twin engine rc plane try one

Ok, there is a story here, I have been flying this plane (modified MikeysRc Yc-14) for about 5 flights with out camera or the upgraded battery's to help balance the weight of the gopro. And during that time I had been doing barrel rolls and inverted flight, so when I took off and got some altitude my co-worker behind me says can you do a loop with that plane to. I said, "sure I can". Only to find out the plane just cant do that with all that weight on board.