September 16, 2005

UAVs are getting smarter when it comes to dealing with engine failure. A common reason for UAVs being lost is engine failure. A pilot on board can detect engine problems early on and  diddle with the controls, or otherwise nurse an ailing engine long enough to get back on the ground in one piece. While the UAV pilot has data readouts from the engine, this provides less info than a pilot, sitting very close to the engine, gets. Most UAVs have only one engine, one of the design decisions taken to keep them cheap. But one of the more expensive UAVs, the Global Hawk, is now costing over $60 million because of more and more powerful (and expensive) sensors being put on board. In effect, Global Hawk is getting space satellite grade sensors. These are enormously useful, but it hurts when one of these birds goes down because of engine failure. Three Global Hawks have suffered engine failures, when their AE 3007H turbofan engines stopped working. Two of those failures led to the UAV crashing. But the third failure, which occurred a few months ago over Afghanistan, did not result in a crash. That Global Hawk had its flight control software modified so that, in the event of engine failure, the UAV could glide down to a dead stick landing. The ground controllers had to tell the UAV where the emergency airstrip was, and the flight control software did the rest. The controllers radioed the guys running the airstrip to explain their unusual visitor. The airbase operators were told to just push the Global Hawk off to the side and put it under guard. The next day, a new engine, and mechanics to install it, were flown in. The day after that, the Global Hawk, which was operating out of a base in the Persian Gulf, flew itself  out of Afghanistan. 

The core components of the AE 3007H turbofan have long been used in C-130 and V-22 turbo-prop engines. And the AE 3007 model is widely used (over 700 aircraft) for regional and business jets. The engine has 7,600 pounds of thrust, and an excellent reliability record. Except with the Global Hawk. The problem is still being investigated, but since the Global Hawk normally flies at over 50,000 feet, and is built to glide very well, the dead stick landing software will probably save the aircraft in future engine failures. The current B model of the UAV weighs 13 tons and has a 131 foot wingspan. The Global Hawk normally flies completely by itself, although a human controller on the ground is often operating the sensors, especially when the UAV is supporting active combat operations on the ground.