Composite fairing for vertical stab

[svyolo]

A couple of weeks ago I was eyeballing how to cover the base of the vertical fin without ruining large and expensive pieces of Oratex. I took a couple of scraps, and covered the left side to see how to attack the problem. Another builder p-mailed me about my opinion of Oratex so far, and said that he had the idea to make a fiberglass fairing for the base of the fin. I believe his reason was maintenance/inspection access. I looked at the Oratex I had just applied, and my mind said "mold". What the heck. I applied some mold release, and put on 2 layers of glass to see how it turned out. I can always apply more later if I liked it.

Yesterday I did the other side with 4 layers of glass, and 2 of CF interleaved inside. I was running low on Epoxy so I bought some airplane branded stuff. Aeropoxy. PH3663 hardener. I like it a lot.

Without any filler and no paint, one side weighs 11 oz. Finished maybe a pound per side, but I can eliminate 2 big Al inspections hatches if i decide to use the fairing, and I get killer access to the tail hardware.

I need to run a couple of fastener ideas by Bob. I think the upper longeron is a lot stronger than it needs to be at the tail. But I think the vertical tail post is not. I would like to just use nutcerts in the tubing, but I think the fin will need a couple of tabs welded on. I will have to ask Bob. Also some 1 or 1.5 inch 4130 strips at the base of the leading edge of the fin, bowed slightly to hopefully match the natural billow of the fabric.

[Bcone1381]

The photo below shows a four place horizontal stab that I saw at OSH once upon a time. The horizontal stab has a fairing where its surface joins with the fuselage's fabric. Could you incorporate that into your fairing and secure the bottom to the Horizontal Stab's inboard rib using nut plates?
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[tailwind]

I made my fairing out of aluminum and secured with no. 6 nutplates. In my opinion it will be hard to build a fiberglass fairing that will be lighter than aluminum. The fairing was made in 3 pieces: leading edge, top and bottom.

[svyolo]

I think it would take too much additional steel welded in to terminate fabric up to that fairing. Right now I only need a strip about 6 inches long on either side of the fin, from the upper longeron to the base of the fin/U-clip for the upper stringers.

I need to decide shortly whether to use this fairing or not. I will see if I can get a hold of Bob about fasteners shortly.

[svyolo]

Bob wasn't in love with my fastener idea for a couple of reasons that he quickly convinced me of. He recommended I weld some tabs on. I was really hoping to avoid welding anything on the fuselage and so far have done that. All that being said my Tig is now good enough to do it no problem. I will decide in the next day or two. I really like the fairing idea for long term maintenance, inspection, and accessibility.

[svyolo]

Here is a couple pics after I covered the top of the fuselage. When the fairing is done I will glass it together at the leading edge and it will be one piece.

So far it is turning out OK. I can still just cover the whole tail conventionally if I don't like it.

[Battson]

Was there much of a weight difference compared to Oratex covering the same area?

[svyolo]

Unpainted the two halves weigh about 20 oz. The tabs I made to mount it another 6 oz. Painting will add another 4-6. But I only need a single 3-4 inch inspection cover, on 1 side. Just enough to install or remove a cotter pin on the elevator and trim horn. Everthing else I can access from the removed fairing much easier than before. Weight gain is total weight minus the weight of inspections covers. I would guess a 1/2 lb to a pound. The Oratex saved me 2-3 in elevator balance weight alone, I can't remember the exact number right now.

The only thing I don't like so far is the the lay of the fabric as it goes over the U-clip that holds the two upper stringers. I thought about grinding the sides down to make the fabric lay a bit more fair. I am now regretting not doing that. I might reheat the glue to failure at the aft end, and grind it down so it lays a bit more fair.

Other than the fabric over the clip, I like it so far. There will be 5 layers of fabric and trim tape over it so it will take a while to chafe through.

[svyolo]

Before I cover the fuselage sides I did need to make sure I can assemble everything, including how big to make the cutouts for the control horns for the elevators. One very small panel on each side should do it. The vertical length of the elevator leading edge plus half the control horn.The opening will be <2" at the widest part, and about 3 3/4" long.

[JCD23]

How are you terminating the Oratex at the transition to the Carbon Fiber?

[svyolo]

I put a .032 4130 strip just aft of the clip holding the two upper stringers. They are slightly curved (and welded to form T for stiffness)to match the natural curvature of the fabric at the point.

[whee]

Before I cover the fuselage sides I did need to make sure I can assemble everything, including how big to make the cutouts for the control horns for the elevators. One very small panel on each side should do it. The vertical length of the elevator leading edge plus half the control horn.The opening will be <2" at the widest part, and about 3 3/4" long.

Is the fairing you are building removable so you can access the cables and cranks for inspection and mx? If so then making the side cut outs small MAY be acceptable.

I wanted a sleek clean look on my airplane so I made the side cutouts as small as possible. I think they are maybe 2” wide and 4” tall. I can do what needs to be done though them but it kinda sucks. When I’m working back there I wish for panels built per the plans. When I’m not working back there I really like the clean look of the small panels.

[svyolo]

Yeah it will be removable in one piece. It is split at the tail post. I can access everything with it removed, even the bolts that adjust the leading edge angle.