Форум Breguet's Aircraft Challenge
There is an article about the Detable in the French monthly aviation enthusiast magazine Le Fana de l'Aviation No. 426 (May 2006) which is heavily advertised on the cover as 'Decouverte : un avion automatique francais en 1918" (Discovery : an automated French aeroplane in 1918).
The development of this pilotless airplane is almost completely unknown outside France, so there is still something to learn in aviation during the Great War.
As you mention the machine was based on a Voisin with the special invented tailpieces / wings by the French engineer Octave Detable. A report about a test flight of 2 July 1917 is enclosed, where the official French military observers state that a distance of 1000 meter was flown without a pilot. One of the observers was the then perhaps not so famous Sadi-Lecointe of later fame.