Blade fold rotary actuator for the maritime version
of the EH-101 helicopter.

 

Embarked military helicopters are generally equipped with two devices that allow the deployment of blades (blade fold) and tail (tail fold). The blade fold of EH-101 is composed by a couple of cylindrical components that joins each blade end (outerlink) to the fork end (innerlink). The first device is the rotary actuator and the second component is the pin that locks the joint after the deployment. Actuator and pin are quite complicated assemblies, with several contacting and sliding surfaces and a lot of inner gears with critical tolerances that must be complied in order to avoid jam or excessive wear.

It must be pointed out that the structure constitutes a vital part for the helicopter. The actuator must be analyzed in dynamic condition during the actuation phase of deployment. Both actuator and pin are then verified for the in-flight condition.

The structures are modeled with 3-D solid elements including not only the rings of the actuator and the pin but also the innerlink and outerlink made of titanium and composite materials. Indeed, the different stiffness of the contacting parts greatly affects the pressure diagram and then the stress and deformation behavior of the rings.

In the finite element model each part constitutes a substructure. The substructures are coupled through the interfaces, defined with gap elements. The first analysis is focused around the region of the engaged teeth. A second model is used to obtain the exact deformed shape of the structures subjected to the actuation loads and flight loads. A final verification regards the fatigue stress analysis under the applied centrifugal force that is variable in intensity and that originates out-of-plane components.