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Written by Paul Kohlmann
Build and fly the Navy’s torpedo bomber
Review
As seen in the December 2019 issue of Model Aviation.

At A Glance

specifications

Specifications

Wingspan: 60 inches

Length: 42 inches

Weight: 4.5 pounds ready to fly

Power system: 650 Kv brushless motor; 60-amp ESC; 4S 3,700 mAh LiPo battery

Plans: http://www.modelaviation.com/kohlmann-devastator

Welcome to the third and final chapter of our 60-inch Douglas Devastator build. Last month we got this project to the point where it could fly. This time around we’ll knock out some detailing that will make this model pop.

the soft balsa oil cooler was roughed out using a wood rasp
01. The soft balsa oil cooler was roughed out using a wood rasp.

a dremel tool was used to shape the inside of the cooler
02. A Dremel tool was used to shape the inside of the cooler.

the oil cooler was shaped in place to fit the wing’s underside
03. The oil cooler was shaped in place to fit the wing’s underside.

Detailing a model of this type can be tricky. The point of a stick-built model is to create a lightweight airframe. If we add too many details then we’ll add too much weight. And to be honest, our stick-built Devastator won’t look as scalelike as a sheeted model; the stringers give the stick-built model away.

That is the rub. If we strategically add a bit of detailing, then we can draw the eye away from the stringers. For me, that means adding key things that are characteristic of the model that you are building, as well as a few odds and ends that break up open spaces.

In the case of the Devastator, defining features include the large oil cooler under one wing half and a landing light faired into the other. The oversize greenhouse canopy is also ripe for detailing.

Underwing Details

The oil cooler was made from soft balsa. Its shape is symmetrical around its centerline. This is an easy piece to create on a drill press. To get started, an oversize block was made by stacking some scraps of soft balsa.

One end of the block was trued so that it would stand up straight. A 3/8-inch hole was bored into the other end of the block. I glued the same size dowel size into the hole to provide a shaft to chuck into the drill press.

A wood rasp was used to rough out the shape of the oil cooler, followed by 60-grit sandpaper. The shape and size were checked periodically by fitting the part to the wing. After the shaping was finished, I bored holes into both ends using the drill press to create a rough entrance and exit to the cooler.

I cleaned up the openings using a Dremel tool. The front and rear faces were blackened with a marker to make it easy to see the edge of the opening as shaping progressed. The goal was to make the black line as narrow and even as possible.

I fitted the oil cooler to the wing by sanding a recess into the top surface. A piece of 60-grit sandpaper was pulled tight over the wing sheeting where the cooler would be attached. The cooler was sanded in place by moving it from side to side until it was seated as shown in historical photos of the Devastator.

A second piece of balsa was hand shaped to represent a mysterious bulge behind the oil cooler. I’m not sure what the bulge was for, but it can be seen in the historical photos. These two parts were sanded with 220-grit sandpaper and sealed with lacquer filler. After another light sanding, they were sprayed with autobody primer then glued into place with Titebond.

A small piece of screen inside the inlet completed the effect. A similar process was used to make the landing light on the other wing. The light lens was made from a piece of packaging that originally held a household lightbulb.

The Devastator’s Canopy

The Devastator’s canopy was massive. It was composed of three fixed and four sliding sections that covered a crew of three sitting in tandem. In the case of this 60-inch wingspan model, the length of the canopy is a whopping 16 inches long!

finished oilcooler parts have been sanded sealed primed and glued into place
04. Finished oilcooler parts have been sanded, sealed, primed, and glued into place.

after reinforcing the cockpit lip the excess height was trimmed back
05. After reinforcing the cockpit lip, the excess height was trimmed back.

Park Flyer Plastics has made getting the size and shape of the canopy correct a snap, but it’s up to the builder to decide how to mount these parts. With four sliding sections, there are plenty of combinations. The most commonly photographed configuration was for the pilot’s slider to be open. Next would be for one or both of the gunner’s sections to be shown in the forward position.

Because the assistant pilot/bombardier position was not used on torpedo missions, this spot was often vacant, and its slider was closed. I opted to go with the torpedo configuration.

Fitting the Canopy

To get started, the cockpit opening needed to be prepared. The upper cockpit stringers would sag down when the covering was shrunk if they weren’t reinforced. Strengthening this area with some infill planking fixed that problem.

I used soft 1/8-inch balsa for this. Beveling the long edges made it easy to press them into place without them dropping through the gap. After the glue cured, the planks were sanded to blend smoothly into the fuselage assembly.

I fitted the plastic canopy to the fuselage so that it sat at the correct height according to the plans. The exact position of the cockpit opening could then be marked onto the sides of the fuselage. The stringers and planking above this line were cut away with a hobby knife.

A cockpit deck was next. After adding a few braces between the fuselage sides, I sheeted the cockpit opening with 1/16-inch balsa. The openings for the crew positions were cut out as marked on the plans.

To make attachment of the numerous canopy sections easier, rails were added to the cockpit deck. These narrow strips of hard balsa gave the appearance of the runners that the sections slid along on the full-scale Devastator. They made it easy to space the sections evenly while gluing them into place.

Detailing the Cockpit

A cockpit this big would look like a vacant lot without some detailing, but it’s easy to go overboard. My suggestion is to start with the things that can be seen during a low pass and stop well before the rudder pedals.

An oversize roll bar is a must-have for the Devastator, especially because the pilot’s slider will be open. The roll bar is interesting. In addition to serving as the pilot’s headrest, it was strong enough to be used to lift the aircraft and housed a limited set of instruments for an assistant pilot.

The headrest and instrument panel were made from balsa scrap. After painting, instrument faces were printed on paper and attached to the panel. The bars were made from 3/32-inch aluminum tubing. The ends of the tubes were flattened and shaped to mimic structural elements. The tubes were epoxied to lugs made from more scrap balsa.

The large fire extinguisher and the direction-finding loop antenna stand out, too. The fire extinguisher was made from 1/4-inch dowel with some aluminized tape to serve as mounting loops. A short piece of 16-gauge wire and another piece of aluminum tubing made up the hose and nozzle. After a coat of red paint, this small detail really stands out!

The directional loop antenna was quite large and can be seen through the slider sections. It was made by wrapping a piece of .032-inch music wire around a punch. Because the antenna had to plug into something, I made a receiver out of some scrap balsa block.

There are only a few things left to do, but they are big ones. A pilot and gunner are in the works, and the gunner’s ring mount and Browning machine gun will be fabricated. Of course, a big Mk XIII torpedo will complete the picture.

Wrapping It Up

This series wouldn’t be complete without a flight report. The prototype Devastator’s maiden flight was made after the covering and paint were applied. The model weighed 72 ounces with a 3,700 mAh 4S LiPo battery installed.

During taxi testing, the wheels didn’t want to stay planted because of the model’s fat wing and light loading. I initially had some issues keeping it going straight because one wheel dragged, but when the rudder became effective, the Devastator pulled away from the runway and reached for the sky. I fixed the sticky wheel when the aircraft returned to the hangar.

download plans online

canopy rails were added to hold the slider sections in place
06. Canopy rails were added to hold the slider sections in place.

the pilot roll bar parts were assembled on the board then transferred to the cockpit
07. The pilot’s roll bar parts were assembled on the board then transferred to the cockpit.

building cockpit details on the devastator is a fun way to use up odds and ends
08. Building cockpit details on the Devastator is a fun way to use up odds and ends, but it can become addictive!

There was a little trimming to be done, and the center of gravity marked on the plans felt good in the air. The 650 Kv motor and 12 × 8 × 3 propeller provided plenty of power, and that led to some basic aerobatics. Once I was comfortable with the model’s behavior, I tried slowing things down. The slow passes were stable and looked great.

I tested the flaps and was surprised to find that they didn’t induce much trim change, even when they were dropped to their full 60° of travel. They slowed things down nicely. I also added a functional tailhook that was slaved to the flaps when no one was looking!

Landing was a breeze with a little power on until touchdown. I’m looking forward to getting more flights in after the flight crew is installed. Then it will be time to think about my next project!

a handful of details make this stick and tissue devastator a convincing model
A handful of details make this stick-and-tissue Devastator a convincing model.

SOURCES:

Model Aviation online

www.ModelAviation.com

Manzano Laser Works

www.manzanolaser.com

Park Flyer Plastics

(817) 233-1215

www.parkflyerplastics.com

RCGroups build thread

https://bit.ly/2yLo4P7

Du-Bro

(800) 848-9411

www.dubro.com

HobbyKing

www.hobbyking.com

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