The Sikorsky XV-2, also known by the Sikorsky Aircraft model number S-57, was a planned experimental stoppable rotor aircraft, designated as a convertiplane, developed for a joint research program between the United States Air Force and the United States Army.

The XV-2 was developed as part of a joint U.S. Air Force and U.S. Army program intended to explore technologies to develop an aircraft that could take off and land like a helicopter but fly at faster airspeeds, similar to a conventional airplane.

The XV-2's stoppable-rotor design was intended to allow it to hover and fly at low speed like a conventional helicopter.

It utilized a single-blade single-rotor design; a counterweight provided stability to the rotor system,[1] while a tip-jet arrangement powered the rotor, which retracted into the upper fuselage when stopped, the XV-2 then flying like a conventional aircraft on delta wings.

[2] A single jet engine was provided for forward flight, and was to be equipped with thrust vectoring for steering in hover and for anti-torque control in lieu of a tail rotor.