The Ava 4A was a low power flat-four (boxer engine) developed for very light aircraft in France in the 1930s.
Marcel Violet was a French racing driver who designed his own two-cylinder, two-stroke engines.
He also designed a two stroke horizontally opposed flat-four, which was built under licence at L'agence general moteurs "Ava" by Jean Aubry of the Société J. Thibault, G Aubry et Cie, alloy metal specialists, as the Ava 4A.
[1][2] It only produced 19 kW (25 hp)[1] and was intended to power small, low cost, single seat aircraft, replacing the aging Anzanis and completing with the French Mengin Type B and the older British Bristol Cherub engines.
[3] It powered several prototypes and also the forty-six examples of the series production variant of the Farman Moustique, the F.451.