Unmanned Systems Technology 025 | iXblue DriX I Maintenance I UGVs I IDEX 2019 I Planck Aero Shearwater I Sky Power hybrid system I Delph Dynamics RH4 I GCSs I StreetDrone Twizy I Oceanology Americas 2019

65 Sky Power hybrid system | Dossier Unmanned Systems Technology | April/May 2019 has been designed with three tiers of functionality. At the base level are the essential programming elements from Sky Power for engine control, such as fuel injection and ignition mapping. The second level comprises information that can be influenced by the vehicle developer, pertaining to key operating functions such as charging management or maximum speeds. The third level is intended for the aircraft operator, and is mainly designed around maximising the visibility of engine data, such as inputs from the various temperature sensors and values for power and torque. Control comms and torque management are also naturally a key part of this level, being vital to the UAV pilot. These factors are locked according to the level of use within the in-house developed UniCal open calibration software, through which Sky Power integrates new powertrain components, behaviours or functions where requested. “We develop our maps for ignition and injection at the dynamometer, and we map for torque and power, correct to mean sea level. These are all uploaded to the control unit,” Seidl notes. “If we have standard atmospheric parameters, we can operate exactly according to the maps developed at the dyno.” However, figures derived for mean sea level cannot be used for normal operations, as the powertrain will typically be used at different altitudes and temperatures. The ECU therefore uses airflow readings to adjust its calculations for torque and power to compensate for this difference. “For example, at 3000 rpm, 20 Nm is about right, while at 6000 rpm the torque might be 30 Nm,” Seidl explains. “If you understand your torque requirements, you can allocate the power required from the engine and the e-drive, but if you’re just operating on the basis of load, you can’t know how to separate the two. It’s generally the same as what’s been done in automotive engines for the past 15 years.” Sky Power’s HKZ capacitor discharge ignition (CDI) system comes with four ignition channels, and was designed to offer much higher energy levels than the company’s previous ignition system. Two key models have been developed. The HKZ215 is used in the company’s two-stroke engines, and normally provides up to 27 mW per channel, 240 ms of burn time, and 17,000 V. The HKZ216, on the other hand, designed for Wankel rotary engines, provides up to 24 mW of energy per channel, with 680 µs of burn time and a typical voltage of 24,000 V. “We could not use standard coil ignition owing to the power restrictions as well as weight constraints common to UAV engines,” Seidl says. “The rotary needs more burn time with less energy, whereas a two-stroke needs more energy owing to the different fuel- air mixture compared to rotaries and four-strokes.” While the coil, capacitors and cable lengths within the ignition system can change from engine to engine, the housing remains the same, weighing between 270 and 330 g. The internal architecture is also designed to be redundant, with two mechanically separated lines running through the enclosure. “Both our rotaries and two-strokes have two spark plugs per chamber,” Seidl notes. “If one ignition line fails, it has no influence on the continued operation of the other one.” The HKZ215 is Sky Power’s capacitor discharge ignition system for two-stroke engines, and provides up to 27 mW per channel, with 240 ms of burn time and 17,000 V