How can I glide longer?

I want to glide longer but I don't know if I need the grappel accelerator and where I can get it? Any hints?

You should have the Accelerator from the very beginning, although you won't be able to use it until you leave Blackgate Prison.

The Grapple Accelerator works in exactly the same way as in Arkham City. Grapple to a ledge and double-tap X (PS3)/ A (Xbox 360)/ Space (PC) while your grapple is still pulling. It only works if you're pulling from a certain distance.

Too glide longer, just simply dive bomb and glide upwards over and over again. To grapnel accelerate just simply grapple onto a ledge and double tap A(X-Box), X(PlayStation), or space for computers.