Cowling
Removable engine covering for drag reduction and cooling.
A cowling, also called a cowl, is a removable engine cover found on cars, motorcycles, aircraft, and outboard boat motors. On planes, cowlings reduce drag and help cool the engine. On boats, they protect the outboard motor while allowing air in and keeping water out of the intake.
The word "cowling" comes from "cowl," which traces back through Middle English and Old English to the Latin *cucullus*, meaning "hood." In aviation, cowlings can reduce drag or direct airflow for cooling. Examples include the NACA cowling and the Townend ring. A cowling may cover parts of the fuselage, nacelles, engine mount, or cockpit. Cowlings differ from fairings in that cowlings are removable for engine access, while fairings are bolted on. The engine-facing side of a cowling must be metal. On jets, cowlings serve as air intakes. They can also be decorative.
On piston-engine planes, the cowling forms a symmetric, circular airfoil, unlike a wing’s planar shape. It channels cool air across the engine’s hottest parts—the cylinders and heads—and reduces turbulence after the air passes the cylinders. Together, these effects cut drag by up to 60 percent. After tests in 1932 proved the NACA cowling’s effectiveness, nearly all radial-engined aircraft used them.
- Drag reduction
- as much as 60 percent
- Test year
- 1932
- Cowling type examples
- NACA cowling, Townend ring
- Material requirement
- engine-facing sides must be made of metal
Lore & Background
The word "cowling" comes from "cowl", which originated from Middle English coule, from Old English cūle, from earlier cugele (“hood, cowl”). This, in turn, came from Ecclesiastical Latin cuculla (“monk's cowl”), from Latin cucullus (“hood”), of uncertain origin. In aviation, a cowling may be used for drag reduction or engine cooling by directing airflow. Examples in aviation include the NACA cowling and Townend ring. On an airplane, the cowling may also cover part of the fuselage, the nacelles, the engine mount and part of the cockpit. Cowlings and fairings are similar, as both streamline airflow, except that cowlings are usually removable (to permit engine inspections and repairs), whereas fairings are bolted in place. Engine-facing sides of the cowling must be made of metal. On jets, they are used as an air intake for jet engines. Cowlings may also be used for decorative purposes. On piston-engined planes, the cowling constitutes a symmetric, circular airfoil, in contrast to the planar airfoil of airplane wings. It directs cool air to flow through the engine where it is routed across the engine's hottest parts, that is, the cylinders and heads. Furthermore, turbulence after the air passes the free-standing cylinders is greatly reduced.
Reader's Guide
The cowling's significance lies in its dual role of reducing drag and cooling the engine, particularly in aviation. On piston-engined planes, the cowling forms a symmetric, circular airfoil that directs cool air across the engine's hottest parts—the cylinders and heads—while greatly reducing turbulence after the air passes the free-standing cylinders. The sum of these effects reduces drag by as much as 60 percent. After tests in 1932 proved the effectiveness of NACA cowlings, almost every radial-engined aircraft were equipped with them. The cowling's removability distinguishes it from fairings, allowing engine inspections and repairs. Its legacy is evident in its widespread adoption across radial-engined aircraft following the 1932 tests, and its continued use on jets as an air intake. The cowling also serves decorative purposes and, on outboard boat motors, must admit air while keeping water out of the air intake.
Did You Know?
- The word 'cowling' derives from Latin cucullus ('hood'), of uncertain origin.
- On piston-engined planes, the cowling reduces drag by as much as 60 percent.
- After tests in 1932, almost every radial-engined aircraft were equipped with NACA cowlings.
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