Savoia-Marchetti SM.81 Pipistrello

Savoia-Marchetti SM.81 Pipistrello

Company type	Aircraft model
Industry	Aviation, Military aircraft
Predecessor	Savoia-Marchetti SM.73
Founded	1935
Products	Bomber and transport aircraft

Template:Infobox aircraft

The Savoia-Marchetti SM.81 Pipistrello (Italian for bat) was the inaugural three-engine bomber and transport aircraft deployed by the Italian Regia Aeronautica. Debuting in 1935, it combined impressive speed, substantial armament, and extended operational range. This model demonstrated its effectiveness during conflicts such as the Second Italo-Abyssinian War and the Spanish Civil War. Although it became outdated as a frontline bomber by the later stages of World War II, the SM.81 remained one of the most versatile, dependable, and significant aircraft within the Regia Aeronautica from 1935 through 1944, adapting well to secondary roles across a variety of missions.

Design and development

Derived from the civilian SM.73 airliner, the SM.81 was a militarized adaptation featuring cantilever wings, three engines, and fixed landing gear. Its development was driven by the ambitions of Italo Balbo, an influential figure in the Fascist government (though later exiled to Libya by Benito Mussolini), who sought a rapid and capable aircraft to support Italy's extensive African colonies.

The wing design closely resembled that of the twin-fuselage S.55 and was identical to that of the S.73, while its fuselage was notably more straightforward. Approximately six months following the introduction of the SM.73, the prototype SM.81 (registration MM.20099) undertook its maiden flight on 8 February 1934 from Vergiate near Varese, piloted by test pilot Adriano Bacula. An initial order for 100 units was placed in 1935 and rapidly manufactured due to escalating international tensions and embargoes linked to the Ethiopian conflict. The earliest aircraft were assigned to 7 Wing stationed at Campo della Promessa airfield close to Lonate Pozzolo.

Although soon replaced as a frontline bomber, the SM.81’s spacious fuselage made it invaluable as a transport platform capable of carrying diverse cargoes. Except for its speed, it generally outperformed the SM.79 Sparviero in multirole applications.Template:Fix/category

Overall characteristics

The SM.81 was a sturdy, three-engine monoplane featuring a fixed tailwheel undercarriage, with the main wheels enclosed within large spats designed to minimize aerodynamic drag, and it accommodated a crew of six. Its construction combined materials: the fuselage framework was built from steel tubes, with the rear section covered in metal, while the remainder utilized wood and fabric coverings. The aircraft's relatively spacious fuselage, an uncommon trait for a bomber, ultimately influenced its adaptation as a transport plane. Due to the relatively modest power of its engines, the fuselage did not integrate smoothly with the nose-mounted engine, even less so than on the SM.79. Numerous windows allowed ample natural light inside, giving the impression of a passenger aircraft.

The wings were entirely wooden and supported by three spars to ensure structural integrity, while the semi-elliptical tail surfaces consisted of fabric-covered metal components. The pilot and co-pilot sat side-by-side within an enclosed cockpit, with separate compartments for the flight engineer and radio-operator/gunner positioned aft of the cockpit. The bomb bay was located behind the cockpit and included a passageway connecting the mid and rear sections of the fuselage, where three additional defensive stations were situated.

Positioned just below the cockpit in a semi-retractable gondola was the bombardier's station, which differed from that of the SM.79 by being larger and better situated to facilitate communication with other crew members; it also offered excellent visibility through glazed panels. Both this station and the cockpit featured escape hatches; however, routine ingress and egress were managed through doors located on the left side of the mid-fuselage and at the aft fuselage. The onboard equipment comprised an RA 350I radio transmitter, AR5 radio receiver, and occasionally a P63N radiocompass. Additional systems included an electrical generator, fire suppression apparatus, and an OMI 30 camera installed in the gunner’s nacelle.

Thanks to its large wing area and strong undercarriage, the aircraft was dependable and comfortable to pilot, capable of operating from various terrain types. It exhibited remarkable speed for its era relative to engine power, notably outperforming similar aircraft like the Junkers Ju 52. Although better armed than the SM.79, its increased drag combined with unchanged engine output resulted in reduced maximum speed, cruising velocity, and operational range. Protective armor was absent except for self-sealing fuel tanks.

Armament

The SM.81 carried six machine guns that provided substantial defensive firepower for an aircraft introduced in 1935. It featured two hydraulically powered retractable turrets—one dorsal turret positioned just behind the pilots’ seats and one ventral-aft turret—each equipped with 7.7 mm (0.303 in) Breda-SAFAT machine guns. Additionally, single 7.7 mm (.303 in) Lewis Guns were mounted to fire through side hatches. The turrets’ rotation was driven by a "Riva-Calzoni" hydraulic system while gun elevation was manually controlled; manual backup mechanisms were installed for both retraction and rotation functions. When retracted, only the upper portion of each turret remained visible, with gun barrels aligned vertically—one behind the other—to minimize drag and create an appearance reminiscent of extra antennae. Given its cruise speed near 270 km/h (170 mph) and fixed bulky undercarriage, aerodynamic improvements from turret retraction were modest.

Unlike typical ventral turrets where gunners occupied ball- or dustbin-shaped enclosures, space limitations required the ventral gunner to crouch inside the fuselage with his head lowered within the turret assembly. This configuration proved relatively ineffective—as was common with ventral turrets—and subsequent Savoia models omitted this feature altogether; however, Piaggio incorporated a dustbin-style turret accommodating a seated gunner on their P.108.

Each side of the fuselage housed one single-gun and one twin-gun mount. Initially outfitted with six 7.7 mm (.303 in) Vickers machine guns, these were later replaced by more reliable Breda models that fired at a slower rate but came with 500 rounds per weapon.

The bomb bay was divided into two compartments separated by a passage linking mid and rear fuselage sections and could carry various ordnance types totaling up to 2,000 kg (4,410 lb) over short distances. Individual bombs weighing as much as 500 kg (1,100 lb) could be stored either horizontally or vertically:

• 4 × 500 kg (1,100 lb) bombs (horizontally stored)
• 4 × 250 kg (550 lb) bombs (horizontally stored)
• 16 × 100 kg (220 lb) bombs (vertically stored), actual weight approximately 130 kg (287 lb)
• 28 × 50 kg (110 lb) bombs (true weight roughly 70–150 lb)
• 56 × smaller bombs weighing 31 kg (68 lb), 24 kg (53 lb), 20 kg (40 lb), or 15 kg (33 lb)
• 1,008 × 2 kg (4 lb) bombs (actual total weight near 1,700 kg/3,750 lb)
• Incendiary munitions

The bomb-release controls were situated on the right side within the bombardier’s compartment.

In comparison to its successor models—the SM.79 and even the SM.84—the SM.81 boasted superior defensive armament despite utilizing smaller caliber weapons but remained vulnerable against contemporary enemy fighters. Its wider fuselage also enabled it to carry a heavier bomb load than the SM.79.

Propulsion

Main article: Savoia-Marchetti SM.81 propulsion

The SM.81 was equipped with three engines, but unlike the Sparviero, it utilized a diverse array of powerplants during its production span:

• Alfa Romeo 125 RC.35, delivering 432–507 kW (580–680 hp). A total of 192 units were produced.
• Gnome-Rhône 14K, providing 485–746 kW (650–1,000 hp). Ninety-six were manufactured.
• Piaggio P.X R.C.15, rated at 501–522 kW (670–700 hp) – 48 built.
• Piaggio P.IX R.C.40, outputting 507 kW (680 hp) – 140 units constructed.
• Alfa Romeo 126 RC.34, with power ranging from 582–671 kW (780–900 hp), also installed in early SM.79 variants. Fifty-eight produced.

Additionally, a unique variant, the SM.81B, was developed featuring only two engines: two inline Isotta-Fraschini Asso XI units each rated at 627 kW (840 hp), combined with a sleek, glazed nose design. This model exhibited poorer performance compared to the three-engine versions and was not pursued further.

Fuel

Consistent with Italian multi-engine aircraft standards of the era, the SM.81 employed metal self-sealing fuel tanks crafted using materials from SEMAPE, a specialized manufacturer. The aircraft housed eight tanks: six within the central wing section (four tanks of 150 L/40 US gallon capacity and two large tanks of 1,140 L/301 US gal) and two tanks in the outer wings holding either 370 L (100 US gal) or, when fitted with Gnome-Rhône 14K engines, a combined total of 780 L/210 US galTemplate:Fix/category. This configuration resulted in an overall fuel volume between 3,620 and 4,400 L (960 to 1,160 US gal).

Operational history

Main article: Savoia-Marchetti SM.81 operational history

File:Savoia-Marchetti S.M.81.jpg

Savoia-Marchetti S.M. 81

The SM.81 made its combat debut during the Second Italo-Abyssinian War, demonstrating versatility by fulfilling roles as a bomber, transport, and reconnaissance aircraft. It also saw action in the Spanish Civil War under the Aviazione Legionaria and was among the initial aircraft dispatched by the fascist regimes during the airlift operation supporting Francisco Franco.

Although largely outdated by 1940 when Italy entered World War II, roughly 290 to 304 SM.81s remained active within the Regia Aeronautica. The first Italian planes engaged in East Africa were two SM.81s: on June 11, one conducted an attack on Port Sudan, while the other performed reconnaissance over the Red Sea. That night, three SM.81s launched a bombing raid on Aden—one turned back early, and one of the remaining two collided with terrain near Massawa during landing attempts. Simultaneously, another flight targeted Anglo-Rhodesian defenses in British Somaliland just before the critical Battle of Tug Argan, signaling a limited use as a tactical bomber.

Due to its slow speed and susceptibility to enemy fighter aircraft, daytime operations confined the SM.81 mainly to secondary roles such as transport duties. However, it proved effective as a nighttime bomber particularly in the North African theater. The aircraft also participated in anti-ship missions but achieved limited success.

By the time of the Italian armistice in 1943, most SM.81s had been retired from frontline service though some continued operating under both the Italian Social Republic and the Italian Co-Belligerent Air Force.

A number of units survived beyond World War II and served with the Aeronautica Militare Italiana, but all were phased out by 1950.

SM.81s deployed in Ethiopia bore distinctive markings for search and rescue missions. Their standard camouflage consisted of yellow, green, and brown tones, while an all-over dark olive green scheme was introduced later when their role shifted exclusively to transport tasks.

Variants

SM.81

A tri-motor aircraft serving as both a bomber and transport, with a total production of 535 units.

SM.81B

A single twin-engine experimental prototype constructed.

Operators

Template:Country data Republic of China

• Chinese Nationalist Air Force: In November 1936, six SM.81Bs were commissioned to be manufactured at the Sino-Italian National Aircraft Works (SINAW) located in Nanchang. Additionally, one unit was procured directly from Italy. This unit arrived in disassembled form at Hong Kong in October 1937 but could not be transported to China due to the oversized packing cases incompatible with rail transport. Two aircraft produced in Nanchang were delivered to the Air Force, while another completed model was destroyed during a bombing raid on the factory in December 1937. All these aircraft were lost during training accidents in February 1938 at Yichang.Template:Fix/category

Template:Country data Kingdom of Italy

• Regia Aeronautica
• Aviazione Legionaria operated 64 units
• Italian Co-Belligerent Air Force

Template:Country data Italian Social Republic

• Aeronautica Nazionale Repubblicana

Template:ITA

• Aeronautica Militare Italiana utilized this model after World War II.

Template:Country data Spanish State

• Spanish Air Force

Template:Country data Yugoslavia

• Yugoslav Air Force operated several SM.81 aircraft during the 1930s through 1945; some are exhibited at the Aeronautics Museum in BelgradeTemplate:Fix/category

Bibliography

• Angelucci, Enzo and Paolo Matricardi. World Aircraft: World War II, Volume I (Sampson Low Guides). Maidenhead, UK: Sampson Low, 1978. ISBN 0-562-00096-8.
• Apostolo, Giorgio. The Savoia Marchetti S.M.81 (Aircraft in Profile number 146). Leatherhead, Surrey, UK: Profile Publications Ltd.,1967.
• Lembo, Daniele, SIAI 81 Pipistrello, Aerei nella Storia, n.33.
• Passingham, Malcolm. "Savoia-Marchetti SM81". Aircraft Illustrated, May 1977, Vol 10 No 5. pp. 182–187.
• Mondey, David. The Hamlyn Concise Guide to Axis Aircraft of World War II. Chancellor Press, 2002.
• Sutherland, Jon & Diane Canwell: Air War East Africa 1940–41 The RAF versus the Italian Air Force. Barnsley (South Yorkshire) Pen and Sword Aviation, 2009. ISBN 978-1-84415-816-4.