Atwin-fuselage aircraft has two mainfuselages. It is distinct from thetwin-boom configuration which has a single main fuselage with two subsidiary boom structures.

Twin fuselages have been adopted for various reasons, and a few types have entered production.

A twin-float arrangement offers stability on the water without the need for wing tip stabilising floats. Mounting the float immediately below, or integrally with, the fuselage provides a strong airframe with minimal additional weight. During and after World War I a number of such twin-fuselagefloatplanes and twin-hulledflying boats were constructed, and a few entered production.

As early as 1913, theRadley-England Waterplane racing flying boat demonstrated the concept at the hands of pilotGordon England.

TheTwin Blackburn of 1915 was a long-range floatplane for anti-Zeppelin patrol. A handful of production examples were delivered but few were used operationally.

Savoia-Marchetti produced two twin-hulled flying boat types. TheS.55 multirole flying boat first flew in 1924. It was built in large numbers, including both civil and military variants. The laterS.66 airliner of 1931 sold less well.

During WWI, Caproni introduced one of the first production landplanes to feature twin fuselages, in theCa.4 heavy bomber, manufacturing around 50 aircraft in a range of variants.

DuringWorld War II the need arose for a heavy glider tug capable of towing the largeGotha Go 242 and even largerMesserschmitt Me 321 Gigant. TheHeinkel He 111ZZwilling (twin) was created by joining two He 111 fuselages with a new wing centre section and adding a fifth central engine. Although liked by its pilots when it first flew in 1941, even the 111Z could not tow a fully laden Gigant, and although a small batch became operational they saw little action.

A few variants were developed for roles such as long-range reconnaissance or air-launched anti-ship missile carrier, but none entered service.

DuringWorld War II a need arose for a heavy fighter, which could not be met by a new design proposal in a reasonable time frame. Joining two examples of an existing light fighter aircraft was one way to achieve this.

The GermanMesserschmitt Bf 109Z twin(Zwilling) Bf 109 prototype was destroyed in an attack by the British in 1943 before it was completed, and the project subsequently abandoned. The laterMe 609 twinMe 309 project was never built.

In 1944 Dornier proposed theDornier Do 635 long-range reconnaissance variant of theDo 335 Pfeil heavy fighter, to have twin Do 335 fuselages and four engines. It was never built.

The ItalianSavoia-Marchetti SM.92 prototype was unusual in being an adaptation of a twin-boom design but did not enter production.

TheNorth American F-82 Twin Mustang arrived too late to enter service during the War but later saw service in theKorean War.

More recently the idea of a dedicated re-usable largemothership, capable of carrying and launching a spacecraft, has gained interest. The twin fuselage configuration offers the advantage of a clean payload area underneath the wing centre section, without the need for exceptional ground clearance beneath the fuselages.

Early concepts included theConroy Virtus and Twin-fuselageLockheed C-5 Galaxy Shuttle transport aircraft of 1974.

Following the success of theScaled Composites White Knight prototype theWhite Knight Two is under development, with the first example being used to flight-test theSpaceShipTwo suborbital passenger craft.

TheScaled Composites Stratolaunch, informally known as theRoc, has the longest wingspan of any aircraft ever flown, at 385 feet (117 m). It is owned byStratolaunch Systems, who are currently developing the air-launched spacecraft envisaged as its payload.

NASA have flown a scaled-down demonstrator of a rocket-assistedTowed glider air-launch system, in which the laden twin-fuselage mothership is towed to altitude as a glider and released. Its rocket engine then ignites, propelling it to a speed and altitude greater than those of the tow plane. The payload spacecraft is then released.

TheFouga CM.88 Gemeaux is constructed from twoFouga CM.8 gliders. It was used as an engine testbed for many years, with either a single engine mounted centrally above the wing or twin engines above each fuselage.

TheBoerboon & Coller Yak-110 is an aerobatic type conceived to be eyecatchingly different. Featuring twin Yak-55 fuselages with a third, centrally mounted jet engine, it is the only trimotor cleared for unlimited aerobatics and performs at events in the USA.

Dates given are of first flight or, for those which never flew, of project announcement.

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