A nacelle ( /nəˈsɛl/ nə-SEL) is a "streamlined body, sized according to what it contains",  such as an engine, fuel, or equipment on an aircraft. When attached by a pylon entirely outside the airframe, it is sometimes called a pod, in which case it is attached with a pylon or strut and the engine is known as a podded engine. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft cockpit may also be housed in a nacelle, rather than in a conventional fuselage.
Like many aviation terms, the word comes from French, in this case from a word for a small boat. 
The Arado Ar 234 was one of the first operational jet aircraft with engines mounted in nacelles. During its development, the four jet engines were merged from having four distinct nacelles, all of which contained their own landing gear wheel, to two nacelles with two engines each.
In recent years, General Electric and NASA have developed nacelles with chevron-shaped trailing edges to reduce the engine noise of commercial aircraft, using an experimental Boeing 777 as a test platform. 
Usually, multi-engined aircraft use nacelles for housing the engines.  Combat aircraft (such as the Eurofighter Typhoon) usually have the engines mounted within the fuselage. Some engines are installed in the aircraft wing, as in the De Havilland Comet and Flying Wing type aircraft. Engines may be mounted in individual nacelles, or in the case of larger aircraft such as the Boeing 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 the Boeing E-3 Sentry radar is housed in a nacelle called a radome.
The primary design issue with aircraft-mounted nacelles is streamlining to minimize drag so nacelles are mounted on slender pylons. This can cause issues with routing the necessary conduits required for the equipment mounted within the nacelle to connect to the aircraft through such a narrow space. This is especially a concern with nacelles housing engines, as the fuel lines and control lines for multiple engine functions must all go through the pylon.  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. 
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines. Common examples of aircraft include airplanes, helicopters, airships, gliders, paramotors, and hot air balloons.
An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115 V AC voltage at 400 Hz, to run the electrical systems of the aircraft; others can produce 28 V DC voltage. APUs can provide power through single or three-phase systems.
The fuselage is an aircraft's main body section. It holds crew, passengers, or cargo. In single-engine aircraft, it will usually contain an engine as well, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage, which in turn is used as a floating hull. The fuselage also serves to position the control and stabilization surfaces in specific relationships to lifting surfaces, which is required for aircraft stability and maneuverability.
A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.
The Shuttle Carrier Aircraft (SCA) are two extensively modified Boeing 747 airliners that NASA used to transport Space Shuttle orbiters. One (N905NA) is a 747–100 model, while the other (N911NA) is a short range 747-100SR.
A propfan, also called an open rotor engine, or unducted fan, is a type of aircraft engine related in concept to both the turboprop and turbofan, but distinct from both. The design is intended to offer the speed and performance of a turbofan, with the fuel economy of a turboprop. A propfan is typically designed with a large number of short, highly twisted blades, similar to the (ducted) fan in a turbofan engine. For this reason, the propfan has been variously described as an "unducted fan" (UDF) or an "ultra-high-bypass (UHB) turbofan."
The Bell XV-15 is an American tiltrotor VTOL aircraft. It was the second successful experimental tiltrotor aircraft and the first to demonstrate the concept's high speed performance relative to conventional helicopters.
The Boeing X-48 is an American experimental unmanned aerial vehicle (UAV) built to investigate the characteristics of blended wing body (BWB) aircraft. Boeing designed the X-48 and two examples were built by Cranfield Aerospace in the UK. Boeing began flight testing the X-48B version for NASA in 2007. The X-48B was later modified into the X-48C version, which was flight tested from August 2012 to April 2013. Boeing and NASA plan to develop a larger BWB demonstrator.
In an aircraft with a pusher configuration, the propeller(s) are mounted behind their respective engine(s). Since a pusher propeller is mounted behind the engine, the drive shaft is in compression in normal operation.
An airplane or aeroplane is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, and wing configurations. The broad spectrum of uses for airplanes includes recreation, transportation of goods and people, military, and research. Worldwide, commercial aviation transports more than four billion passengers annually on airliners and transports more than 200 billion tonne-kilometers of cargo annually, which is less than 1% of the world's cargo movement. Most airplanes are flown by a pilot on board the aircraft, but some are designed to be remotely or computer-controlled such as drones.
A blended wing body (BWB), also known as blended body or hybrid wing body (HWB), is a fixed-wing aircraft having no clear dividing line between the wings and the main body of the craft. The aircraft has distinct wing and body structures, which are smoothly blended together with no clear dividing line. This contrasts with a flying wing, which has no distinct fuselage, and a lifting body, which has no distinct wings. A BWB design may or may not be tailless.
A hardpoint is a location on an airframe designed to carry an external or internal load. This includes a station on the wing or fuselage of a civilian aircraft or military aircraft where external jet engine, ordnance, countermeasures, gun pods, targeting pods, or drop tanks can be mounted.
A twinjet or twin-engine jet is a jet aircraft powered by two engines. A twinjet is able to fly well enough to land with a single working engine, making it safer than a single-engine aircraft in the event of failure of an engine. Fuel efficiency of a twinjet is better than that of aircraft with more engines. These considerations have led to the widespread use of aircraft of all types with twin engines, including airliners, fixed-wing military aircraft, and others.
A cowling is the removable covering of a vehicle's engine, most often found on automobiles, motorcycles, airplanes, and on outboard boat motors. On airplanes, cowlings are used to reduce drag and to cool the engine. On boats, cowlings are a cover for an outboard motor. In addition to protecting the engine, outboard motor cowlings need to admit air while keeping water out of the air intake.
A convertiplane is defined by the Fédération Aéronautique Internationale as an aircraft which uses rotor power for vertical takeoff and landing (VTOL) and converts to fixed-wing lift in normal flight. In the US it is further classified as a sub-type of powered lift. In popular usage it sometimes includes any aircraft that converts in flight to change its method of obtaining lift.
A podded engine is a jet engine that has been built up and integrated in its nacelle. This may be done in a podding facility as part of an aircraft assembly process. The nacelle contains the engine, engine mounts and parts which are required to run the engine in the aircraft, known as the EBU. The nacelle consists of an inlet, an exhaust nozzle and a cowling which opens for access to the engine accessories and external tubing. The exhaust nozzle may include a thrust reverser. The podded engine is a complete powerplant, or propulsion system, and is usually attached below the wing on large aircraft like commercial airliners or to the rear fuselage on smaller aircraft such as business jets.
The aircraft design process is a loosely defined method used to balance many competing and demanding requirements to produce an aircraft that is strong, lightweight, economical and can carry an adequate payload while being sufficiently reliable to safely fly for the design life of the aircraft. Similar to, but more exacting than, the usual engineering design process, the technique is highly iterative, involving high level configuration tradeoffs, a mixture of analysis and testing and the detailed examination of the adequacy of every part of the structure. For some types of aircraft, the design process is regulated by civil airworthiness authorities.
The Conroy Virtus was a proposed American large transport aircraft intended to carry the Space Shuttle. Designed, beginning in 1974, by John M. Conroy of the Turbo-Three Corporation, it was to incorporate a pair of Boeing B-52 Stratofortress fuselages to form a new craft using existing parts for cost-savings. While the project was seriously considered, it proved impractically large and NASA chose to develop the Boeing 747–based Shuttle Carrier from surplus commercial aircraft instead.
The Aurora D8, also known as the D8 Airliner, is an airliner concept under development as of mid 2017. The project was initiated in 2008 by Aurora Flight Sciences, the Massachusetts Institute of Technology (MIT) and Pratt & Whitney under NASA's sponsorship of $2.9 million.
The Antonov An-325 is an evolution project of Antonov An-225 "Mriya" designed to launch spacecraft of various purposes into circular, elliptical and high-circle orbits, including geostationary orbit. It was planned to be an enlarged and improved version of the An-225, but it was never built.