I thought I would do a little bid of Googling on this subject and top of the hit list as you would expect came Wikipedia which had this to say:
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The predecessors of the flying vimanas of the Sanskrit epics are the flying chariots employed by various gods in the Vedas: the Sun (see Sun chariot) and Indra and several other Vedic deities are transported by flying wheeled chariots pulled by animals, usually horses (but the Vedic god Pūsan's chariot is pulled by goats, as is that of Norse Thor).

The Rigveda does not mention Vimanas, but verses RV 1.164.47-48 have been taken as evidence for the idea of "mechanical birds":

47. kṛṣṇáṃ niyânaṃ hárayaḥ suparṇâ / apó vásānā dívam út patanti
tá âvavṛtran sádanād ṛtásyâd / íd ghṛténa pṛthivî vy ùdyate
48. dvâdaśa pradháyaś cakrám ékaṃ / trîṇi nábhyāni ká u tác ciketa
tásmin sākáṃ triśatâ ná śaṅkávo / 'rpitâḥ ṣaṣṭír ná calācalâsaḥ

"Dark the descent: the birds are golden-coloured; up to the heaven they fly robed in the waters.
Again descend they from the seat of Order, and all the earth is moistened with their fatness."
"Twelve are the fellies, and the wheel is single; three are the naves. What man hath understood it?
Therein are set together spokes three hundred and sixty, which in nowise can be loosened." (trans. Griffith)

In Dayananda Saraswati's "translation", these verses become:

"jumping into space speedily with a craft using fire and water ... containing twelve stamghas (pillars), one wheel, three machines, 300 pivots, and 60 instruments."

But likelier in the original Indian symbolism when that hymn was composed, the wheel is a year, the 12 "fellies" are months (lunations), and the 360 spokes are days.
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As I suspected and is often the case with ancient writings it is all in the translation. Most of us cannot read ancient texts in their original form and must rely upon the work of others to provide us with the supposed evidence. It is often here that the first "corruption" of the original story appears as the translator repackages the words to either suit a modern audience or to present the information in a way that supports his point of view.

Let us not forget some very important facts about technologies they are the products of their own time and culture built upon with gradual improvements.

If a 21st century electronics engineer were "magically" transported back to early Victorian England and went to have a meeting with IK Brunel, Babbage or the Stevensons or any of the other great engineering and mechanical minds of those times and said "Hey guys I have a great idea to build a machine that can do accuracte calculations at high speed and help with all your projects". He would not have got very far in a society which was still grappling with basics of direct current produced from lead acid cells. So what, if he could draw diagrams of and explain to them how a microprossor works, nobody including him could make one given the tools and materials available in the 1840s.

Similarly for an ancient culture to have had aircraft as advanced as we have today or even spacecraft more advanced than we have yet built, then they would have needed the industrial base to build it and support it. No single Royal Appointed Engineer, no matter how visionary, could construct a modern air force without all the trappings of an industrial society. Where were the powerplants to power the factories, where were the factories for the fabricating the avionics, the tyres for the landing gear, insulation, sound proofing, not to mention all the copper wire or fiber optics. The refinerys for producing the fuels, the mines to obtain the aluminium and other essential materials. If all that had existed way back then you can be sure that some evidence of it would still be found today.

If on the other hand you are going to suggest that the ancients did not need crude machines like turbojets but that their aircraft could be flown by the mental power of levitation, then I suggest you take that to a Supernatural forum not here. Furthermore if the anicents posessed such powerful forces as modern fighter and bomber squadrons then they would have certainly retired all their war elephants, in which case there would be no mention of those animals in their battles. When was the last time you heard of a Cavalry Brigade charging into battle on horseback supported by a squadron of jets up above. It has never happened because it does not make technological sense. Furthermore if you are going to credit an ancient civilisation with advanced technologies they have to fit into their own rational chronology. There is no point in one account suggesting they had antigravity propulsion while at the same time describing how in another verse that their machines made sounds like jet engines - cherry picking the odd phrase here or there from some ancient writing and then by using dubious translation to find equivalent modern words to say "look! they are are talking about a nuclear submarine" is something I am always deeply sceptical about.

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Note 1. All requests for planetary demolition must now be submitted in quadruplicate on form UX-565/B4 and be counter-signed by the assistant administrative officer for interstellar traffic calming - department QG-7. Subject to approval by the chief planning officer and the infrastructure development coordination sub-committee.