According to the Horizon web site, the Arrow ARF comes with an 11 ounce tank.
http://www.horizonhobby.com/Products...arts%20Listing

I would think the Arrow RTF would have the same tank but didn’t find that documented anywhere.

With a .46 class two stroke engine you should easily get 10 to 12 minute flight times. As has been mentioned before, that is a long time.