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Sierra Scale's 1/48 Curtiss–Wright CW-21B Demon

By Bob Swift

History

For those airframes that evolved to classic stature during WWII, there are an equal or greater number that can only be considered as mediocre, also-rans. The CW-21B, more or less, fits this description, but like so much of the first line Allied equipment at the outbreak of hostilities, especially in the Far East, it was there, it was available, and for better or worse, that’s all there was.

Design work on a lightweight interceptor fighter based on the CW-19R two seat, general purpose aircraft was initiated by the St. Louis Airplane Division of the Curtiss-Wright Corp. in 1938. Known as the CW-21, Demon, it first flew in 1939. The CW-21 was an all-metal aircraft that featured main gear which retracted aft into thewing under-surfaces and were covered by protruding split fairings - the tail wheel was not retractable. Armament consisted of two machine guns firing through the propeller arc, these could be two .30’s, two .50’s, or one of each weapon. The initial order came from the Chinese for three completed airframes, tools and drawings for license production in China, and thirty-two sets of component parts.

Curtiss was later approached by the Dutch expressing an interest in a modified version of the fighter for deployment to the Netherlands East Indies Army Air Force. In 1940, an order for twenty-four CW-21B aircraft was placed in 1940. It was modified with greater fuel capacity, main gear that retracted inboard into the fuselage, a semi-retractable tail wheel, and the provision for four machine guns of mixed caliber, two .30 and two .50 weapons firing through the propeller. A 1000 horsepower Wright Cyclone R-1820-G5 nine-cylinder radial engine provided power.

On Dec. 8, 1941 the Netherlands declared war on Japan. At this time the CW-21Bs were based at Andir on Java with seventeen aircraft on strength. Not much happened until Feb 3, 1942, when Japanese operations began in the East Indies, and the A6Ms appeared. The Zero’s 20mm cannon made short work of the CW-21B, and within two days, only five Demons remained operational.

Modeling the CW-21B

The kit is packaged in a sturdy corrugated box with a line-drawn label on the cover, nothing fancy. Inside, the white molded sheets were carefully wrapped in bubble-wrap with all lesser parts contained in small zip-locked bags. The plastic molding is done in .040" white styrene sheets of high quality, later discovering that this material is just soft enough to be very workable. Close examination of the surface revealed the cleanest molding of this type I have ever seen. Parts layout was well done, with generous space allowed for parts removal and pieces of blank stock to use if needed. Surface detail was excellent and very even overall. The wingspan of this kit hits a scale 35 ft. on the nose.

Cockpit and other small components are on a fret of injected molded resin. Detail isvery good, but it suffers from a common problem found with low-pressure molding, lots of flash! Care is required in removal and cleaning of these parts. A note on the instruction sheet advises that the auxiliary control panel, which fits below the main panel, is too large and needs to be reduced along its long dimension by a considerable amount in order to fit correctly.

Two canopies are supplied, which is a nice touch, considering that this is always a potential problem area with vacuformed clear parts. The material is crystal clear and frame segments are well defined.

White metal parts are provided from Aeroclub and include rudder pedals, control column, main gear struts, propeller, engine, tail wheel and pitot tube. No exhaust collector ring, or exhaust stacks are provided and a note explains that these were molded incorrectly and pulled from the kit. Overall these parts are fairly well done. Another note on the instruction sheet requires that the rudder pedals be cut down for use with this kit, since they were cast for a different model. The control column and linkage is nicely done. A good bit of clean up was required on these parts to remove mold lines, etc.

Markings on this aircraft are fairly uncomplicated, and a small decal sheet from Microscale is provided.

Parts Preparation

After all the vacuform parts were separated, they got a bath in mild detergent to remove mold release agent and skin oil. Lots of sanding follows. On a kit this size,parts are small enough that a standard clipboard with sheets of 400 grit wet-or-dry is adequate for the job. Where possible, a sanding line was drawn on edges as a guide using a black felt tip marker. All trailing edges were sanded down to as thin a profile as possible. I actually could have gone further with this, but I had concerns about distortion once glue was applied in these areas. Frequent dry fitting of parts is essential. Another bath and we’re ready for the assembly process.

Moving to the metal castings, I found that they cleaned up well with a file and a small wire brush in the Dremel, set to low speed. The propeller needed the most attention. While sanding brought it down to the proper thickness, many pits still remained. Using a nitrocellulose based auto-body filler, I applied a generous coating on both sides of the blades, then sanded with 800 grit wet-or-dry. I hand-painted what needed it next, then put the parts back in the little bags for later.

I separated and cleaned the cast resin parts next. These include the cockpit sidewalls, floor, control panels, air intake, and prop spinner. There is lots of flash to overcome and this requires patience.

Assembly

Starting with the fuselage halves, I added small fish-plates every half inch to one side, cut from .010 styrene sheet to provide alignment and bridge the gap between sides. I allowed these to dry overnight, then tacked the two pieces together with liquid glue, making small adjustments to alignment before it dried. Given the very skinny rear portion of this plane, the whole fuselage has a very flimsy attitude about it. Fortunately, the fuselage is wide open and accessible from top and bottom. I mixed small batches of 5 min. epoxy and reinforced all seams from the inside. The vertical tail joint portion is really delicate - a large well exists here. I added a small spruce block to the bottom to use as a reinforced tail wheel mount and filled this completely with 24 hour epoxy. Care must be taken with accelerated adhesives of most kinds, especially epoxies, as the cross-linking reaction is exothermic, and when a large amount is confined in a small area, enough heat is generated to actually melt things. A slower acting epoxy is in order for these cases.

I glued all tail surfaces together and used putty on the seams. Take care to dry fit the vertical tail to the fuselage, the filets are critical. The tail was then joined to the fuselage and filled when dry.

Two bulkheads are provided: the front bulkhead has a molded boss to for the engine mount, while the other is the rear cockpit bulkhead to which the seat and floor are attached. Dry fitting these pieces revealed that both were a full 1/32" too small around the edge, or a total of 1/16". New bulkheads were cut from the scrap kit sheet. The original front bulkhead was centered and glued to the new one so the engine mount could be used. Cockpit side plates were glued in, then the floor/ rear bulkhead, and finally, the control panel subassembly. The bottom of this construction was firmly anchored to the fuselage sides with scrap plastic and epoxy.

The wheel well molding was trimmed for a snug fit, centered and glued into the lower wing with epoxy. Mounting blocks were added to this piece for the main gear struts. After measuring carefully, two tapered wing spars were added to reinforce the wing. I used strips of 1/4"x 1/16" spruce for this, any wood other than balsa will do.

Pieces of 18 gauge copper wire were glued into the horizontal tail surfaces as spars, offset from each other slightly, and protruding about ¼". Holes were drilled in the appropriate places in the fuselage and the horizontal stabs were glued in place.

There is a triangular fairing that joins the lower wing and rear fuselage. The instructions say to fix this piece to the lower wing, then join the assembly to the fuselage. I just couldn’t get this to work as the alignment would always be off enough to look bad at one end or the other. I finally gave up and glued these in separately. While it made more work with filling/sanding, it looked better when finished.

The upper wing halves were placed on a sheet of bond paper and the compound curve of the inboard edge was carefully transferred, using a drafting pencil lead, to the paper for each segment. A ½" strip was cut, slightly larger than the width of the wing segment and the tracing line trimmed carefully. These strips were wrapped around the top of each about 1/16" in from the edge and fixed with masking tape at the ends. The curve was traced onto the wing surface, and removing the paper, each segment was carefully cut with a new blade and the material removed. Light sanding smoothed the edges and dry fitting showed the joint was almost a perfect fit to the fuselage.

Painting

All interior openings were sealed, except the wheel wells, and two light coats of solvent based flat white applied. Lightly sanding with 800 grit paper after each coat took care of surface irregularities. When dry, fuselage stripes were masked off and the next color prepared for spraying. The color scheme on this aircraft was olive drab 41, and medium green 42. At first I thought the under-surfaces were left natural metal, but found two references that stated this was actually a coat of aluminum lacquer, and included the wheel wells. That simplified things quite a bit. The under-surface was given two coats of Model Master Non-Buffing Aluminum. The upper-surface color join lines were soft edged, the under-surface to upper-surface was a hard join line. The canopy was covered inside with masking tape and then sprayed overall with two coats of olive drab.

Decals

Markings for this aircraft were not complicated, national markings under the wings and again on the fuselage. The aircraft numbers are white on the sides, with the name "HERMANS" on both sides, just forward of the cockpit. On the fuselage, the small orange and black triangles are supposed to go down over a narrow white band, but the Microscale decals are too thin to hide the underlying camouflage and white band. I measured the orange area carefully and cut two stencils in bond paper. I secured them with small pieces of masking tape. Sealed off both sides of the rear fuselage with Parafilm and mounted the small tip to the airbrush. I sprayed two light coats of MM Insignia White. I then matched the orange with Poly S colors and sprayed two light coats after the white was completely dry. It turned out just fine. After everything had dried for a few days and any residue from glue and setting solution removed, the work was sealed with a 2:1 mix of Poly S matte satin coating.

Finishing Touches

I added hydraulic brake lines made from .006" Monel wire, and ring and bead sight from Fotocut. The ring sight hangs down from the arched portion of the canopy in front of the pilot. Next, the engine was drilled out to accept the prop shaft. Exhaust stacks were fabricated from 1/16" aluminum tubing, shaped to hang down from the cowling, painted with burnt steel paint, glued to a strip of scrap, and epoxied into place. Gun barrels for the machine guns were added to the upper decking and, even though not too visible, between engine cylinders at the two and ten o’clock positions using micro tubing liberated from the trash at work.

Summary

Cost of the kit is relative to what is happening in today’s market, and given the quality, the $27.95 was not outlandish. The time required to build the kit was about a week longer than I usually take on a model of this size. While the problems were never insurmountable, those that did develop were more a matter of my own lack of experience with this type of kit than with inherent flaws. Overall I am very pleased with the results when I consider how long it has been since I did the last vacuform kit.