Super-Silent Owl Drone Will Spy on You Without You Ever Noticing

[Eugen Leitl]

http://www.wired.com/dangerroom/2012/07/owl/

Super-Silent Owl Drone Will Spy on You Without You Ever Noticing

By Robert Beckhusen July 19, 2012 | 1:00 pm | Categories: Drones

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The Great Horned Owl. Photo: ahisgett/Flickr

For spy tools, drones are pretty easy to spot. And hear, because theybre as
loud as a gut-busting rock concert. But now the intelligence communitybs
research division, Iarpa, plans to start designing a silent drone inspired by
quiet, creeping, flying owls.

Iarpa has reportedly awarded a $4.8 million contract to Connecticut firm
D-Star Engineering to develop the ultra-quiet drone, Aviation Week reports.
Itbs the next step in developing a workable drone as part of the agencybs
Great Horned Owl Program, which the agency hopes will let the military
collect intelligence bwithout anyone knowing you are there,b (.pdf) according
to an agency briefing.

Sound, after all, is the number one signature bthat gives away the location
of low-altitude UAVs and gives away their presence.b Which sort of defeats
the point of having a secret surveillance eye in the sky. In some cases, you
might want people to know youbre watching. At other times, you want to sneak
up quietly.

But itbs hard to do without sacrificing payload. The added weight of sensors,
and the ability to operate for longer periods, comes with trading out
stealthiness. Drones powered by batteries: Theybre quiet, but canbt stay in
the air for long. Then therebs the added noise caused by airflow generated
from propellers, and noise from gasoline or diesel engines (not counting
batteries), with their moving pistons, turbofan and gears.

Iarpa wants to keep these efficent and relatively noisy engines for normal
flight. But when the drone needs to be stealthy, its operator would switch to
battery power, like a hybrid car. That means b for the duration of battery
flight b the noisy gears would shut off. The propellers would also likely be
ducted, which would mean less noise from vortices whipped up by the
propellers and fewer moving parts. Likely, the drone will take off
vertically.

The agency doesnbt expect the drone to stay ultra-quiet for more than 30
minutes, though, at which point the gasoline-powered turbine engine would
switch back on, recharging the batteries. Not enough for (say) a sustained
surveillance operation, but quiet enough to take a peek at an enemy without
being noticed.

The first step is keeping the sound levels in battery mode below 100
decibels, about equivalent to a chainsaw when up close. But give perhaps a
few thousand feet of distance, and the noise drops. Iarpa also wants to
reduce noise by cutting down the dronebs bphon curveb b or the level of sound
pressure interpreted by the human ear. Iarpa plans to start by testing the
sound levels of an uninstalled version of the engine.

Iarpabs owl drone is also not the first talk of an owl-inspired aircraft.
NASA has looked into the owlbs stealthy feathers for inspiration. But it may
take years before owl-based aircraft migrate into service.  Robert Beckhusen

Robert Beckhusen is a writer based in Austin, Texas, where he covers Latin
America for War Is Boring.

Read more by Robert Beckhusen