Il Savoia-Marchetti S.M.84

Il Savoia-Marchetti S.M.84 è stato un bombardiere medio/aerosilurante trimotore prodotto dall'azienda italiana Savoia-Marchetti nei primi anni quaranta ed impiegato dalla Regia Aeronautica durante la seconda guerra mondiale. Progettato come sostituto dell'ormai superato S.M.79 Sparviero, si rivelò deludente sotto molti aspetti non riuscendo ad eguagliare il suo predecessore.

Originariamente la designazione di Savoia-Marchetti S.M.84 era stata data ad un bimotore da trasporto passeggeri che volò nell'ottobre 1935. 

A questo prototipo fu però preferito il concorrente Fiat G.18 e l'S.84 non fu mai costruito in serie, lasciando così libera la numerazione.

Storia

Sviluppo

Progettato dall'ing. Marchetti, manteneva l'impostazione generale del suo predecessore, con fusoliera di sezione rettangolare e configurazione trimotore, ma in comune con l'S.M.79 aveva le sole semiali e il carrello principale. Presentava impennaggio bideriva, per consentire una maggiore stabilità in volo ed un miglior campo di tiro alla mitragliatrice dorsale, ora sistemata in una torretta Caproni-Lanciani Delta E girevole a 360° in luogo dell'arma a limitato brandeggio presente nella caratteristica gobba dorsale dell'S.M.79.

Disponeva inoltre di un vano bombe più spazioso che consentiva di alloggiare gli ordigni orizzontalmente, al contrario dei precedenti modelli Savoia-Marchetti dove le bombe erano stivate verticalmente. Quest'ultima soluzione dava grave pregiudizio alla precisione del lancio, in quanto il flusso d'aria dovuto al moto dell'aereo investiva lateralmente le bombe in uscita dalla stiva, disperdendole su un'area più estesa. L'apposita gondola per il puntatore, obbligatoria a causa della formula trimotore che impediva l'uso della parte frontale della fusoliera per disporvi tale postazione, era di forma più aerodinamica rispetto a quella del vecchio S.M.79.

Nonostante le notevoli migliorie strutturali ed aerodinamiche, che lo rendevano un apparecchio decisamente più moderno del precedente, e l'adozione di più potenti Piaggio P.XI RC.40 da 1.000 CV il nuovo aereo si rivelò poco più che mediocre, con manovrabilità nettamente inferiore al suo predecessore e velocità di poco superiore.

La manovrabilità, in particolare, era un requisito fondamentale per un aerosilurante perché indispensabile nelle brusche manovre evasive che si mettevano in atto dopo il lancio del siluro per sfuggire al tiro contraereo delle navi.

Anche le mitragliatrici di bordo, di tipo Scotti, non erano ottimali in quanto facilmente soggette ad inceppamenti a differenza delle assai più robuste ed affidabili Breda-SAFAT. L'S.M.79 si rivelò quindi insostituibile e continuò ad essere prodotto anche dopo l'assegnazione del primo ordine di 246 esemplari del nuovo S.M. 84. Ad ogni modo queste macchine prestarono onestamente servizio dal 1941 fino all'armistizio, sia in veste di bombardieri che di aerosiluranti.

Impiego operativo

Italia e Mediterraneo

A partire dal secondo anno di guerra gli S.M.84 cominciarono ad affiancare nei reparti da bombardamento della Regia Aeronautica il CANT Z.1007bis, il Fiat B.R.20 ed anche l'S.M.79 che nel contempo passava ai reparti siluranti. Il 41º Gruppo Bombardamento Terrestre fu il primo reparto a ricevere gli S.M.84 nel febbraio del 1941 ed il 28 giugno successivo nasce la 282ª Squadriglia con 4 esemplari aerosiluranti al comando del Capitano Marino Marini (aviatore).

Il principale teatro operativo dell'S.M.84 fu il Mar Mediterraneo. L'unico successo come aerosilurante sembra essere quello vantato dagli aerei del 36º Stormo aerosiluranti che il 27 settembre 1941 riuscirono a silurare la corazzata HMS Nelson, danneggiandola gravemente e mettendola fuori combattimento per parecchi mesi. Nel corso dell'azione lo stormo subì gravi perdite, con sei degli undici velivoli impiegati risultati abbattuti. Tra essi anche quello del comandante di stormo, colonnello Riccardo Hellmuth Seidl, probabilmente abbattuto dal fuoco contraereo della corazzata Prince of Wales e dell'incrociatore Sheffield .

Il 14 giugno 1942, 15 S.M.84 del 36º Stormo, decollati dalla Sardegna, attaccarono il convoglio proveniente da Gibilterra e diretto a Malta (operazione Harpoon), ma sei aerosiluranti non ritornarono alle basi.

Dall'autunno del 1942 gli aerei furono progressivamente tolti dall'aerosiluramento e passati al bombardamento. Gli esemplari ancora efficienti nel 1943 vennero relegati ad impieghi secondari. All'ordine originale di 246 esemplari se ne aggiunsero altri per un totale di 309 effettivamente consegnati alla Regia Aeronautica in varie versioni.

Slovacchia

Un lotto di 6 esemplari tra S.M.84 e S.M.84bis vennero forniti all'aeronautica slovacca, in un periodo successivo al 1942.

Versioni

• S.M.84 prima versione avviata alla produzione in serie. Equipaggiata con motori Piaggio P.XI RC.40 radiali a 14 cilindri raffreddati ad aria da 1.000 CV.
• S.M.84bis versione dotata di ala modificata con diedro positivo e altre migliorie alla cabina di pilotaggio, agli scarichi dei motori e al sistema di sgancio dei siluri.
• S.M.84ter versione con ala maggiorata e motori Piaggio P.XII RC.35 radiali a 18 cilindri raffreddati ad aria da 1.500 CV al decollo e 1.350 CV a 3.500 metri di quota. Prodotta in un solo esemplare.

Su alcuni esemplari furono installati motori Alfa Romeo 128 RC.18 da 860 CV ciascuno.

Utilizzatori

• Italia - Regia Aeronautica - Aeronautica Cobelligerante Italiana - sei esemplari inquadrati nella 241ª Squadriglia del 132º Gruppo Trasporti istituito dopo la firma dell'armistizio di Cassibile con unità in carico al 98º Gruppo del 43º Stormo Bombardamento Terrestre.
• Repubblica Sociale Italiana - Aeronautica Nazionale Repubblicana - acquisì almeno 10 esemplari dei quali uno risulta essere operativo in carico ad una Squadriglia speciale da trasporto.
• Italia - Aeronautica Militare - operò con l'unico esemplare di S.M.84ter fino all'ottobre 1946, quando l'aereo andò perso per incidente.
• Slovacchia - Slovenské vzdušné zbrane.

ENGLISH

The Savoia-Marchetti SM.84, not to be confused with the Savoia-Marchetti S.84 airliner prototype, was an Italian bomber aircraft of World War II. It was designed by Savoia-Marchetti as a replacement for its successful SM.79, and shared its three-engine layout. Despite entering service with the Regia Aeronautica in 1941, it was retired from service before the SM.79 and never fully replaced it.

Development

Development of an aircraft to replace the SM.79 started in 1939, with Savoia-Marchetti choosing to produce an improved development of the SM.79, using the same wing as its predecessor, but with a new fuselage and more powerful engines. The first prototype flew on 5 June 1940, just 5 days before Italy's entry into World War II.

It was hoped to replace the SM.79s in service, which were fast, but obsolescent, and yet to be adapted as torpedo bombers. The main improvement was the adoption of new and more powerful engines, giving a total output of 2,237 kW (3,000 hp). The machine was put into series production at the end of 1940.

Design

Basically it was an enhanced SM.79, with more modern solutions and systems It shared the basic design of a three-engine mixed construction monoplane as the SM.79. Wood was used for the wings, supported by three spars. Steel tubing was used as a skeleton for the fuselage, covered by metal (forward), fabric and wood. The new fuselage housed a crew of five to six, with the pilots sitting side-by-side. Behind them there were a radio-operator and flight engineer. There was a large windscreen and eight windows in the fuselage.

The armour was much improved compared to the almost nonexistent protection fitted to the SM.79. It was said there was a total of 700 kg (1,540 lb) fitted, but it is unclear if this also included the self-sealing fuel tanks, bullet-proofed up to 12.7 mm (.50 in) rounds. One noticeable difference was the twin tail, which gave a better field of fire to the dorsal gun, and helped to cope with the greater power and weight compared to the SM.79.

Armament was similar to the Cant Z.1007, rather than the SM.79. There was a dorsal Caproni-Lanciani Delta turret, with a 12.7 mm (.50 in) Scotti machine gun, and 350 rounds. Another Scotti was in the ventral gondola. Other two Scotti were in the flanks with six 120-round belts. It was a theoretical improvement, though Scotti machine guns, even with a slightly higher rate of fire, were much less reliable than the Breda. Another disadvantage was the inability of the turret to fire directly forward, through the propeller's blades, so the aircraft had no defence from frontal attacks.

The bomb bay was in the middle of the fuselage. Horizontally mounted, the aircraft could carry two 500 kg (1,100 lb), three 250 kg (550 lb), 10 100 kg (220 lb), or 10 50 kg (110 lb) bombs. Outside the fuselage it was possible to mount two 500 kg (1,102 lb) or 800 kg (1,760 lb) bombs, or two torpedoes, or multiple smaller bombs. Generally, the aircraft carried only one torpedo or around 1,000 kg (2,200 lb) of bombs. The aiming apparatus was a Jozza U3, fitted in the bombardier's nacelle, just below the cockpit. It was retractable when not in use, to reduce drag.

An OMI camera was fitted in the fuselage, while in the tail section it was possible to mount one of three different cameras, like the AGR.90 or 91.

Three Piaggio P.XI RC.40 engines, giving 746 kW (1,000 hp) at 4,000 m (13,120 ft) were fitted. There were 16 self-sealing fuel tanks inside the wing and the fuselage, six for the central engine (1,070 L/283 US gal) and five for each wing engine (1,095 L/289 US gal). Total fuel load was 3,260 L (860 US gal), which was less, despite the more powerful engines, than previous Italian bombers. It was possible, however, to mount another three fuel tanks: two of 415 L (110 US gal) in the fuselage, and one of 2,500 L (661 US gal) in the bomb-bay.

With these engines, at full load the SM.84 was capable of:

• 400 km/h (250 mph) at 1,000 m (3,280 ft).
• 418 km/h (260 mph) at 2,000 m (6,560 ft).
• 437 km/h (272 mph) at 3,000 m (9,840 ft).
• 456 km/h (283 mph) at 4,000 m (13,120 ft).
• 467 km/h (290 mph) at 5,000 m (16,400 ft).
• 450 km/h (280 mph) at 6,000 m (19,690 ft).

Climb rates to:

• 1,000 m (3,280 ft) in 2 min 32 sec.
• 2,000 m (6,560 ft) in 5 min 25 sec.
• 3,000 m (9,840 ft) in 8 min 2 sec.
• 4,000 m (13,120 ft) in 10 min 54 sec.
• 5,000 m (16,400 ft) in 14 min 48 sec.
• 6,000 m (19,690 ft) in 19 min 18 sec.

The maximum practical ceiling was 8,200 m (26,900 ft). At 5,500 m (18,050 ft) and 397 km/h (247 mph), it had 5 hour 17 minutes endurance, and a range of 2,040 km (1,270 mi). As was expected, the performance of the SM.84 was superior to the SM.79.

Operational history

The first unit to operate the aircraft was 12° Stormo (Wing), 41° Gruppo (Group), on 2 February 1941. Based at Rodi, the first actions of this Group were not successful, and two aircraft landed in Turkey being lost (their crews later returned to Rodi).

36° Wing (108 and 109 Gr) received its SM.84s on 7 May 1941, and was based at Decimomannu airbase, Sardinia, from September 1941. On 27 September 1941, 12 aircraft of 36° Wing took off to attack a British convoy to Malta (Operation Halberd). One aircraft turned back after developing a mechanical fault, but the remainder pressed on with their attack. The first group, led by Arduino Buri, attacked the British ships and Buri managed to torpedo HMS Nelson, putting her out of action for six months. Of the first section, one aircraft was shot down, and the second section had two aircraft shot down out of three. When Seidl went in with his five aircraft, he was shot down together with another two. While the damage to Nelson was a success, the only one of this type that Italian torpedo bombers obtained, it was paid for by the loss of six aircraft, and almost all their crews, more than thirty men. The next day a merchant ship, Empire Pelican, was sunk by SM.79s with only one loss. The rest of the convoy reached Malta with their supplies.

After these losses, 36° Wing continued in its task of attacking enemy ships and sank the merchant ship Empire Defender in November, and 9 SM.84s badly damaged HMS Penelope on 9 April 1942. 282° Squadriglia was also involved in such missions, with some success.

7° Wing (4 and 5 Gruppos), based in Sicily, used SM.84s to bomb Malta in July 1941. In mid-October 1941, 32° Wing were equipped with SM.84s, one group of torpedo bombers and the other of bombers, to best optimize the attack against ships. This Wing took part in attacks on the Allied landings of Operation Torch, but by the end of December the unit had lost 20 aircraft and was retired from operations.

In June 1942, 14 torpedo bombers of 36° Wing and nine bombers of 4° Gruppo attacked the Malta convoy of Operation Harpoon, with at least two losses to Spitfires, and one downed by Anti-aircraft fire.

During Operation Pedestal in August 1942, 10 SM.84s used special Motobomba circling torpedoes to attack the convoy, losing two aircraft to enemy fighters. Aircraft of 32° and 36° Wing also attacked the convoy. The heavy German and Italian attacks, including those by SM.82s resulting in only five of the fourteen ships of the convoy reaching Malta, however their supplies were fundamental to saving the garrison, after the almost total failure of the previous operation.

While other groups were still receiving the aircraft, 36° and 7° Wing had stopped flying it by October 1942, while 32° went in action against North African targets. It lost 20 aircraft and returned in Apulia to regroup in December 1942. Soon 38° Gr had the new SM.84 Bis (early 1943), this last version was delivered to 8° Stormo (27° and 28° Gruppos). The decline had already started. The use of the aircraft with 8° Stormo to resupply troops in North Africa was a failure: despite having a far higher speed than the SM.82, the useful payload of the SM.84 was too small. The aircraft was gradually phased out, replaced by the Cant Z.1007, and even the SM.79. By 10 July 1943 43° Wing, flying from Gioia del Colle, in Apulia, was the only unit still flying the SM.84.

In September 1943, despite the almost extinction of bombers units, there were still 150 SM.84s in available, with over 100 serviceable. Almost all of these were captured by the Germans, though they were rarely used. Some were sent to the Slovenské vzdušné zbrane, and 10 remained with RSI's Aeronautica Nazionale Repubblicana, but were not used. Seven were used by the Italian Co-Belligerent Air Force as transports. Shortly after the end of the war, the aircraft was phased out of service.

Overall, SM.84 was a failed design (Francesco Pricolo called it a 'wrong aircraft', while Ettore Muti complained in 1941 about its awful handling and take off). It was never liked by its crews and never capable of replacing the SM.79. When the final version of the Sparviero, the SM.79 bis, became available, the SM.84 was withdrawn. In the bomber role it was inferior to the CANT.1007 ter, especially at altitude (the SM.84 was almost impossible to fly above 5,000 m).

Torpedo-bombers were required to be agile and fast in order to engage their targets and many designs experienced problems with higher weights and wing loading than they were designed for. The SM.84 was far heavier than the SM.79 and when the final version the SM.79bis became available, it was preferred to the SM.84. The SM.79bis, with improved engines was still lighter than the SM.84 and a better aircraft (with lower wing loading and better power-to weight ratio) for the role.

Another critical report about SM.84 came from the 43° Stormo B.T. command, in an official document. It reports how this bomber wing performed its task, starting with bombing missions from Gioia del Colle on 13 July 1943. The 41° Stormo commander complained the very small attack force was not enough to saturate the enemy's strong defences, even by night; the small number of pilots trained for night operations and thus the small number of sorties and the very poor performance of the SM.84.

Variants

• S.84bis - With several modifications, but not a substantial evolution.
• S.84ter - A single aircraft, completed in 1944, fitted with 1,119 kW (1,500 hp) Piaggio P.XII engines, capable of speeds over 500 km/h (310 mph). Destroyed by fire during a landing accident in 1946.

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