Dave, Leishman has stated that he believes the Cornu Helicopter required 30HP to hover. So it could not have hovered using the 1907 Antoinette V8 engine quoted at 24CV. My only disagreement is whether the 24CV quoted is actually 24HP.
The 1908 Antoinette V8 is quoted at 50CV, so even if Cornu did not actually hover in 1907 he came damn near close.