Composite Surface Hinging Question
 

I won't mention any names, but I don't think it will take long for anyone to figure out which aircraft/manufacturer I am talking about here. The dilemma, is the lack of hinge back up blocks in a sealed composite surface, (wings, rudder, ailerons, etc;) and what balsa that is there.... is very soft. With an 1/8 inch balsa leading edge and an 3/16 Robart hinge point embedded, you just don't have much glue surface, and no way to access to install back up blocks without cutting into the nicely detailed surfaces.

After gluing a couple of hinges into the surface ( 2 ton devcon epoxy), I did a pull test and it did not take much effort at all to break the hinge loose and remove it. This is really poor engineering on the manufacturer's part, with little that the modeler can do to correct.

(Note) First pic, I tried to get a view so that you can see the thickness of the cross section in the balsa leading edge.
Last pic is a mockup, and essentially what you would end up with...not good!!!

So, the question is...anyone know a solution to this without having to sacrifice the surface detail.

RE: Composite Surface Hinging Question
 

Use BVM glue gun with a short nozzle and inject aeropoxy in the hole. Put in a lot. tape the holes. Stand the surface on the edge and tap on it to cause the epoxy to move down against the balsa edge. When dry, redrill and aeropoxy again. It should work...work at your own risk :)

RE: Composite Surface Hinging Question
 

What about using the expanding type of polyurethane glues like Elmer's or Gorilla glue??? There is a lot of room in the control surface cavity to allow for expansion---When I have used this type of glue I could not pull the hinge out. When allowing the glue to cure stand the part up so that the hinges are facing downward. This will allow full contact of the glue to the leading edge of the control surface. Check your work to see if there is any seepage of the glue toward the hinge and remove before curing...Any cured polurethane glue dries cement hard and is very difficult to remove. Although the Robart hinges are barbed I still roughen them up a bit with 80 grit and clean well with alcohol before installing...Just a thought....


Kevin

RE: Composite Surface Hinging Question
 

Why not drill out to larger size and install hardwood dowel then redrill for hinges.

RE: Composite Surface Hinging Question
 

Another time honored method, is to drill or Dremel a 3/16" hole about 1/4" behind the 1/8" spar, (top and bottom) and after inserting the hinge, fill the area that the hinge lives in with BVM AeroPoxy. The AeroPoxy is thick enough to not run all over the iplace inside the surface, but it will connect the top and bottom skins to the hinge body. After the pucky turns to stone, sand it flush with the control surface, then fill and fair if/as required.


This technique is used on the Super Bandit ailerons,flaps, elevators and rudder to make a "bulletproof" hinge system.

Harley Condra
BVM REP
JetCat REP