With regard to the periodic dropping of the left wing, it seems so regular that I suspect the arduino, BEC, or receiver is overheating or partially shutting down for a moment, then coming good. I had a similar experience with a faulty esc that gave 5 volts, but not when the servos were under load. Also if you are using an arduino, or any micro controller (including the receiver), I have seen them do this too (sometimes called a "brown-out", where the voltage sags and the micro gets all upset). Poor power supplies are a major problem for all electronics as they create mysterious behaviours all over the place. Try running directly from a separate receiver battery, and test on ground with all servos driving hard back and forth. Also a bad servo or partial short somewhere can sap power from the BEC, leaving not enough for the other servos to work properly.
