Build Logs
Rotor Build Part 3: Fin and Stab Installation
By J.S. Decker
May 3, 2008, 15:27

After getting the wings mounted, it is time to mount the fin and stab.

1. Fit & Tack Fin In Place:  Lightly sand the portion of the fuse where the fin will be mounted.  The wrap sandpaper on around that region of the fuse with the grit outward and sand the fin to conform to the fuse.  Lightly sand the portion of the fin where FG will lap onto the fin to reinforce the joint.  Tack glue the fin to the fuse, I use 15-minute epoxy mixed with some microballoons for foam core bagged fins.
   
   
2. Bias FG Joint Reinforcement Strips:  Use multiple layers of light weight bias FG.  Here I used three layers of 1.6 oz FG scrap.  The FG layer against the fuse is 1.5-inches wide, the layer on top of that is 1.25-inches, and the top layer is 1-inch wide.  The centerline of the strip is marked to help align the strip on the joint.  I make the strips by applying a light dusting of 3M77 spray glue to the a piece of wax paper and apply the wax paper to the FG.  The FG can be easily cut without stretching out of shape or the edges unraveling.
   
   

   Fin tack glued onto fuse. Strips of bias cut FG laid out. Three strips for each side and each strip is a 1/4-inch narrower than the previous one.

   
   
   
3. Fillet Joint:  Mix resin and mix a portion of the resin with microballoons.  Apply a fillet of resin and microballoons to the joint.  Doctor off excess material.  Do NOT let the resin cure before proceeding to the next step.
   
   

   Filler applied to joint. Excess will be doctored off, prior to applying the FG using 3M77 spray glue.

   
   
   
4. Apply FG Strips:  Using 3M77 apply the FG strips over the joint.  Apply the FG so that edges are steppe by about 1/8-inch.  The tapered application multiple layers of light weight FG helps finishing.
   
   

   All three layers of FG applied using 3M77. Note the stepping placement of the edges.

   
   
   
5. Wet FG & Blot Excess:  Wet the FG with resin and blot the excess resin out of the layup.  Allow to cure.
   
   

   FG wet out and curring.

   
   
   
6. Install Stab Bolt Tubing:  Drill mounting holes in stab and glue short sections of metal tubing in stab.  You want the metal tubing go through the composite skins.  I mount the Rotor stab with two steel 2-56 cap screws and install 1/8-inch tubing in the stab with CA.
   
   

   Stab with 1/8-inch diameter tubing glued into the bolt holes.

   
   
   

   T-nuts captured to the stab.

   
   
   
7. Cut Stab Incidence& Slot for Nuts:  Cut the top of the fin at the proper angle for the proper stab incidence.  Drill holes for mounting nuts and bolts and slot around the holes for the T-nut heads.
   
   

   Fin top trimmed to the correct stab angle. Top 1/2-inch of sides sanded for bonding. Holes for T-nuts drilled and top slotted for T-nut heads.

   
   
   
8. Tack Glue T-nuts:  With the stab mounted in proper alignment, tack glue T-nuts into the top of the fin with CA or quick set epoxy.
   
   
9. Apply FG to Stab Bottom:  Apply FG to wax paper and apply to bottom of stab with 3M77.  I used 9-oz bias cut FG.  Apply the wax paper side to the stab with a light dusting of 3M77.
   
   

   9 oz FG applied to wax paper with 3M77 and wax paper sided applied to bottom of stab with 3M77. Waxed bolt heads poking through FG.

   
   
   
10. Mask Top of Fin:  The next part is messy, so I mask off the fin.
    
    

    T-nuts tack glued in place and taped off for mounting stab.

    
    
    
11. Wet Stab FG:  Mix resin and sparingly wet a portion of the FG on the stab.
    
    

    FG sparingly wet out.

    
    
    
12. Apply Goo to Fin:  Mix some of the resin with milled FG and microballoon and apply the goo to the top of the fin.
    
    

    Goo applied to top of fin.

    
    
    
13. Mount Stab:  Mount the stab to fin.
    
    
14. Form Fillet:  Form a fillet  around the top of the fin.  I usually make a small fillet, apply the layer of FG over the small fillet, and then apply more goo to form the fillet.
    
    

    Stab mounted and fillet formed.

    
    
    
15. Check Align:  Check the alignment and allow to cure.
    
    

    Alignement check.

    
    
    

    Stab mounting fillet curing.

    
    
    
16. Sand Out: After the resin cures, carefully remove the stab (that is why you use just a dusting of 3M77 to hold the FG onto the stab), and sandout to taste.
    

Cured stab saddle after removing the the fin.

Sanded out stab saddle.

After the stab is mounted Elvis always like to do a little bench racing...

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