Tuesday, 12 January 2016

C17 tail modifications

I've spent some time today arranging the tail structure, to ensure it is easy to build, align, and modify if tail incidence changes are required.  Here is a picture (click for full size):



  • The fin spars will be underneath the veneer sheeting, incorporated into the build right at the start.  They are different lengths to meet the changing taper in the bottom of the fuselage at the right point.
  • Fin top plate is a 1/4" (6mm) birch ply plate.  It is gorilla-glued to the top of the foam in the fin, and the fin spars should pass through it slightly so a puddle of epoxy will secure it.  A duplicate of this plate (for facing the upper part) will be glued to the underside of the fin box sides / tailplane spar assembly.  Captive nuts will be secured under the top plate.
  • Fin box side plates will be 1/8" hard balsa, grain vertical.  This will resist compressive forces well, and they are epoxied to, and held apart by the two tailplane spars.
  • Tailplane spars front and rear.  These are inserted into slots cut into the foam after joining the tailplane halves.  Gorilla glue bonds them.  A channel will need to be made through one of the holes in the rear spar for cabling.
Everything above the fin top plate un-bolts and is removed in one piece.  Shims can be added at the back or front if needed.  Location is retained by two large dowels and the whole lot will bolted up with stainless socket head cap screws.  All of the shape of the fairing will be achieved with XPS (blue or pink extruded foam), and glassed for a finish.

UPDATE :

I have added a picture here of the elevator servo positioning, as requested by Dave.  The model will use an elevator per servo, and the dotted lines show intended cable routing.