ORIGINAL: cowboychris244
Should the elevator be up or down when flaps are employed?
Depends on the model, airfoil of the main wing and the specific center of gravity of your plane. Most will need some down elevator (5 to 20%) when the flaps are down Others up elevator. Flaps add lift and also drag; which affects different models in different ways. Problem is the flaps may or may not have as sudden an effect as the elevator, and vise versa. That is, even when trimmed to keep a level attitude at a low speed the initial deployment may cause the model to balloon or dip until they "catch up". Some radios allow a elevator mix delay that helps in some cases. The only sure way is to start with small movements and try them on your model. I generally "cheat" and slow the model then give a tad of down elevator a heartbeat before I flip the flap switch (with a down elevator mix). The initial deployment needs more correction than the final landing approach.
I generally set the flap to where I like it after repeated landings (or takeoffs) and then worry about the elevator mix. I also assign a switch so I have the choice of elevator mix or not. As just mentioned - during a Short Take-Off with flaps you might not want the elevator mix fighting you.
Also, the flaps can be in two stages. I arbitrarily picked 20% and 80%. What are your thoughts on these numbers? Thanks for your help.
20% flaps is a good number, but 80% is a tad much, especially for full-width flaps. 10% & 20% might be a better place to start. My Contender has a 60 degree drop (1-3/4"), but that is only the 12" central apron flap. Without the down elevator that will pitch the nose up 45 degrees with any speed on at all on approach . . . and the Contender glides like a turnip without flaps so there is usually some speed on during approach. The flap makes a world of difference on that model. My SK-50 had full strip flaperons and they made little difference at all. Depends a great deal on control throw and the area of the control surfaces. My Hot Stik has HUGE control surfaces and dual servos in each wing so I can set the outer ailerons to lift while the inner ones drop (aka "CROW"). That's great fun to play with.
Be sure when deploying flaps your airspeed is slow. Deloying flaps at higher speeds will cause the model to pitch violenty and may overstress the flap/servo(s)/hinges. There is a lot of drag on a deployed flap.
Note also, most trainers already have lift out the giggie and raising the flaps ("spoilers") instead may give you a better landing approach.