Twin-lift design
UMD has participated regularly in the AHS Student Design competition, which challenges teams to come up with novel concept rotorcraft for specific mission requirements. The year in which I participated (2010), the Request For Proposals deviated from the usual "design a new vehicle" statement. Instead, we had to choose two currently operational rotary-wing platforms and develop control co-ordination techniques to cooperatively carry an underslung load - a "twin-lift" configuration. Our winning paper design uses two CH-53E super stallions to carry a 8x8x40 ft container using an innovative spreader bar that can be collapsed, stacked and carried inside the cargo hold of a single CH-53E.
A tablet-sized device gives pilots situational awareness and augmented AFCS signals with stabilizing inputs based on position sensors placed on the spreader bar. Once the load hook-up is completed, the twin-lift control is handed to one pilot, and relative position co-ordination is handed off to the controller. Both vertical and lateral spacing between the two helicopters are provided for adequate safety margins in forward flight. In case of emergency, the load is jettisoned simultaneously from both helicopters, co-ordination is turned off and the AFCS attitude/airspeed hold of each turned is turned on for ten seconds, while the twin-lift interface tablet notifies the pilot to resume control.
The secondary goal was to acquire an off-the-shelf R/C helicopter, and improve its thrust without increasing the power. Using Blade Element Momentum Theory and custom manufacturing of composite blades, our team demonstrated a 17% increase in thrust for the same power consumption.