Written by Peter Conquergood
Turning a kit into a detailed scale model
As seen in the April 2017 issue of Model Aviation.
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This is the story of a model of a de Havilland Beaver Mk I, Serial #1, C-FFHB. The first Beaver was built in 1947 and used as a prototype and for flight testing. It was later sold and served as a bush airplane until 1980. The aircraft is currently on display at the Canada Aviation and Space Museum, in Ottawa, Ontario.
The model is 18% scale with a 103-inch wingspan and weighs 33 pounds. It is built from a kit by MR Aerodesign and powered by an O.S. Max 1.20AX two-stroke glow fuel-powered engine. It is controlled with Futaba servos and a Spektrum receiver. The airplane is fitted with a muffler from Bisson Custom Mufflers, Glennis Aircraft wheels, and a pilot figure by Warbird Pilots. It’s finished with graphics by Cal-Grafx and painted with Klass Kote.
The traditional construction includes laser-cut plywood forming the main structure. It’s sheeted with 3/32-inch balsa and covered with fiberglass cloth and resin.
One of the few things that I did not care for in the kit was the hinges for the flaps and ailerons. The hinge point is in the right scale position relative to the wing, but the parts do not look very scalelike.
I made my own hinge parts from 0.04- and 0.06-inch aluminum sheeting. They are bolted to the ribs in the wing, aileron, and flap. The hinge pin is a 2-56 bolt set in a nylon bushing to avoid metal-to-metal contact.
The side view of the completed aileron hinge.
The wing mounting uses a tube, which is a strong and simple system. Most wing tube mounting systems use bolts through the fuselage and slide into the wing root to lock the wing in place. The problem I had was that with the finished interior, the “locking” bolts were not accessible.
Instead, I built a metal tab that extends from the fuselage side into the wing root, and a 4-40 bolt comes up from the bottom of the wing, through the tab, and into a blind nut to lock the wing in place. The bolt head is recessed into a stub of 1/4-inch tube.
The access hatches for the flap and aileron servos were purchased from J&B Access Panels and mounted flush with the skin. The simulated maintenance access hatches were created using automotive aluminum foil tape. I burnished the tape to remove any surface coatings, primed, then cut and trimmed it to size with the help of the CAD drawings. The hold-down screws are #1 screws.
Wing Panel Lines
With the wing halves assembled and wrapped in fiberglass, it was time to add the details. Most of the wing panels on the Beaver are overlapped, making a ridge on the surface. The panel lines and reinforcing plates were done with the conventional technique of masking tape and spray primer.
I used two layers of tape to get the thickness right. They were sprayed with three coats of automotive spot filler and primer in a layer tapered toward the tape, followed by a light sanding on the edge of the tape before removing it.
There are a few butt joints in the panels, mostly on the aileron and flaps. These were simulated by painting over a piece of 1/64-inch drafting tape and then sanding down to the tape before removing it. For the wing root cuff and fairing, an extra thickness of primer was used. It needed four layers of tape.
The bottom wing roof cuff and fairing. The wing’s top panel lines and reinforcing plates were created with the conventional technique of masking tape and spray primer.
After the panel lines were in place, simulated reinforcing plates were added to the bottom of the wing. These were scaled from the prototype photographs, fabricated from 0.005 styrene sheeting, and glued in place with vinyl canopy glue.
Control Surface Corrugations
The full-scale Beaver has corrugated aluminum on both sides of the rudder, both surfaces of the elevator, and on the bottom of the flaps and ailerons. They are all the same: corrugations at 3 inches center, roughly 3/8 inch high and 3/8 inch wide at the bottom, tapered to approximately 1/8 inch at the top, and rounded. On the model, this worked out to a spacing of 0.54 inch and a height of 0.068 inch.
Trying to replicate these caused a lot of head scratching. These would be a fine feature, but they needed to be approximately the right spacing to look good, and, of course, parallel to each other. Trying to glue on individual bits to simulate the ridges seemed too daunting and too prone to inaccuracy.
I tried manually scribing ridges into thin aluminum, but got inconsistent results. A friend suggested building a machine to make the crimps—it’s probably the same way that full-scale ones are made—but I had neither the knowledge nor the tools to make such a device.
My solution was to mold them. I obtained a piece of 1/4-inch aluminum plate and a machinist friend cut shallow slots into it at the right shape and spacing. He was able to shape his cutting tool so that the slots had the correct profile.
Rudder and elevator corrugations.
It was then a theoretically simple matter to cast thin sheets of material to replicate the aluminum sheeting on the full-scale Beaver. I state theoretically because it actually took a fair number of rejects before I got the technique to properly work.
In the end, I was casting the sheets with polyurethane casting resin. I embedded a sheet of 3/4-ounce fiberglass into each one as it set to give the part some strength. The finished sheets were cut to shape and glued to the model with 30-minute epoxy.
In the photos, you can see that the mold is taped off to make an aileron skin, and there is a sample piece of the finished skin. The trim tab hinge is a piece of styrene tube notched with a hobby saw.
Aileron Mass Balance
The aileron mass balance is the last step on the wing build before the rivets. The support is a slightly flattened 5/32-inch brass tube, and the weight was carved from a piece of 5/16-inch dowel.
The pitot is a 1/4-inch diameter brass tube inset into a 9/32-inch tube in the wing. It is removable and held in place with a rare earth magnet holding a steel rod inset in the removable part.
The pitot tube is 1/4-inch diameter brass tube, inset into a 9/32-inch tube in the wing. It is removable and held in place with a rare earth magnet, holding a steel rod inset into the removable part.
The front tip was made from aluminum tubes inset into the 1/4-inch tube. The bracket on the wing was made from styrene sheeting and a tube. Most Beavers have a fin on the front of the pitot, but not the C-FFHB.
The landing light was mounted on an aluminum foil-covered bracket set into the wing’s leading edge (LE). After covering, the hole was cut out. The cutout was covered with a piece of clear 0.01 ABS sheeting, and the mounting ring was made from 0.01-inch aluminum sheet held in place by #0 screws.
The landing light was mounted on an aluminum foil-covered bracket set into the wing’s LE.
The front seats used several techniques. The seat frame was vacuum-formed using 0.04 sheet styrene. This was my first attempt at vacuum forming. It was not as difficult as I expected. I built a small forming box and connected it to my shop vacuum. The tricky part was waiting long enough for the styrene to soften in the oven.
The seat cushions are carved from balsa blocks. The pedestal is a block of balsa sheeted with aluminum glued to the balsa. The seat belts are a piece of shoelace. The working seat belt buckles were fabricated from aluminum sheet. The control column is fabricated in brass, with details discovered in the “Illustrated Parts Manual.”
I chose to install cockpit detail, which meant moving the fuel tank to the center of the fuselage. I then decided to hide the fuel tank and radio system inside of the simulated cargo. While building the cargo, I discovered that I could run 1/64-inch and 1/32-inch plywood sheets through my inkjet printer and make stencils on the cargo.
The interior floor with cargo box and seats. The fuel tank and radio system are hidden inside of the simulated cargo.
Having gone that far, I figured that I had to put some sort of lining on the inside of the cabin, so I sheeted the inside of the cabin with 1/64-inch plywood. I did this before sheeting the exterior of the fuselage and before installing the firewall. To fit it in smoothly, I had to do some trimming on a couple of the bulkheads. This step also meant that I had to install some of the wiring early.
A molded resin instrument panel was an option for the kit. It was detailed by gluing on instruments, painting knobs and switches, and adding colored pins for the engine-control levers. The bottom of the cockpit area was covered in 0.01 aluminum sheet to simulate the unpainted cockpit floor. The engine fuel lines were run under the raised center section of the cockpit floor.
A molded-resin instrument panel was an option for the kit. It was detailed by gluing on instruments, painting knobs and switches, and adding colored pins for the engine control levers.
Fuselage Porthole Window
The location for the porthole window was not shown on the plans, so careful measurements from the three-view drawing and photographs were required to locate them. A sheet of 1/16-inch plywood was laid on the fuselage with a cutout for the window, and then raised to allow for the sheeting thickness on the rest of the fuselage.
The glazing fit on the inner side of the plywood after painting. An internal frame holds the glazing in place. The frame was initially fabricated from wood and plastic, and then molded and cast in resin.
The battery hatch is used to access two of the servos. The hatch is held in place by two magnets. The hinges are hardware store brass hinges, but without hinge pins so the hatch can easily be removed and the paint won’t bind the hinge. The wing nuts were fabricated by soldering a #2 washer onto the head of a #2 screw, and then grinding off the part that did not look like a wing nut.
The battery hatch is used to access two of the servos.
Fuselage Panel Lines
The techniques used for the panel lines on the fuselage were the same as those used on the wing. The main challenge was marking the vertical lines for the panel lines and rivets at the bulkheads. The bulkhead locations were identified by data in the illustrated parts manual.
I mounted the fuselage vertically on my kitchen table (not enough head room in the shop) and used a trammel to mark the lines by rotating the fuselage.
The rivet template and the applicator tool used to make glue dots.
The cowls were detailed by adding small screws. Number 1 screws were a close match for the Dzus fasteners on the prototype. Number 2 screws were used to mount the cowl. A hinge was simulated on the rear cowl by gluing on a small styrene rod and notching it with a fine saw. Simulated cowl latches were made from aluminum sheet and mounted on a block of plywood in a cutout in the cowl.
Reinforcing Plates and Repair Patches
A number of reinforcing plates, maintenance access hatches, and repair patches were added to the fuselage after the panel lines. The materials used to reinforce the wing were also used here, including thin styrene sheet, aluminum foil tape, and small screws.
Doors, Door Hinges, Handles, and Latches
Each of the doors opens. Cast-resin scale hinges were provided in the kit and can be seen in the included photos. The door handles on each of the prototype doors are different. The latch mechanism and door handles were fabricated with bits of brass and brass tube. A piece of 3/32-inch square tubing transfers the door handle rotation through the door to the latch mechanism.
The doors are 1/8-inch light plywood, with a 1/4-inch balsa frame on the inside to enclose the latch mechanism and window glazing. A rabbet was routed around the inside edges of the door and the window openings to reduce the apparent thickness. The 0.03 ABS windows are set into the rabbet. The inside of the front door is skinned with 0.01 aluminum, and the inner skin on the rear doors is 1/64-inch plywood.
Each of the doors opens, and cast resin scale hinges were provided in the kit.
Passenger Door Steps
The front passenger door steps required careful measurements from the documentation. The steps were fabricated from brass tube soldered together in a jig. Some of the tubes were partially flattened in a vice to create the oval cross-section. They are mounted to the fuselage with brass #1 lag bolts screwed into a 1/4-inch dowel set into the fuselage.
Tail Surface Corrugations
The tail surface corrugations were made using the same technique that was used for the aileron and flap corrugations.
Landing Gear and Brake Detail
The landing gear has been modified to include the stub axle on the inside of the landing gear and the ski attachment loop. The axle was altered to have a threaded end so that a more scalelike acorn nut could be used to retain the wheel. This was done by shortening the end of the original 7/32-inch outside diameter landing gear wire, then sliding a 1/4-inch diameter brass tube over it. The tube was slotted roughly half of its length so that it extended to the inside. The inside part of the tube was reinforced over the slot by larger tubing soldered into place. A short length of threaded rod was soldered into the outer end of the 1/4-inch tube.
The wheels and hubs are from Glennis Aircraft. The brake disc is from 0.04-inch aluminum sheet. The brake caliper assembly on the Beaver sits mostly inside of the hub.
First, a prototype assembly was made from sheet styrene and brass screws, then a mold was made and the final parts were cast using a polyurethane casting compound. The cast parts are lighter and stronger than the prototype.
Internally, the landing gear fairing supplied in the kit contains an aluminum hinge plate and formed piano wire struts. These connect through a hinge pin to 1/4-inch aluminum plates built into the fuselage, and to a rubber shock-absorber system similar to what was used on the prototype.
Externally, the landing gear fairing was fitted with one disc step and one step bar. The disc step was fabricated from a hardware store picture hanger. Most Beavers have two disc steps, but the C-FFHB was different. Panel lines and rivets were added, as was a simulated weld bead.
The hydraulic hose was made from a combination of 1/16-inch music wire, 3/32-inch brass tube, 1/8-inch aluminum tube, insulation from 16-gauge wire, #2 x 1/4- inch brass lag bolts, and #1-72 brass nuts.
Antennae and Other Small Components
A number of small components are found on the prototype. Some of these were scaled from photographs and some measured on the prototype. The trim-tab rods on the rudder and elevators were made from rod, wire, and small ball joints, and are mounted on tabs made from .01-inch aluminum. There are two attachment plates on the bottom that are used when floats are fitted to the aircraft. These were created from .01-inch aluminum.
On the bottom of the fuselage is a raised section that allows access to the fuel drains and other fittings. This was fabricated from balsa and styrene sheet. The vent louvres were made using a heat-forming jig, which was used for the navigation lights.
A simulated maintenance access hatch was created using automotive aluminum foil tape.
A number of small drain pipes made from brass tube are found on the fuselage. The steps at the rear cabin doors were also assembled from brass tube—some of which were flattened to give a streamline shape. Soldering them together required making a special jig.
The removable tail cone has some unusual fastener retainers that were made from .01-inch aluminum and held in place with 1/32-inch aluminum rivets. There are four antennae: two radio, one emergency locator transmitter (ELT), and one trailing wire long-wave antenna. The trailing wire antenna runs from an insulator on the fuselage top to a hook on the fin, then to a clip on the wingtip.
The ELT antenna mount and insulator were turned from a brass rod. The insulator has a #0 rod that screws into the top for fastening the trailing antenna. The mounts for the two radio antennae were fabricated from brass tubing. The removable radio antennae are 0.047-inch music wire. The antennae are held in place by magnets inside of the structure. An access step on the front right of the fuselage and a handle on the top were built from brass tubing and sheeting.
The last items to be installed before applying the clear coat were small unpainted screws that retain the wingtips, wing root cuff, and fin fairing. These are small eyeglass screws. I ordered a box of 1,000 online for $4. They were screwed into 3/64-inch holes. I expect the paint to hold them in place.
The scale propeller was assembled from a cast resin kit of a Hamilton Standard constant speed propeller from Scale Specialties. It was painted with Alclad II paint, which is commonly used by plastic model builders to obtain a polished aluminum appearance.
The scale propeller was assembled from a cast resin kit of a Hamilton Standard constant-speed propeller from Scale Specialties.
Color and Painting
The model was painted with Klass Kote two-part epoxy white paint. The blue was custom mixed by Klass Kote to match the prototype’s paint. I took a number of paint chips from my local store with me when I visited the full-scale prototype in the museum. I had one that was a perfect match for the blue, and used that to match the model paint.
The blue trim on the fuselage cowl and fin were painted over the white. The wing also had a white base coat. A special jig was used to hold the wing and fuselage during painting so that they could be rotated, allowing all sides to be painted in one go. The dowel in the 2 x 4 was sized to fit into the wing tube.
A number of 1 x 2-inch wooden frames were built to hold the smaller parts during painting. The parts were held on the frames with wire.
The Norcanair graphic on the fuselage and the compass graphic on the fin were created by Cal-Grafx using photographs of the full-scale prototype’s markings. The fine yellow stripes were also prepared by Cal-Grafx.
I figured that it would be too challenging to mask the yellow stripes, paint them, and have them come out looking uniform and equally spaced from the blue. The yellow stripes created by Cal-Grafx were .08-inch wide and color matched to the prototype.
Each of the stripes had a clear strip .091-inch wide on one side. This was the spacing to the blue trim. It was an easy task to lay down the yellow stripes by running the edge of the clear on the edge of the blue. The vinyl stripe material was flexible enough and the adhesive strong enough to allow the trim to fold around small parts and in tight corners (e.g., over the door hinges).
The white call sign lettering was obtained from my local sign shop. The yellow ELT label was a decal created on my computer.
Weathering can add character and depth to a model, but it is easily overdone. The aircraft should look the same as the photos in your documentation. I was modeling an aircraft with years of experience and based on photos of it in service, not in the museum. I tried to make it look used, but not abused. I applied small amounts of weathering in nooks and crannies, and a few oil and exhaust stains on the underside of the airplane.
The visible part of the shiny aluminum exhaust pipe was treated to give it a dirty, heated, and stained appearance.
After all of the graphics, details, and weathering were complete, the entire model was given a coat of clear coat. The coat was a 50/50 mix of gloss and satin, which resulted in some gloss, but it wasn’t as shiny as fresh paint.