Launching drones

Keywords: Aircraft, Flight

Propelling a shipboard drone into flight used to require that an expendable fibreglass rod be launched as well. Launch technology resembled a modern-day bow and arrow, said Bill White, with the bow being an air cylinder and the arrow being its rod. White, who conducts maritime unmanned air vehicle development and operations for the US Naval Air Systems Command in Patuxent River, Maryland,said that the Navy was plunging quite a few arrows into the sea. Rodless cylinders, however, bring along their own set of design challenges. The biggest of them, a mechanical applications engineer at Hoerbiger- Origa of Glendale Heights, Illinois was calculating a way to disperse the energy m the cylinder after the drone was under way. Most of the energy left with the drone, but enough remained in the cylinders to break the end caps.

In 16 feet of stroke, Hoerbiger-Origa engineers had to accelerate the 100-125 lb drone, payload and launch cradle to 70 feet per second. To do that, they required full air pressure from the start. An 8 bar nitrogen or compressed air source acting through enlarged 11/2-inch cylinder ports gave the drone just the boost it needed. In about a half-second the pistons catapult the pilot-free aircraft off the cylinders.

The consumable rod used for the older design solved the problem of residual energy effectively, if not economically. The drone continued flying while the rod fell away. The Navy challenged Hoerbiger-Origa to come up with a different system.

At first, the engineers devised a deceleration mechanism for the new cylinder to absorb excess energy. It worked, but only up to a certain speed. Next, the engineers designed a hydraulic shock absorber that they integrated into the cylinder end cap.