Actually, they are Sopwith Snipes (or maybe Salamanders), not Camels. The artwork is by the very talented Fredrick M. Blakeslee, who created dozens of covers for
Dare-Devil Aces and also "G-8 and his Battle Aces" in the 1930's.
Dare-Devil Aces' first issue came out in February 1932. For about the first two years of publication, Blakeslee's covers depicted only WWI types of aircraft in combat with other WWI types, and by the standards of the pulp magazines they were fairly accurate in outline and appearance, if not in color schemes. Blakeslee had done his research, and had traveled to Europe to see a number of aircraft types such as Guynemer's preserved Spad. I really like his WWI aircraft, and usually they were rendered fairly accurately.
Then starting with the December 1934 issue, he (or his editors) started to run out of ideas for relatively historically realistic combat scenes, and began to involve some fantastical science-fiction type scenarios. Then starting in September 1935, the covers regularly featured WWI period aircraft in combat with more up-to-date, highly advanced aircraft from the other side. I don't know quite how they explained these scenarios, but they were common subjects from then on. Take a look at this wonderful website, which has all of the covers of Dare-Devil Aces.
http://www.philsp.com/data/images/d/...ces_193509.jpg
As I said, Blakeslee also created the covers for the more outlandish tales of "G-8 and his Battle Aces," which regularly featured G-8's Spads and German Fokkers involved with occult or science-fiction elements. In the old days, I posted dozens and dozens of covers by Fredrick Blakeslee in this group on the Forum.