Sem Model 1/72 SIAI-Marchetti SM.73
Transport
by Riccardo Orlandi


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The SIAI-Marchetti company was famous, especially during World War II, for a series of engine aircraft they started building in the 1930s. The first of these planes to make its appearance was a civil transport plane, the 73, which made its debut in 1934. This aircraft laid the foundation of a construction formula that proved sound for many years and resulted in some exceptionally fine planes. Some of the 73s were requisitioned by the Italian air force and served all through the war as troop transports. They were remarkably long-lived and tough aircraft.

The prototype took to the air for the first time on June 4, 1934. A triple-engine low-wing monoplane, this aircraft had a wood-and-metal skeleton and fabric-and-plywood skin. This first plane had a row of windows down both sides of the fuselage. The propellers were wood, four-blade for the central engine and two-blade for the side engines. The production model had a different arrangement of windows, and all the engines had three-blade metal propellers. The tail and rudder were also modified. The first engines were 600 hp Gnome Rhone Mistral 9K radials, and they were also installed in the first five production models, whose delivery to Sabena, the Belgian airline, began in 1935. Later a variety of engines were installed in the SM.73, including the 700hp Piaggio Stella X.RC, the 770 hp Wright Cyclone GR-1820, the 750 hp Alfa Romeo 126 RC, and the 615hp Waiter Pegasus II M2. All the variant models were outstanding in performance and cargo capacity. Some planes carried up to eighteen passengers and a five-man crew.


The SM.73 was a great commercial success. The first five planes, consigned to Sabena, flew the London-Paris-Brussels-Hamburg-Copenhagen-Malmo route, the line that connected Brussels with Lille and Ostend, and the London-Ostend run. The Italian Ala Littoria company bough about twenty SM.73s in various models, equipped withPiaggio, AIfa, Romeo, and Wright Cyclone engines. Ala Littoria flew the planes along the main routes of Europe, North Africa, and East Africa. The Avio Linee Italiane took six SM.73s. Three aircraft were sold to CSA, the Czechoslovakian airline, in 1937, and two more soon afterward. These were the only planes equipped with Waiter Pegasus II M2 engines. In 1937 seven SM.73s were built under licence in Belgium for Sabena, which used these aircraft on its toughest runs, on the route from Brussels to Elisabethville in what was then the Belgian Congo. These were modified SM. 73s that carried only eight passengers instead of the standard eighteen. This flight took almost two days: 44 hours flying time.











Construction

Since I was a boy (decades ago) I had been dreaming to build an SM 73, commercial predecessor of the better known SM 81 Bat bomber. When the Italian manufacturer SEM Model released a specific conversion set I realized it was time for me to make my old dream come real.

This is all you need: A Supermodel (or Italeri, itís the same plastic) kit to supply you with wings and landing gear, a conversion set for fuselage, engines and fin and some documentation.




I started with the resin fuselage: the quality of the parts is extremely high and only a really minimum preliminary work is required. Little will be visible once the two valves are glued together so no need to spend time in overdetailing. As I decided to open the access hatch on the port side I replicated the internal structure and the floor a little bit longer. The rear side of the instrument panel has to be detailed as it will be visible through the front glasses.


Painted the interior in Verde Anticorrosione I built up the assembly; the entire process took no more than eight hours.


The most complex phase was the wings-fuselage junction. Here I operated differently from the instructions in order to get a stronger connection:
First of all I glued the plastic upper half of the wings to the resin fuselage, then 4 steel spikes were added using the blessed internal plastic lip and eventually the lower halves were put in place. A limited use of water based putty is required to fill some gaps.


Then the cowlings: not so many SM 73 were built but they were powered by a number of different engines with different cowlings, so itís necessary to refer to pictures do determine which one was used in the machine you want to represent. In my case neither those available in SM 81 kit nor those supplied by SEM were usable, so I decided to use the three of a wrecked Airfix SM 79 that have a perfect diameter and are only marginally longer.


And now itís time for painting. First of all a primer, than a coat of white to uniform the shade, tail cross and fuselage band masked and we can start.


I usually use Gunze aqueous colours but this time I opted for the Italian Mr Kit acrylic paints as this manufacturer has the only realistic Bianco Avorio (Ivory white) in the market, needed to paint all lower surfaces. These colours are difficult to manage and the only way to make them controllable is to use Future floor wax to dilute but final results are great.

Upper surfaces received a coat of Giallo Mimetico with wide spots of Verde Mimetico and Bruno Mimetico while the rings on the cowlings are in Giallo Cromo. The decals come from the sheet supplied by SEM and are very good. Weathering products and water based filters of the Italian manufacturer True Earth were used before the final coat of mat paint that made this job come to an end.


I created a little diorama that also sees a FIAT 621 truck of Polish origin (First to Fight kit) and some figures of the Italian manufacturer Waterloo.


This was a very satisfactory build that gave me the opportunity of using an old kit (if you want to reproduce an SM 81 the recent Italeri historic upgrade box is a much better choice) and getting a replica of a little known but nevertheless fascinating Italian airplane of the 30s. I have already bought a second SEM conversion, as I am going, sooner or later, to build a plane of the Italian national airline ďAla LittoriaĒ whose insignia are produced by the Italian manufacturer Tauro Model.

Technical Specifications

Aircraft: SIAI-Marchetti SM.73
Manufacturer: SIAI-Marchetti
Type: Civil Transport
Year: 1934
Engine: Three Alfa Romeo 126 RC 34, 9-cylinder R radial, air-cooled, 750 hp each
Wingspan: 78 ft 9 in (24.00 m)
Length: 57 ft 3 in (17.44 m)
Height: 15 ft 1 in (4.59m)
Weight: 23,800 lb (10,800 kg)
Cruising speed:174 mph (280 km/h)
Ceiling: 23,000 ft (7,000 m)
Range: 620 mile (1,000 km)
Crew: 4-5
Passengers: 18

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June, 2018
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