@Narf Don't look for realism or accuracy in a fantasy manga. It's just a power trip about the Empire and Tanya. Obviously, the enemy will be blind and stupid compared to the main characters.
Actually, this manhua/story had a lot of potential but I always get the impression it goes nowhere. We all love cute lolis, big boobs and panty shots, but the story is a mess.
@Le_Flemard actually, at first, they were just firing straight through the propeller arc and "hoped for the best".
The blades were fitted with "deflectors" to avoid damaging the propeller.
Synchronized gear came a bit later.