Batman: Arkham city question?

In many of the batman:Arkham city trailers, i see scenes where batman is gliding, grapnels on to an object, but instead of landing flies forward and continues to glide. i got the game and i cant figure out how to do this. help please? I have an Xbox 360.Batman: Arkham city question?
It's called the Grapnel Boost. Once you've completed the basic AR training you will be able to get this upgrade.Batman: Arkham city question?
Near the beginning of the game there will be blue objective markers the letter W inside. These are AR (Augmented Reality) Training programs. Essentially the Bat-Computer will upload a training program to ur cowl. Green holographic rings will appear and all u hav to do is glide through them all without touching the ground. Complete all four Lv.1 AR training programs and Alfred will send u an upgrade called the Grapnel Boost. Once obtained u can use it to launch urself into the air instead of landing on a roof or vantage point. On Xbox press A twice and hold it the second time while grappling. If u r grappling over a far enough distance, u"ll hear a motor sound in the grapple and u'll start to move much faster. Once u reach the point u were grappling to u'll b launched into the air. Since u were a already holding A u'll begin to glide. This upgrade makes getting around Arkham City much easier. It comes in handy on the Zsasz side missions.Batman: Arkham city question?
Once you've unlocked the ability, while grappling towards an object double tap A(360) or X(PS3) and you'll speed up and instead of landing use the object as a boost.
well, i dont know how to do this , but i would recommend you to maybe browse some videos on youtube , orrr -- maybe google this problem -- some research will surely be of help :) GL