Biographical information on Hubbell is sparse on the Internet. Sketchy sources are here and here.
As I've probably mentioned elsewhere, possibly years ago on the 2Blowhards blog and probably here on Art Contrarian, professional aviation art tends to be torn between two approaches. One approach is to meticulously depict an aircraft, perhaps even to the point of showing rivets on the metal (if there were any on the actual airplane). This tends to please a certain breed of airplane fan who expect the illustration to show everything. The other approach tends toward somewhat painterly, somewhat impressionistic views of aircraft. Here planes are depicted correctly in terms of their dimensions and the perspective from which they are viewed. But details are more selectively chosen, usually with one area in tighter focus in the way humans actually see things. Hubbell leaned towards the latter approach, though his skill level fell short of later aviation artists such as R.G. Smith, who I mentioned here.
Below are examples of Hubbell's work. Most or all are from those calendars, and most were probably painted 1946-1949. The first five Great War images from the 1947 calendar are those I viewed on my bedroom wall when I was young, my dad having obtained one of those calendars.