Fyredrake (oz12378)

About this Plan

Fyredrake. Free flight power model.

Quote: "A triple-threat design to consider in your search for the ultimate Half-A - it climbs, glides, and penetrates. Fyredrake 1/2A, by Larry Sicuranza.

Firedrake is one answer (mine!) to a knotty problem. The problem is double-category 1/2A competition. Unlike their bigger brethren, 1-/2A's don't fly too well to begin with, and current designs tend to emphasize either climb or glide. The results are 200 inch bombs that climb like balsa prices and glide like anvils, or 350 inch overcasts that will do 7 minutes from an altitude of 63 feet. They will also, exhibiting all the penetration of an overcooked artichoke, drift out of sight in 2 minutes and 49 seconds. Considering that a pair of each is needed for a busy season, you'll see why I view 1/2A competition as a problem - if not a four-star pain. I also view it as a helluva lot of fun, what with relatively inexpensive planes and hordes of flyers.

The logical step, then, is to try to design a ship that can climb, glide and penetrate. All three, not the best two of! Firedrake (a kind of little dragon) does the job. He doesn't have a terrifying contest record, because he's fresh-hatched, but four other flyers have the plans so time, as always, will tell. The kit that is in planning will also help in this regard. Seems the chugbugs that win the most come out of boxes, so watch the Digest.

Design philosophy is not so simple as you might think, since 1/2A's are not visions of efficiency, due to their size. Scaling down bigger birds often results in mini-duds, so Firedrake started life as what he is. I call it 'he' because it is no lady. He'll bust you in the ear quick as a wink if you don't pay attention.

As far as numbers are concerned, the aspect ratio is set at 7 plus to allow some airfoil efficiency. Foil thickness is near 11% for the same reason. Reynolds number is not found only on boxes of aluminum wrap! Incidence is low, as is stab area, but it's placed way back. That's why no down-thrust is needed. Aft fin is used because it looks better than underslung and is less likely to be damaged, being light and built-up. The fin is thick to allow for better alignment and less criti-cal tab adjustment. CG position is moderate (75%-80%), and tail moment is long. Left thrust is required for VTO stability, and wash-in is used in the right main wing panel to keep it up in the power phase. Parabolic surfaces are used because of their warp resistance, their ease of plotting, and their extra 5% of area over an equivalent ellipse. Also I think they're pretty. I like to cant the engine to keep exhaust glop off the timer(s) and/or fuse. The big pylon makes a nifty baffle. Finally, a pressurized fuel system is pretty well neces-sary for consistency.

Construction is very simple, since it's lifted off Tom Hutch inson and salted with Satellite dust! It's best to build the flying surfaces first as they can stay pinned down for a couple of days. That's right - days! I like pretzels too, but to chomp, not fly. Since this is not a beginner's bird, I'll only bore you with the fussy stuff.

The stab should be built using epoxy for light weight and high strength. A little dab'll do ya. The turbulator spar notches are cut after the ribs and top spar are fitted. Let the completed struc-ture dry pinned down for at least 24 hours. The diagonals are optional, I didn't use them. The tapering outline provides lots of stiffness. When thoroughly dry, sand and apply two coats of un-thinned dope to edges, then sand off fuzz and set aside.

The fin can be built with epoxy or old-type model cement. Glue and pin both ribs in place and, when dry, sand edges to mate with the other side. You can try a sheet fin if you like, but dig a fox-hole first! Sand the fin edges smooth, but don't pre-dope it.

The only flat panel in the wing is the left main. The right main and both tips have build-in warps. To make sure the warps stay in, follow the sequence. Pin down leading and trailing edges and bot-tom spar. Fit and glue the ribs and let dry (don't install dihedral break ribs yet). On the right main panel, remove the pins from the leading edge, except for one at the root. Block up the leading edge at the tip dihedral break 3/16 inch, and slip a 3/32 shim under the leading edge at the mid-point. Now pin the leading edge down against the shims, install upper main spar and fit and glue the diagonal ribs. On the tip panels, unpin the trailing edge, except at the in-board end, and shim up 3/32 at the point indicated. Pin at this point and finish assembly. When all panels have dried at least 24 hours, remove and trim spar ends to dihedral angle. Fit dihedral ribs and epoxy panels together, blocked to correct angle. Again, let set as long as possible. When thoroughly dry, remove and epoxy in gussets. If you fly over hard ground, a piece of 1/32 ply backing up the top main spar at the center di-hedral break will help absorb DT shock. Finally, install turbulator spars and hold-down rubber braces. Carve and sand leading edge and tips and apply two coats of unthinned dope to the edges.

The fuselage is of the familiar profile type, but is deeper than average because the greater cross-section is more warp-resistant. The little beast is l000ng. The nose length and shape depends on the type of mount used. Use epoxy to install the pylon and laminated firewalls. Sand in at least 1° of left thrust before installing firewall. Epoxy a bit of 1/2 inch nylon or fiberglass tape around the fire-wall and cheek fronts. Once again, leave the structure pinned down for at least 24 hours, especially if white glue is used..."

Fyredrake, Model Builder, September 1975.

Direct submission to Outerzone.

Supplementary file notes

Article pages, thanks to RFJ.

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