Written by Jim Dutton
This information may help builders (Glasair and other composite aircraft) who have not yet closed their horizontal stabilizers avoid the dreaded offset in the elevator hinges.
Background
This problem started when Stoddard-Hamilton changed the horizontal stab spar and rib bonding procedure to use Milled Fiber/Resin instead of Cabosil/Resin. The Milled Fiber/Resin mixture requires a change in the procedure to insure the amount of Milled Fiber/Resin is equal on both flanges of the spar and ribs to maintain symmetry. If you do not make such a change you will be very lucky if the trailing edges of the stab skins are equidistant from the centerline of the spar and the skins are symmetrical to the cord of the stabilizer after closing.
Change to ensure accuracy
At the point in the stabilizer construction process when you are ready to locate the elevator hinges – STOP. Now is the time to locate the horizontal stabilizer skin for closing.
To do this you need to fasten 4 vertical datum points to the table at the leading edge of the stabilizer. Put one at each end rib location and one at each center rib location. These are necessary to control the horizontal relationship (fore to aft) of the skins. The horizontal relationship(side to side) can be controlled by reference lines or whatever mechanism you choose. Next insure the flanges of the ribs and spars are sanded in preparation for bond- ing, so you don’t have to do it later. After sanding, apply small patches of Milled Fiber/Resin to the spar and ribs, about 3/8 inches in diameter and at least as thick as the Milled Fiber/Resin bonding the spar and ribs to the other skin. Place these pads at the intersection of each rib and spar – on the spar. Also place a pad on each rib about 2-3 inches aft of the leading edge. Once these pads have cured, fit the skin to the stabilizer by sanding the pads to achieve symmetry of the skins to the cord line, to insure the trailing edges of the skins are parallel to each other and equidistant from the centerline of the spar. At this point the milled fiber/Resin pads are controlling the vertical relation- ship of the skin to the cord line of the horizontal stab and the centerline of the spar. Now you can install the elevator hinge brackets with the assurance the position of the skin will not change during closing.
During closing brush some resin on each pad, do not put Milled Fiber/Resin on the pads. Make sure the milled fiber/resin mixture between the pads is high enough to achieve a good bond with no gaps.
