This is the first major boss fight you will encounter. During your initial run in with Tyrant he will prevent you from climbing the stairs to go back to the palace. Hit him with some grenade shots, but save your explosive arrows and BOW rounds for your grenade launcher. Once aboard the plane and you enter the boss fight where you are stuck with him in the cargo area, unload your BOW rounds into him. Then, fire around 4 to 5 explosive arrows. Flip the switch for the storage container to send him flying out the plane. This should take around a minute if done properly. Very quick and easy.
Note that if you do not have grenade rounds or explosive arrows, this gets really tricky and can spell your doom. The Tyrant does not go down easy without these weapons, meaning your regular grenades, all 12 of them, will do next to nothing. Your bow gun is your next best bet, however, it will take around 30 arrows to subdue the Tyrant. In the meantime you must run around doing your best to avoid his hits. Keep in mind that if you're against a wall near him he will definitely hit you and you need to get out of there quick. If he gets on a rampage with two or three hits in a row, you're dead! Learned this the hard way.