Gas turbine aircraft engines and operation thereof

A propulsion arrangement for an aircraft, the arrangement comprising:

• a heat exchanger mounted to an external surface of an aircraft component so as to define part of an aerodynamic surface to a flow of ambient air;
• a gas turbine engine having a compressor with a bleed offtake configured to bleed gas from the compressor;
• an oil system configured to route engine oil through the heat exchanger, and a duct arrangement fluidly connecting the bleed offtake to the heat exchanger and configured to direct a flow of the compressor gas across the heat exchanger in heat-exchange relationship with the engine oil, the arrangement further including a flow controller actuable to regulate the flow of the compressor gas across the heat exchanger.

A method of operating a gas turbine aircraft engine supported by a pylon, the pylon defining an aerodynamic surface and incorporating a heat exchanger, the gas turbine aircraft engine having a compressor, an oil system configured to route engine oil through the heat exchanger, and a duct arrangement fluidly connecting the compressor to the heat exchanger, the method involving:

• flowing engine oil through the heat exchanger, directing a bleed flow of compressor gas drawn from the compressor along the duct arrangement and into heat-exchange relationship with the engine oil in the heat exchanger, and exhausting the bleed flow of compressor gas into wake produced by the pylon.

An aircraft propulsion arrangement, the arrangement including:

• a gas turbine engine supported by a pylon and having a compressor with a bleed offtake configured to bleed gas from the compressor, the pylon defining an aerodynamic surface and incorporating a heat exchanger;
• an oil system configured to route engine oil through the heat exchanger;
• and a duct arrangement fluidly connecting the bleed offtake to the heat exchanger and configured to direct a flow of the compressor gas across the heat exchanger in heat-exchange relationship with the engine oil and to exhaust the flow of the compressor gas into wake produced by the pylon.