By the standards of the 1930s the S.81 was a heavy bomber. It could deliver a 2000Kg (4400lb) bombload. It was only the second series production bomber in history with that capability. However when it was loaded with the relevant 2000Kg bomb load fuel was only 820Kg. This restricted combat radius badly, but it was relevant to short range bombing missions over Spain. Outside Spain the S.M.81 was employed mostly as a medium bomber with a 1000Kg bombload allowing 1820Kg fuel in any variant. Consequently within FS9 I decided to load this heavy bomber for a medium bomber mission by default. To limit combat radius to simulate a heavy bomber mission we must use the FS9 fuel and payload menu to add 2200lbs (1000Kg) to the bombload and deduct 2200lbs (1000Kg) from the fuel load.
The Regia Aeronautica did not publish 'pilots notes' specifying operating norms. They published a technical manual with cautions and limits. Individual aircraft captains, or the squadron commander, created or promulgated their own 'local' operating instructions. These might correlate more closely to the length of the available runways, at the permanent operating base, than to the aircraft itself.
The handling notes supplied for use on screen in FS9 need to work from any runway, at any base, and the in flight 'norms' promulgated average out squadron variation. In real life all bar very late production examples had continuously variable flap which was extended and retracted via 72 cycles of a jack handle used to pump the flaps operated by pilot not flying. This was a slow process whose delay is replicated within FS9. Full flap takes 24 seconds to deploy.
In FS9 the flap settings are reduced to the three which approximate the maximum for take off, the minimum for landing, and full flap which was the norm for landing. From long runways any version of S.M.81 could depart without using flap and could land with only STAGE 2 flap deployed; provided Vref was increased to 130 KmIAS. Rotation in either case was based on getting the tail fully up and not related to a specified Vr. Vmc does not seem to have been much of an issue in this trimotor. Feel free to experiment with the various flap settings only if you are sufficiently experienced.
The performance tables which we see in the 'Boys Book of Wonderplanes' are true, but they are only propaganda. They often relate to propaganda flights during which the engines were revved beyond war emergency thrust. The original test reports survive for some of those 'tests'. The aircrew who flew these aircraft in combat could not afford to either overboost the engines, or over rev the engines beyond their specified limits. The handling notes supplied explain what the real war emergency and combat limits were. If you desire realism, you have to impose it upon yourselves. Realism cannot be scripted for you. The air file must supply C2 and RPM up to the highest limits for any circumstance. You must use the handling notes to determine the current limit of either thrust input. It may be one or the other that limits realistic performance.
Although I had access to the relevant technical manuals from mid 1936 most of the aircraft depicted in this release are shown at much later dates. It proved very difficult to establish how many S.M.81s were retrofitted with controllable pitch airscrews after 1936 and when. The only original test report available for the Gnome et Rhone version indicated that it had controllable pitch screws when tested. The other 1936 tests were undertaken with ground adjustable pitch screws locked in course pitch. The supplied flight dynamics are based on those government test reports. Consequently all versions bar the Gnome et Rhone version have fixed pitch screws in FS9. In thick air at low level the drag on the screws correctly precludes high rpm and restricts engine power. To obtain high performance from any version of the S.M.81 it is essential to climb to high altitude to spool the engines up in thin air. The optimum altitude depends on the variant.
Supercharged engines and (effectively) fixed pitch screws are a combination that was common from the mid 1920s to the early 1940s. Within FS9 these are usually misrepresented as constant speed screws. In the S.M.81 release that has been avoided. Consequently at some altitudes, and during some procedures, we must avoid overboosting the engines, but under other circumstances we must avoid over revving the engines. We must be more vigilant than when operating aircraft with constant speed screws, whose engine rotation, and whose turbine rotation, we can control with an RPM lever. See individual variants.
All versions of the S.M.81 had varieties of the Bristol Jupiter engine built under licence in Italy. The nine cylinder Bristol Pegasus built under licence by Piaggio and Alfa Romeo was more or less the seven cylinder Bristol Jupiter with two extra cylinders. The Gnome Rhone Mistral Major was more or less two Bristol Jupiters arranged as a two row radial with 14 cylinders. The S.M.81 was delivered with a bewildering array of engines built by many different Bristol licensees, but they have most of their parts in common and maintenance procedures were similar. However the 14 cylinder Mistral Major was obviously much heavier than the 9 cylinder Pegasus.
Engine start up and shut down procedures were conducted mostly by the flight engineer. All engine variants had compressed air starting. The flight engineer also managed fuel feed and transfers between the three engines and eight tanks. Hands on simulation of the flight engineer's role do not form part of this release. The main panel had only fuel pressure indicators. Fuel contents indicators for three of the eight real tanks are present on the engineers sub panel. They indicate total fuel % remaining.
The manifold pressure of Italian military engines is regulated using pressure measured in kilogrammes per square centimetre (Kg/cm^2) which is abbreviated to C or C2 (per square centimetre) on the relevant gauges, within this document, and in the supplied handling notes. This Italian form of metric measurement differs slightly from the German method of measuring manifold pressure in Ata (Atmospheres).
Maximum cruise speed is not a relevant concept. Any engine setting up to rated C2, or rated rpm, depending on the engine type and limits was used to battle headwinds, but using rated C2 or rated RPM squanders fuel rapidly unless used to battle headwinds.
The Savoia S.M.73 airliner and the S.M.81 bomber shared a common prototype. Both had very strong fixed landing gear and were optimised for use from short rough desert and bush runways within the Italian Empire in North and East Africa. The Regia Aeronautica planned to acquire the faster, more delicate, retractable gear S.M.79 for use in Europe. Production of S.M.81s for use in Europe would have been quite limited if the Spanish Civil War had not caused a sudden demand before the S.M.79 became available early in 1937.
The turrets and gondola of the S.M.81 are semi retractable. The turrets were deployed only if the S.M.81 was threatened by day fighters. They must be retracted for landing. There turret and gondola extension retraction controls are on the engineers sub panel in FS9. Profile drag will respond.
Longitudinal trim was via a variable incidence tailplane. That is replicated. The S.M.81 must be correctly trimmed for take off. This must be accomplished via the engineers sub panel and may require use of the FS tooltip.
The ailerons had only fixed tabs. The rudder had a servo tab. In other words the S.M.81 had power controls for the rudder only. An engine failure could not be trimmed out, but rudder forces were very low thanks to servo assistance. There was no rudder trim. There was no autopilot in real life either. In FS9 a typical late 1930s Italian autopilot of the type fitted in some / many S.73 airliners has been made available on a pop up within the pilot panel, but is not visible by default. A Lorenz Beam and co-located DME receiver is available in the same way. It is likely that some aircraft operating in the transport role were fitted with these during WW2. The LBA tutorial is within the Savoia Marchetti S.73 (V2) release. A pilot interpreted radio goniometer was standard in all varieties of S.M.81 and is visible by default; (again see tutorial within the S.73 (V2) release).
Delivery of the S.M.81 to the Regia Aeronautica predates delivery of the S.73 to Italian airlines. These bombers had older less advanced systems all round. The S.M.81 has two comparison compasses, but neither is a gyro compass. The lower barrel is the assigned heading. The upper barrel is just a wet magnetic compass. The S.M.81 has a single independent barrel gyro compass on the P1 panel. The S.M.81 was delivered without a deviation compass. We believe they were retrofitted to some and an Askania deviation compass is provided on the IFR and AP pop up sub panel. The assigned heading is dialled into all comparison compasses by PNF using the knob on the upper central master compass. How PNF deduced the heading to assign to PF is explained within the earlier S.73 (V2) release.
In common with earlier aircraft designed to operate in and above cloud the S.M.81 had two normal altimeters and two sensitive altimeters. The lower sensitive altimeter is used for instrument approaches and should then be reset to QFE for that purpose (see S.73 (V2) tutorials). The upper altimeter is always set to QNH.
The co-pilot had a complex integrated Blind Flying Unit called "complesso Biseo" which incorporated a low intertia magnetic compass (bussola statoscopica), a vertical VSI, a vertical ASI and the turn rate with slip gauge. This was a head down display (HDD) projected onto a screen. This complex instrument is simulated in the VC. A conventional turn and slip gauge is available within the IFR and AP pop up panel. The S.M.81 never had an AP in real life. It was very stable and did not really need one.
The earliest versions of the S.M.81 had Piaggio P.IX engines with powerful two speed superchargers driving four blade fixed pitch screws for use within and over Ethiopia, during and after the Italian invasion of that nation. That earliest (1935) version is absent from this release. All other confirmed versions are present and the flight dynamics represent their different performance envelopes and operating requirements when deployed in 1935 - 1936. Subsequent improvements to the performance envelope were limited to retrofitting controllable pitch screws to improve take off and climb performance.
This was the second version of the S.81. It was optimised for bombing strategic targets in Europe from medium level and was the version most frequently employed during the Spanish Civil War. Squadron deployment from late 1935. Later augmented by aircraft with more powerful AR126 engines, (q.v.), but not retired. These were however the first variants relegated to transport duties.
This variant had exceptionally low powered Pegasus engines. These aircraft were strictly for deployment in Europe, not Africa, but they were compatible with rough alpine runway operation. These engines are rated at 2300 RPM for war emergency, 2200 RPM in combat and only 2090 RPM for climbing and outside combat operations. We must throttle the engines accordingly throughout the flight. The resulting C2 will vary with the weather.
The superchargers are very powerful and can deliver war emergency power to 3500 metres. This makes the engines complicated to operate. We are allowed to use full throttle continuously for climb *provided we do not exceed 2090 RPM*. This limit whilst climbing applies to all types of operation. The higher the altitude, the thinner the air, the less the drag on the screws and the more the danger we will over rev the engines. Provided we climb at the mandated 190 KmIAS we will achieve a good rate of climb and we will not over rev the engines. We must be very precise in our IAS targeting in this aircraft during climb; else we will need to throttle the engines.
Once we enter cruise we have a C2 limit to observe as well as an RPM limit to observe. This is 0.9 C2 for tactical cruise which would include a combat paratrooping operation, but not ferrying, training or normal transport operations. For those operations we target C2 = 0.8. If we need to extend endurance during a combat operation we will not exceed 0.8 C2 or 2090 RPM whilst cruising and we might seek the altitude at which 0.8 C2 delivers 2090 rpm at the current weight in the current weather. Mountains, ice, etc., may require otherwise and cruising below 5000 metres squanders velocity to increase endurance at all relevant power settings.
Procedures for battling headwinds are explained in the Propliner Tutorial available from www.calclassic.com. In this aeroplane we would never exceed 2200 rpm when battling headwinds and when doing so we might seek the altitude at which 2200 RPM was full throttle. Our optimum cruising altitude is always 5000 metres (ISA weather and nil wind conditions). If we cruise at a different altitude we must still observe the same limits and suffer any cruising velocity penalty arising from cruising at an inefficient altitude.
In descent we will only exceed 2090 RPM if there is an urgent need and we will never exceed 2200 RPM unless there is an emergency. That will normally limit our rate and angle of descent; but we must also avoid exceeding a profile drag of 310 KmIAS since if we encounter turbulence we may suffer structural failure with greater profile drag already applied to the tail.
*************************************************************
Gnome et Rhone (Isotta Fraschini) GR14K Mistral Major engines
*************************************************************
This was the third version of the S.81 deployed from early 1936. By far the heaviest, and with much more fuel than other versions, it was based only in Libya from where its extra fuel allowed it to threaten both Tunis and Cairo. Most, perhaps all, had controllable pitch screws to improve take off and climb at high weights from and over the desert. This version was also the best suited to long range overload maritime patrol missions. Arguably the best version of all its location ensured that saw no combat until June 1940. After initial deliveries from France the engines were built under licence by Issotta Fraschini. The overload fuel for long range maritime patrol can be added only via the aircraft.cfg and only after removing all bombs via the FS9 payload menu.
The idea behind these 14 cylinder two row radials was to generate less power per cylinder to make overheating less of a problem and to allow the engines to have fewer operating restrictions. The heavy 14 cylinder GR14 engines could generate a lot of power continuously without using powerful turbines to boost the manifold pressure. This engine was impossible to over rev in level flight. Apart from an overriding 2390 RPM limit when diving it had only C2 restrictions and was much simpler to operate than the AR125. However this engine is easy to overboost. Unless we encounter a war emergency we must ensure that we do not apply more than 1.0 C2 after take off. The combat (rated) boost is 1.0 C2. We will use that setting to climb, or to battle headwinds, and we will not need to monitor RPM even if we decide to cruise climb at high IAS to make progress down range. However we must be careful not to squander fuel through excessive use of combat (rated) C2.
Probably because this version was much heavier, and destined to operate only from the Libyan desert, it seems to have been fitted with controllable pitch screws from delivery. FS9 does not support such screws. Within FS9 our virtual flight engineer will select fine pitch for take off and post take off climb. He will monitor RPM. Provided we do not allow RPM to exceed 2390 in fine pitch he will retain fine pitch, but as soon as the engines are in danger of being over revved our virtual flight engineer will select course pitch to protect them. We will see rpm suddenly decay. Our Vy climb target is 190 KmIAS and provided we do not exceed about 200 KmIAS, even in fine pitch, we should not over rev these easy to handle engines in any weather. Provided we handle the aircraft in accordance with the supplied handling notes we will achieve an excellent rate of climb using the fine pitch screws.
In real life the flight engineer could switch screw pitch back and forth. In FS9 our virtual engineer can only select fine pitch for take off and climb. Once he selects course pitch because we are threatening to over rev the engines we cannot reselect fine pitch in FS9.
Because the engine rpm limits are very relaxed in this aeroplane we must be more careful to avoid exceeding a profile drag of 310 KmIAS in descent since if we encounter turbulence we may suffer structural failure with greater profile drag already applied to the tail.
This was the fourth and lightest variant of S.M.81. Like the Gnome et Rhone variant it was relatively rare. More powerful than previous versions only at low level. Performance at high level was poor. Squadron service from late 1936, primarily as maritime patrol and anti shipping assets based in Eritrea and Somalia from where they monitored and threatened the vital shipping lanes exiting the southern end of the Suez Canal. Strategic bombing capability retained to threaten French Djibouti and British Aden, but this version needed to bomb from lower levels and was more vulnerable. These aircraft were also used for counter insurgency operations within Italian East Africa 1936-1940. During 1940 some were relegated to become the standard Regia Aeronautica IFR trainer, moving to Littorio airport (Urbe) near Rome for that purpose. The rest were destroyed by bombing or otherwise lost in action during 1940.
Like the AR125 the P.X requires a rated rpm technique. Only the war emergency and combat limits are higher. These engines are rated at 2475 RPM for war emergency, 2350 RPM in combat, but still only 2100 RPM for climbing, cruising, and outside combat operations. We must throttle the engines accordingly throughout the flight. The resulting C2 will vary with both weight and weather. These engines also have a potentially restrictive continuous C2 limit when climbing. They are optimised for low / medium altitude flight over the Red Sea.
In descent we will exceed 2350 RPM only if there is an emergency and we will never exceed 2475 RPM. Because the engine rpm limits are very relaxed in this aeroplane we must be careful to avoid exceeding a profile drag of 310 KmIAS in descent.
This was the fifth and final version of the S.81. Deployed from late 1936 it had the most powerful engines and the best cruise performance. It was optimised for use as a medium level bomber for use against government targets in Spain, but had a secondary anti shipping capability. Compared to the AR125, the AR126 has significantly higher TOGA and War Emergency ratings at significantly higher RPM and can depart shorter and higher runways. Due to the increase in available TOGA power full throttle climbing becomes forbidden and the engines must be throttled to 1.0 C2 for climb.
Originally for deployment in Spain, but subsequently deployed in Italy, Albania, Rhodes, Ukraine, Russia, Austria, Czechoslovakia and Germany. They were the fastest variants provided they were climbed to very high altitude where they were not restricted by their 2200 maximum continuous RPM limit. Maximum continuous boost ratings were hardly better than the earlier AR125 and the AR126 is essentially the same engine allowed to run at higher rpm with the same boost. However the AR126 engines were also better cowled which improved cruising speed at all levels, The AR126 engines are rated at 2400 RPM for war emergency and 2200 RPM at all other times, including routine transport use and training. It is easier to cruise climb with the AR126, versus the AR125, since our RPM limit becomes 2200 versus 2090. Depending on weight and weather 0.9 C2 may exceed 2200 RPM and it may be necessary to throttle the engines to 2200 during tactical cruise. They are nevertheless easier to operate than the AR125 since once we have set C2 it will not increase and we barely need to monitor RPM provided we comply with the C2 restrictions.
With AR126 engines our optimum cruising altitude is 5000 metres (ISA weather and nil wind conditions) with bombs aboard, but becomes 6000 metres both without bombs and for best cruising velocity using only economy power. If we cruise at a different altitude we must still observe the same limits and suffer any cruising velocity penalty arising from cruising at an inefficient altitude.
In descent we will exceed 2200 RPM only if there is an emergency and we will never exceed 2400 RPM.
**********
DEPLOYMENT
**********
These vintage era aircraft can only be understood properly if they are operated in the locations where they were based in real life.
Thirty-six S.M.81 bombers with Piaggio P.IX engines driving four blade fixed pitch screws deployed to Asmara, the capital of Eritrea, in December 1935 and immediately joined the tail end of the bombing campaign against Ethiopia. All subsequent S.M.81 bombers destined for service in Italian East Africa would be powered by later Piaggio P.X engines. Apart from Asmara and Addis Ababa the Piaggio engined S.M.81s were also based at Macalle (now called Mekele); Gura (now called Gurae), but we should use Axum in FS9; Assab; and Scenele (now called Chinile) but we must use Dire Dawa in FS9.
The S.M.81s powered by GR14K engines were based in Tripoli, Benghazi, and El Adem, (just south of Tobruk), all in Libya. El Adem is now called Gamel Abd El Nasser (by Microsoft). As Libya was overrun by the British Army in 1942-43 these aircraft retreated to Lampedusa, then Pantalleria, and finally to Palermo and Catania. None seem to have survived the allied invasion of Sicily.
In July 1936 a squadron of Regia Aeronautica S.M.81s with AR125 engines set off from their base in Cagliari for Nador in Spanish Morocco where most of the Spanish Army was based. Three crashed or made forced landings en route. On arrival the squadron commander realised that Spain had no access to military grade 87 Octane AVGAS. It was a bad start, but for two million pounds sterling, (equivalent to eight million 1936 US dollars), paid in cash, Franco had acquired nine examples of the only heavy bomber in the world produced outside the Soviet Union. Whats more it could operate from African bush strips. The first Italian military AVGAS tanker didnt dock in Spanish Morocco until August and combat operations from Morocco against Spain could not begin until it did.
Meanwhile the Italian aircrew who had managed to reach Spanish Morocco resigned from the Regia Aeronautica and joined the Spanish Foreign Legion, which now operated the nine surviving S.M.81s. Their first task was to escort the Armada which carried the Spanish Army from Africa to Spain, but soon after they were bombing Spain from their new base in Africa. Of course in reality this was the beginning of the Second World War, but English speaking authors, politicians and historians impose different nationalistic definitions to match the parochial experience of their own linguistic population.
After also operating from Melilla and Tetouan in Spanish Morocco the now Spanish S.81s moved to Seville and eventually to airfields nearer the front line, but Seville remained the maintenance base. Once losses up on the front line airfields mounted Spanish S.M.81s were progressively based in Palma (Majorca) bombing the Spanish east coast cities that were under democratic government control.
By mid November 1936 Soviet fighter opposition over Spain forced the S.M.81s to abandon daylight attacks for a while and switch to night bombing. At this point the Spanish decided to call the S.M.81 'the Bat' which in Spanish is 'Pipistrello'(the same in Italian). This Spanish name was later also adopted by Italian aircrew, but was never official.
About sixty five Alfa Romeo powered S.M.81s flew combat missions with the Spanish Nationalist Air Forces during the civil war, but by 1940 all forty survivors had been converted to transports. By then twenty were based in Vilanubla maintaining military communications across mainland Spain. The other twenty were based in Palma (Majorca), maintaining communication between the Balearic Islands and between Palma and Madrid via all the relevant mainland east coast airfields all of which were in fascist hands after the civil war.
During 1936-37 Piaggio X engined S.M.81s undertook pre-deployment training from Bresso, Vicenza, Naples, Bologna, Catania and Cagliari before moving to their combat bases in Italian East Africa where the main servicing facility for Piaggio engines was located, (at Harar Medar). All bar a handful of these Piaggio engined S.M.81s were lost as British Dominion forces overran Italian East Africa in 1940-41.
Several squadrons of S.M.81s, with different engine types, formed at Vicenza in turn before deploying to Africa. Oddly it seems that the only S.M.81 Stormo fully dedicated to maritime patrol and anti submarine warfare was based in or near Bologna for an extended period before deploying to Tirana and Valona (now called Vlora) in Albania.
During the 1930s a heavy bomber was defined as one that could lift a 2,000Kg bomb load (4400lbs). The first such bomber was the Tupolev TB-3 deployed by the Soviet Union from mid 1932. The second nation to deploy heavy bombers was Italy who deployed the Savoia S.M.81 in the spring of 1935. By December 1935 S.M.81s were flying intensive combat operations over some of the worst terrain imaginable from some of the worst airfields imaginable. A few weeks after the Regia Aeronautica deployed the S.M.81 the RAF deployed the truly awful Fairey Hendon I monoplane night bomber. The S.M.81 was 50% faster than the Hendon and carried almost three times the bomb load. The awful Hendon was barely a medium bomber.
The third nation to deploy heavy bombers was Spain, but of course these were S.M.81s transferred from the Regia Aeronautica from 1936 onwards. The fourth nation to deploy heavy bombers was France who deployed the Farman 222 in the Spring of 1937. These were augmented by the LeO 451 from the end of 1938. The fifth nation to deploy heavy bombers was Germany, but not until February 1938. The maximum bombload of the Heinkel He 111E-1 was also 2,000Kg. It was the first Heinkel able to carry a heavy bomb load. The sixth nation to deploy heavy bombers was Britain who did not manage to deploy the Wellington I (max bomb load 4500lbs) until October 1938. By then the S.M.81 heavy bombers of the Regia Aeronautica were being augmented by the superior Cant Z.1007 Alcione.
Only those six nations possessed heavy bombers before the 1940s. The seventh nation to deploy heavy bombers was the United States which did not deploy its first heavy bomber, the B-17B, until April 1940, five years behind Italy. Its maximum bomb load was 4800lbs, just 400lbs more than the S.M.81. By then Italy had deployed almost six hundred heavy bombers and they had flown many thousands of combat sorties. It is pointless to compare the S.M.81 to aircraft of a different decade. Aircraft from later decades are always superior.
Italy bided its time until French morale collapsed after the German invasion and then declared war on both Britain and France in June 1940. By then the Regia Aeronautica retained 397 S.M.81s on charge, but only 304 were still airworthy. 42 of those with P.X engines were with bomber squadrons in East Africa and about the same number with GR14 engines were in Libya. Just over 100 with AR126 engines were with bomber squadrons in Italy, Sardinia and Sicily. Some of those soon moved to Rhodes to threaten Cairo and the northern end of the Suez Canal. Just under 100 with AR125 engines had already been relegated to the transport squadrons. These were mostly based in Southern Italy and Sicily supplying Libya.
To cut a very long and very interesting story short Britain responded by moving forces into Kenya and then moving north invaded Italian Somaliland, Ethiopia and Eritrea in turn. Regia Aeronautica bombing attacks against Egypt from Eritrea, Libya and Rhodes began. By the middle of 1941 more and more S.M.81 bombers were being converted to transports for air supply duties. Some S.M.81s were used in paratroop training. Special forces combat operations were conducted by S.M.81 transports based in Tripoli. Others became glider tugs and were used to train glider crews in Italy, probably at Viterbo. The two S.M.81s allocated to Mussolini and the King of Italy at the end of 1936 were based in Rome, though the Centocelle airfield no longer exists, so we should probably use Urbe in FS9 to simulate S.M.81 armed VIP transport missions.
The S.M.81 bomber-transport always had a troop and cargo transport capability, but cabin space was occupied by defensive gun positions limiting the transport capability in the delivery configuration. As the primary role of the S.M.81 progressed from bombing to air mobile warfare the defensive armament was removed step by step, to free up valuable cabin space, until the S.M.81 looked more and more like its twin brother the S.73 airliner.
By this time we will mostly be sneaking backwards and forwards between Libya and Southern Italy with small urgent payloads flying only by night crawling slowly along at very low level under the lobes of the RAF radar stations on Malta which are directing Mosquito night fighters in attempts to intercept us. To increase our chances of survival we will fly in cloud and foul weather as much as possible. What was once proudly called the Pipistrello will increasingly be called the Lumaca (Slug).
By late 1942 almost all of the surviving S.M.81s had been converted to military transports, many disarmed and quite difficult to tell apart from a true S.73 airliner. S.73s and S.M.81s now served alongside one another in the same transport units. Disarmed S.M.81 ambulances increasingly evacuated Italian wounded from Libya to Lecce (by day) and as the Italian Army retreated further and further westwards, eventually from Tunis to Palermo or Viterbo.
During 1942 the 18 Stormi Transporti, based in Libya, flew 4,105 sorties totalling 10,860 flying hours carrying 28,613 troops and over two thousand tons of cargo. A transport Stormo typically had 24 aircraft so that's roughly one 2.66 hour sortie every other day per aircraft. We can see that the standard passenger load was still only seven or eight troops. By 1942 military grade AVGAS was in short supply in Libya.
From March 1941 the Italian Army became more and more reliant on the Deutsche Afrika Korps and the Luftwaffe for offensive operations in North Africa. Italy gradually owed more and more favours to Germany. So in the summer of 1941 Italian forces deployed to the Eastern Front to fight the Soviet Army. The Regia Aeronautica deployed S.M.81s to Bucharest and Stalino, (now called Donetsk), in January 1942. S.M.81 transports now maintained a military air bridge; Lecce - Tirana - Bucharest - Odessa - Donetsk
In February 1943 one of the two squadrons at Stalino fell back to Odessa and the other returned to Lecce. Odessa was abandoned in April 1943. I believe S.M.81s may have been flying some night bomber raids until that date. The S.M.81 had been combat ineffective against the radar equipped RAF since early 1941, but the Soviet Air Force had no more effective deterrent to night bombing than a flak barrage and the S.M.81 was no more vulnerable to flak than any other heavy night bomber. Most surviving S.M.81s now assembled in Palermo, first to evacuate the Italian Army from Tunis and then for the airlift to Lampedusa and Pantelleria. These were the last intensive air mobile operations by the S.M.81 in Regia Aeronautica service.
By the time that Italy surrendered to the allies in September 1943 only an half dozen were in good enough condition to later serve with the allied Italian co-belligerent air force. As far as I can tell they were still based mostly at Lecce. One S.M.81 transport was captured intact at Benghazi and then served with 112 Sqn RAF while they were based at Benghazi in 1942-1943.
On the Mediterranean front apart from Lecce the main Regia Aeronautica S.M.81 bases in Europe had been Bologna, Viterbo, Rhodes, (in the Dodecanese Islands), plus Tirana and Valona, (now called Vlora), both of which are in Albania. S.M.81s also flew high endurance maritime patrol and anti submarine patrol and convoy escort missions 1936-1942.
Aeronautica Nazionale Repubblicana S.M.81s in northern Italy, all transports not bombers by then, were seized by the Luftwaffe when Italy surrendered and thereafter operated in Luftwaffe markings (Transport-Gruppe 10 (Ital.)) with the Italian flag under the cockpit (Gruppo Aerotrasporti "Terracciano"). They were based at Orio al Serio (Bergamo). In March 1944 these moved briefly to Goslar (Germany), but were then used to supply the retreating German armies. I believe they were mostly based in Warsaw, Prague and Vienna in the early stages of the retreat before finally moving to Bautzen-Litten, near Dresda (August 1944). We should use Drutte (EDVS) instead in FS9 to represent a late WW2 Luftwaffe transport base. These must have been the last S.M.81s to fly combat missions. When simulating the operation of these transport aircraft in FS9 remember that they are STOL bush planes. They belong on airfields the size of Drutte.
Italy had attempted to sell the S.M.81 to the air forces of Austria, China, Germany, Uruguay and Venezuela during the 1930s, but apart from Germany none had any hope of acquiring military grade AVGAS from the then oil superpowers, (Britain, France, Holland, USA, USSR). They could only have purchased the earliest version and although many nations desired heavy bomber capability it was too lacking in performance compared to the latest airliners with American engines to attract any export orders. Germany decided to persevere with development of the He 111 until it could match the capability of the S.M.81, three years later.
We should remember at this point that the Ju52/3m was only a medium bomber with half the maximum bomb load of the S.M.81 and with pathetically weak defences. Although the S.M.79 medium bomber had an earlier designation it was in fact a later aircraft, also able to carry only half the bomb load of the S.M.81. The S.M.81 underwent torpedo bomber trials but the smaller S.M.79 was superior in that role and so operational S.M.81s were never converted to carry torpedoes even though they flew many anti shipping missions.
The bombs were loaded vertically into the bomb bay, nose down. They tumbled badly after release. All the bomb load was internal, which was particularly impressive in the mid 1930s. The S.M.81 could actually achieve the design cruise velocities in the supplied handling notes, with a full bomb load, provided the turrets were retracted. Heavy bombers that carried half, or all, of their bombs externally could not achieve their claimed cruising velocities in practice.
Any S.M.81 could carry 4 x 500Kg bombs, but use of bombs larger than 100Kg seems to have been rare. In practice the bomb bay had only sixteen tail lugs for 100Kg bombs. However when attacking built environment targets including dockside warehouses or hangars the balance of 2000Kg could be loaded as incendiaries and small anti personnel bombs, potentially with clockwork delay fuses to disrupt fire fighting. The S.M.81 could not deploy sea mines. This was a deficiency by later standards, but in 1935 no bomber could deploy sea mines.
The defensive armament was truly impressive. Both turrets really were hydraulic powered turrets, not just gun cupolas trained slowly and with difficulty by the muscles of the gunner. Both turrets had excellent fields of fire compared to the poor gun mountings in bombers like the Heinkel 111, and both had twin guns. The S.M.81 could also carry a single WW1 surplus Lewis gun on a Scarf Ring between the beam hatches. Some early examples may have had two Lewis guns on pintle mounts. The retractable ventral turret design was hardly bettered in the 1940s and when extended it created much less drag than equivalent installations of the 1930s.
The defensive positions were only extended and manned if a Savoia came under fighter attack. Four hydraulic fast training machine guns with an almost uninterrupted field of fire remained an impressive defensive capability for many years after 1935 and certainly put much later German bombers to shame. Later the twin 7.7mm guns in the original dorsal turret were sometimes replaced by a single 12.7mm in a new Lanciani turret more than doubling the firepower of the dorsal turret.
By the end of 1945 the only significant remaining operator of the S.M.81 military transport was the Spanish Air Force. By then it is likely that their aircraft had been re-engined with the Alfa Romeo 126. All had been relegated to transport duties six years earlier. They didnt last much longer. In common with most aircraft of this era there was no airscrew de-icing and no airframe de-icing of any kind. When simulating the operation of these aircraft in FS9 remember that the flaps installed on airliners and heavy bombers in this timeframe were very fragile. This is not an all metal wonder from Boeing or Douglas. The wing is just bits of dead fir trees stuck together with the sticky bits from a dead horse. We must treat it carefully or it will fall apart. It will start to fall apart of its own accord after about ten years anyway without any abuse from us.
The place names given in this text are those used by Microsoft in FS9 in their world/goto menu. If a named location has several airfields in the 21st century the smallest should be used to replicate the 1930s. In addition we should take off and land either side of any modern hard runway to allow the higher friction of the surrounding surface to be experienced correctly.
On screen and separate printable handling notes are supplied elsewhere in this package.
