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

70 Focus | Maintenance for critical engine functions must be conducted, for example by collating logs from the crankshaft position sensor and running scripts in analysis software to find out-of-specification conditions for the position, rotational speed and timing of the crankshaft. Similar examinations across the range of temperature, pressure and fluid sensors are recommended as well. Also, cross-referencing multiple data sets produces equally if not more important analysis. It is common, for example, for UAS maintenance depot staff to track the correlation between throttle position and rpm over time. Having to feed more fuel into an engine to produce the same rpm is a particularly strong indicator of premature wear, and cause for replacement and overhaul. Crucial to the effective exploitation of engine sensor data and confirmation of performance within acceptable tolerance levels is their comprehensive examination through carefully designed test facilities, with engine test rigs with data acquisition and control for both rotary and piston combustion engines. Such facilities can be designed within controlled spaces, with soundproofing and ventilation to account for excessive noise or harsh environmental conditions. For UAV servicers and engine OEMs it is essential to compare engine performance during initial end-of-line production testing and after overhauls to ensure it meets its original design criteria. Analysis of logged data can then determine if the engine meets standards for return to the customer, and identify any trends that could indicate a variation in the manufacturing process further back down the line. Small gasoline-powered engines may not have enough sensors for logging or tracking performance in this way. Major overhauls and upgrades should be undertaken to bring such engines up to a reliable standard to avoid excessive wear, intermittent performance or even frequent failures. A range of other routine tasks make propulsion systems generally the most time-consuming area for maintenance crews. In addition to periodic oil changes every five, ten or 25 hours (depending on the engine), pre-flight inspections must also check for safety wires still being in place, and whether there is any damage to isolation/vibration mounts – which can be hard to discern but are detrimental to electronics if not addressed. Bolts, air filters, electrical connectors and fuel connectors must also be inspected and tested before every flight to minimise accidents or underperformance. Maintenance of reciprocating and rotary engines generally follows the same lines. However, rotaries have a higher requirement for spark plug maintenance, as fouling occurs more often than in reciprocating engines, in which case the spark plug may need to be removed, cleaned and gapped. Examining April/May 2017 | Unmanned Systems Technology Engine test rigs can run test profiles for hours or days, monitoring parameters such as fuel or oil consumption (Courtesy of Haiden Technology) Maintaining propulsion systems takes up most of a UAV technician’s time, for pre-flight inspections covering connectors, safety wires, bolts and air filters (Courtesy of Northwest UAV)