A gremlin is a sort of mythical fairy that RAF pilots blamed for causing mechanical problems with their aircraft as far back as World War I. This sounds like a bad thing, but apparently, gremlins were actually good luck charms for pilots. As long as you listen to your Irish girlfriend and feed them cream. Or something.
Anyway, Gremlins is also the name of a new DARPA program that’s seeking proposals to develop the technology to launch swarms of low-cost, reusable unmanned aerial vehicles (UAVs) over great distances and then retrieve them in mid-air.
In November of last year, DARPA asked for ideas for how to turn military planes into flying drone aircraft carriers. Gremlins seems to be an extension of that, with a particular focus on safe, reliable aerial launch and recovery of multiple UAVs. From a recent DARPA release:
The program envisions launching groups of gremlins from large aircraft such as bombers or transport aircraft, as well as from fighters and other small, fixed-wing platforms while those planes are out of range of adversary defenses. When the gremlins complete their mission, a C-130 transport aircraft would retrieve them in the air and carry them home, where ground crews would prepare them for their next use within 24 hours.
The gremlins themselves are somewhere in between disposable drones and conventional drones that are intended to last for years or decades. DARPA wants each gremlin to be able to fly a few dozen missions at most, making them more cost effective than disposable systems but also way cheaper than bigger, more complex drones that need continuous maintenance. Plus, the gremlins can always be used like disposable drones if necessary, undertaking missions that might be too risky for a more expensive drone.
The real tricky bit about this whole business is going to be the mid-air retrieval: how could a massive C-130 possibly go and snatch an in-flight drone? DARPA suggests UAV capture systems for ships might provide some inspiration. Specifically, DARPA references SideArm, a project that Aurora Flight Sciences has been working on that might look something like this:
In this concept image, which may or may not represent what the final SideArm system will look like, you’ve got a drone with a hook thingy on it, and a ship with a dangly thingy on it. The drone approaches the ship at speed and does its best to engage its hook thingy with the dangly thingy on the ship as it flies past. If everything goes well, the drone will be brought to a very abrupt and dangling stop. Fundamentally it’s a lot like the ground capture system (called SkyHook) that Boeing has for its ScanEagle UAV:
In this case, the ScanEagle UAV runs into a vertical wire with its wing, and the wire catches a hook on the UAV’s wingtip. It doesn’t look like a heck of a lot of fun for the UAV, but it was designed for this, so it doesn’t mind. So far, this is just about the best general idea we’ve got for stopping a UAV at a fixed point, and (for whatever it’s worth), it’s the best general ideal we’ve got for stopping a manned aircraft at a fixed point, too.
If we let our imagination go wild for a second, or maybe not even that wild, we could imagine a SkyHook-type system that could be attached to the back of a C-130, where UAVs hook onto it and slide right on into the cargo bay, one after another. And that’s even a little bit what the concept picture at the top of this article looks like, doesn’t it?
Before we end, if this whole thing sounds vaguely familiar in a retro sort of way, that’s because you’re thinking of goblins, not gremlins. The McDonnell XF-85 Goblin was a prototype for a chubby little jet fighter that could be deployed, retrieved, refueled, rearmed, and deployed again from the bay of a B-36 bomber in flight. There’s a lot of parallels between the Goblin and DARPA’s vision for Gremlins, if you throw a half century in between them. And from half a century ago (give or take), here’s an overview video of the Goblin test flight program:
[ DARPA ]