Return of the Parasites

DARPA wants new tech for an old idea.

An F-84 experimental parasite fighter attaches to a B-36 (U.S. Air Force)
airspacemag.com

The Defense Advanced Research Programs Agency (DARPA) is calling for ideas on how to create a sort of airborne aircraft carrier, a system that can both launch and recover unmanned air vehicles (UAVs) mid-flight. It’s not as far-fetched as it sounds.

In the early days of World War I, German Zeppelins bombed allied cities with near impunity: the small, underwhelming fighter aircraft of the time simply didn’t have the performance to take off from a distant airfield, climb to the Zeppelin’s altitude and attack it, to say nothing of a safe return. It quickly occurred to the British that by strapping an airplane onto an airship of their own, a “parasite” fighter could “take off” from altitude, full of fuel. They could even put one on larger airplanes, to help defend what would ordinarily be slow, lumbering targets. Even though the British, Americans and Germans all carried out successful tests, the idea was not widely adopted, and there is no evidence it was used in combat.

But the seed was planted, and the idea stayed in the minds of military planners. Between the world wars, the Americans, British and Soviets kept experimenting with mixed success. Meanwhile, big airships were phased out in favor of fixed-wing aircraft, and fighters became larger and heavier, meaning they took a bigger bite out of the host aircraft’s own range and performance. By the time World War II began, the parasite idea was mostly discarded; strategic bombers simply couldn’t spare the performance to haul a modern fighter into combat. A few parasites were flown in combat by the Soviet Union, Germany and notably Japanese kamikazes, but occurrences were rare and the idea never went mainstream.

That didn’t stop the U.S. from trying anyway. Cold War strategy had bombers flying from the U.S. to the Soviet Union, well beyond a normal fighter’s range, which left them vulnerable to Soviet fighters. To compensate, the U.S. flew a number of experimental parasites, from detachable F-84s strapped onto the wingtips of a B-36 bomber to the bizarre, custom-built XF-85 Goblin. None of them worked very well, and the invention of reliable aerial refueling methods diminished enthusiasm for parasite fighters.

But the idea kept bubbling up. Many crewed experimental aircraft were hauled to suitable altitude and then dropped by B-52s, completing their flight with a landing at Edwards AFB in California. Converted target drones, equipped with cameras, were launched by DC-130s during the Vietnam War. The drones would fly a pre-programmed route over Vietnam on missions deemed too dangerous for crewed aircraft, then turn back out to sea, where they would be captured mid-air and flown to waiting ships.

Today’s missiles and bombs are smart enough to track their own targets—the launching aircraft crew just tells it what to hit and fires away, letting the weapon figure it out from there. Some “loitering munitions,” like the IAI Harop or AeroVironment Switchblade, can even fly circles waiting for a target to show up before diving in and self-destructing.

The problem is the same as in the airship days: The UAVs have limited fuel and performance. So DARPA’s recent thinking is to use a B-52 to carry them to their mid-air launching point. And it would be helpful to retrieve expensive UAVs at the end of the mission.

But recovering is the hard part. Most small UAVs “land” simply by running into the ground at a shallow angle, without flaring like traditional aircraft; others are purposely designed to stall out near the ground and absorb the impact of the resulting crash. The Scan Eagle has a small hook on its wing that catches on a suspended rope. Even the mighty Predator has to be turned over from its operational pilot to a local pilot who lands it on the runway via a line-of-sight datalink. The operational pilot, who controls the Predator through a satellite link, can’t respond quickly enough to ensure a safe landing. It’s awkward.

Getting the UAV to link up with another airplane in mid-air is another challenge. It’s been done before, tested by two Global Hawks (and according to rumor by other classified military UAVs) for midair refueling, which requires a similar precision. But this is different. For one thing, even though DARPA is currently just asking industry what the options are, they are not thinking of something with Global Hawk-like performance, but rather a smaller aircraft for more tactical observations. Smaller UAVs tend to have relatively low airspeeds and operating altitudes, and would have real trouble catching up to a C-130, much less a B-52 or B-1, as the DARPA request for information suggests.

Dropping bombs can be difficult enough, though they’re meant to drop away and out of the slipstream quickly. If the bomb (or rather, UAV) slowly comes back and attaches to your hardpoint again, the aerodynamics get even trickier. Any solution will almost certainly need folding wings so it can fit on the host airplane, and making the transition from aircraft to payload is not a simple one.

Still, DARPA must think it can be done. And perhaps, given the rise in intelligent munitons, it’s inevitable.

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