91av

“BING, BONG. This is your captain speaking. We are now coming into land.
Would passengers please put on their oxygen masks and start blowing—as we
need to inflate the wings.”

Implausible, yes—but not as impossible as it seems. NASA scientists are
indeed testing inflatable wings. The idea is to give hypersonic aircraft
increased lift on landing, or let large mother ships drop scores of
ultra-lightweight drones whose wings will inflate as they are jettisoned.

Next week, NASA is due to start testing a scaled-down version of the X-24a, a
stumpy “lifting-body” aircraft. To reduce drag, the X-24a has no wings. Instead,
its aerofoil shape generates lift
(see it at http://users.dbscorp.net/jmustain/x24a.htm). But NASA wants to give vehicles like this one additional
lift when they need it. “You wouldn’t inflate the wings until right before
touchdown,” explains Jeff Bauer, a project manager at NASA’s Dryden Flight
Research Center in California. His colleague, engineer Joe Pahle, says
lifting-body designs have always involved a difficult trade-off between drag
reduction for fast flight and giving the planes enough lift for them to land
safely.

NASA reckons the ideal solution is for the aircraft to “grow” a pair of wings
when it needs them the most. “There are multiple applications for the technology
if it can be matured,” says Bauer. Besides reusable launch vehicles they could
also be incorporated into the design of the International Space Station’s
“lifeboat”—otherwise known as the X-38 crew return vehicle.

Uninhabited aerial vehicles (UAVs) that earth scientists use for remote
sensing could also have inflatable wings. Bauer envisages long-endurance planes
with large wingspans—such as the solar/fuel-cell powered Helios craft
(91av, 22 July 2000, p 30)—carrying many smaller
vehicles under their wings. The carrier vehicle would conduct large area
surveillance, he says. “But it could release one of these small aircraft to do
more precise localised monitoring.”

A carrier could stash away a lot more UAVs like this because their inflatable
wings would take up less room than fixed-wing planes. Once released, the
aircraft would inflate their wings and go about their business, controlled
entirely by elevators and rudders in their tail.

Before being inflated, the wings will probably be stored folded, concertina
fashion, within the fuselage. For the test flights, however, they are simply
strapped to the side of the craft. “Our research is not currently looking at how
best to stow the wings, but what happens once they are released,” explains
Pahle.

A single canister of nitrogen gas at a pressure of nearly 3.5 megapascals
(about 35 atmospheres) will inflate the wings. Once inflated, the wings are kept
at a pressure of about 1.3 megapascals by a regulator the team borrowed from a
paintball gun. Bauer says it’s vital to get the pressure right during inflation.
“You don’t want to put in too much in case you cause a blowout,” he says.
Similarly you don’t want it to go too slowly in case it folds. In all,
deployment take less than a third of a second and doesn’t seem to disrupt the
aerodynamics of the vehicle.

Bauer is also interested in using inflatable wings for vehicles being sent to
other planets. “Being able to efficiently package that aircraft would have an
obvious advantage in terms of limiting the payload,” he explains. Last week,
NASA said it would fund a six-month University of Nevada study that will look
into sending three gliders to Mars in 2007.