Bird strike emerges as open rotor concern

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Bird-strike damage protection rules could emerge as a key design hurdle facing developers of a new generation of fuel-efficient open rotor engines, according to a specialist on propeller powerplants.

Speaking at the Towards Sustainable Aviation Propulsion event organised by the Institution of Mechanical Engineers, Dowty Propellers performance engineer Josef Trchalik said: "The bird-strike test represents a key certification requirement of any aircraft engine. It is not clear yet whether open-rotor blades would be certified according to rules that apply for propellers or if they will be certified as fan blades.

"If the latter is the case then the structure of the open rotor blades will have to be reinforced, which would result in heavier rotor blades and might also restrict the choice of material for the blade structure."

Current bird strike certification requirements differ for propellers and turbofan blades, with propeller blades required to withstand the impact of a significantly lighter bird than fan blades.

Trchalik says bird-strike is a more serious issue for a 'pusher' configuration, which has a similar intake arrangement to a regular turbofan, as there is no fan to shield the engine. Impact-resistance requirements are more easily met with a 'tractor' configuration as the air intakes of an unducted fan would be shielded by two rows of propellers.

Trchalik adds that locating the engines at the rear of the fuselage would increase the chance of debris hitting the blades. "On the other hand, wing-mounted engines are more likely to suck in debris from the runway surface as they are located closer to the ground," he says.