The French had no modern large jet engines, and had already concluded they would buy a British design anyway (as they had on the earlier subsonic Caravelle).[22] As neither company had experience in the use of high-heat metals for airframes, a maximum speed of around Mach 2 was selected so aluminium could be used – above this speed the friction with the air warms the metal so much that aluminium begins to soften. This lower speed would also speed development and allow their design to fly before the Americans. Finally, everyone involved agreed that Küchemann's ogee shaped wing was the right one.[20]