Anacelle (/nəˈsɛl/nə-SEL) is a streamlined container foraircraft parts such asengines, fuel or equipment.^[1] When attached entirely outside the airframe, it is sometimes called a pod, in which case it is attached with apylon or strut and the engine is known as apodded engine.^[2] In some cases—for instance in the typical "Farman" type"pusher" aircraft, or theWorld War II-eraP-38 Lightning orSAAB J21—an aircraft cockpit may also be housed in a nacelle, rather than in a conventionalfuselage.

Like manyaviation terms, the word comes fromFrench, in this case from a word for a small boat.^[3]

TheArado Ar 234 was one of the first operational jet aircraft with engines mounted in nacelles. During its development, the four engines had four distinct nacelles. They once had their own landing gear wheel, but they were later combined to two nacelles with two engines each.

Around 2010,General Electric andNASA have developed nacelles with chevron-shaped trailing edges to reduce the engine noise of commercial aircraft, using an experimentalBoeing 777 as a test platform.^[4]

Usually, multi-engined aircraft use nacelles for housing the engines.^[5] Combat aircraft (such as theEurofighter Typhoon) usually have the engines mounted within the fuselage. Some engines are installed in the aircraft wing, as in theDe Havilland Comet andFlying Wing type aircraft. Engines may be mounted in individual nacelles, or in the case of larger aircraft such as theBoeing B-52 Stratofortress (pictured right) may have two engines mounted in a single nacelle. Nacelles can be made fully or partially detachable for holding expendable resources such as fuel and armaments. Nacelles may be used to house equipment that will only function remote from the fuselage, for example theBoeing E-3 Sentry radar is housed in a nacelle called a radome.

• Edward Turner used the term to describe his styling device introduced in 1949 to tidy the area around the headlamp and instrument panel of hisTriumph Speed Twin,Thunderbird andTiger 100 motorcycles. This styling device was much copied within the British industry thereafter, although Czech motorcycle manufacturerČeská Zbrojovka Strakonice was using it beforehand. Indeed, theRoyal Enfield Bullet still retains its version, the 'casquette', on its current models. The last Triumphs to sport nacelles were the 1966 models of the 6TTriumph Thunderbird 650, 5TATriumph Speed Twin 500, and 3TATriumph Twenty One 350.^{[6][citation needed]}
• Thegenerator and gearbox "shell" – with rotator shaft – on ahorizontal-axis wind turbine (HAWT).^[7]
• A forward projection of a catamaran's bridgedeck designed to soften the impact of seas or make more space inside the cabin.
• In theStar Trek franchise it is also used as a term for the housing containing coils that generate the warp field. This is separate to the engine that powers them.
• Harley-Davidson refers to the streamlined headlamp and fork triple tree covering on the Milwaukee-Eight version of theHarley-Davidson Fat Boy as the "Headlamp Nacelle."^[8] The replacement kit also refers to it as the "Fat Boy Nacelle Kit."

The primary design issue with aircraft-mounted nacelles is streamlining to minimisedrag so nacelles are mounted on slender pylons. This can cause issues with directing the needed conduits mounted within the nacelle to connect to the aircraft through such a narrow space. This is especially concerning with nacelles containing engines, as the fuel, and control, lines for multiple engine functions must all go through the pylons.^[5] It is often necessary for nacelles to be asymmetrical, but aircraft designers try to keep asymmetrical elements to a minimum to reduce operator maintenance costs associated with having two sets of parts for either side of the aircraft.^[5]

• Aircraft components

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