Flapper valve for aircraft engine

A valve assembly for an aircraft engine, the valve assembly comprising:

• a base defining an air opening passing therethrough from an upstream side of the base to a downstream side of the base, the air opening configured to receive airflow therethrough in a flow direction from the upstream side to the downstream side;
• a stopper extending from the downstream side of the base adjacent the air opening;
• a flapper plate pivotably mounted to the base about a pivot axis, the flapper plate having an upstream surface and a downstream surface opposite the upstream surface, the upstream surface extending from an inner edge adjacent the pivot axis to a remote outer edge;
• the flapper plate being pivotable relative to the base and the stopper from a closed position to a fully open position when the flapper plate is acted upon by a force generated by the airflow, wherein in the fully open position the downstream surface of the flapper plate abuts the stopper, and in the closed position the flapper plate obstructs the air opening;
• and
• a force augmentor for generating an additional force on the flapper plate in a direction towards the stopper to maintain the downstream surface of the flapper plate abutted against the stopper in the fully open position.