The Super Firefly Boost Glider



There's kind of a long story behind this model, and it starts at Estes, even though Estes never heard of the end product.

Once upon a time (as they say), Estes sold a kit for the Mini-Bomarc, a BT-20 scale (probably really Sport Scale) model of the Bomarc ramjet-powered antiaircraft missile from the 1960s.  This was a follow-on to a larger Bomarc, which was originally sold in a version with an ejecting motor pod and movable elevator, which flew as a rear-engine boost glider.  Now, though the Mini-Bomarc wasn't designed to glide, the surface shapes, sizes, and positions were correct for it to do so, and someone at some point thought of putting the same surfaces (with a little dihedral added) onto a balsa stick fuselage to make a simple parasite glider, which was eventually sold by Estes as the Firefly.

Much later, I downloaded plans for the Firefly parasite glider from JimZ's plan archives, and noticed that it was a little on the small side to fly as a pop-pod boost glider -- and that the wing aspect ratio and area were under size for the best glide performance for a glider in that size and weight range.  This led me to redraw those surfaces with double the original span, but the same chord.  That, though, looked like an awful lot of balsa sheet to be dragging around with a 1/2A3 miini motor (by this time, I was considering use of this glider in a 1/2A Boost Glider Duration contest that was coming up in a couple months) -- but then I remembered that at about the time I quit flying indoor flree flight models (say about 1989), the most competitive were starting to use built-up wings, similar in concept to the stick-and-rib wings on larger, slower free-flight models (albeit more robust).  I decided to see if I could build a paper-covered framework wing that would be robust enough to stand boosting on a pop-pod.  A little more time with my drawing program, and I had a frame plan, as well as a color pattern for a wing skin that I could print on a color ink jet printer, and I'd started work.  The glider went together quickly and easily, along with a boost pod, and I was ready to fly very soon.

Unfortunately, the first time I flew the bird, the glider popped off the pod under boost -- proving the robustness of the wing, since the glider looped after release at around 50 mph without damage, but indicating more work was needed on the hook.  After a couple more failures, I managed to redesign the hook so the glider stayed on through boost, and then to work on retrimming the glider to minimize looping during boost and coast -- looping caused by the decalage that lets the glider fly stably as a glider, and which was minimized by retrimming with less decalage and less nose weight.

At this point, the glider flies in gentle circles about 50 feet across, with a light floating glide.  It's a couple grams lighter than a comparable sheet wing would be (the sheet wing would have used lighter balsa than the frame, but I still saved some weight), and about as robust, plus it looks better with the color printed wing skin.  It boosts to around 150 feet on a 1/2A3-2T, transitions to glide reliably (when it doesn't pick up a piece of wadding on the tail, as it did the first time I got it to stay on the hook through boost), but hasn't been flown in contest yet -- the contest I built it for was postponed due to excessive wind, and the rescheduled one won't take place until early October.  We'll see where we stand then . . . but there are more improvements I can make.

So far, this is just a flat-plate, single surface wing with the framework exposed on the bottom (draggy); in addition, the leading and trailing edges of the wing were left square in the interest of proving the concept with a minimum of labor.  That done, it shouldn't be hard to build a new glider or replace the wing on this one with a wing skinned on top and bottom, lighter wood in the wing frame, and sanded to a slight airfoil shape to increase the lift to drag ratio and thus improve the glide still further.



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