Unmanned Systems Technology 013 | AutonomouStuff Lincoln MKZ | AI systems | Unmanned Underwater Vehicles | Cosworth AG2 UAV twin | AceCore Neo | Maintenance | IDEX 2017 Show report

72 the rotor tip seals for wear and effective oil supply is also important, given their ‘distance travelled’ and work performed relative to the rest of the engine. For reciprocating engines, piston rings are at risk of carbon build-up, so they need particular attention. Propellers must also be thoroughly scrutinised. Any debris caught up in them during take-off or landing causes minor scratches and larger dents, regardless of prop material. It is common to sand the damaged area, clear out any debris and then fill the void or dent with an appropriate epoxy before sanding it back into shape, although doing this repeatedly will eventually cause prop balance to deteriorate, making replacement necessary. Electrical systems UAVs that rely on electric propulsion benefit from the high reliability and low maintenance requirements of brushless dc motors. As with propellers, gravel or sand can get into the coils, after which the spinning of the outrunner/rotor may drive the dirt into the stator and cause short- circuits between the internal linings, at which point an overhaul will be needed. Batteries however need far more attention, but they come with comprehensive manufacturer guidelines on their handling, storage, charging procedures and connecting/disconnecting to the vehicles. The lengthiest process is the charging, although that is being reduced as new technologies and battery chemistries emerge. Tracking logs of a battery’s charge- discharge cycles and temperature over time is vital to its health and longevity. Batteries have a defined number of cycles, after which they must be retired and replaced. A leading cause of UAS failures is insufficient rigour when maintaining and using lithium batteries, so maintenance staff must keep to strict procedures for measuring the output current and resistance in each cell, potentially from the moment they arrive from the factory. Airframes Modern UAV airframes vary widely in their design, and each one has its unique trouble points. For small multi-copter UASs with folding arms, for example, repeatedly locking and unlocking the arms can cause the locking mechanism to break. Across all rotor-wing systems, repeated landings will put stress on the landing gear. Increasingly, however, smalller UASs are built from composites that tend April/May 2017 | Unmanned Systems Technology UAV airframe maintenance increasingly calls for familiarity not only with metals but composite materials such as glass or carbon-reinforced plastics (Courtesy of Robotic Skies) Regardless of a UAV’s size or mission, a proper record of its flying hours must be kept in order to schedule the inspections