Hi there, I own a Predator 'gasser' which has a 23cc petrol engine, I can get almost 40 minutes with a full tank....but in reality I can get 30 mins with some fuel still in the tank....for safety.
The Predator is powerful....it can lift its own weight....ie 5 kgs. I use mine for carrying a camera that only weighs 300 grams.
Some flyers use auto stability devices for thier AP helis....but to have something that can fly out of sight? for 2 hrs? You might be able to do this with a normal petrol engined helicopter....but you might be looking at carrying the fuel load to do this....which can be done I am sure.
The biggest question is the electrical equipment.....I am thinking of getting a generator for my Predator....this is powered by the engine...and will supply all the electrical needs...plus keep the flight battery charged...a battery is needed in case of a failure.
The GPS, auto pilot and other requirments are a special subject....it might pay to visit other sites for advice.
Try
www.rotory.com
and
www.rotorworks.net (I think this is the correct site) this site seems to have some serious petrol heli flyers...that carry AP rigs....but its not a busy site as such.
Good luck
Rob