Gull-wing door

Gull-wing doors have also been used in aircraft designs, such as the four-seat single-engine Socata TB series built in France.

The Mercedes SLS solved this problem by fitting explosive bolts in the hinges, which would blow up if the car rolled over, causing the door to fall off altogether.

[8] 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.

The DeLorean solved these problems by using a patented cryogenically set stainless steel torsion bar spring (manufactured by Grumman Aircraft Engineering Corporation) to partially counterbalance a full-sized door, and then added a gas-pressurized (pneumatic) strut similar to those found in hatchback cars.

The torsion bar is most important in the first foot of movement from the bottom, where the geometry of the strut is pointed at the hinge and therefore at a mechanical disadvantage.

As the spring relaxes through the door's rotation open, the strut gains a better moment arm and gradually takes over the effort.

It also makes sealing the car against water leaks and snow intrusion more difficult because of the shape and movement path of the door itself.