A mock-up of the RP-99 was constructed, but no test or production drones were ever built
by Northrop. The design of the RP-99 was sold to the government of Belgium, which
fabricated several drones inspired by Northrop’s design. The Belgian drone is known as
the Epervier (Sparrow-Hawk), and the X-1 version is powered by a Wankel engine. The X-
2 and X-3 versions have Hirth piston engines, while the X-4 uses a Rover TJ125 turbojet
for propulsion. The Epervier has a wing span of 5.8 feet (1.8m), a length of 7.1 feet
(2.2m), a height of 2.5 feet (0.76m), and a weight of 214 pounds (97 kg).
