ORIGINAL: wsmalley
Building all moving stabs on my SU-27. Original plans called for elevator, but I wanted scale. They will function as 'ailerons' coupled with flaperons. Two questions: (1)What is the formula for determining the pivot point and (2) should they be 'nose' heavy or 'tail' heavy? I know this has been discussed before but can't find anything in the new RCU search. Bill S.
Hi Bill,
Place the pivot point in the scale location. It is located at ~20% MAC. It is unnecessary to balance the stab. This subject has been covered numerous times in the jet forum.
If you insist on balancing, balance the stab at 25% MAC. Yes, I know this is aft of the pivot point, but that is what you want. You definitely do not want the stab balanced at or ahead of the pivot point.
As an example, you'll notice that in all the static shots of all the jets when the hydraulics system is relieved of pressure, does the trailing edge droop or the leading edge? In all cases, the trailing edge droops which says that the stab is balanced aft of the pivot point.
Same for the Piper airplanes with full-flying stabs. Pivot at ~20%, balanced aft of pivot point. (confirmed by Piper owner/drivers)
Dan