RUBBER HINGING TECHNIQUES

By Harley Michaelis

Hinging with rubber allows butt fitting of rudder to fin or elevator to stab. During deflection, the moving surface pivots on one side or the other of its leading edge and the rubber stretches. The typical rubber used is .025" x 1" flat surgical rubber applied as a tourniquet in taking a blood sample or as a strap to secure a disposable urine bag to a person’s leg. Wash the rubber to get rid of the talcum treatment on it or it won’t bond well.

To slot the structure for the hinges, get a cheap, plastic-handled fingernail file. Cut it off square leaving _" or so by the handle. Sharpen the cut end by equally beveling both flat surfaces.

At hinge locations, make opposing centered slots either side of the hingeline. Typically rubber pieces _" to 3/8" wide and 1-1/4" or so long will do. Cut with sharp scissors. Size slots so one can just be slipped in with the fingers. If necessary, find some other tool to slightly open the slots.

In the fin TE member, solid fin or rudder post, see that the hinges can be slipped in 3/8" deep. If the fit with the slot is sloppy, apply a little water with a syringe to swell the wood to the rubber for good contact.

With the hinges nicely squared-up, apply thin CA glue either side of a hinge to wick it in place. Let cure, pull on each to be sure it is secured.

 If the rudder is an open frame structure, it is covered after hinging is done. Before hinging, the rudder LE is wrapped with film covering, the film is slit and the raw edges are heat-sealed inward at the slots. Just heat the fingernail tool against a sealing iron and run it in a little way.

The trick of getting hinge loose ends into the rudder LE slots is to "deflect" the rudder 180 degrees, align slots and curl hinges to insert them. Pull to remove slack, straighten the rudder and tape it to the fin.

For the rudder to freely deflect, it must be possible for some rubber to stretch. Therefore CA glue cannot be used to bond the rubber into the LE slots. Rather, with all slack removed, a cleat of balsa is positioned as illustrated and a small drop of thin CA wicks the cleat to the rubber. If extra hands are available, slightly stretch a hinge, then glue on a cleat for a more snug butt fit.

If the rudder is not open frame, apply a coat of paste wax along the butting surfaces. Then glue hinges first into all fin slots or rudder slots. Trim to 3/8". Then on the left or right side of the fin or rudder where they go, also apply wax. On that side, centered 3/16" from the hingeline, using your slotting tool as a depth gauge, drill 3/32" holes down to the slots. Insert all the loose ends and one by one apply thin CA into the 3/32" holes to bond them. Pick up CA dribbles with toilet tissue. Spackle over the holes or apply a trim strip, etc.

The rubber does not readily deteriorate. I have had ships several years old with all hinges still good as new. However, extended direct sunlight may be bad, so at the field, position your ship so the rays do not fall directly on the hinges, especially if you did not do a good butt fit that shades them.