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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

wing construction begins with assembling
01. Wing construction begins with assembling the center section. The ribs, wing bolt plate, LEs, and TEs are builtup before the panels are assembled.

the completed wing assembly has been sanded
02. The completed wing assembly has been sanded and the servos and wiring are ready to install.

the hinges are dry-fitted in place
03. The hinges are dry-fitted in place after the built-up horizontal stabilizer assembly is sanded to final shape.

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.

the built-up rudder assembly
04. The built-up rudder assembly is sanded to final shape.

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.

the fuselage formers are scalloped between the stringers
05. The fuselage formers are scalloped between the stringers to eliminate unsightly bumps in the cover.

the battery is in the front cockpit
06. The battery is in the front cockpit and is accessible by removing the cockpit hatch. Note the location of the magnets used to retain the canopy.

Lift the frame from the board and add the formers using the framing plans and provided cross-sectional views for reference. Use the wing to dictate the actual location of former 6B. Add the top, bottom, and middle side stringers to prevent damaging the formers. Fit and glue the servo mounts in place in the rear cockpit and mount the servos as shown.

Add the WSF, RB, and the remaining stringers. Next, to stiffen the wing saddle, cover the gap between B1 and WSF with file folder paper. Now you can remove the crosspieces in the wing saddle and cockpits.

Laminate 3C and 3D, and glue in place using the Section 3 cross-sectional drawing for reference. Glue FBP in place and reinforce with 1/4-inch triangle stock, followed by B2 and B3.

Run in the elevator pushrod tube. Note where the tube exits the fuselage and fit a scrap balsa support between the stringers flush with the outside edge. Support the tube at the servo rail and at Station 8 using the PRG pushrod guides. Tape the rudder in place and run in the pull-pull cables. Tie the cables to the control horn and mark the exact location where they exit the fuselage for later reference after the fuselage is covered.

Fit the wing into the fuselage and drill and tap the holes for the 8-32 wing holddown bolts. With the wing bolted in position, glue formers BP1 through BP4 in place. Add the stringers, along with the 3/32-inch square balsa fill, at F1, F2, and F3 between each of the formers. Align and glue BP4A in place at each hold-down bolt location flush with the stringers.

Build up the motor mount assembly and glue it in place on FW. Hook up the ESC and test-run the motor to ensure proper rotation. Mount the motor using washers on the left side to build in some right thrust. Fit and glue the cowling blocks in place and mount the cowling.

Fit and glue the canopy frame in place against IP then build up the front and rear cockpit hatch assemblies. Assemble them in place on the fuselage using waxed paper in the openings to prevent the assemblies from sticking to the fuselage frame. Halfscale drawings are provided that show the part numbers and locations.

Add the details and paint the aircraft as desired. Using the provided patterns, cut the canopy glazings and glue them in place on the frames. Fit the magnets into the fuselage frame between the main frame and stringers. Place a magnet in each corner of the rear cockpit, and one on each side at the center of the front cockpit.

To set the depth of the magnets, dry-fit the 1/8-inch scrap balsa supports into the fuselage between the main frame and stringers then drill the supports. Glue the magnets in place flush with the top of the support blocks. To glue the blocks in place, place another magnet on top of those in the support blocks. Stick the magnets to a steel ruler and fit the blocks into the fuselage. The steel ruler will ensure that the depth is correct. Align and glue the blocks in place.

To locate the magnets on the hatch, place a small drop of CA on each of the stacks of magnets, prime the wood with accelerator where each magnet will make contact, and set the hatch in place. Lift the hatch from the fuselage and permanently glue each of the magnets to the hatch.

Covering the Helldiver

To prepare for covering, give the entire frame a good detail sanding to remove any unwanted bumps or inconsistencies. It’s also a good idea to scallop the fuselage formers between the stringers for a smoother covering job. Finally, reassemble the model without the covering and correct anything that’s not right while you can still get to the insides.

The model can then be covered with silkspan and dope or any lightweight, iron-on covering material. The cowling can be painted and detailed as desired and graphics added. Vinyl trim sheet is used to add the canopy frames.

Final Assembly

To install the horizontal stabilizer, first bolt the wing in place then slip the elevator into the fuselage, followed by the horizontal stabilizer. Trim the saddle as needed. When you’re satisfied that it won’t need to come back out, glue the hinges in place. Finally, glue the horizontal stabilizer and vertical fin in place. Now the aileron and rudder hinges can be glued in place as well.

in the air, the helldiver
07. In the air, the Helldiver is smooth and docile.

Using the dimensions taken earlier, pierce the covering, run in the rudder cables, and secure them on the control horn. Make a Z-bend on the elevator pushrod and secure it to the servo arm. Make a Z-bend at the elevator hinge line, set the elevator to neutral, and glue the control horn in place. Construct the aileron pushrods in the same fashion and glue the control horns in place. Then connect the receiver and set up the control throws as shown on the plans.

Mount the landing gear struts using #2 sheet metal screws and washers to secure the struts in the mount blocks. Add the desired landing gear detail and mount the wheels. Balance the inverted model on the main spar, locating the battery to your best advantage. My battery ended up in the front cockpit. Set up the battery tray as required and secure the battery with Velcro. From here you can add any desired details to complete the model and it will be ready to fly.

Flying the Helldiver

The Helldiver is a stable and docile flier; however, because of its short-coupled tail, the elevator is noticeably lively. Set it up as shown on the plans and it is manageable. The ailerons exhibit some adverse yaw, so a little rudder when entering a turn is a good idea. The rudder is effective but not overly sensitive, so ground handling is good.

The model is easy to fly, cruises nicely at half power, and goes where you point it. Before the first flight, drop in a freshly charged battery then make a final walk-around to ensure that the center of gravity is correct, and that the controls are properly set up and move in the right direction.

Takeoffs are easy—throttle up to approximately 2/3 power, and when the model is ready to fly, add a pinch of up-elevator and you’re off and running. Trim the aircraft for straight-and-level flight at a comfortable speed.

In the air, the Helldiver tracks nicely and turns easily with little input. It will also turn extremely tightly at approach speeds, with no indication that it’s going to snap out from under you. The stall is benign and uneventful and breaks right down the middle. When the nose drops, it immediately begins to fly again.

The Helldiver penetrates well, so only a little power on the landing approach is needed. Keep the nose down and fly the model all the way down. At roughly a foot from the ground, ease the nose up and wheel it on. Keep just a touch of power on, steer with the rudder, and the aircraft will track straight and true as the tail comes down.

Overall, the Helldiver flew far better than I expected. Looking at the short-coupled fuselage, I anticipated some low-speed handling quirks, but it turns out that the model really has no vices. I believe it’s going to see a lot of air time.

Sources:

Manzano Laser Works

tomj@tularosa.net

www.manzanolaser.com

4 comments

Do you make a large scale version of this plane? Maybe 2x the scale here = a 96"+ version?

Where do i sign up for the free digital plans for the Helldiver? It's not given with the article.

Hi Frank! You should be able to download them above.

Very cool! Looks like a interesting and fun build! KWC

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