Trailing edge questions

[szicree]

On page 36 of my manual it says: "Trowel a thin fillet of adhesive inside and against the bottom sides of the trailing edge. Make sure to fill any voids between the rib capstrips, webs, and the trailing edge."

Are they saying to fill the triangle shaped space that occurs at each rib/trailing edge junction? They don't mean the entire length of the trailing edge, right? Am I filling these little voids in anticipation of the aft-most flap hanger bracket rivets passing all the way through the trailing edge? Also, doesn't that aft rivet look kind of unsightly from the bottom? Any advice and/or photos would sure help.

[HighWing]

Steve,
There was a recent thread that included some comments on fabric shrink temps. It was mentioned that on the Kitfox, Polyfiber recommended small incremental temp increases with checks to see if the longerons / trailing edges begin to sag in and if so stop there. The person posting that comment mentioned he didn't do anything with the trailing edges - as I recall - with very good results. With that said, on both of my Model IVs, I used carbon fiber arrow blanks between the ribs running between trailing edge and spar - Hysoled in place as stiffeners. I then shrunk to the recommended temps. On the first IV I failed, however to fill the space between the aft of the rib and the internal surface "V" of the trailing edge, and eventually, on the non flaperon hangar ribs, the glued only trailing edge came loose and fabric tension collapsed the trailing edge there into the space resulting in a rather ugly wrinkle on the fabric right at the rib. The thinking on the arrow blank idea was hopefully to save a bit of weight. I know of others who have glued in lengths of "hard" aluminum tubing where the manual says to apply the adhesive. I think if I was doing the adhesive thing, I would opt for some epoxy stiffened quite a bit with Micro Balloons (at least 25% by weight which will expand the volume about four times). "Micro" is very stiff and quite light weight. That is what I used this time between trailing edge and all ribs - and lots of other places to smooth things out a bit before covering and painting. It is used extensively on the composite airplanes for filling gaps and leveling surfaces.
Lowell

[jiott]

I wondered about that fillet statement myself and came to the conclusion that I needed to fill any void between the aft end of the ribs and the inside of the trailing edge so the fabric tension would not break the glue bond and collapse the trailing edge as Lowell had happen to him. This problem was a non-issue with me as I was able to pull the trailing edge up tight against the aft ends of the ribs and the edge remained perfectly straight, so there was no void to fill. I clamped them up tight against the ribs while the epoxy set up. In case you have to hold some of the trailing edge pieces back a little from the rib aft end to keep a straight line, then you would need to make sure that void was filled with epoxy. That was my take on the statement in the manual. Also be careful not to get too much epoxy into that vee shape or you won't be able to slip the flaperon bracket reinforcing plates into place on the sides of the aft part of the odd numbered ribs (don't ask how I know this).

Regarding the aft most rivets on the flaperon brackets, the factory assembly guy told me at the Arlington Air Show that they use a shorter rivet in that spot on their factory build SLSA so it doesn't show thru the bottom and look ugly.

Jim

[szicree]

Thanks for the info guys. Jim, I found on my wing that if I brought the trailing edge up against the ribs I would only measure about 11-1/4 instead of 11-3/8. Also, thanks for the heads-up about the flaperon bracket interfering with the goop.

[jtpitkin06]

Ooh!!! What a great idea, Lowell, using arrow shafts instead of Aluminum tubing for the trailing edge reinforcement. A good use of alternative materials. Light, strong, cheap and available at sporting goods and hobby stores.

Put that one in the builder's tips!

John Pitkin
Greenville, TX

[szicree]

If I understand correctly, the tubing recommended in the manual runs spanwise inside the trailing edge, whereas Lowell's idea puts the arrowshaft chordwise from trailing edge to spar. I think the arrowshaft would be significantly more effective at resisting bending.

[jtpitkin06]

Yes, the instructions in the SS7 manual recommend the 3/8 tubing snapped inside the trailing edge spanwise and bonded with Hysol.

The tubing is optional. I asked John McBean about it at Oshkosh.
Ans: If you shrink to 250, you don't need it. If you shrink to 350 you'll need the additional reinforcement to prevent trailing edge scallops.

I used aluminum tube and it really stiffened things up. It takes all the flimsy feeling out of the trailing edge. I was worried the thin trailing edge could be damaged easily without the tubing. Not any more. Had I known about arrow shafts I would have used 3/8 shafts in the same spanwise position bonded in place with Hysol. Arrow shafts are lighter and if bumped or banged will resist kinking and bending much better than aluminum tubing.

Spanwise installation inside the trailing edge will resist vertical displacement of the trailing edge as well as scallops.

John Pitkin
Greenville, TX

[MotReklaw]

I would like to see a picture of this with the adhesive/carbon fiber, or tubing method.... I'm having a problem picturing it in my feeble mind....

Mot, a visual learner....

[jiott]

The 3/8" tubing just snaps into the gap between the two edges of the trailing edge. On mine it was quite a tight fit and I had to kind of roll it in starting at one end. Deburr the sharp edges of the trailing edge first; it will greatly help snaping it in. Squirt the epoxy in the gap first with a syringe and the tubing will lay nicely in a bed of Hysol when it snaps in.

Jim

[Tom Waid]

A photo:



On my kit the short outboard trailing edges accommodated 3/8 tubing. The rest would only accommodate 5/16". Before ordering the tubing I did a trial fitting with drill bits. My guess is that the factory has multiple suppliers which explains the slight variation.