Is there anything I can do to make the skin hinge more flexible on my Monarch 2M?

When I activate the flaps, my Sanwa 141AL servo (Identical to Airtronics 141) BUZZ. This is due to the excess stress caused by the strong skin hinge used in this plane (monarch 2M) ...

Anything I can do to make the skin hinge more flexible. Should I make a narrow sander from a stick and grind off some material? I am not interested in cutting the flaps apart from the wing and then tape hinge it.

From : Don Stackhouse

If you're getting an excessive amount of servo "buzz", you're probably trying to get too much flap deflection. About 40 to 45 degrees down is the most you should need. This equates to more lift and about the same amount of drag as a conventional narrow flap deflected twice that far. In addition, by using a wide chord flap with a smaller deflection, the effects of the flaps on glide angle are more linear, making the glidepath easier to predict.

Check that you're not trying to get too much flap travel. Also make sure that your linkage uses the entire travel of the servo. If you set up the linkage with too much travel (servo arm too long and flap horn too short) and then used your computer radio to limit the travel, then your servo is forced to do a lot of hard work without any leverage. Set the travel programming in your transmitter to almost full (like about 95%, so you use most of what's there but still have 5% left for fine adjustments), then use the pushrod placement in the control arms to set the travel.

Another trick that helps is to set the servo arm so that it is perpendicular to the pushrod when the flaps are up, but pointed forward nearly parallel to the pushrod when the flaps approach full down. This gives the servo maximum mechanical advantage when the flaps are deflected the farthest (with the highest spring forces in the skin hinges, and the highest airloads on the flaps). This also gives the servo more leverage to help protect the gears if you land on hard, rough ground with the flaps down.

If you find that you're deflecting the flaps the right amount but still getting what you feel is too much load on the servos, the best thing to do is to widen the hinge slots very slightly. From an engineering standpoint, a skin hinge acts like a type of leaf spring. One of the best ways to reduce the stiffness of a leaf spring is to make it longer, "length" in this case meaning the width of the hinge slot. Just be sure to do this a little at a time; if you widen the slots too much, you can have problems with ripples in the upper wing skin, and slop in the controls. Be VERY careful if you take this approach, it's possible to ruin a wing if you go too far.

Don Stackhouse @ DJ Aerotech
djarotec@bright.net
http://www.bright.net/~djwerks/