Curtiss Helldiver

Written by Pat Tritle
Build the last dive bomber operated by the Navy Product
Review
As seen in the March 2019 issue of Model Aviation.

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The SB2C Helldiver was a dive bomber designed by Curtiss to replace the aging Douglas Dauntless. The Helldiver was developed in 1940 but suffered setbacks until it finally entered service. The early design was underpowered, handled poorly, and was not well accepted by those who flew it.

After nearly 900 changes in design and production, the Helldiver entered service in late 1943. The "Big-Tailed Beast," or simply "the Beast," among other names too colorful to mention here, proved itself a capable warrior with a fine combat record in the final two years of World War II.

At A Glance

Specifications

Wingspan: 48 inches

Length: 37-3/4 inches

Wing area: 396 square inches

Flying weight: 24.3 ounces

Wing loading: 8.84 ounces per square foot

Materials List

Wood: Sheet balsa is required if the laser-cut parts package is not used

Five 1/16 × 4 × 36-inch balsa

Four 1/8 × 4 × 36-inch balsa

One 3/16 × 3 × 36-inch balsa

One 1/32 × 8 × 18-inch birch plywood

One 18 × 4 × 8-1/2-inch light plywood

One 1/32 × 4 × 18-inch balsa

Two 1/16 square × 36-inch basswood

Eighteen 16 × 1/8 × 36-inch balsa

Two 1/16 × 3/8 × 36-inch balsa

Eighteen 3/32 square × 36-inch balsa

Two 3/32 × 1/4 × 36-inch balsa

Eight 1/8 square × 36-inch balsa

One 1/8 × 1/4 × 12-inch hard balsa (servo rail)

Two 1/8 × 3/8 × 36-inch balsa

One 3/8 × 1/2 × 12-inch basswood (landing gear mount)

One 1/4 × 6-inch triangle stock

One 1/8 × 6-inch dowel

One 3/16 × 1-inch dowel

One wood toothpick

Wire: One .025 × 18-inch steel wire

One .032 × 18-inch steel wire

One .046 × 12-inch steel wire

One .093 × 36-inch steel wire

Miscellaneous: One pair 2-1/12-inch main wheels

One 1-inch tail wheel

Three feet of nylon thread (rudder pull-pull cable)

Four 3/32-inch wheel collars

One manila file folder

Two 8-32 × 1 nylon socket head bolts

Twelve 3/16 × 1/16-inch rare earth magnets

One .008 × 8 × 18 clear acetate

One 3/16 × 8 × 18 artists foam boards

One 3 × 6 × 8 mm Depron sheet

Twelve #2 flat washers

Twelve #2 × 3/8 sheet metal screws

Power: Suppo 2217/9T outrunner brushless motor

20-amp ESC

APC 11 × 5.5E propeller

2,000 mAh 2S LiPo battery

Guidance: Two Suppo S-60 servos (ailerons)

Two Suppo S-90 servos (rudder and elevator)

Three 6-inch servo extensions

One 6-inch Y lead

The SB2C was a big airplane with a wingspan of 49 feet, 9 inches and an overall length of 36 feet, 8 inches. Power was provided by a 1,900 hp Wright R-2600-20 Twin Cyclone radial engine, with a gross weight of 16,616 pounds. Its maximum speed was 295 mph, with a cruise speed of 158 mph, and a service ceiling of 29,100 feet.

Armament included two AN/M2 20 mm cannons in the wing, two 7.62 mm machine guns in the rear cockpit, 2,000 pounds of bombs or a single Mark 13-2 torpedo in the weapons bay, and 500-pound bombs on the underwing hard points.

The Model

The purpose for building the Helldiver was to offer a tribute not only to the crews that manned and maintained these airplanes during the war effort, but also to those stateside who built them. Without their efforts, the crews would not have had airplanes to fly. To them, I would like to offer a big debt of gratitude.

The model was designed with a 48-inch wingspan at 1:12.5 scale. The idea was to provide a simple park flyer-style model that could be built and flown by anyone with intermediate modeling and flying skills, was large enough to fly well, yet would be easy to transport.

The model is primarily built from balsa and plywood. The fuselage features an internal truss frame with external formers and stringers, and the wing is of egg-crate-style construction.

Guidance is four-channel RC with power provided by an economical brushless outrunner motor powered by two battery cells. Access to the internal components is through removable canopies on the front and rear cockpits. The wing is also removable.

Meanwhile, don’t let the full-scale Helldiver’s checkered beginnings scare you away from pursuing this project. The model is a solid, stable flier that can be flown easily by anyone with some "low-wing" experience.

Building the Helldiver

Full-size patterns are provided to cut out the shaped parts. A list of additional materials is also provided on the plans, along with the full-size bowing patterns. To aid less-experienced scratch builders, a laser-cut parts and plastic pack is available from Manzano Laser Works.

Construction begins with the various subassemblies. Start by bowing up the laminated outlines using the forms made from foam board. Bend the landing gear struts to shape and make up the landing gear mount blocks. Fit and glue the stiffeners in place on formers 7A, 8, and 11. Finally, build up the wing spars according to the detail drawing provided.

Tail Section

Begin by building up the vertical stabilizer assembly directly over the plans using the part numbers and wood sizes shown. Shims are used to center the leading and trailing edges (LEs and TEs) on the ribs. Remove the assembly from the board and sand to an airfoil shape.

Fit and glue the tail wheel strut in place as shown. Cut in and dry-fit the hinges and drill the hole for the toothpick control horn. Build the horizontal stabilizer in the same fashion.

Wing Assembly

Cut the left- and right-hand wing panel drawings from the plans and tape them together at the centerline. The wing is built directly over the plans beginning with the center section. Fit ribs R1 and R1A onto A1 and A2 and pin in place over the wing plans. Fit and glue WBP in place followed by the TE. Laminate the LE (inner) together and, using the 3/16-inch wing hold-down dowel to aid with alignment, glue the LE in place.

Unpin the wing from the board and move it up onto the left-hand panel and pin it in place. Fit and glue SM, the ribs, A3, and the laminated balsa LE and balsa TE in place. Trim the angles into the spar tips and TE, then fit the tip bow and glue in place. Note that the tip bow will offer some resistance toward the TE, but that actually builds washout into the completed panel. Add the balsa bracing at SM, the basswood wingtip brace, gusset G, and balsa turbulator spars to complete the wing panel.

Sand the angle into the bottom of AS using the R7 rib drawing for reference. Build the aileron in place directly over the plans. When completed, rock the wing over onto the right-hand panel drawing, block it in place, and build the other wing half. When completed, lift the wing from the board, cut the aileron free from the wing, and sand to shape.

Dry-fit the hinges into the ailerons then add the balsa TE blocks at R6. Fit the landing gear blocks into the wing and glue them in place with 5-minute epoxy. Fit and glue F1, F2, and F3 in place, flush with the bottom of the R1 ribs, and sand to shape. Align and glue the paper fairings in place at the inboard LE and R1. Finally, glue the servos in place with silicone caulk. When it is dry, run in the extension leads and secure at R1A with WG.

Fuselage Assembly

Build the fuselage side frame directly over the framing plans using the part numbers and wood sizes shown. Build two identical frames. To join the frames, pin them upside down over the top view and add the top and bottom crosspieces from Station 6 forward. Pull the tail post together and glue it and add the remaining crosspieces.