I actually set mine to 38°. This gives me a little margin for the gap seal.
At 40° if someone leans on the flap, it's not uncommon for the gap seal to pop out and hang on the wing trailing edge.
Mel Asberry..DAR since last century
A&P/EAA Tech Counselor/Flight Advisor
Specializing in Amateur-Built and Light-Sport Aircraft
North Texas (8TA5)
RV-6 Flying since 1993, 175hp O-320, 3-Blade Catto (since 2003)
Legend Cub purchased 12/2017
FRIEND of the RV-1
Eagle's Nest Mentor