Stephen Hi!
A lot of confusing info runs through the web and the specialized press about the various Voisin planes. It took me quite a time to find the original French sources that allowed me to put some order in all this mess. The main source of confusion is in the denomination III, V etc.. which was totally unknown during ww1. The french sources speak of:
1) "Voisin 13,50m" (13.50m wingspan) with Gnôme 80ch rotatif
renamed "Voisin L" after when engine with a Salmson 130Hp.
2) "Voisin LA" (14.74m wingspan)with a Salmson 140Hp
3) "Voisin LAS" (S for "sureleve" as the engine whas "pushed upwards" by comparision with the Voisin L and LA) (14.64m wingspan her too) witha Salmson 140 or 150 Hp
4) Voisin LBP/LBS (different cabin enabling to mount a forwards firing cannon, same wingspan) Salmson 150Hp
Beyond the differences in engines and wingspan, the wing profile was diffrent:
a) for Voisin "13,50m 1913" and Voisin L both wing are of same width, the lower ailerons are attached to the wing edge and therefore protruding behind this wing edge ____-----------------------____
b) for voisin LA, the upper wing is now larger (14.74m) than the lower wing but (13.50m) but the wing profile remains similar to the Voisin L
c) voisin LAS wing dimensions imilar to the Voisin LA but the ailerons are now integrated in a widenned wing chord, with a "gap" at the position of the propeller ______________---------______________
d) Voisin LB/LBS/LBP the upper wing is displaced slightly forward to ensure stability of aircraft when firing teh gun.
get a look to the 3dmodels I have created for exporting to Il2 to get a visual impression of all this:
http://imageshack.us/photo/my-images/827/voisinl.gif/
http://imageshack.us/photo/my-images/23/voisinla.gif/
http://imageshack.us/photo/my-images/13/voisinlas.gif/
http://imageshack.us/photo/my-images/638/voisinlb.gif/
http://imageshack.us/photo/my-images/824/voisinlbp.gif/
http://imageshack.us/photo/my-images/850/anatravoisinivanov.gif/
PS if someone has a plans/clear line drawings of the Isotta Fraschini Voisin - I'd be delighted!