August 21, 2011:
On August 15th, a U.S. Army RQ-7 UAV and a U.S. Air Force C-130 transport collided. The RQ-7 hit a wing of the C-130, between the two engines. The RQ-7 was destroyed, while the C-130 had the skin of the front of that wing torn open and some of the interior spars bent. One of the props on the inboard propeller was destroyed (and that engine had to be turned off). But the C-130 was able to land safely, and the air force reported that parts and technicians could be flown in to repair the C-130 where it was.
An RQ-7B Shadow 200 weighs only 159 kg (350 pounds), compared to 70,000 kg for a loaded C-130, so the outcome of this collision is not surprising. Shadow is small, being 3.5 meters (11 feet) long with a wingspan of 4.1 meters (12.75 feet). Most UAVs in the air over combat zones are even smaller. Most of them are the tiny two kilogram (4.4 pounds) Raven. Bystanders have seen a few of them destroyed, or simply knocked out of the air by a passing aircraft, usually a helicopter. Raven operators suspect that many of those that were lost for unknown reasons were similarly hit or caught in the backwash of low flying aircraft. A few have been seen getting attacked by birds. There have been very few recorded collisions.
The small, plastic, Raven would not do much noticeable damage to an aircraft. The Shadow collision was understandable because the Shadow is the largest UAV that often operates at low altitude (under 300 meters) and uses military airfields to land and take off.
The army is developing a new radar system (GBSAA, or Ground-Based Sense And Avoid) to increase safety for UAVs. GBSAA is mainly a software system using existing radars to track UAVs and manned aircraft, and alert UAV operators when their UAVs are too close to other aircraft (manned or unmanned). GBSAA can be expanded to use transponders (which commercial aircraft have been using for a long time) and more flexible software. But the basic idea is to insure that UAV operators are no longer “blind” to what is in the air nearby.
GBSAA will likely be more in demand by potential civilian UAV users. Battlefields have much lower safety standards than civilian air space, what with all those artillery and mortar shells, plus the bullets and rockets. But civilian air space has lots of small aircraft and helicopters, so UAVs are generally banned. GBSAA could change that, and make battlefields safer as the UAV traffic becomes denser.