Hi All,

I just got my Somethin Extra ARF and I'm enlarging the rudder and elevator by 1". I was planning on adding a 1" counter balance to both as well. Is that enough of a counter-balance to make a difference?

One more thing, I was told the counter balance will not only add surface area to the control surface, but also put less stress on the servo since it is on the other side of the hinge line (working with the servo to move the surface). My question is this, if I put a counter balance (on the rudder for this example) of 1", half the surface added above the original top of the rudder will be behind the hinge line. So, doesn't the benefit of what's in front of the hinge line get negated by what you have to add behind the hinge line? I'm not a aerodynamics whiz as you can see....it just doesn't make sense to me. Can anyone enlighten me on this.

Thanks,
Harold

Since your SE in ARF, I would just glue a about 1 inch strip of balsa to the trailing edge of rudder. This simple mod transformed my SE -- unlimited knife edge & more relaxed hover.

Balance would certaily help with servo load but it is nor really a broblem in this size category. In real 3D planed balance is used to give more agressive control response.

The Sig SE is a fun plane to fly... easy to if your rates are turned down. I have owned two and modified the rudder on both, I even added wing tip plates; however, it still doesn't knife edge well. Sure, it will hold a KE, but nothing like my other aerobatic planes. Still, I liked my SE so much that I have built a Sig SE from scratch scaled up to a six foot wing span, uses a YS140L for power and smoke... loads of fun.

About your question on counter balances, it is common on full scale to add mass and control area in front of the hinge line. IMO models typically should not have thier control surfaces mass balanced however adding control area in front of the hing line is fine.

Think about the loads on the control surface when it is moved. The airflow will try to push the surface back to neutral. The only thing holding the surface up (or down) is the servo. When you add area to a control surface in front of the hing line it too is pushed by the airflow; however, it is not being pushed back to neutral. Instead, it's pushed in the direction the control surface was moved. The next effect it that this assists the servo such that less torque is required to move the control surface.

I'm not sure what you mean by negated. Servo tabs do direct airflow so they are an effective part of the control surface. If you add more area in back of the hinge line you will need more area in front of the hinge line to offset the extra load caused by adding area in back of the hinge line... if that sentence made any sense. In that respect I supposed adding area to both kinda has a negated effect, but only with respect to the servo load. If you add more area to any control surface, be it behind or ahead of the hinge live, the surface will be more effective. In general, the rule of thumb I use is: Area in front of hinge line should not be greater than 25% of the area in back of the hinge line. As long as you stay at or below 25% you should be fine. Make you servo tab too big and bad things will happen.

thanks guys...appreciate the insight.

Best,
Harold

tuomo what engine are you using in your sig se? i am using a os 70 and i to just added a 1 inch strip to my rudder

I sold my SE away. It had Rossi 53 with quiet Weston minipipe. The best propeller was APC 13x4 narrow blade (not 13x4W). this combo performed effortless knife edge circles. Hovering was at around 1/2 throttle.

I loved te Rossi. Reliable and easy to use. Apc 12,25x3,75 gave even better performance but was too noisy for our field.

I am sure OS 70 works allso well once you get the rudder basics sorted. If you look for better knife edge, try moving the CG rearward. 13 inch propellers need a taller LG, 12 inch is ok if you are carefull.

BTW I had a HS 225 in tail driving rudder. This gave no-flex linkage and made it more easy to balance that hefty Rossi. Mine balanced without any extra weight. Trimming was done by moving battery around the tank/radio area.