Gullwing door
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The term gull-wing door is an automotive industry term describing car doors which are hinged at the roof. They are so named because, when opened, the doors evoke the image of a seagull's wings. Conventional car doors are typically hinged at the front-facing edge of the door and allow the door to swing outward from the body of the car. The most well-known examples of road-cars with gull-wing doors are the Mercedes-Benz 300SL from the 1950s, the Bricklin SV-1 from the 1970s and the De Lorean DMC-12 from the 1980s.
Practical considerations
Despite the common misconception that the gull-wing doors are mere stylistic affectations, the design is a very practical one. The advantage is that when properly designed and counterbalanced (for example, the De Lorean), they require little side-clearance to open (about 27.5 cm, or 11" in the De Lorean[1]) and allow much better entrance/egress than conventional doors. This is especially important for vehicles like the De Lorean whose width would make conventional doors awkward to use when the car is in a conventional urban parking space.
Design challenges
Gull-wing doors have a somewhat questionable reputation because of early examples like the Mercedes and the Bricklin. The 300 SL used the door design to allow an unusual chassis design which required a very high door sill and forced the doors to be smaller than would otherwise have been optimal. The Bricklin was a more conventionally-sized door but the actuation system was problematic in day-to-day use and led to unreliable operation. In addition, there was some concern that in making the doors as light as possible they wouldn't provide adequate protection in side-impact accidents. There was, however, no indication that this concern was justified.
The De Lorean solved these problems by using a solid-steel torsion bar (supplied by Grumman Aircraft Engineering Corporation) to counterbalance a full-sized door and then used simple pneumatic struts similar to those found in hatchback cars to open the doors and dampen their movement.
Other disadvantages of the system were not so easy to address. For example, the gull-wing design makes creating a convertible version of the car virtually impossible since, for optimal efficiency, the hinges must be placed as close to the center of the car as possible. This was never a concern for the De Lorean since no convertible version was ever planned (though there were rumors of a four-door family car based on a front-engine chassis with room for four passengers).
It also makes sealing the car against water leaks more difficult because of the shape and movement path of the door itself. Many De Lorean owners report leakage when taking their vehicles through automated car-washes because of the high-pressure water jets, though in ordinary rainfall the seals are more than adequate.
