On Wikipedia page we can read:
Vimāna is a mythological flying palace or chariot described in Hindu texts and Sanskrit epics.
Early 20th-century sanskrit Vaimānika Śāstra claim that the vimānas mentioned in ancient Sanskrit epics were aerodynamic flying vehicles.
The topics covered include, "definition of an airplane, a pilot, aerial routes, food, clothing, metals, metal production, mirrors and their uses in wars, varieties of machinery and yantras, planes like ‘mantrik’, ‘tantrik’, and ‘kritak’" and four planes called Shakuna, Sundara, Rukma, and Tripura are described in greater detail.
The question is: what are the main differences between those four planes?