So, I'm trying to get a concept drawn up for this aerial predator, taking a lot of inspiration from [Barlowe's Expedition and its Skewers](https://waynebarlowe.com/artwork/expedition/). I would like to give it a unique mechanism for in-flight propulsion, but I am having trouble thinking of what might fit for it. Ecologically it'd climb to great heights and then dive, potentially using its propulsion mechanism to continually build speed until it finally impacts its prey.