The CZAL (Aero) factory at Karlin, led by Jaroslav Slechta, developed the XE-1 two-seat helicopter project in 1947, fitted with twin inter-meshing rotors and a 100hp Praga M-197 engine. This led to the XE-II (OK-FYA) which flew on 14 December 1949. It was an open single-seater with a single three-blade main rotor and 75hp Praga D engine.

R.Simpson "Airlife's Helicopter and Rotorcraft", 1998

A model of this project worked out at Karlin was shown at Brussels in July 1947. It had two intermeshing two-bladed rotors, the hubs of which were very close together.

Also provided was a tricycle landing gear with the rear wheels directly below the twin vertical fins.

P.Lambermont "Helicopters and Autogyros of the World", 1958

Technical data for Praga E-1

Engine: M-107 rated 81kW, rotor diameter: 9.0m, length: 5.92m, height: 3.60m, gross weight: 710kg, empty weight: 490kg, maximum speed: 145km/h, cruising speed: 120km/h, hover ceiling: 400m, service ceiling: 3000m, range: 180km