Double tail girder
A double tail girder is a type of aircraft tail . These are two longitudinal arms that connect the front fuselage with the tail unit . The booms can include additional equipment such as fuel tanks. Airplanes with double tail girders differ from double-body airplanes like the North American F-82 in that they have a single, central fuselage.
construction
Airplanes with double tail girders differ from double-fuselage airplanes in that they have a separate, short front fuselage that contains the cockpit and payload. The twin tail girder was developed to solve or circumvent various design problems in aircraft with conventional fuselage.
Engine construction
In single-engine aircraft with a propeller in pusher configuration or a jet engine with a conventional fuselage, the propeller or the engine outlet must be placed very far back, which requires a very long drive shaft or a very long jet pipe , which reduces the efficiency of the drive. An aircraft design with a double tail girder allows a much shorter and more efficient construction. An example of this are patterns 21 (propeller in pusher configuration) and 21R (jet engine) from the Swedish manufacturer Saab . In these designs, the elevator is mounted on the upper part of the two rudders in order to remain free of wake turbulences from the engine . SpaceShipOne and SpaceShipTwo have two separate tail units, as the rocket exhaust gases exit at a larger angle.
Double tail girders are also used in twin-engine aircraft such as the Lockheed P-38 Lightning if the engines are equipped with voluminous units such as turbochargers or coolers .
Field of view
In order for observers or rear gunner to have an unobstructed field of view, it is necessary with a conventional fuselage to move such positions very far into the stern, which can lead to problems with weight and balance . Without the conventional stern, this position can be moved much further forward, which solves the balance problem. One example of this is the Focke-Wulf Fw 189 .
Nevertheless, the continuous horizontal stabilizer obstructs the view somewhat and rear guns have to be designed so that they cannot fire to the side.
Loaded
The loading and unloading of large cargo such as vehicles or containers requires large hatches. With conventional fuselage constructions, these must be in the side or in the nose , which requires heavy reinforcements. Side doors limit the length of the cargo to the width of the doors. In addition, engines or the landing gear can be in the way. Double tail girders allow a large hatch to be positioned in the rear of the aircraft, such as on the Armstrong Whitworth AW650 . However, access to the rear is limited by the tail unit, especially for approaching trucks, so that a high rear is preferred in many cases.
Performance
Aircraft with twin tail girders generally have greater drag than conventional designs. Typically, twin tail girders are flatter than the rest of the fuselage and therefore less stiff, which makes additional reinforcements necessary to ensure a rigid stern. On the other hand, the two-sided fastening of the elevator avoids turbulence at the ends and the elevator can be made smaller and lighter. Furthermore, the distribution of the load along the wing can limit the structural forces between the two arms, thus reducing the overall weight.
history
Double ladder girders have existed since the early days of open truss structures . With the realization that this construction method entails enormous air resistance , more compact structures covered with fabric were developed during the First World War . A well-known example of this are the three-engine bombers made by the Italian manufacturer Caproni .
At around the same time, the first monocoque hulls were built and it did not take long before this construction method was also used for double tail girders. One of the first aircraft of this type was the Nieuport Pusher , whose fuselage was covered with Bakelite- impregnated paper. The more well-known designs, however, were the AGO CI and C.II , whose body consisted of shells made of wooden strips laminated over a mold. After the development of aluminum-clad monocoques during the First World War, this technology was also used for the construction of double ladder girders from the early 1920s.
Many of the early aircraft designs used double tail girders to make room for a tail propeller. During the First World War, various larger aircraft with double tail girders were developed to provide space for a rear gunner without having to position it too far from the center of gravity and thus avoid balance problems.
During the Second World War , the need arose to transport large loads and vehicles by air. As with the Gotha Go 242, for example, the concept of the double tail girder made it possible to create a large loading hatch in the rear.
With the beginning of the jet age, the space requirement for a rear propeller was eliminated, but was replaced by the need for a free path for the hot exhaust gases. The efficiency of jet engines was limited by the long intake and jet pipes used in many of the early designs. One solution to this problem was the use of double ladder girders such as the de Havilland Vampire and the de Havilland Venom , which made it possible to make the nozzles much shorter.
Few designs used double tail girders for other reasons - for example the Lockheed P-38 Lightning , in which the booms housed the extremely long engines with turbochargers that would otherwise have had to be housed in unusually long engine nacelles . One of the newest applications of double tail girders is to support wings and canards with extremely large aspect ratios like the Rutan Voyager . In addition, most of the fuel can be carried in the middle, which significantly reduces the forces acting on the wings.
Despite the expected advantages, aircraft with double tail girders are the exception. For most applications, the booms are less efficient in structure and create more drag. When using double tail girders to improve the downward field of fire, the field of fire is severely narrowed to the side. The booms offer better access to the fuselage for transport aircraft, but trucks have to be driven extremely carefully to the tail so as not to damage the horizontal stabilizer. Therefore, for example, the Fairchild C-119 remained an exception and most post-war transport aircraft such as the Lockheed C-130 Hercules were again built with a conventional tail.
literature
- Gordon Swanborough, William Green: The complete book of fighters . Salamander Books Ltd., 1994, ISBN 978-1-84065-269-7 (English).
Web links
Individual evidence
- ^ Martyn Chorlton, Tony Buttler: De Havilland's First-Generation Interceptor . Airplane Icons, 2014, p. 6 (English).
- ^ Gordon Swanborough, William Green: The complete book of fighters . Salamander Books Ltd., 1994, ISBN 978-1-84065-269-7 , pp. 512,513 (English).