The Payen Pa 49 Katy was a small experimental French turbojet powered tailless aircraft, designed by Nicolas Roland Payen, and first flown in 1954. It was the first French aircraft of this kind and the smallest jet aircraft of its day. When the flight testing programme ended in 1958 Payen gave the aircraft to the Musée de l'Air et de l'Espace at Le Bourget.

The Payen 49 was the first French delta wing aircraft and made its first flight on January 22, 1954. The 300 subsequent research flights of the aircraft were used to check the performance of the delta wing and the "crocodile" rudder, which served both for steering and as an airbrake. The data generated by these research flights was studied for the Concorde prototype development and also Rockwell International for the Space Shuttle.

This experimental delta-winged aircraft first flew in 1954, powered by a small Turboméca Palas turbojet.