F/FSport P
by david mitchell You can reach David Mitchellat 230 Walnut St. NW, Washington, District of Columbia 20012, or via e-mail at
davedge@me.com
at Murray came to the F/F Champi- onships in Muncie this year with a great flying Beriev BE-12 twin rub- ber job in his fleet. This unusual 1960’s Russian anti-sub aircraft has quite a challenging layout. A project like this surely benefits from having a disciplined building process behind it, so I was really pleased when Pat posted a bunch of build pics to his Flicker account on-line:
http://tinyurl.com/n2duyyz. With his permission, I snagged a few of the shots that illustrate one of my all-time favorite construction techniques—using a building box to facilitate assembly of compli- cated fuselages. There are some fuselages that just don’t lend themselves well to tradi- tional box-and-stringer methods, and even half-keel methods (think Guillow’s or Ster- ling F/F kits of the ’70s) can fall short. Any- body who finds it challenging to build a fuse- lage that is properly aligned—who doesn’t? —or who has a penchant for complex and knotty airframes owes it to themselves to try this out.
There are a number of variations on the theme, but the basic idea is to first assemble a keel outline, and then tack glue temporary crosspieces to it in between the former sta- tions. The crosspieces are left long enough to span across the edges of a building box or stiff frame, and are secured to it by one means or another—pins, rubber bands, tape, glue, etc.
In the method illustrated in the photos, full-profile formers are cut out and notched for the primary keel and stringer positions, and are then glued in place on the keel. If applicable, any remaining keel pieces are glued in place, and then you run primary outline stringers followed by secondary stringers and whatever various sub-assem- blies—wing saddles, nose sheeting, hard points for scale detail, etc.—may be a part of the structure.
All the while, the building box keeps the structure straight and true, until you are ready to detach the fuselage and its cross- pieces from the box, remove the crosspieces
PHOTOGRAPHY: PAT MURRAY
Foam support strips are tack glued to the keel layout. Pat Murray likes to use R/C 56 glue for the purpose. Note that he has begun to draw former position layout marks on the keel.
from the keel, and finally reveal the blessed thing in all its uncluttered glory. Buzz Trabbic of Rocky Top Models www.
rockytopmodels.com sells a nifty, well-de- signed and sturdy laser-cut “Universal Fuselage Building Fixture” for about $24. It takes the hard work out of coming up with a suitable jig for the task. They have a neat picture tutorial posted to their website illus- trating its use that is well worth checking out.
Having found that his Rocky Top jig was a bit too small for the expansive Beriev, how- ever, Pat came up with a solution that fit his needs perfectly. Rather than make a new building box out of plywood or solid wood, he used stiff foam insulation board. It’s easy to find at your local hardware store, cheap, light, easy to cut and assemble into a box of practically any size required, and holds a pin well. Pat also used stiff foam strips for the cross strips that support the keel pieces, tacking them into place with R/C 56 glue. There are however any number of differ- ent approaches you might take to using a fuselage building jig. First of all, if you look at the RockyTop tutorial, Buzz suggests us-
ing the building jig as an assist for what is otherwise a pretty straightforward, Guil- low’s-style half-shell building method. You would start by laying down the keel pieces, gluing one half of each fuselage for- mer in its proper place, and running all the stringers on that side. However, rather than at that point lifting the half-fuselage from the plan and then gluing up the other half unsupported, with nothing to keep it from getting twisted out of alignment, Buzz sug- gests you first tack glue the aforementioned crosspieces to the keel, then lift the whole half shebang from your building board and strap it to the building jig.
Now you have secured the completed half- fuselage against twisting and/or bowing, and can glue up the other side with confi- dence. This is a little different than Pat’s ap- proach, but no less viable. Buzz’s method gives you a more robust structure to handle before you start lifting things off the plan, and folks may find it easier to insure that the formers are square to the keel building this way.
Personally, I have come to like working with full formers, and tend to build more “in
Gluing up the full fuselage formers (at left). Overlapped joints will be extremely strong. Next, the formers will be notched for the keel pieces. The keel/crosspiece assembly (above) is pinned to the foam building box. Note the completed, partially notched formers in the background. It looks like Pat opts to notch for the stringers after the formers are glued to the keel.
32 NOVEMBER 2013
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