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47 AUVSI’s Xponential | Show report the servos into a 300 kg OPV,” Volz said. Volz also reported the success of the 30 g full brushless servo, the DA15-N, introduced three years ago. One US customer bought more than 1000 units in 2015 to replace a brushed Volz model that was qualified for 300 flight hours before replacement; the DA15-N has proven good for 1500 hours, hugely reducing the cost per flight hour. Co-located with propeller manufacturer Sensenich, Aerovate attracted interest at the show with an innovative range of variable-pitch propellers for UAVs, which the company describes as being unique in the industry. Most small to medium UAVs use fixed-pitch propellers, which may be adjustable on the ground. While these are simple, reliable and inexpensive, they are inflexible as they must either be optimised for one phase of the mission, such as take-off, climbing to operating altitude or cruising, or make do with a compromise design that is adequate at best in all three. Like a car with a continuously variable transmission, an aircraft with a variable-pitch propeller can adapt to the changing load and speed conditions to get the best performance available throughout the flight envelope. However, propeller pitch change mechanisms tend to involve costly and expensive hydraulic or electric actuation. “It’s self-adjusting, passive, which means that there are no hydraulics and no electronics. You simply bolt it on and go,” said Aerovate’s Andrew Kondor. The hub is a patented design in which spring loading applies force towards coarse pitch, but allows the aerodynamic loading to overcome that force to push the blades toward fine pitch. At maximum thrust during zero forward velocity, the blades are pushed to maximum fine pitch; energy is stored in the spring and gradually released as forward velocity rises, allowing the spring to move the blades back to coarse pitch. The two blades are linked so that any slight deviations from one side to the other can be normalised throughout the whole pitch range. Propeller sizes start at a diameter of 10 in with two blades up to the largest built so far, a 37 in three-bladed propeller. Ultimately, said Kondor, the company hopes to size them for Rotax 914 engines in the 100 hp range. One smaller example has been tested at up to Unmanned Systems Technology | June/July 2016 Volz has introduced a range of clutched servos designed for use in optionally piloted vehicles One of Aerovate’s self-adjusting and variable-pitch UAV propellers