SAVOIA-MARCHETTI SM.79

Alex Whittaker admires Ken Sheppard’s ex-ARTF cartoon scale Italian trimotor

The Savoia-Marchetti SM.79 Sparviero (Sparrowhawk) first flew in September 1934. It was a low-wing, triple-engine cantilever monoplane of wood and metal construction. Operated as a medium bomber it was easily recognisable by its distinct fuselage hump. Indeed, its crews, who generally seemed to like the aircraft, dubbed the design 'il gobbo maledetto', or damned hunchback.

It required a crew of five, or six in the bomber version. Conceived as a fast passenger transport, it was a very quick aeroplane and at one time held 26 speed records. The Fascist Italian Government quickly recognised the design’s military potential and for a time she became the fastest bomber in the world. The SM.79 saw active service in the Spanish Civil War and became the key bomber in the Italian Air Force.

There was also a torpedo bomber variant, which operated with some success against the Allies. Its wooden structure meant that if it ditched in the Mediterranean Sea it could stay afloat for about half an hour thus giving its crew ample time to evacuate. There was even a radio-controlled drone version.

No other WWII Italian bomber was built in such numbers and overall about 1300 of the type entered service. Both Yugoslavia and Romania bought examples. Examples remained in service in Italy until 1953.

THE MODEL
Although he is Editor Emeritus of Aviation Modeller International magazine, noted scale modeller Ken Sheppard is these days probably best known as organiser of the very popular ModelAir events at Old Warden. However, Ken has a bit of a penchant for SM.79s. After all he has built three! The first was an electric powered own design of about four-foot span. He then constructed a larger one, built from a greatly modified ARTF twin.

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Ken gives scale to his 100” (2.45m) span Savoia Marchetti SM.79.

Ken notes that both had high wing-loadings and quick arrival speeds. Indeed, one was lost in a tip-stall on the final turn onto a landing approach. At this point Ken decided that his third SM.79 should have a lower wing loading! This third SM.79, covered here, has its own interesting history, as Ken relates:

“Quite a few years ago I received a large kit to review, the Seagull Models Miles Sparrowhawk, a 30cc powered ARTF, spanning about 80. This flew very well for a couple of seasons until, as it was looking quite tatty and I needed the engine and radio for another project, it ended up stored in my shed. I had ear-marked it for a makeover sometime in the future.

Last year, carrying out an infrequent ‘clear out’ of the shed, the sadly neglected, but perfectly sound airframe came to the fore and the decision to ‘move it on’ or ‘do something with it’ was made. At the same time, I happened to find my copy of the Signal-Squadron Publications ‘In Action’ series for the S.79 in a pile of old mags. I have to say that I’m a great believer in co-incidences and thumbing through the book, the fact that the name Sparviero means Sparrowhawk and that I had a Sparrowhawk airframe, albeit the Miles variety, was too much of a co-incidence to ignore.

Getting out the tape measure and calculator, a few quick measurements and calculations gave me the idea that I could have my larger, lighter SM.79. It meant major surgery, but it would still be quicker that building from scratch – and it would give new life to the old, tatty ARTF...”

CLUBMAN SCALE
When I first saw Ken’s model, I really liked her quirky style. I’d have said she was Clubman Scale. At a push, perhaps even Character Scale. However, Ken prefers the term Cartoon Scale. That notwithstanding, there is no doubt his re-imagining does capture the character of the prototype. Ken’s SM-79 attracted many favourable comments at the early season scale meeting where I first saw her fly a few years ago. She looks very good in the air and just as pleasing on the ground.

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Ken calls her Cartoon Scale, but she is an attractive flying scale model.

Like all who saw her, I was fascinated at Ken’s highly creative recycling of an old ARTF airframe. Indeed, I suspect that most of us have such relics lurking in our shed. The model uses the ARTF wings (with tip extensions to increase the span), the tailplane (modified tips and new elevators) and the fuselage (narrowed and reshaped with profile-altering inserts). Ken then fabricated a completely new fin and rudder.

WINGS
The donor Seagull Sparrowhawk kit was a one-off pre-production model. It featured plug-in wing panels (the production kit featured a bolt-on wing), which means the model breaks down into three pieces for transportation.

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At 100” span this is not a small model. Note ailerons and the dummy flap line.

The joiner tube was replaced with a longer one to allow it to pass through the full width of the nacelles to take the landing loads.

MOTORS & BATTERY
Ken soon decided that electric power was the way to go. He chose three .60-sized out-runners. The three motors develop more than enough power whilst giving the necessary up front ‘weight’ to help balance the model at the correct Centre of Gravity.

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Trimotors are always fascinating.

Twin 6S 5000mAh LiPos connected in parallel are used to give a useful flight duration.

BELLY HATCHES
Two hatches in the belly allow access to the nylon wing retaining bolts and allow routing of the motor power cables forward to the fuselage nose, where the harness connectors are fitted. Ken’s good friend, Graham Iredale made up the harnesses to Ken’s specification.

NACELLES & RETRACTS
Getting the nacelles and retracts correct formed a significant part of the conversion, since the wing-mounted nacelles have to carry the main undercarriage. These comprise a pair of pneumatic and sprung oleo retracts.

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Ken's SM.79 has spring/air retracts in the nacelles.

CANOPY & COWLS
Ken intended to mould a canopy/top hatch from acetate but ended up carving one from blue foam and painting on the glazing. As Ken points out it is cartoon scale after all…

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The top front fuselage is quite a complex shape. Note the gun - there's another at the rear!

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Cowls were supplied by Vortex Vacforms.

FINISHING & DECALS
The model is covered in Solartex, then spray-painted using Tamiya Acrylic paints. Ken then sprayed a coat of satin fuel proofer to give a neat finish. Dirtying up was kept to a minimum, just a little ‘black finger’ application on the sides of the fuselage to highlight those fabric-covered stringers.

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Ken’s rendition of the tail. Note dual struts and the slim rudder.

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Roundels and cowl insignia use a variety of fasces symbols. Pyramid supplied the vinyls.

Pyramid Models supplied the decals at a very reasonable price, with a very quick turnaround.

FLYING NOTES
Ken told me that the first flight was a bit fraught. She was twitchy for a number of reasons, not least of which was swapping from Spektrum to Futaba transmitters. These use different ways of applying exponential, and the values applied were working the wrong way! Ken notes that pitch control was rather sensitive... In all, Ken did very well to complete the maiden flight without mishap. There were also additional issues with the thrust-lines, which he corrected.

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The model uses five channels and has retracts, but no flaps.

Ken remarks:

“It is a bomber after all, so aerobatics are not attempted, except for steeply banked turns, and figure of eights. It’s hard to appreciate how the model looks when you are flying it, but club members' comments have been very complimentary, so I’m happy with that.

I keep the power down for take-off; full power is far too excessive for scale acceleration and climb out, but it is useful to have it in reserve. I know some people will decry the use of electric, as there is no substitute for the sound of three IC engines on song, but for me it is the only practical, reliable solution. The lack of vibration allows the weight to be kept down and lighter models - bigger, lighter models - fly better!”

DATAFILE
Model Name: Savoia-Marchetti SM.79
Owned By: Ken Sheppard
Donor Kit: Seagull Sparrowhawk ARTF
Scale: 1/8 scale approx.
Span: 100” (2.45m)
Motors: 3 x 500kV outrunners
Battery: 2 x 6S 5000mAh Lipo
Functions: 5 inc. retracts, no flaps
Weight: 20lb (9kg) approx.

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