Medevac Variant

Sikorsky CH-34 "Choctaw"

in 1:32 scale
by ModelArt

by Mark Johnson

Model photographs by Mark Johnson; Pima Air and Space Museum photographs by Saul Jacobs

HISTORY

The Sikorsky S-58/CH-34, first built in 1955, is a lengthened and more powerful version of the Sikorsky H-19 Chickasaw cargo helicopter. It can carry up to 16 troops or eight hospital litters, and it has also been configured as an assault helicopter with several different configurations of guns and rockets. It was used in the assault role by the USMC in Vietnam and by the US Army in many other roles. The S-58 was also built in Great Britain as the Wessex.

Power is provided by a single Curtis-Wright R-1820-84C "Cyclone" 1425 hp piston engine, installed in the nose. The engine drives the four bladed main rotor through a long driveshaft to the transmission located in a large housing behind the cockpit.

The Choctaw was a very successful design with over 1500 examples built during a ten-year construction run. It was used for many different missions and continues in service today. Some of the photos in this article show an executive transport Choctaw that was used by President Eisenhower and is currently being restored by the Pima Air and Space Museum, Tucson, AZ. These pictures, taken by Saul Jacobs, who volunteers as a docent for the museum, were provided for reference in the design of this model.

Other missions included general troop transport and utility, air assault, SAR, ASW and, as modeled here, medevac. The C-34/S-58 was also developed in the 1950s as a civilian passenger helicopter and some aircraft were converted to turbine power in the 1970s.

CHARACTERISTICS

THE MODEL

KIT DESCRIPTION

The ModelArt kit is currently available in three versions, US Army medevac in white, US Marine troop carrier in dark green, or Israeli Air Force in camouflage. In 1:32 scale this is a large and impressive model. The designer, Dr Emil Zarkov, has included a great deal of detail, including a fully detailed cockpit and interior. One especially intricate assembly is the main rotor, which is built up of 50 separate parts. Many of the parts are quite delicate, yet they fit together perfectly and the assembly is quite strong when completed.

The white color of the medevac version, featured in this review, is especially suited to card modeling since the cut edges don't show up against the white surfaces. The model builds beautifully, although it presents a challenge due to the high parts count, compound curvature, and high level of detail.

The kit comes nicely printed on semigloss heavy paper with a page of color photographs of the assembled model, plus 6 pages of diagrams. Also included is a sheet of clear plastic for the windows, with the outline printed on the plastic. Finally, there is a supply of cardboard for reinforcing components.

CONSTRUCTION

The instructions suggest that you build the model according to the part numbering sequence. I found this to work very well. One begins by laminating many of the framework parts with thick cardboard to improve the overall structural integrity of the model. I used thick white craft glue (commonly called "tacky glue") for the entire model. The instructions suggest a non-water-based glue and, although that would probably work better, I like to avoid the fumes from solvent based glues. The key with using white glue is to limit the water that is transferred to the paper. I've had good success by using the thick varieties sparingly, and pressing flat surfaces within a book while drying. Any full-page lamination must be pressed in a book and well weighted down for several days to get a good result.

The Fuselage frame assembled very easily, although there is an error on the central frame, part number 6. Beneath the floor, this part must be notched to allow it to join with the bulkhead, part number 3. Build the frame carefully, since the aircraft skin wraps around the frame and any error made here will make it difficult to get the skin on straight.

Add the cockpit and interior details next. The pilot and copilot seats are very simple assemblies but they look quite good when installed. The instrument panel, circuit breaker box, control sticks, and rudder pedals complete the cockpit.

Parts are provided to configure the interior in several ways. Since this is the medevac version, I chose to install two banks of stretchers and one short bank of troop seats. You could also fit a complete set of troop seats, or leave the interior open for cargo. The troop seats and stretcher assemblies are very detailed and delicate. They take a while to build but look great when installed inside the finished model. Don't forget to assemble and mount the fire extinguisher on the forward bulkhead. The diagrams don't show this, and it's easy to overlook (as I did).

The next step is to wrap the frame with the primary fuselage skin. Prepare the skin by cutting out the windows, then add the transparency material you want to use for simulated glass, pre-form the skin, and add the connecting strips. Carefully test the fit, because this is the most difficult step in the assembly. Be sure to form the skin by rounding the corners with a dowel before you even think about applying glue. The better you dry fit the part, the better the result will be. When ready, I glued the bottom first, centering the part carefully on the keel. When dry, I continued up the sides, and finished with the top.

The nose is a study in compound curves. It's also a testament to Dr. Zarkov's skill in computer aided design since it fits together perfectly. Each section is connected to the adjacent section with a connecting strip. The assembled nose is attached to the connecting strips previously applied to the main skin.

There are three Fuselage sections behind the main cabin. They are formed into cylinders, shaped with a series of bulkheads, and connected to one another with thin paper strips. I had a problem getting the glue to hold at the joints. I would recommend changing the thin paper connecting strips for cardstock to help give a better base for these joints. It's also important here to pre-form the sections because the bulkheads cannot do it alone.

Probably the most challenging part for me was the windscreen. I scored the bends and pre-folded them before cutting anything out. Shape and glue up the assembly before installing the glass. Because I haven't yet discovered a strong glue for paper-plastic joints, I substituted a very thin plastic for the kit plastic. The thin plastic conforms to the shape of the frame better and lets me get by with white glue. When the frame is ready, cut out each window and glue in place. When all the windows are done, glue the windscreen to the cockpit.

At this point all that is left are a few details, the two rotor assemblies, and the landing gear. The rotors are similar in construction and are built up from many small parts. I assembled the parts and then drilled a hole for the wire pivot shaft. A better approach would be to pre-drill each part before assembly. The diagrams do a good job of showing the order of the hub assembly parts, but not a very good job of showing the final assembly. If you follow the order, and carefully think it through, the highly detailed hubs turn out quite nicely and even rotate on a wire axle. The rotor blades are assembled in the conventional manner; just be sure to press them flat under pressure while drying to avoid warped blades. The tail rotor transmission is another study in compound curves but with a bit of encouragement, everything lines up quite well.

The very simple landing gear consists of a wishbone that contains a small wire axle and is attached to the bottom of the fuselage. A very distinctive hydraulic strut supports the wishbone. To assemble the strut, roll it without glue around progressively smaller diameter rods until you get the right cross section. Apply glue to complete and attach to the wishbone and the fuselage side. The tire/wheel assembly is laminated, sanded for contour, then painted tire black to finish. Drill a hole the same size as the wire axle and attach to the wishbone. The tail wheel assembly is also nicely detailed. Fold, shape and glue the parts, being sure to open up the cutout areas. Install the assembly in the cutout beneath the tail. Final details include the winch, windshield wipers, and rear view mirrors.

CONCLUSIONS

Overall, this model took about three weeks of spare time (approximately 25 hours). That's about average for a card model of this size and complexity. It is a very impressive model when finished, it was a pleasure to build, and I highly recommend it.

SUMMARY