The D-39 was a motorised version of the D-38 sailplane, with wings moved down from the latter's shoulder-wing position to the bottom of the fuselage.
A Limbach SL 1700 flat four engine was conventionally mounted in the nose; the propeller could be removed but not folded away in flight.
It landed on a retractable monowheel, fitted with a drum brake and assisted by a small, fixed tailwheel.
[1] By July 1982 it had been modified into the D-39b, with a greater span, revised wing roots and fitted with two-bladed Hoffmann Propeller airscrew and three pitch positions.
The „D-39HKW“ was developed on the fuselage of the D-39, using 20-Meter flapped wing V[2] Data from Jane's All the World's Aircraft 1981/2[1]General characteristics Performance