The first effective drag reducing cowling that didn't impair engine cooling was the British Townend ring or "drag ring" which formed a narrow band around the engine covering the cylinder heads, reducing drag. The National Advisory Committee for Aeronautics studied the problem, developing the NACA cowling which further reduced drag and improved cooling. Nearly all aircraft radial engines since have used NACA-type cowlings.[Note 1] Because radial engines are often wider than similar inlines or vees, it is more difficult to design an aircraft to minimize cross sectional area, a major cause of drag, although by the beginning of the Second World War, this disadvantage had largely disappeared as aircraft sizes increased, and multi-row radials increased the power produced in relation to the cross sectional area.[citation needed]