Gas turbine engine having an air-oil heat exchanger

1. A gas turbine engine including:

a core engine surrounded by a core fairing;

a propulsive fan;

a nacelle surrounding the propulsive fan, the core fairing and the core engine;

a fan duct for receiving a bypass air flow accelerated by the propulsive fan, the fan duct being defined between the nacelle and the core fairing;

an air-oil heat exchanger for cooling engine oil using an air flow diverted from the bypass air flow, the heat exchanger being mounted behind a wall of the fan duct;

a flow passage which receives the diverted air flow at an inlet in the fan duct, delivers the diverted air flow to the heat exchanger, and returns the diverted air flow to the fan duct at an outlet which is downstream of the inlet;

a deflector movable between a deployed position and a stowed position, wherein

in the deployed position, the deflector is deployed from the wall of the fan duct and is in a position to deflect the bypass air flow away from the outlet and thereby locally reduce a pressure in the fan duct adjacent the outlet,

in the stowed position, the deflector is stowed to the wall of the fan duct, and

the deflector in the deployed and stowed positions is between the inlet and the outlet without covering the inlet and the outlet; and

the deflector comprising

a panel pivotably rotatable about a front edge of the panel to move between the deployed position and the stowed position, the front edge located upstream, relative to the bypass air flow, of a back edge of the panel, wherein

the back edge of the panel projects into the bypass air flow in the deployed position, and the deflector is configured to be urged to the stowed position due to an aerodynamic force from impingement of the bypass air flow upon the panel of the deflector, wherein the deflector is spring biased to the deployed position.

2. The gas turbine engine as claimed in claim 1 , wherein the heat exchanger is mounted inside the core fairing.

3. The gas turbine engine as claimed in claim 1 , wherein the heat exchanger is mounted inside an aerofoil body which traverses the fan duct between the nacelle and the core fairing.

4. The gas turbine engine as claimed in claim 1 in which the wall of the fan duct has a recess configured to receive the deflector in the stowed position such that the deflector is flush with the wall.

5. The gas turbine engine as claimed in claim 1 , wherein the air-oil heat exchanger is a matrix air-cooled oil cooler.

6. The gas turbine engine as claimed in claim 1 which is a geared fan gas turbine engine.