the wings from folding while in flight, I knew that the upper wing root would be in compression and the lower in tension. With such a small model, I guessed (accurately, as it turned out) that a pair of 1
/8 -inch magnets in each
corresponding panel would hold the upper wing to its root, but that the lower wing would need something more. The original’s design would
A close-up of the folded wing shows the brass tab that is part of the wing-lock mechanism.
be too hard to replicate on a small model, so I settled on a spring-loaded locking pin mounted in the lower stub wing that would trap a brass tab coming in from the unfolding outer panel. The 1
/16
completely without merit. I loaded up the four hinge
holes in the outer panels with epoxy and stuck the wings on, posing them in their in- flight configuration while the glue dried. Roughly an hour later, I pulled the locking pins and folded the wings back without issue. Magnificent! I débuted the model at the
-inch steel pin slides
through a pair of plywood spars, trapping a holed brass tab in between. This locks the wing and provides enough resistance against the flight loads.
The servo leads to the fuselage were installed as close as possible to the hinge.
that my loved, but ignored, Swordfish deserved a better life. I would build in the ailerons and, to further complicate my life, folding wings. I hacked off the upper and
lower wings and redesigned them in my 2-D CAD program with a D-box leading edge structure and full-depth spars. The ailerons were already there in CAD, but I now had to pay attention to the wing geometry at full fold—would they bump the fuselage? Plus, the folding wings would require that the now- separate lower stub wings support themselves and not rely on anything from the
rest of the wing panel. Hitec (
hitecrcd.com) came
to the rescue by providing a pair of ultrasmall HS 35HD servos that fit perfectly in the model’s slender lower wings and were strong enough for the four ailerons. The outer panels were built
fairly quickly, and were quite sturdy with the new D-box. I used the largest Robart (
robart.com) pin hinges I could fit in the wing panels for the hinge mechanism and affixed them in the aft corners of the inboard panels, installing them so that they would rotate somewhat close to parallel. Turning to the locking mechanism needed to keep
Properly installing the supporting interplane struts and rigging was critical because the outer wing panels are now separate and have to completely support themselves. This process had to be performed with the model trammeled to a stand to set and maintain the proper alignment and dihedral while the wings were joined by the struts. I did the interplane installation first and then the rigging and, as a result, the wing panels became sturdy. For the struts, I used streamlined aluminum tube; for the rigging, I used .013- inch music wire. At this point, the moment of truth had arrived—installing the wings on the model. I felt that if the folding wing thing didn’t work, at least I had the ailerons, which was my original intent anyway. My fears were
famous NEAT (Northeast Electric Aircraft Technology) Fair, an all-electric event held each September in New York’s Catskill Mountains. I didn’t tell anyone, but if you got too close to the model, you could still smell a trace of wet paint. As expected, the aircraft
now flew like a real airplane and it handled beautifully. My torpedo drop still needs some work, but the rudder can now be used as originally intended—for coordinating turns and making landing adjustments. The big hit with the
show’s attendees was the afterthought folding wings, since such features are not usually seen on models at ARF-dominated events. A biplane at rest—torpedoed up, wings folded, and sitting on the tarmac—simply looks as though it is more complicated than it really is. Plus, it looks cool. It’s hard for me these days to walk by the model without playing with the wings or taking it to the field. It took me approximately
three weeks of nights on and off to rescue what essentially was a good model, and it really did my modeling soul some good since the Swordfish and I go way back. The real one is on my top- five favorites list and now I have a model of it that’s a great flier. What’s better than that?
THEPARKPILOT.ORG 37
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