In the previous article I discussed the pros and cons of wing mounting and made specific recommendations about screw size, spacing and maintenance. In this article I describe modifications to kits, replacing rubberbands and dowels with nylon screws.
If the model is already built then the easiest method is to use filled epoxy for the wing bolt slugs in the wing center section and for a combination wing saddle and double nut. The materials required are:
Begin by cutting two 1/4 inch diameter holes for syringe access near the wing root. If it is a two piece wing like the Olympic II, cut the holes in the root ribs about 1-3/8 inches in front of the main spar. If the center section is one piece like the Paragon, cut the holes in the bottom sheeting one inch in front of the spar and one inch either side of the center rib. Prop the wing up so the bottom surface is vertical and the trailing edge is at about 45 degrees to the horizontal. This will allow the filled epoxy to form a triangular puddle between the front of the spar and the root (center) rib. Put on the latex gloves. Mix about an ounce of epoxy according to the directions on the container and stir in filler until the mixture reaches the consistency of sour cream. Cut off all but 1/4 inch of the plastic tip of the syringe. Load the syringe with the filled epoxy and inject the mixture into the wing through the 1/4 inch hole until the mixture is up to the hole. Fill only the uppermost hole at this time. Wipe off any excess. Allow the epoxy mixture to set before moving the wing.
When the epoxy has set, reposition the wing and repeat for the other side.
Put the two halves of the wing together with their joiners. Cover at least six inches of the bottom center section of the wing with plastic kitchen wrap and pull it smooth with small pieces of masking tape around the edges. Fold it around the leading and trailing edges so they too will be protected. This film will act as a parting agent while molding the wing saddle. Cut a former from the 3/32 birch plywood to fit horizontally inside the fuselage and about 3/8 to 3/4 inches below the wing saddle (depending on the size of the model). This plywood former must extend fore and aft of the slugs of filled epoxy in the wing (when the wing is mounted to the fuselage). Glue the former into the fuselage. When the glue has set, don your latex gloves and mix up a batch of epoxy. Stir filler into the epoxy until the mixture reaches a peanut butter like consistency. Spread a little epoxy mixture all over the wing seat on the fuselage and put enough on the 3/32 ply former to reach from one side of the fuselage to the other and 1/2 inch fore and aft of where you are going to drill for the wing bolts. Pile the former with filled epoxy until the mixture is a little above the wing saddle. Align the film-protected wing center section over the wing saddle and press it into the epoxy mixture. Adjust the position of the wing on the fuselage until it is aligned in every direction. Weight or rubberband the wing in position until the epoxy sets.
When the epoxy has set firm but is still green remove the weights or rubber bands and peel off the masking tape from the wing. Remove the wing from the fuselage. Peel off the parting film from the wing saddle. Cut away any excess epoxy mixture that has oozed out. When the epoxy has cured hard (second day) align the wing over the fuselage and rubberband it in place. Double check the alignment. Using the proper drill size for the tap, drill (2) through the epoxy slugs in the wing into the epoxy block in the fuselage. Countersink the holes in the top of the wing for flush screws and enlarge the holes through the wing so the nylon bolts will just slide through without excessive play. Tap the holes in the fuselage. Run the tap in and out several times and check the fit of the nylon screws. They should turn freely with the fingers. If necessary, lubricate the screws with a dry teflon spray.
Cut off any dowels that protrude from the fuselage and repair the covering. For center rubberbands, as in the Gentle Lady or Paragon, close the hole in the fuselage behind the wing. Mount the wing with the nylon screws and snug them up. Check the wing by rotating it on the saddle. It should give several inches at the tip before the nylon bolts shear. It should also ease back into position as it is realigned. There should be a definite detent feel as it is properly positioned.
That's it. Go fly with confidence. You have improved the L/D by about two percent and the wind penetration glide slope by about four to eight percent. Better yet, the wing won't lift off the saddle during launch (as happened to a flying buddy in a Labor Day contest).
I will be glad to answer any questions about nylon wing mounting (except the cause of my crashes). I can be reached on the internet at ocwilson@sunline.net