A gravity knife is a knife with a blade contained in its handle, and that opens its blade by the force of gravity. As the gravity knife requires gravity or spinning motion to propel the blade out of the handle, it differs fundamentally from the switchblade, which opens its spring-propelled blade automatically upon the push of a button, switch, or fulcrum lever. The main purpose of this opening method is that it allows opening and closing to be done one handed, in situations where the other hand is occupied. A major historical use has been in issue to parachutists to cut off their parachutes when tangled in a tree or in similar situations.
The gravity knife uses a button, trigger, or fulcrum lever to release the blade from both the open and the closed positions, and may use a side-folding or telescoping (out-the-front, or OTF) blade. While most military gravity knives utilize a locking blade design, other types may not mechanically lock open but rely instead upon friction to wedge the rear section of the blade against the interior of the handle. Factory-made gravity knives have various types of buttons, triggers, and fulcrum levers, which usually are used to release the blade from both the open and the closed positions.
Design and operation
Flieger-Kappmesser / Luftwaffe Gravity Knife (LGK)
One of the most recognizable gravity knives is the World War II-era Flieger-Kappmesser (literally: Flyers-Cutting Knife), which utilizes a four-inch (100 mm) telescoping (OTF), gravity-propelled locking blade. First produced in 1937, the often so called Fallschirmjägermesser was initially issued to German flight crews and paratroops, primarily for the purpose of cutting a trapped parachutist from his rigging in case he landed with a tangled parachute, or became entangled in trees or in the water with the shroud lines. The spike was used to untie knots while packing the parachutes. Luftwaffe air crew members used the knife to cut themselves out of their harnesses or cut through the aluminum hull of the aircraft after a crash landing. Though not intended for use as a fighting knife in the first place, the LGK was introduced to the 1st Skijäger Division and SS units at the Russian Front to be used primarily as a close combat weapon from 1944 on.