Chuck:
I remember being told by Cliff Faber, the original Glasair tech support guru (whom we sadly lost to ALS many years ago) that if the surfaces were prepared correctly (i.e. sanded and cleaned), and the layups were properly applied using the correct resin, a one-inch overlap on either side of a seam was as strong as a continuous piece of cloth. With that in mind, you should be able to estimate how far the overlap needs to be in each layer. I'd taper just as you've proposed, by an inch on each. Overlaying with the larger pieces is a good idea, to spread the load across a larger area.
That said, I am not a composites engineer, though I'm building a Glasair Super II-F/T <g>. But if this were my airplane, I would evaluate the proposed repair as you have, and though I might be inclined to do another layer or two in a similar way, I'd be comfortable with that repair on my own ship.
I would, however, be sure that you use the original Derakane Momentum (411) resin, to insure good crosslink bonding with the original structure. I used some polyester resin on mine, but only in non-structural items, like small fairings, and fillers like Bondo, before painting. You just won't be able to ensure a strong a bond if you change to a polyester resin on top of the Vinylester.
The bidirectional cloth used has been #7781 all along, according to information give to me by S-H back in the day. I'd stick with that, too. Both resin and cloth are still available from Aircraft Spruce, if for some reason you can't get it from Glasair.
If it were a wing, or the horizontal stab, I'd be more concerned about possibly getting some professional assistance. But the vertical fin, though important, is nowhere near as heavily loaded. It has to take sideloads from gusts, and provide longitudinal stability, but the primary loading will be with the rudder deflected, I'd think.
I think it would also be prudent to splice into the vertical fin shearweb (spar) to provide at least as much strength as it had before. I'd use a similar technique, and make sure the repaired area was well overlapped onto the original, which needs to be carefully prepared before applying the laminates. And as someone else mentioned, I'd try to duplicate the original thickness as much as possible.
The good thing about the bidirectional glass used in this kind of construction is that the laminate schedule is pretty simple for most parts, and I'm sure it is there. In general, almost all parts have layups cut on the bias, i.e. 45 degrees to the weave. There are very few parts where the orientation is different from that. The number of layers is the most important thing, and you can probably estimate that from a measurement of thickness, and possibly even by careful "dissection" of the damaged area.
You'll want the surface repair, as well as the deeper stuff, to be "scarfed", i.e. sanded at a very flat angle, to expose more area for the new bond to "crosslink" with the old structure substrate. For a repair of a 5 or 6 layer surface, I'd try to make the scarf joint at least several inches across, to give the resin plenty of space to attach to the underlying fibers.
With all that being considered, I'd also look into the possibility of consulting with one of the fiberglas repair outfits out there. I know there are many out there. I'd ensure they've actually done Glasair work, not just fiberglas work, if possible. (Absent a good airplane repair shop who'll help you, you'd be better off with a really experienced boat repair shop than just using someone who's done car repairs, etc., since they'll be more familiar with using the bidirectional glass than the chopped mat stuff a lot of cars use.) Check out homebuilt.org's page here:
http://homebuilt.org/vendors/services/construction.html
I'd get hold of a construction manual if you can find one for the G-1, and pay special attention to the vertical fin area for guidance on layups, etc. The G-Super II area, for reference, uses 4 layers to complete the seam on the front of the vertical fin. There is also a good discussion of the process for installing the vertical fin shearweb, which may be very useful for you.
There was also a couple named Chuck and Debbie Raymond who built a II-S F/T, who had to do a serious repair to their wing many years ago. A landing incident left the airplane with a nose wheel and I think one main gear torn off by colliding with the edge of a newly constructed runway, and the right wing (I think) was ground down a couple of feet from the wingtip, including damage to the spar. They did a much more involved, but similar repair, to what you are contemplating. Look in the FAA registry database for N16CD if you might want to contact them. The airplane is still flying, apparently.
And I know there are others out there who had upside-down Glasairs returned to flying after similar accidents to yours.
Let me know if you have trouble finding a manual. I have some parts (most) of the one for the Super II in .PDF files.
Beyond that, I'd think it's certainly doable, though I'm glad I'm not having to do it.
Ron
Glasair Super II F/T - ALMOST ready to go.
Originally Posted by Duffworld
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