Autonomous camber morphing of a helicopter rotor blade with temperature change using integrated shape memory alloys

The present study proposes and explores a new autonomous morphing concept, where a 12–13° increase in camber is realized over a spanwise section of a helicopter rotor blade with increase in ambient temperature. The camber change is achieved through integration of Shape Memory Alloys (SMAs) on the lower surface of the blade, aft of the leading-edge spar. For a reference rotor of a utility-class helicopter generating 21,000 lbs thrust, a loss in lift of 2590 lb was observed due to operation in hot conditions. With the SMA camber morphing section extending from the blade root to 25%, 50%, and 75% span, the rotor recovered up to 11%, 43%, and 82% of the lift loss at high temperature (compared to a no-SMA blade). If the morphing section instead spans the outboard 25% of the blade (from 75% span to the blade tip), up to a 66% lift recovery is achieved due to the higher dynamic pressures over this region. While these results are achieved with existing SMA properties, idealized target values are also presented. For the SMA considered in the study, while a 40–115°F temperature change was required to achieve the full 12–13° design camber change, partial camber is achieved over a smaller temperature range. The paper identifies desired SMA properties that would produce a 12–13° camber change over an 80–100°F temperature change.