U.S. Patent Specifications

In an aircraft having a cabin space and a propulsive engine provided with a lubricating system circulating hot oil including a duct for carrying hot oil from the engine and for returning the oil to the engine; the combination of a liquid medium circulating system external of the engine including duct means for said medium and a pump for circulating said medium through the duct means, a relatively small liquid supply tank connected in the second named system, a larger supply tank connected with the small tank to replenish the liquid in the second named system, means responsive to the liquid level in the small tank for controlling the delivery of liquid from the larger tank to the small tank, heat exchanger means connected in said systems for bringing the hot oil in heat transfer relation to the liquid circulating in said second named system to heat said medium, and means for bringing said heated circulating medium into heat transfer relation to the air in said cabin space to heat the same.