Electric Seagull (oz14272)

About this Plan

Electric Seagull. Radio control powered sailplane model. Wingspan 78 in, wing area 660 sq in. For electric power with 05 geared motor.

Quote: "Want to fly like a bird? Then why not give this electric powered Seagull a try. Electric Seagull, by Bob Harold.

The Electric Seagull started out as a 6 inch gull-wing glider cut from an aluminum can. My pattern for the aluminum can gull appeared in Jim Gray's Soaring column. I had always been interested in gull wing models but only had limited success. The aluminum gull flew so well that I made a 10 inch model of balsa that was an excellent flier. An electric gull seemed like the thing to try.

The starting point for the design was the article I had read on the Astro Challenger by Bob Boucher. I wanted a soaring glider with the 05 Astro Cobalt geared motor with seven cells and a folding prop. The electric system is not light, so the wing loading would be on the high side and the model would glide fast rather than float. The Eppler 193 airfoil was selected. The wingspan was picked at 80 in to give a compromise on climb rate, glide performance, and portability. The one piece wing will not fit in a subcompact car. The wingtips that slope down may reduce the tip losses. The span-wise circulation of air should be away from the tip instead of toward it. Seagulls and albatrosses soar with their wingtips tilted down.

Construction: Wing construction is conventional. The rear of the balsa trailing edge has a piece of 1/16 x 1/8 basswood attached to permit a sharp trailing edge. Block up the front of the trailing edge by 1/16 to preserve the undercamber. The ribs are cut from 1/16 balsa except for the three ribs at the joints:, Mark and cut the spar notches in the ribs after the spars and notched trailing edge are pinned in place. Make certain that each Tibia' down fully on the bottom spar before gluing with CA. Add the top spar and glue it after making certain that it is flush with the top tit each rib. Cut and glue the 1/16 balsa shear webs in place with medium speed CA. The box spar with vertical shear webbing and the wide trailing edge give the needed torsional rigidity to the wing. A single piece wing was chosen to save the weight of joiner rods. Since the wing spars join at a compound angle, conventional bracing cannot be used, The 1/16 plywood braces join the spars at the second rib.

When joining the wing panels make the center joint last, after making the tip joints. See the sketch on the plans for making the proper angles. Use extreme care to have all four wing panels at the same incidence angle when making the dihedral joints. After the spars are sanded to make a good match they are glued at the proper dihedral angle and then the plywood brace is added, and then the 1/8 joint rib is cut to fit and added along with the balsa gussets.

The bottom of the wingtips are covered with 1/64 plywood for the last two bays but so far the wingtips have not shown any wear. An outer tube of a Sullivan pushrod assembly is built into one wing for the antenna. The center bay of the wing is covered top and bottom with 1/16 balsa. A 3/8 thick spacer block is carved to fit over the top of the trailing edge at the center to give the hold-down rubber bands more tension at the rear of the wing.

On the original, carbon fiber was used to reinforce the top and bottom of the three wing joints but these joints broke anyway when the plane crashed in the early flight testing. Apparently the joint angle was too great to obtain the benefit of the carbon fiber. I used CA adhesive and double glued all joints. When construction is finished, sand the wing taking care to sand the shear webs flush with the spars and yet not sanding away part of the wing ribs. The wing was covered with pearly white Micafilm. Micafilm is lightweight and tough. You have to be careful when applying Balsarite to overlapping joint to keep your iron clean. At final assembly make 4 wing keys of split 1/8 dowel, 1/2 in long. Glue the keys to the bottom of the wing at the LE and TE so they fit snugly against the sides of the wing saddle.

Fuselage: The belly of the bird is just fat enough to contain all of the radio and electric gear. Initially the ruddervators were controlled by electronic mixing but the Futaba FGK7 transmitter would only set up with two stick operation that way. The two stick control system for the ruddervators required more coordination than my thumbs could deliver and the first crash happened. A Du-Bro mechanical Vee tad mixer was added to give single stick rudder and elevator controls.

The fuselage is built upside down on a 1/8 horizontal crutch. Lay the two horizontal keels over the plans and glue together at the rear. Fit up the lower keel and former F-4 and glue in place. Add formers F-5 through F-9. Remove from plans. Tack glue a temporary vertical spacer to the front of the upper keel to maintain the proper spacing from the lower keel. Glue the upper keel in place and add formers F-9A. F-10. and WF-3. Fit the 1/" ply motor rails into the slots in F-4, sanding the slots as necessary to get the required down thrust of 6 degrees. Tack glue a horizontal spacer to the front of the rails. When everything is aligned correctly glue the former F-1 in place and glue the rails to F-4 and F-5. Add F-2 and F-3.

Lightly tack glue or tape the 1/8 balsa motor cowl rails on top of the ply rails. Add formers MC-1 through MC-4. Cut away the slot in the top keel for MC-6 and WF-1. Trim MC-5 and MC-6 to fit, and glue in place to the cowl..."

Direct submission to Outerzone.

Scan by MarkD, cleanup by Circlip.

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