Sopwith Baby Sea Scout

Sopwith Baby Sea Scout

Tanzer, John

THE “BABY” WAS a refinement of the prewar Sopwith “Tabloid” and “Schneider” racing biplanes. It was powered by either a 110hp or 130hp Clerget rotary engine housed in a horseshoe-shape (inverted-U) cowl. Armament varied: some aircraft were fitted with an upward– and-forward-firing Lewis gun, and others were equipped with a synchronized forward-firing Vickers gun. The Baby could carry two 65-pound bombs for antisubmarine patrols. The floats were twin, non-stepped, box, “sea-sled” type with a tail float and an aft water rudder. For land use, I replaced the box floats with wheel and axle gear using the original struts plus new Shorthorn skids and axle saddles. I replaced the tail float with a steerable tailskid. The Sopwith Baby saw widespread use with the Royal Naval Air Service and was produced under license by British companies including Blackbarn and Fairey.

I chose to model a Blackburn-built Sopwith Baby float– plane, which was based at Great Yarmouth, England, during 1919. It had a red-and-white checkerboard cowl. I also built the landing gear and tailskid. Converting from floats to landing gear takes only minutes. I had saved a 3-view of the Baby from the February 1978 issue of Model Airplane News, After 20 years, it came in handy as a guide to design and build a good replica.

The model is 1/4 scale, and some accessories, such as guns, wheels, cowls and pilots, are available. I used a cowl from Fiberglass Specialties* (part no. MCB-8), and it worked out fine. I used an instrument panel kit from Arizona Model Aircrafters*. This is an excellent kit, and it makes a realisticInn looking instrument panel for WW I aircraft. I originally installed a Q-42 engine and replaced the stock engine mount with a flat steel plate mount to keep it short. The nose on the Baby is very short, and the plane did come out tail-heavy. To balance it, two pounds were needed in the nose. 1 decided to install a 3.1ci Roper engine, as it is two pounds heavier and can turn a 24×8 propeller at 6,000rpm. The engine runs smoothly with more-than-enough power.

CONSTRUCTION

This is a builders’ project-not difficult, but time-consuming. Balsa, spruce, plywood, lite-ply and some metal parts are used.

Wings. The four outer wing panels are identical: two left and two right; the upper and lower center sections differ slightly. The semisymmetrical ribs have a flat spot between the lower spars that allows each wing to be built flat on the workbench. I started by cutting out all the parts to make two wing kits.

Pin down the 1/4×3/8-inch spruce main spars. Use a rib as a gauge to locate and pin down the 1/4-inch– square spruce rear spar. Note that the ribs at the ailerons have 1/8×1/4-inch notches. Also, when building the top wing panel, use lite-ply for the R-3 ribs. When building the lower wing panel, use lite-ply for the R-2 ribs. Now Zap* all the ribs into place. Add the top spars and the 3/32×7/8-inch subleading edge. Tape the two 1/16×1-inch trailing edge (TE) sheets together at the rear. Open these sheets like a book and Zap them to the rib ends. This ensures a straight TE. Glue in R1-AR rib tail at the aileron leaving a 1/16-inch gap.

Remove the wing panel from the plan and glue in the 1/8×1/4-inch strips at the aileron, then glue the 3/32-inch verticalgrain shear webs in place and add the 1/8-inch-balsa wingtip. Glue in the 1/4-inchply interplane strut plates and reinforce them with balsa triangle stock. Build the rest of the wing panels in the same way, but remember that the top wing has the 1/4-inch-ply plates on the bottom and the lower wing has them on top.

Use the same wing plan to build two upper and two lower wing panels. Build the upper and lower wing center sections using the same building system. Before you join the wing panels to the center section, install the 1/-inch paper tubes. Cut halfway through the bottom of the tube at the dihedral break so that the tube will bend up. With the center section pinned flat on the workbench, slide the wing panels onto it, and prop up both tips 7/8 inch at the last rib. This gives the proper dihedral angle. Use epoxy to glue in the ply dihedral braces. Next, glue the 1/4-inch– balsa ribs R1-D1, R1-D2, R1-D3. With the wing removed from the bench, glue in the 1/4-inch-ply cabane and interplane strut plates and reinforce them with triangle stock. Note: all 1/4-inch-ply plates are lhs inch above the rib surface and will be flush with 1/16-inch-balsa skin. Now glue on the 1/16x/4-inch-balsa sheeting, cutting around the 1/4-inch-ply plates then attach all the 1/16×1/4-inch-balsa capstrips. When sheeting the top, weight down the center section so it remains flat on the workbench, glue on the sheeting, then do the same with the other wing panels, one side at a time. The top sheet forms a D-tube structure and this ensures a straight wing. Add the 1/2×1/8-inch balsa leading edge (LE), then plane and sand it to shape. Line the wing cutout and center bay with 1/4-inch balsa (the center bay will remain open).

Now is the time to cut out the ailerons; use the rear spar as a guide. Glue in balsa hinge blocks, then sand them flush and face the aileron opening with 1/8-inchbalsa sheet. Fit and glue in the1/8-inch-ply control-horn mount. Dry-fit the hinges, mount the aileron servo, and keep the control rod short. I use a servo at each aileron (four in all).

Now finish the lower wing. The center section has balsa blocks at the wing-bolt and wing-dowel areas and it is fully sheeted. Completely finish both wings, as they will be needed to complete the fuselage.

Fuselage. Start by cutting out all the parts needed to make a left and a right side. Mark the inside of the lite-ply sides for the cabane pocket locations. Pin down all the pieces for the right side, then Zap them all together. The left side is built over the right side, so cover all the glue joints with wax paper. The left lite-ply side must be blocked up to be flush with the outside.

With the sides removed from the plan, glue in 1/32– inch-ply gussets where shown. Glue in the 1/4– inch-balsa wing-saddle doubler. At the top of the lite-ply sides, glue in 1/4×3/8– inch spruce filler and 1/8×3/8– inch spruce scarf joints to form the cabane strut pockets. Now, using the plan, cut the ply cabane struts (two front and two rear), and note their angle at the airfoil. Use the struts as a guide to glue in 1/4– inch-square balsa slot runners, being careful not to glue the struts into place; they are removable. Screws will hold them in place later in the construction. Glue the 1/8-inch ply plates across the runners at the top and bottom of the channel. Now cut the front ply landing-gear mount, wing-bolt plate, balsa tail wedge and 1/4×3/-inch-balsa crosspieces back to former F-4. Pin the crosspieces to the top view of the plan, then place the fuselage sides, (top side down) next to the crosspieces. Pin and block the sides into place. Tape the landing-gear mount and wing plate into place, square up the fuselage, then Zap everything together. Now pull the rear ends of the fuselage together with the balsa wedge in place, and temporarily clamp the tail shut until all crosspieces have been cut, installed and glued.

Remove the fuselage from the plan and glue in all the 1/32-inch ply gussets and the 1/4-inch rear ply landing-gear mounts. At this point, with the fuselage upside– down on the workbench, lay the lower wing in the saddle to check the fit. With the wing in the saddle, use the landing– gear mount as a guide and drill two 3/8inch holes in the LE for the 3/8-inch winghold-down dowels.

Remove the wing and glue 3/8-inch dowels into the holes in the wing, then recheck the wing’s alignment with the fuselage. Drill and tap the wing-bolt plate for 1/4-20 mounting bolts. Remove the wing and set aside for now. Cut firewall F-1 out of 1/2– inch ply and install it in the fuselage using epoxy and screws (through the sides). Reinforce with balsa triangle stock. Cut formers F-8 out of 1/8-inch balsa and formers F9 from 1/4-inch balsa. Glue on all the top– deck formers, glue on the 3/32-inch-balsa sheeting from F-4 forward, and cut out the areas for the cabane-strut pockets. Glue on the 1/4-inch-square stringers from formers F-5 to F-8. Cut out the cockpit, make the headrest from a balsa block, and glue it on. Cut F-C from 1/4-inch ply and glue to the firewall. Cut two 1/64-inch-ply cowl cheeks and glue them into place. Glue hardwood cowl-mounting blocks to F-C, and fit the cowl into place. Trial-fit your engine and try to keep it as short as possible; use a flat plate mount and drill a hole in the firewall for the rear shaft. A 50 engine works well here.

Tail feathers. The rudder and stabilizer outlines are made of four strips of 3/32×3/8– inch balsa that have been laminated together. Drive pins around the inside line on the plan, soak the balsa strips in water, wipe them dry and glue them together with carpenter’s glue. While the glue is still wet, bend the strips around the pins and clamp in place until the glue is dry. Cut the laminated outline to size and fill in the rest of the structure with 3/8-inch– balsa pieces. Dry-fit the hinges.

Assembly and alignment. To install the top wing, cut slots at the top of the cabane struts to fit the sheet-metal brackets; epoxy and 2-56 bolts will hold them in place in the struts. Drill a 1/4-inch hole in each bracket for the 1/4-20 wing bolts. Round off the edges of the struts that extend from the fuselage.

Slide the struts into the fuselage pockets, and drill through the side and into the strut for the sheet-metal screws. Now, lay the wing upside-down on a foam pad, then place the fuselage upside-down on the wing. Mark, drill and tap the wing plates for the mounting bolts. Install the lower wing and check for alignment. Set the plane upright and check the wing incidence, (1 degree positive on both wings). Glue on the stabilizer and the fin. Check the stab for 2 1/2 degrees of positive incidence.

Now make the interplane and mount brackets. Drill and tap the wing plates for the mount bolts, then bolt the brackets to the wing. Cut slots in the ends of the struts and epoxy the struts to the brackets. The cabane and interplane struts are reinforced with 1/16-inch music wire and Du-Bro* solder links. Cut the pin side from the solder links, drill out the hole for a 2-56 bolt, and bolt the links to all the struts where shown on the plans. Cut music wire to fit between links then solder them in place. Wrap the music wire with thin wire and solder where the music wire lengths cross to eliminate metal-to-metal “noise.”

Landing gear. Cut the gear struts from 1/4-inch aircraft ply. Make the brackets from sheet metal, and assemble the gear using 2-56 bolts, as shown on the plans. Drill and tap the gear and mount it on the fuselage and the lower wing block with 1/4-20 bolts. With the gear installed in the fuselages, square it up, and reinforce it with 1/16-inch music wire and solder links. This is very important; without the wire/links reinforcement, the gear will not survive its first landing.

Install the 1/4-inch axle and vintage wheels. Rubber bands are used for shock-absorbing bungees. If you plan to have floats, build another set of landing-gear struts. The removable, steerable tailwheel and tail float are built according to the plan.

The floats are cut from expanded-bead white foam and covered with sheet balsa. The tail-float’s wire bracing is control-line cable pulled tightly from bolt to bolt while the float is mounted on the fuselage. I built a lower wing center section to bolt to the fuselage so that I would be able to transport the fuselage with the landing gear attached. Brace the tail with spruce struts and Kevlar cord to keep it light.

To control the Baby, six servos are used-one for the ailerons and two for the elevator (one for each side). One servo is used for the rudder and one for the throttle. Keep all servos and batteries as far forward as possible

Covering and finishing. I covered the top of the aircraft with olive green Coverite* and the underside with buff Coverite, then I brushed on two coats of nitrate dope. The roundels, graphics and the red-and-white checkerboard cowl are cut from 2-mil sign makers’ vinyl. The rudder is sprayed with red, white and blue paint. All the wooden struts were stained with Minwax 223 Colonial Maple then coated with Minwax clear satin polyurethane.

The instrument panel is Arizona Model Aircrafters kit no. AZM-220. A 1/4-scale Vickers gun and 7-inch vintage wheels add finishing touches.

I really enjoyed designing, building and flying this 1/4-scale WW I aircraft, and I hope you like it enough to build one. Happy landings!

*Addresses are listed alphabetically in the Index of Manufacturers on page 134.

Copyright Air Age Publishing Feb 1999

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