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This is the second part of an article by Don regarding using and constructing flaps for Giant Scale model aircrart. You are encouraged to read Part I.
Flaps should be made from a 5-ply aircraft grade plywood, 1/8 inch think and ribbed on the inside for extra strength. You would not believe the amount of G forces that hit flaps! Are you ready for this? Up to 12 G's and more are tugging on the flaps of some giant scale aircraft! Scary, isn't it? That is why it is especially important to deploy flaps at less than half throttle and only on your final landing leg, after the crosswind leg ready for set up and landing approach. Modelers that know how to use flaps have learned how to do so from modelers that are or have been full-scale pilots.
Correct flap hookup is mandatory. There are many ways that flaps can be hooked up, but only several good ways as far as I am concerned. At full deployment, flaps should be in a locked position, and this is where many installations fail. Some modelers prefer to have a "fixed" deployment, whereas they use the retract channel to either have the flaps full down or full up. Having the ability to use small or large portions of flaps is, in my mind, a much better method and much safer. Gradual deployment is more scale-like.
Using one servo for each flap allows for more authorative strength per flap, and you need strength beyond all reason on fligher planes and fast attack style, high wing-loaded models. This is how I managed to get a locking system using a 45-inch ounce servo per flap.
With the flap in the "up" position and the servo(s) mounted with wheels or arms (I prefer wheels for strength), hook up your receiver to the servos and from the transmitter add full "down" to the servos. At this time you do not yet have a linkage made up from servo to flap horn. The wheel on the servo will be at full deflect direction. With a marker, mark a line on the wheel that aims directly at the flap horn (see drawing). This mark will represent the actual position of an aluminum arm that you will make up and install directly over and onto the servo wheel. The length of this aluminum arm will determine how much Down deflection you will obtain. The arm will extend 3/4" beyond the servo wheel rim. Drill two or three holes at the end of the arm to take a large DuBro ball, the new locking ball joint system that DuBro has recently invented. Wonderful! You then bolt the aluminum arm directly to the servo plastic wheel over the straight line mark that you made on the wheel, aimed at the flap horn.
Next, turn the radio on and put the servos in full UP deflection after you install the wheel-arm arrangement. You then make up your direct-line lickage using balls by DuBro, adjusted so that the flap is now being held in the UP position by the servo, not too tight, not too loose. Once you have the lickage made up and installed, you are ready for some flap action. Turn the radio on again, and slowly deploy the flaps until they hit full DOWN position. The question now is "do the flaps go down far enough?" By "far enough", I mean do they come close to a 90 degree angle, and if so, you're all set. If not, you will have to lengthen the servo arm for more DOWN deflection. Too much deflection means that you will have to move the ball in towards the servo arm center, at least one hole.
It won't take you long to understand this principal
of hooking up a "locking" way of using regular servos. You'll note that
when you have the flaps in full down position, the servo arm, the arm
that you made up and installed on the top of a servo wheel, is aiming
directly at the flap horn. No angle, just perfectly straight.
THis removes any strain on the servo gear train and puts the G forces
on the servo output shaft only at full deflection. The use of large
DuBro locking balls is mandatory. The balls allow for freedom from
binding at any angle and always remain smooth throughout the movement
from up to down.