Douglas A-4 Skyhawk. T-tail - The horizontal stabiliser is mounted on top of the fin, creating a "T" shape when viewed from the front. T-tails keep the stabilisers out of the engine wake, and give better pitch control. T-tails have a good glide ratio, and are more efficient on low speed aircraft. However, the T-tail has several disadvantages. It is more likely to enter a deep stall, and is more difficult to recover from a spin. For this reason a small secondary stabiliser or tail-let may be fitted lower down where it will be in free air when the aircraft is stalled. A T-tail must be stronger, and therefore heavier than a conventional tail. T-tails also tend to have a larger radar cross section. Examples include the Gloster Javelin and McDonnell Douglas DC-9. Fins The fin comprises the fixed vertical stabiliser and rudder. Besides its profile, it is characterised by: Number of fins - usually one or two. Location of fins - on the fuselage (over or under), tailplane, tail booms or wings Twin fins may be mounted at various points: Twin tail A twin tail, also called an H-tail, consists of two small vertical stabilisers on either side of the horizontal stabiliser. Examples include the Antonov An-225 Mriya, B-25 Mitchell, Avro Lancaster, and ERCO Ercoupe. Twin boom A twin boom has two fuselages or booms, with a vertical stabiliser on each, and a horizontal stabiliser between them. Examples include the P-38 Lightning, de Havilland Vampire, Sadler Vampire, and Edgley Optica. Wing mounted midwing as on the F7U Cutlass or on the wing tips as on the Handley Page Manx and Rutan Long-EZ Unusual fin configurations include: No fin - as on the McDonnell Douglas X-36. This configuration is sometimes incorrectly referred to as "tailless". Multiple fins - examples include the Lockheed Constellation (three), Bellanca 14-13 (three), and the Northrop Grumman E-2 Hawkeye (four). Ventral fin - underneath the fuselage. Often used in addition to a conventional fin as on the (North American X-15 and Dornier Do 335). V, Y and X tails An alternative to the fin-and-tailplane approach is provided by the V-tail and X-tail designs. Here, the tail surfaces are set at diagonal angles, with each surface contributing to both pitch and yaw. The control surfaces, sometimes called ruddervators, act differentially to provide yaw control (in place of the rudder) and act together to provide pitch control (in