Wing Morphing and Fuel-Efficient Planes

Drastically change the shape of a wing in flight and you get something that can potentially fly fast as well as be agile when slowly coasting. But the U.S.’s first real stab at producing a variable wing was on the F-111, a swing-wing aircraft that was not known for being maneuverable.

Things got better with the Navy’s F-14 Tomcat. The highspeed interceptor was fast enough to go toe-to-toe with Migs but could extend its wings to turn sharply, dogfight, and make lowspeed carrier landings.

Fast forward to today. Darpa’s Morphing Aircraft Structures program has generated designs such as folding wings that vary their wingspan length, aspect ratio, sweep angle, and other qualities. Researchers have tried other morphing concepts such as partially inflatable wings as a means of controlling roll.

But what is billed as the first “cost-effective and practical morphing wing” is part of an unmanned aircraft called V-Star, for VTOL Swift Tactical Aerial Resource. Frontline Aerospace Inc. calls the UAV a Humvee of the air because it can theoretically work in several roles besides its main job of hauling gear to frontline troops.

Frontline says the weight, complexity, and reliability penalties associated with morphing a wing have so far been problematic. To keep things simple, it came up with a set of folding extensions that flip out to let the plane loiter at 275 knots and retract for dashes at 400 knots.

The V-Star’s boxplane-type design tends to promote fuel efficiency because of its inherent minimum induced drag for a given lift and span. But the plane also sports a special kind of recuperator to further promote economical operation. The recuperator, a heat exchanger, extracts heat from the engine exhaust and transfers it to the compressed engine air before combustion. Frontline claims this can double the engine’s thermal efficiency. The patentpending design also manages to keep down weight by using hypodermic-needle material for heat transfer. Company officials claim the device can improve fuel consumption by as much as 40% and weighs less than 40 lb.

It will be awhile before V-Stars are ferrying gear to troops. Frontline is working on a 50% scale version for wind-tunnel testing and hopes to complete those tests next year.