During the first world war, de Monge engineered, designed and produced aircraft propellers, selling some 40.000 to the French government. De Monge then worked with a Mr. Buscaylet, making conventional parasol monoplanes. Later, he designed twin-engined lifting wings, reminiscent of the Burnelli UB-14, such as his models 7.4 and 7.5. The rights to these were acquired by Bordeaux shipbuilders Dyle et Bacalan who wanted to develop transatlantic airliners from them, but nothing came of it beyond some prototypes like the Dyle et Bacalan DB-10 heavy bomber. In 1925, de Monge joined car and motorcycle makers Impéria at Liège as chief research engineer. Some of his work there included torsion bar suspension and automatic transmissions. de Monge left Impéria in 1937 to join Ettore Bugatti, to design the Bugatti Model 100P racing aircraft. This had been almost completed in Paris in 1940 but with the of the occupation of France by Germany was moved to the French countryside where it was hidden for the next thirty years. It eventually went to the U.S.A. where it is now in the EAA AirVenture Museum.