
The idea is not excactly impossible one. A rocket-powered interceptor was suggested in France during World War I:
[img]https://rec.aviation.military.narkive.com/dYYPYv7o/1917-riffard-rm-1-rdp-rocket-plane:i.1.1.full
[/img]
https://rec.aviation.military.narkive.c ... i.1.1.full
Technically, it is not impossible for blackpowder rocket of enough size and in enough quantity to propel the light biplane. Pre-war "photographic rockets" - reconnaisance rockets designed to launch a photo camera into sky and return it on parachute - were good enough. Of course, a dozen or two of such engines could led to the point of catastrophic failure very fast... but hey, only the most daring ones went into early aviation anyway)
So the idea: let's someone outside the Charis develope the idea of rocket-powered plane.

P.S. IMHO, but it would fit the Deshnari pretty good. For their noble-based culture, the idea of "knights of the sky", roaring on rockets upward to meet Charisian airships would fit perfectly. During World War 1 (after cavalry proven itself outdated), quite a lot of young, eager aristocratic cavalerists found thenselves in aviation, where they could express their personal skill, courage and general coolness.