Tank introduced a further refinement to this basic concept. He suggested placing most of the airflow components on the propeller, in the form of an oversized propeller spinner whose outside diameter was the same as the engine. The cowl around the engine proper was greatly simplified, essentially a basic cylinder. Air entered through a small hole at the centre of the spinner, and was directed through ductwork in the spinner so it was blowing rearward along the cylinder heads. To provide enough airflow, an internal cone was placed in the centre of the hole, over the propeller hub, which was intended to compress the airflow and allow a smaller opening to be used. In theory, the tight-fitting cowling also provided some thrust due to the compression and heating of air as it flowed through the cowling.