The pre-war German airshow flier Gerhard Fieseler enlisted Lippisch's help in designing a two-seat tailless touring aircraft for the 1932 Euro-parundflug - the air races and trials then held every four years. Fieseler’s F3 Wespe (Wasp) or Delta IVb had delta wings which folded (Rundflug aircraft had to be able to fit into a small storage shed) and two engines arranged in a centreline-thrust push-pull configuration. Fieseler flew it before Lippisch was fully satisfied with the design. He crashed, and rapidly lost interest in tailless aircraft.

The F3 had tractor and pusher engines, and rebuilt, he hired a young man named Wiegmeier, who proceeded to crash both Deltas III and IV on consecutive flights. Lippisch fired him.

Lippisch was able to rebuild the Wespe once again as the DFS 39 Delta IVc, a single-engined two-seater with a drastically modified wing plan-form incorporating sharply drooped tips. The modified type was awarded a certificate of airworthiness in 1936 and won Lippisch leadership of the design team for Projekt X.