 Consequently, Multhopp was approached by Kurt Tank in 1938, who offered him employment at Focke-Wulf.At Focke-Wulf, Multhopp was promoted to assistant in charge of the aerodynamics department in 1940, then was promoted to advanced design bureau chief in 1943.One of his innovative projects during this time was the "Multhopp-Klappe", a combined flap and dive brake apparatus, which was installed on the unsuccessful Focke-Wulf Fw 191.