about how exactly the flexible structure is built and actuated, but the company’s website hints that composite materials, combined with aluminium or titanium, are involved. The system is designed to have jointless mechanisms, using the elasticity of the materials for shape morphing, and with built-in actuators and sensors.
The finished article is sitting on a cradle near the Gulfstream III at Nasa Armstrong, awaiting installation. The high-gloss white surface looks plastic, with some flat parts, and some gently corrugated sections to allow bend and flex.
Movement is limited at this early experimental stage, but eventually the entire wing could be fabricated from these materials, allowing it to constantly change shape during flight, much like a bird’s wing. It could be twisted in real time to help cancel out the loading effects of gusts of wind, for example. If wings could dump heavy loads they would no longer have to be built to be strong enough to withstand their full force, potentially allowing them to be lighter and therefore help make planes more fuel efficient.
Stephens adds that the activity around the Gulfstream III is approaching a critical point. “We’re trying to finish the instrumentation,” he says. “We’re going to be integrating on the aircraft soon, and then we’ll start our flight test process.”
“It’s very nerve-racking, adds Ethan Baumann, chief engineer on testing project. “It’s quite a lot coming together in these last few months.”
Bauman gives me a tour of the interior of the plane. Any trappings of luxury have been removed. “We pulled the fancy leather couches and everything else out of here, and basically gutted the aeroplane,” he says. The body is now full of racks of equipment, connected by a spaghetti of cables. “Basically we have this airplane instrumented six ways to Sunday!” he exclaims.
Only one chair is left – a window seat over the wing for the instrumentation engineer. The test pilots have been preparing in simulators to ensure they’re ready for anything the aircraft could do in flight, including possible emergencies. The tests are being conducted at Edwards Air Force Base, in restricted airspace, and with large, flat lakebeds nearby in case emergency landings are needed.
“It’s exciting stuff,” says Tim Williams, a Nasa research pilot. “There are some serious risks here, but we are mitigating them.”
Test flights start later this summer, and run until June next year. By then we should have a better idea of whether shape-shifting planes can deliver the benefits those developing them promise, and become a common sight at airports in the years to come.