Butterfly doors or vertical doors are a type of door sometimes seen on high-performance automobiles. They are similar to scissor doors. While scissor doors move straight up via hinge points at the bottom of the A-pillar, butterfly doors move up and out via hinges along the A-pillar.. This makes for easier entry/exit at the expense of requiring more opening space than needed for scissor doors.
The McLaren F1, Alfa Romeo 33 Stradale, Saleen S7, Enzo Ferrari, Toyota Sera - EXY-10, and the Mercedes-Benz SLR McLaren, among others, use butterfly doors.
It was also a common feature for Group C and IMSA GTP/Camel Lights prototype racers as they incorporate teardrop top which allows the driver to get in and out of the car more quickly than conventional and gullwing doors, especially in a cramped pitlane environment such as the pre-1991 Le Mans circuit.
Since then, butterfly doors have been an adopted design of closed top sportscar racers, such as the Toyota GT-One, Bentley Speed 8 and more recently, the Peugeot 908 HDi FAP. The Toyota Sera, released in 1991, was a limited-release car designed exclusively for the Japanese market which used this design.
The Mercedes-Benz SLR McLaren Roadster was one of the few open top cars to use butterfly wing doors. This is made possible by having the doors hinged at the side of A-pillar instead of at top by the roof. The McLaren MP4-12C has a unique system where the butterfly doors do not use a top hinge meaning that the car can use frameless windows which allows for the cars upcoming convertible version to retain them.