About Hinduism:
Q. We used to have Flying Carts in Ramayan/Mahabharata. Where did they go..? Why do they not exist anymore..? If we had that Technology so long ago, why don't we find them now..? Why did we need to make those Airplanes when we actually had Flying Carts to begin with....?


A silly but important question..... ... ok for a simple answer... tell me if you want a longer one..... 

Well it is said that this is the Kali Yug and a lot of what we knew in the Yugs before have been lost in this..... this is the Yug when our capacities are the minimum and so is our life cycle..... as Ramayana and Mahabharata are representatives of a Dwapar and Treta Yugs respectively, Humans might have had other capabilities then than we dont have now...... or may be that we are building them all over again..... 
I agree that we are in the Kali-yug. 

But, I find it very hard to believe that Valmiki ji had the time to write a whole story on Ramayana, but did not find enough time to pen down the art of constructing those Flying Cart. Is there an explanation to these Flying carts and Flying Horses other than plain "Magic" ..? 

Another point to mention is that if a "Book" written by Valmiki ji made it through all the "Yugs" , why did not a single Flying Cart, made of Iron, make it through..?
Well do you know how long is a yug??? a very long time...... and Valmiki didnt really write down the book.... that is a misnomer..... that is because till about 1000 CE nothing was written in India... only spoken..... all arguments were verbal only.....

so as long as one person who knew all the knowledge by heart survived the transition to the next yug so did the information.... but metal, my friend, does not survive even a 100 years out in the open......