Aeroplane Configurations

Aeroplanes come in all shapes and sizes. Usually, the configuration of an aeroplane is driven, or at least strongly influenced, by its mission requirements. For example, a commercial airliner has a large fuselage cabin area due to the requirement to transport passengers. 

A military fighter jet may have a highly swept wing to allow it to fly a supersonic ally. A utility aeroplane that must be able to take off and land on snow might have skis for landing gear. These are a few examples of aircraft configurations that may be driven by the mission requirements. 

It may be possible to satisfy the mission requirements with a variety of design solutions, limited only by the imagination and creativity of the aeroplane designer, and influenced by advancements in technology.

It is quite common for aeroplanes to have a single fuselage, whereas twin-fuselage aeroplane designs are somewhat rare. A twin-fuselage aircraft may offer some advantages for some applications. The twin-fuselage aeroplane may have reduced design and development time and costs if an existing single-fuselage aeroplane can be used as a baseline.

A sampling of possible aeroplane configurations

North American F-82 Twin Mustang twin fuselage airplane. Note that there is a pilot in each fuselage cockpit. (Source: US Air Force.)

This was the case for the North American F-82 Twin Mustang, developed near the end of World War II. Based on the single-fuselage XP-51 Mustang, the F-82 was designed as a very long-range fighter escort aircraft, with a nominal range of over 2000 miles (3200 km). The F-82 twin fuselages were from the single-fuselage P-51, which was stretched by 57′′ (1.45 m), allowing for the installation of additional fuel tanks.

Both cockpits were retained from the single-fuselage aeroplanes so that a pilot in either cockpit could fly the aeroplane, which was advantageous for very long-duration flights. The F-82 saw combat during the Korean War, being the first fighter to shoot down a North Korean aircraft.

The F-82 Twin Mustang still holds the record for the longest, non-stop flight by a propeller-driven fighter aeroplane, when it flew from Hawaii to New York, a distance of 5051 miles (8128 km), in 14 hours 32 minutes on 27 February 1947.

Virgin Galactic White Knight Two and Spaceship Two

Three-view drawing of the Virgin Galactic White Knight Two (Spaceship Two not attached). (Source: US Design Patent D612,719 S1, US Patent and Trademark Office, July 25, 2008.)

The twin-fuselage configuration has found an application for aeroplanes that carry a large, centerline payload, such as the Virgin Galactic White Knight Two, which carries the Spaceship Two. The twin-fuselage White Knight Two is the first stage of a two-stage space launch system, with Spaceship Two being the second stage.

Only the right fuselage of the White Knight Two is configured to carry pilots and passengers, but, conceivably, the left fuselage could be designed to do so also. All three fuselages, the two White Knight Two and single Spaceship Two fuselages, are similar in design.

This is an interesting design philosophy, whereby the White Knight Two is configured to be flown like the Spaceship Two, with a similar cockpit arrangement, equipment, and pilot sight picture. This allows for training and proficiency flying in the White Knight Two aeroplane which simulates, at least, the glide, approach, and landing phases of Spaceship Two.

Similar to the twin-fuselage configuration, an aeroplane may have twin longitudinal booms that extend from the main wing to the tail. The twin-boom configuration may be advantageous for powerplant integration or for ease of access to aft fuselage cargo doors.

The twin booms also provide additional volume for carrying fuel or equipment. The Cessna 337 Skymaster is an example of a twin-boom, twin-engine aeroplane that has been used as a general aviation and military utility aircraft.

The twin booms allow both engines to be mounted on the fuselage centerline, with one in a puller or tractor configuration (forward-mounted engine) and the other in a pusher configuration (aft-mounted engine).

An advantage of having both engines along the aeroplane centerline, versus mounted on either side of the fuselage, is that lateral-directional control is not degraded in the event of an engine failure, i.e. there is no yawing tendency with the power loss of one engine.

An aeroplane with tailwheel landing gear, also sometimes called conventional landing gear, is the Extra 300 aeroplane. The Extra 300 is a two-place, Single-engine, high-performance, aerobatic, general aviation aeroplane with an all-composite, carbon fibre main wing. The tailwheel configuration is needed to provide ground clearance for the large-diameter propeller at the front of the aeroplane.

The wing is attached to the middle of the fuselage, hence, it is termed a mid-wing configuration. The North American Twin Mustang is a low-wing monoplane and the Cessna Skymaster is a high-wing monoplane, where the main wing is attached to the bottom and top of the fuselage, respectively.

An example of a forward-swept wing configuration is the Grumman X-29 experimental, supersonic research aircraft. The X-29 investigated forward-swept wing manoeuvrability and other advanced technologies.

Three-view drawing of the Cessna Skymaster. (Source: Courtesy of Richard Ferriere, with permission.)

Two X-29 aircraft were built, with test flights conducted by NASA and the US Air Force. The single-seat X-29 had a forward-swept main wing and trapezoidal-shaped canard surfaces forward of the wing. Forward-swept wings are susceptible to divergent aeroelastic twisting, so the X-29 wing was fabricated with advanced composite materials, which could provide the required structural stiffness with low weight.

The forward-swept wing X-29 was inherently unstable, requiring a state-of-the-art “fly-by-wire” flight control system, where the aircraft was constantly flown and stabilized by computers. A single General Electric F404 turbofan jet engine powered the X-29, enabling a top speed of Mach 1.8 at 33,000 ft (10,000 m).

The first flight of the X-29 was on 14 December 1984. The two X-29 aircraft completed 422 research test flights over a period from 1984 to 1991. Most of the aeroplane configurations that we have discussed so far are single-wing or monoplane configurations.

An example of an airplane with two main wings, a biplane, is the Russian Antonov An-2Colt The two wings need not have the same dimensions. In fact, a biplane’s wings can differ in size, airfoil shape, wing sweep, or other characteristics.

A three-view drawing of the Grumman X-29 forward-swept wing aircraft. (Source: NASA.)

The An-2 is a large, rugged, single-engine aircraft designed to perform a variety of utility tasks such as cargo hauling, crop dusting, water bombing (for fighting forest fires), parachute drop, glider towing, or military troop or civilian passenger transport. Designed by the Antonov Design Bureau, Kyiv, Ukraine in 1946, the An-2 was produced for the next 45 years.

Because of its sturdy construction, relatively simple systems, low-speed capabilities, and large load capacity, the AN-2 has become a popular “bush” plane for flying people and cargo in and out of remote, unimproved areas.

Known as a short takeoff and landing, or STOL, aeroplane, the An-2 can takeoff in less than about 600 ft (180 m) and, due to its extremely low stall speed of less than 30 mph (48 km/h), it needs only about 700 ft (210 m) to land has conventional landing gear, but with skis for operation on snow-covered terrain replacing the tyres.

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