SkyFly Hinge Modification
I noticed that the hinges on the elevator seem to offer different levels of resistance. When looking at the plane from the tail end, the far right side of the elevator seems to have more play in it then the left side. I think this is due to the weakening of the hinges and the off-center pull from the fishing line and rubber bands. I tried to adjust/strengthen the hinges before using clear packing tape, but it didn't seem to resolve the issue. I don't think this torquing of the elevator caused any problems in flight, but it seems to me that it could cause the plane to tilt left or right when elevator is applied.
I decided that I would replace the horizontal control surface while I have my plane apart for a pushrod mod. While at the LHS, I came across the Du-bro nylon hinges (Part 116). They look well built and seemed very light...just about the same size as the SkyFly hinges. Here we go...
First, I lined up a nylon hinge with the SF hinge and put a pencil mark where the hinge will start. I also pencil marked the width of the hinge on the elevator and flap...and on the bottom and top.
Next, I cut the SF hinges to remove the elevator flap. I then removed the SF hinge from the flap.
Next, I chose a knife with a wide, angled blade. This will allow me to cut straight down, and outward at the same time. A narrower blade would not yield the same results. I drew a line on the knife that is roughly the same depth as the hinge. I wanted to make sure my cut was deep enough, but not too deep. I carefully cut the slots for the hinges...trying my best to keep the slice in the middle of the foam...and horizontal to both edges.
Next, I inserted the hinges and dry-fitted the flap to the tail. If the hinge pins are not in horizontal alignment with the edges of the foam, the hinges bind. This will cause resistance on your servos and causes a clicking sound in the hinges.
The Du-bro package recommends epoxy to glue the hinges into the wing. I thought about using Sumo glue or UHU Creativ' (my favorite glue), but decided I would stick with the manufacturers recommendation. I used my 5-minute epoxy for plastics. You do need a little "work time", so 20-minute epoxy would be good too.
I inserted my knife into the cuts and twisted it slightly to open. I worked fast and used a tooth pick to put a little glue in the slits. If you use too much glue and you risk getting it into the hinge (rendering it useless). When epoxy starts to set up, it starts getting messy. Work as quickly as possible.
Next, I lined up the edge of the hinge with the pencil marks. I inserted one edge of each hinge into the flap and then joined the flap to the tail by inserting the remaining half of each hinge into the tail.
I tested the control surface and found that one or two of the hinges were binding (clicking). I adjusted the ones that were clicking...just in time as the glue was starting to get stiff. The flap now swings freely. No more weakened and distorted foam hinges.