Paolo, this is a mystery thread, logically the French F class designation is also a mystery

Thanks for looking through STAé reports, never seen them myself though.
In the meantime I have done some research about the
engines of the Van den Born F5
Le Rhône 80 hp 9-cylinder
Salmson Z-9 230 hp 9-cylinder
Engine on the mystery 3-engined triplane
Unfortunately the picture of the engine of the mystery plane is not very sharp, so the distinguishing bougie at the side of the Le Rhône cylinders cannot be distinguished. Looking at the 'pipes' I have a slight preference for the Le Rhône, but this is no fact. Perhaps the engine experts can do a sure identification?
Cheers
Kees