Savoia-Marchetti SM.81

Infobox Aircraft
name=Savoia-Marchetti SM.81


caption=Savoia Marchetti SM.81 in action (escorted by Fiat CR.32 fighters)
type=Bomber and transport aircraft
manufacturer=Savoia-Marchetti
designer=
first flight=1934
introduced=1935
retired=1950
status=
primary user=Regia Aeronautica
more users=Spanish Air Force
Aeronautica Militare Italiana
produced=
number built=534
unit cost=
developed from=Savoia-Marchetti S.73
variants with their own articles=

The Savoia-Marchetti SM.81 "Pipistrello" (Italian: bat) was a three-engined bomber/transport aircraft serving in the Italian Regia Aeronautica during World War II. Despite being too slow to remain competitive as a bomber, it was one of the most flexible, reliable and important aircraft of the Regia Aeronautica from 1935 to 1944, and adapted to second line duties in performing a wide range of tasks.

Design and development

The SM.81 was a militarised version of Savoia-Marchetti's earlier SM.73 airliner, having cantilevered wings, three engines and a fixed undercarriage. The origins of this version were in pursuit of the interests of Italo Balbo, a brilliant exponent of the Fascist regime (but nevertheless "exiled" in Libya by Mussolini), who required a fast and efficient aircraft that was capable of serving the vast Italian colonies in Africa.

The SM.81 had wings that were roughly similar to those of the double-fuselage SM.55, but had a much simpler fuselage. Around 6 months after the SM.73s first appearance, the SM.81 prototype (MM.20099) first flew from Vergiate, near Varese, on 8 February 1935, controlled by test pilot Adriano Bacula. The first serie, ordered in 1935, was for 100 aircraft and was quickly put into production as a result of the international crisis and the embargo caused by the war in Ethiopia. The first examples were sent to 7 Wing, Lonate Pozzolo.

Although it was quickly superseded as a first line bomber, the SM.81 continued to serve as a transport aircraft by virtue of its wide fuselage, which allowed it to accommodate a wide range of armament. Apart from its speed, it was generally superior to the SM.79 "Sparviero" as a bomber and multirole aircraft.Fact|date=September 2007

Overall characteristics

The SM.81 was a robust, three-engined monoplane, with large aerodynamically-shaped fixed main undercarriage gear, and had a crew of five. The aircraft was of mixed construction: the fuselage had a framework of steel tubes with a metallic-covered aft portion, while the rest was wood- and fabric-covered. It had a relatively large fuselage, an unnecessary characteristic for a bomber, which determined its future as a transport aircraft. Since the engines were quite small, the fuselage did not blend well with the nose engine, even less so than the SM.79. Many windows were present to provide the fuselage interior with daylight, giving the impression that it was a passenger aircraft.

The all-wooden wings had three spars to provide the necessary support, whereas the semi-elliptical tail surfaces were fabric-covered metal. The cockpit had several engine- and the flight instruments: three oil-temperature gauges (one for each engine), three pressure gauges , two rev. counters, a 1,000 m altimeter, an 8,000 m altimeter, a climb-meter, compass, clock, and five other sundry indicators, accommodated in three panels. The pilot and co-pilot were seated side-by-side with the radio-operator/gunner behind. The bomb bay was behind the cockpit, together with a passage which linked the mid and aft fuselage, where there were three further defensive positions.

The bombardier's position was located just below the cockpit, and differed with that of the SM.79, being both larger and in a location which was more favourable for communicating with the crew, and provided excellent visibility thanks to the glazed panel. Both this position and the cockpit had escape hatches, but for normal entry and exit there was a door in the left, mid-fuselage, and one in the aft fuselage. Equipment included an RA 350I radio-transmitter, AR5 radio-receiver, and a P63N radiocompass (not always fitted), while other systems comprised an electrical generator, fire extinguishing system, and an OMI 30 camera (in the gunner's nacelle).

The aircraft, having a large wing and robust undercarriage was reliable and pleasant to fly, and could operate from all types of terrain. It was surprisingly fast for its time and given the power of its engines, especially compared to the similar Ju-52. It was better armed than SM.79s, but the increased drag combined with the same engine power reduced the maximum and cruise speeds, as well as the range. No armour was fitted, except for the self-sealing fuel tanks.

Armament

The SM.81 was equipped with ten x 7.7 mm Breda-SAFAT machine guns, providing a heavy defensive complement of arms for a 1935 aircraft. Two powered retractable turrets, one dorsal (just behind the pilot's seats) and one ventral-aft, were each fitted with two machine guns and an external aiming reticle. The turrets were rotated by a "Riva-Calzoni" hydraulic system while the gun's elevation was manual, and manual back-up mechanisms were provided for both the retracting and rotating systems. Once retracted, only the upper part of the turret was visible, with the gun barrels positioned vertically, one aft of the other to reduce drag, and gave the impression that the aircraft had additional antennae. Given the SM.81's cruise speed of around 270 km and the presence of a massive fixed undercarriage, the aerodynamic gain was relatively small.

The ventral turret was operated in a different fashion to those fitted to other aircraft where the gunner occupied the ball- or dustbin-shaped structure; instead, due to lack of space, the gunner crouched in the fuselage with his head down inside the turret. This proved to be not very effective as were most ventral turrets,Fact|date=September 2007 and they were not fitted to further Savoias, although Piaggio fitted a dustbin-style turret accommodating the gunner to their P.108.

Both flanks were covered by one single and one twin gun installation. Initially six Vickers machine guns were fitted, but later replaced by reliable, if not very fast-firing models made by Breda together with 500 rounds of ammunition for each gun.

The SM.81's bomb bay was divided into two parts with a passage linking aft and mid fuselage between, and could accommodate a wide range of ordnance up to 500 kg individually, arranged either horizontally or vertically:

*4 x 500 kg (stored horizontally)
*4 x 250 kg (ditto)
*16 x 100 kg (stored vertically, as all the smaller ones), true weight around 130 kg
*28 x 50 kg (true weight, around 70 kg)
*56 x 31 kg, 24 kg, 20 kg, or 15 kg
*1,008 x 2 kg (true weight, around 1,700 kg.)
*Incendiary bombs
*Some examples, two torpedoes

The bomb-release mechanism was located on the right side of the bombardier's position.

The SM.81's defensive armament was better than its successor, the SM.79, and even the SM.84's, but still insufficient when faced with modern enemy fighter opposition. It was also capable of carrying a greater bombload than the SM.79, due to its wide fuselage.

Propulsion

The SM.81 had a three-engine configuration, but different from the "Sparviero", it was fitted with a wide range of engines throughout its production:
*Alfa Romeo 125 RC.35, 580 hp (or 680, depending on source) at take-off, 650 at 3,500 m.(1,740-1,950 hp total)
*Gnome-Rhône 14K, 650 hp at take-off, 740 at 3,000 m.(1,950-2,220 hp total)
*Piaggio P.X RC.15, 670 hp at take-off, 700 at 1,500 m.(2,010-2,100 hp total)
*Piaggio P.XI RC.40 (possible), 780 hp at take-off (2,340-? hp total)
*Alfa Romeo 126 RC.34, 680 hp at take-off, 750 at 3,400 m.(2,040-2,250 hp total), also fitted to early versions of the SM.79.

This wide range of engines drove 3.4 or 3.5 m diameter three-bladed propellers having Duralumin blades on steel hubs. Two 1,140 litre and four 150 litre self-sealing fuel tanks were located in the central wing, with a further two 370 litre tanks (or 780 litre when Gnome-Rhône 14K engines were fitted) in the outer wings, providing a total capacity of 3,620 or 4,400 litres.

Operational history

The SM.81 first saw combat during the Second Italo-Abyssinian War, where it showed itself to be versatile serving as a bomber, transport and reconnaissance aircraft. SM.81s also fought in the Spanish Civil War with the "Aviazione Legionaria" and were among the first aircraft sent by the fascist powers to aid Francisco Franco.

Despite their obsolescence, by 1940, when Italy became involved in the Second World War, more than 300 (290-304 depending on source) SM.81s were in service with the "Regia Aeronautica". Its low speed and vulnerability to fighter aircraft meant that during daytime, it was restricted to second line duties, finding use as a transport. At night the SM.81 was an effective bomber, particularly in the North African theatre. Anti-ship actions were also carried out, but without significant success.

Most SM.81s were withdrawn by the time of the Italian armistice of 1943, though some remained in service for both the Italian Social Republic and the Italian Co-Belligerent Air Force.

Several examples survived the war and went on to serve with the "Aeronautica Militare Italiana", but by 1950 these had all been retired.

SM.81s serving in Ethiopia had the "white avorium" markings applied to distinguish them in SAR missions. The normal camouflage pattern was yellow, green and brown mimetic. The all-over dark olive green scheme was introduced later, when the aircraft were used only in transport missions.

Variants

;SM.81: Three-engined bomber, transport aircraft, 535 built.;SM.81B: Experimental twin-engined prototype, one built.

Operators

;China as ROC
*Chinese Nationalist Air Force received three aircraft, all were lost in training accidents in February 1938 at Yichang.;flag|Italy|1861:
*"Regia Aeronautica"
*Italian Co-Belligerent Air Force
*"Aeronautica Militare Italiana" operated this type postwar.;flagicon|Italy Italian Social Republic
*"Aeronautica Nazionale Repubblicana";flagicon|Spain|1939 Spain
*Spanish Air Force

pecifications (Savoia-Marchetti SM.81)

aircraft specifications

plane or copter?=plane
jet or prop?=prop

ref=

crew=6
length main=18.3 m
length alt=58 ft 5 in
span main=24 m
span alt=78 ft 9 in
height main=4.3 m
height alt=14 ft 7 in
area main=92.2 m²
area alt=1,001 ft²
empty weight main=6,800 kg (AR.125 engines)
empty weight alt=13,900 lb
loaded weight main=9,300 kg
loaded weight alt=19,000 lb
max takeoff weight main=10,505 kg
max takeoff weight alt=20,500 lb

more general=
engine (prop)=Piaggio P.X RC.15 (or Alfa Romeo 125 RC.35, 126 RC.34 or Gnome-Rhône 14K)
type of prop=radial engines
number of props=3
power main=522 kW
power alt=670 hp
max speed main=320-347 km/h
max speed alt=211 mph
range main=2,000 km ferry range, 430 km with 2,000 kg and 640 km endurance with the same load, max practical combat range 1,500 km.
range alt=1,240 mi
ceiling main=7,000 m
ceiling alt=23,000 ft
climb rate main=
climb rate alt=
loading main=101 kg/m²
loading alt=
power/mass main=4.9 hp/kg
power/mass alt=

more performance=Performance when fitted with Alfa Romeo 125 engines:

*Maximum speed 340 km/h at 4,000 m
*Cruise speed 260 km/h
*Minimum speed 110 km/h.

Climb to:
*1,000 m (3,280 ft) in 4 min 15 s
*3,000 m (9,840 ft) in 11 min 48 s
*5,000 m (16,400 ft) in 20 min 36 s
armament=
*6x 7.7 mm Breda-SAFAT machine guns
*Up to 2,000 kg (4,415 lb) of bombs

ee also

aircontent
related=
SM.79 Sparviero

similar aircraft=
Junkers Ju 52

sequence=

see also=
lists=

References

* 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.
* Mondey, David. "The Hamlyn Concise Guide to Axis Aircraft of World War II". Chancellor Press, 2002.

External links

* [http://www.ipmsstockholm.org/magazine/2004/05/stuff_eng_davies_sm81.htm S.81]
* [http://bunker.altervista.org/wwsm81.html S.81 specs ]
* [http://avia.russian.ee/air/italy/savoia_s-81.php S.81 Avia.ru]
* [http://www.aerei-italiani.net/SchedeT/aereosm81.html Datasheet about S.81]
* [http://en.wikipedia.org/w/index.php?title=Savoia-Marchetti_SM.81&oldid=155451937| Complete S.81 page version]