Consistently one of the biggest deductions on Uneven Bars is BENT ARMS. I hear coaches encourage, threaten, bribe, beg and cry to get their gymnasts arms straight. (OK- maybe not cry).
Gymnasts need to learn straight arms through series of drills and exercises on the floor and on floor bars. If they cannot keep their arms straight on that, they certainly cannot keep their arms straight as they move around the bar.
Here are some drills that we do daily to work straight arms.