Florine, N. “Elements du Calcul de Stabilite d’un Helicoptre” in Bulletin du Service de l’Aeronautique. No. 10, May 1930, pp 1-50. Also with M. Risack, “Note Concernant de l’Etablissement des Equations du Mouvement” on pp 51-55. Original wrappers. There’s an old fold going through the center vertically through the publication, otherwise the publication is a solid VG. Scarce. $200

• “Nicolas Florine worked at l’Administration de l’aéronautique, based in the buildings of the Hotel des Monnaies in Saint-Gilles (Brussels). In 1926 he was responsible for initiating the Centre d’aérodynamisme …He was involved in the creation of Belgium’s first wind tunnel…The studies Florine performed…in 1926 led to patents related to helicopter control and in particular how to counteract the torque resulting from using two rotors. The results of the studies were published in the article “Eléments du calcul de stabilité d’un hélicoptère”. Herein, the principle was described of a helicopter with two rotors. These rotors turned in the same direction, in contrast to the current tandem helicopters…This publication formed the basis of all his designs that would follow.”—Wikipedia