Although the current release relates only to the Savoia S.73 airliner it will be followed in due course by a release featuring the S.73 airliners twin brother the S.M.81 heavy bomber. Their development and deployment history is so closely related that this text explains the history of both types.
It would be a shame to treat the Savoia Marchetti S.73 and its twin brother the S.M.81 bomber as just another two FS aircraft. They are worth studying in some detail. There is much that can be learned. These vintage era aircraft can only be appreciated and understood if they are operated in the locations where they were based in real life and in context; so let's begin with the historical context.
As the nineteenth century progressed to the twentieth the Turkish (Ottoman) Empire was in steep decline. All the European Empires wanted to grab a slice. France seized Tunisia, Algeria and half of Morocco. Spain grabbed the other half. Italy seized Libya carrying out the first ever air combat operations with aeroplanes in the process.
Britain seized Egypt, the Sudan, Eritrea and most of Somalia, but France moved quickly to seize the only deep water port in Somalia known as Djibouti. Britain and France built the Suez Canal linking the Mediterranean to the Red Sea and the Indian Ocean. Surrounded by all this mostly British occupied territory lay the Coptic Christian nation of Ethiopia which had never been a Turkish Islamic province. Italy attempted to invade Ethiopia in 1896 but was defeated. Ethiopia was flourishing, as the demand for ivory grew and grew. By the end of 1912 the Imperial European powers had seized all of north and east Africa, save for Ethiopia. Some of these new colonies had valuable resources and some had none. Most had dreadful communications links and a hardly explored hinterland.
Then in 1914 along came the First World War. Britain was desperate to bribe Italy to declare war on the Central Powers, which were Germany, Austro-Hungary and Turkey. In 1915 Italy agreed to join the allies in return for the gift of Somaliland and Eritrea which the British regarded as more trouble to govern and subdue than they were worth. Ethiopia was suddenly surrounded by two Italian armies of occupation on its eastern and southern borders. Italy soon set about converting the small Eritrean port of Massawa into a major naval base from which the Italian Navy could blockade the southern approaches to the Suez Canal which ran through British occupied Egypt. All was fair in love and imperialist wars still to come.
The post war treaties would give most of the Turkish offshore Islands, (the Dodecanese), including the most important (Rhodes), to the Italian Empire as part of the victors spoils of war. Italian naval bases, and soon major air bases, were slowly but steadily surrounding the Suez Canal which lay at the heart of the British Empire.
When the Italian Fascist party under Mussolini came to power in 1923 British relations with Italy suffered further decline. However the British were keen to begin airline services to Alexandria in Egypt which in reality was the hub of the British Empire. This would require Imperial Airways to procure landing rights in Italy and would require the appeasement of Mussolini. However the British had no intention of allowing any Italian airline to serve Britain and no Italian airline was allowed to serve Britain until 1938.
Italy grudgingly allowed Imperial Airways to set up a flying boat base near Brindisi on the heel of Italy, but refused overflying rights so that the Imperial Airways service to Alexandria from London terminated in Paris where Imperial Airways passengers had to board the overnight express train right across Europe to Brindisi. This impasse stood for many years with neither side prepared to make further concessions.
Then in the mid 1930s Mussolini decided that it was time to expand the Italian Empire again. The Italian Army invaded Ethiopia again, this time from both ends whilst the Regia Aeronautica conducted a chemical warfare campaign from the skies. Italy soon controlled a large slice of the very lucrative ivory trade.
The larger the Italian Empire became the more Italy desired Imperial Air Routes the length and breadth of their growing Empire. It was what all the European Empires desired, but Italy had no way to reach its growing Empire in the Horn of Africa by air without landing rights in both Egypt and Sudan, both of which were under British military occupation.
It was finally time for some determined Imperial horse trading. Italy agreed to allow Imperial Airways to overfly Italy, but would grant no new landing rights to Britain and in return Britain would allow a single 'chosen instrument' of the Italian Government landing rights in Egypt and the Sudan. Italy remained without landing or overflying rights of the British Isles, but was granted the right to manufacture under licence certain British aero engines and superchargers for military use.
Both Imperial governments set about subsidising and procuring aircraft to fly the new services that the newly agreed landing and overflying rights permitted. Both Imperial governments would ensure that the airliners procured could be turned into combat aircraft with no trouble at all. This was standard Imperial practice. Like Britain, Italy had many barely solvent small airlines. They would now be forced by the Italian government to merge into the equivalent of Imperial Airways. Thus Ala Littoria was born as the chosen instrument to serve the Italian Empire across the sea
The aeroplane the British taxpayer procured for their chosen instrument, (Imperial Airways), to fly the new London - Marseilles - Brindisi service was the Avro Anson. From February 1936 the Anson equipped nine anti-submarine squadrons of RAF Coastal Command and Ansons were soon flying with the air forces of Australia, Ireland, Finland, Estonia, Greece and Turkey. Those supplied to the last two air forces were perfectly placed to bomb Brindisi or Rhodes and any Italian shipping or submarines.
Savoia Marchetti, like Avro, spent the early 1930s manufacturing trimoters with high wings, either under licence from Fokker, or as near pirate copies of Fokker designs. These aircraft had their wings above the fuselage because all these aircraft belonged to the Pioneer era of aviation. They were navigated solely by visual reference to the surface and low wings blocked the view of the terrain, line features and land marks being used for navigation.
On all continents the switch to low wing monoplanes was conditioned by progression from the pioneer era of aviation to the vintage or classic era in which navigation was conducted primarily by radio direction finding, whether point source over the continental United States, or wide source RDF = GPS everywhere else.
Unlike the Avro Ansons used by Imperial Airways all Savoia S.73s had multi stage flaps to further improve low speed safety and to improve visibility ahead at low IAS on the approach. This was also true of its twin brother the S.M.81 bomber transport which entered service with the Regia Aeronautica in May 1935. These had production priority over the S.73 which began to appear in Ala Littoria livery about October 1935. These had however been preceded by five S.73s for SABENA earlier in 1935, but we will get back to the Belgian S.73s later.
Thirty-six S.M.81 bombers deployed to Asmara, the capital of Eritrea, in December 1935 and immediately joined the tail end of the bombing campaign against Ethiopia.
One obstacle remained to be solved. Ala Littoria needed landing rights in French Somaliland (Djibouti) and for a while it seemed that the invasion of Ethiopia might delay this, but France like Britain wanted to profit from Italian militarism. France did not want Britain to tie up all the military production licensing deals. Landing rights in Djibouti were quickly forthcoming.
The Imperial route which Ala Littoria had been created to service was originally intended to start in Paris, proceed via Rome, and terminate in Mogadiscio, (now called Mogadishu), the capital of Italian Somaliland. A new 24 passenger, four engined airliner, the Savoia Marchetti S.74 had been ordered for the high density flagship stopping service between Paris and Rome.
The original intention was that the long Trans Mediterranean legs of the Ala Littoria Linea Imperiale south of Rome would be flown by the Cant Z.506 seaplane airliner powered by the same Wright Cyclone F52 engines as the Ala Littoria S.73s, but the Z.506 development project had run into various problems and deliveries were delayed. Consequently it was decided that the Ala Littoria S.73s that were originally intended to be based in Benghazi on the coast of Libya would instead be based initially in Mogadiscio, and would open up the southern end of the Imperial route first.
The delay to S.73 production, arising from the priority given to the S.M.81 bomber variant, allowed the larger and superior S.74 to initiate Rome - Paris services even before the S.73 began to operate air services from Mogadiscio. The prior existence of the superior four engined S.74 meant that the S.73 was never needed on the Ala Littoria service north of Rome.
I believe the original November 1935 service was;
Mogadiscio - Djibouti - Assab - Massawa - Asmara
Within weeks a branch line was opened to the newly conquered capital of Ethiopia;
Asmara - Addis Ababa
Soon afterwards the original service was extended through British occupied Sudan and Egypt to Libya;
As it became clear that delays to the Cant Z.506 would be substantial it was decided that the S.73 service would fly all the way to Rome until they arrived;
Benghazi - Catania - Rome
This situation lasted for about the first five months of 1936. Around May 1936 the Cant Trimotor Seaplanes finally took over the Trans Mediterranean legs as planned, leaving the Ala Littoria S.73s operating only from Benghazi to Mogadiscio plus the long climb up the branch line to Addis Ababa.
Those who fly the S.73 where they usually fly every other aircraft in FS9 will never understand it. Flying the Cyclone engined 'flagship' version of the S.73 over the 'Linea Imperiale' attempting take off and climb out from Addis Ababa en route to Asmara is the only way to understand it, and is why it needed the best American engines available for export in 1935.
Now that brings us to a wider point which will lead into later military use of the S.73 and S.M.81, but also relates directly to wider issues of flight dynamics in MSFS. It is time to confront the random numbers and nationalistic bias published in the many different books about aircraft which are collectively only worthy of the title, 'The Boys Big Book of Wonderplanes'.
Pick up any of the many 'Boys Book of Wonderplanes' that deal with the S.73 or S.M.81 and we will almost certainly be confronted with the information that it had 550/760hp engines. These data are either randomly chosen numbers from the certification schedule or more likely they are intended to denigrate Italian aviation in the 1930s.
A Wright R-1820-F52 Cyclone is the same engine whether it powers a DC-2, an S.73 or a Cant Z.506. Read the 'Boys Book of Wonderplanes' by an American or British author about an American aeroplane that used this engine and we will be assured that it was a wonder engine of the day producing 875hp. Read about the same engine in an Italian aeroplane and suddenly it is a puny, worthless 550/760hp engine. Those Italians sure were useless at aviation. Look how they screwed up truly great American aero engines!
Well of course they didn't!
But the trouble is that most MSFS flight dynamics authors take these data at face value and replicate it in air files. Of course what is really happening is that all the authors of all the many 'Boys Book of Wonderplanes' since WW2 just plagiarise the last one all the way back to an original journalistic source written just before, or just after, WW2 when it was compulsory to denigrate Italian militarism in all its aspects. Freeware web pages just plagiarise the payware plagiarism.
Of course Italy isn't the only nation subjected to this nonsense, but the S.73 and S.M.81 provide an ideal opportunity to grasp what those apparently random quoted numbers 550/760hp in the Boys Book of Wonderplanes are all about when the Wright R-1820-F52 Cyclone is well known to produce 875hp for take off.
Use of TOGA power was only allowed if the tank selected for take off contained military grade high lead 87 octane AVGAS. Under all other circumstances take off was conducted using only METO power. This is why there were 8 fuel tanks for 3 engines. Military grade AVGAS was only available to Ala Littoria in a very few places along the Imperial route, which were both under Regia Aeronautica control, and easy to supply by ship. The military grade fuel was carefully safeguarded in its own tanks and never adulterated with airline grade 76 Octane in the other tanks.
Once power was retarded from TOGA the flight engineer switched tanks to one containing only airline grade fuel for climb and cruise. The tanks containing military grade fuel were used as little as possible to ensure that some would remain available for subsequent take offs and approaches at the airfields down the Linea Imperiale which were not controlled by the Regia Aeronautica.
Tanks containing military grade fuel were selected when downwind to land so that go around power would be available on final if required. If it became necessary to top up a tank normally containing military grade fuel with airline grade fuel all subsequent take offs and go arounds had to be flown using only Rated power until the tanks were drained and refilled with military grade fuel at a major Italian military base.
Quoting TOGA power for American aircraft, but only Rated power and/or max cruise power for non American aircraft with the exact same engine is intended to denigrate and confuse. Replicating that denigration and confusion within MSFS just propagates misinformation by new means and helps nobody to understand anything.
Now lets get back to November 1935 when the 3 x 875hp Savoia Marchetti S.73 first entered revenue service. Italy wasn't a backward insignificant nation struggling to get to grips with modern aviation in 1935. The Regia Aeronautica was flying more combat missions than every other air force on the planet put together. The Regia Aeronautica also had more military transport aircraft than every other air force bar that of the Soviet Union and it was the Regia Aeronautica that was pioneering the air mobile combat operations that would soon be copied everywhere.
That is the context for operating the S.73 to and from places like Addis Ababa, where no one else attempted scheduled air services in 1935. That short, tough, heavily braced landing gear may cause a lot of drag, but it is essential to the task. The efficient, but fragile flaps are essential to the task. The large, multi discipline, crew is essential to the task. Tasking the S.73 to do something trivial in FS9 in a different infrastructure, at low altitude, on long flat runways, using point source navigation aids, is pointless. It will just seem mundane and backward.
Armchair generals discuss strategy and tactics. Real generals plan logistics.
Ala Littoria did not receive the Cyclone powered S.73 until adequate supplies of military grade 87 Octane AVGAS were available in Mogadiscio, Massawa, Asmara and Benghazi. Of course military grade AVGAS was in place in Egypt, Sudan and possibly French Somaliland for use by the relevant Imperial Air Force, but Ala Littoria could not buy military grade fuel at British and French run military airfields, even though they had landing rights on those airfields.
Thus there were places that Ala Littoria could load only airline grade 76 octane fuel, which potentially precluded use of TOGA power.
From the invention of the poorly named Octane rating system by Ricardo in the early twenties, to 1945 and beyond, what differentiated nations was their ability to source military grade AVGAS and ship it to all the places they might need to use it. Only a few superpowers had an oil industry which could create it and only a few favoured client nations were allowed to purchase it from them.
Belgium was a minor Imperial Power. It had few bargaining chips at the Imperial table. The Belgian Empire had no access to military grade AVGAS. Consequently SABENA had no such access and could not order first rate American engines to power its aircraft. It could only order second rate engines that would run on 76 Octane airline grade AVGAS which could be bought on the open market. SABENA could order and deploy the S.73 before Ala Littoria because SABENA did not need to wait for military grade AVGAS to be in place anywhere. Belgium wasnt able to buy any anywhere.
SABENA chose the Gnome Rhone Mistral engine which required only 76 Octane airline grade fuel to develop its lesser TOGA power.
But aviation journalism and publishing was then, and is now, dominated by authors whose first language is English, and whose publishers have the narrow minded nationalistic prejudices to match. They are just as biased against French developed technology, or Belgian deployed technology, as they are against Italian deployed technology. Consequently almost every copy of the many different 'Boys Book of Wonderplanes' will misinform us that the Gnome Rhone Mistral installed in SABENA S.73s was a 600hp engine. This is once again nothing more than anglophone nationalistic bias. The Gnome et Rhone GR9Kfr Mistral installed in the SABENA S.73s was TOGA rated at 770hp at 720 metres.
600hp is only the Rated power of this engine. Once again a European continental product is deliberately denigrated in the many different English language 'Boys Book of Wonderplanes' to make British or American engines seem vastly superior by comparison. From the perspective of MSFS fight dynamics development the many different 'Boys Book of Wonderplanes' must not be trusted and of course their deliberately false content is plagiarised all over the internet, often translated into continental European languages, making us less suspicious of nationalistic bias which is nevertheless present in large measure.
The Belgian Empire lay in the Congo Basin of central Africa thousands of miles south of Belgium. The Belgian Congo which the SABENA S.73s were procured to serve then included the three modern African nations of Zaire, Rwanda and Burundi.
However when SABENA took delivery of their first five S.73s from February 1935 they were at first judged too good to be used on the Belgian Imperial route. They were therefore initially used to displace less capable Fokker F.VII/3m Trimotors that were immediately redeployed to inaugurate the Belgian Imperial route, also from February 1935.
So for most of 1935 the routes being flown by the first five SABENA 3 x 770hp Mistral powered S.73s were;
Brussels - (Lille) - Ostende - London
Brussels - (Lille) - Paris
Brussels - Hamburg - Copenhagen - Malmo
OO-AGL was the second SABENA S.73 and it flew all three routes during 1935. Most of these stages were compatible with carrying a full load of 18 passengers
SABENA were delighted with the S.73 and sought a licence to produce it in Belgium which was duly granted by Savoia Marchetti. SABCA delivered seven more to SABENA before the end of 1937 but all of these were powered by the much more powerful GR14K Mistral Major engine. These had only eight or ten seats and were used on the Imperial route to the Congo from October 1936.
The flying time from Brussels to Elizabethville (now called Lubumbashi) fell to 44 hours when the S.73 replaced the Fokkers. Of course there were still three night stops in hotels along the way and four days of hard flying 11 hours per day instead of six such gruelling days and five night stops in a Fokker Trimotor.
After the S.73 took over the Imperial route to Elizabethville the Fokkers which had been flying it were based in Stanleyville (now called Kisangani) to provide extensive Imperial regional services, but especially the seven stop route right across the Congo basin to Leopoldville, (now called Kinshasa), in the far west. Brazzaville the capital of the French Congo lay just across the river on the other bank. But for colonialism and the aftermath of colonialism Kinshasa and Brazzaville would be a single city with a major river running through it. They are still in different countries.
The original five S.73s including OO-AGL seem to have had the number of seats aboard reduced to ten and later joined the Belgian Congo service as demand increased, but continued to fly the European services above as well.
Of course Belgium needed overflying and landing rights across the French Empire to reach the Belgian Congo, but this was no problem since Air Frances colonial subsidiary Air Afrique required overflying and landing rights in the Belgian Congo to reach French Madagascar. Belgium had the necessary bargaining chips at the Imperial table.
As far as I can tell the Belgian Imperial S.73 service routed;
Nowadays Stanleyville is called Kisangani and Elizabethville is called Lubumbashi. On the entire Belgian Imperial route only Elizabethville (Lubumbashi) lies within the modern state of Zaire. Kigali has become the capital of Rwanda and Bujumbura has become the capital of Burundi. All points prior to Kigali lay within the French Empire and none have changed their names after independence from France.
By this time Air France already had a subsidiary holding company known as Air Afrique which managed a variety of French colonial airlines operating in Africa. The pre existing Air Afrique interline service, (which was effectively code and ticket sharing with SABENA), obviously started in Paris and then continued beyond Elizabethville, via a further five stops, through the British and Portuguese Empires, to Tananarive the capital of French Madagascar. This route required eight consecutive days of long hard flying.
It was Air Afriques subsidiary Compagnie Transafricain dAviation which inaugurated the first Trans Saharan service to the Congo River basin in September 1934 using Bloch 120 Trimotors. I believe they routed;
Paris - Marseilles - Algiers - Bou Saada - Ghardaia - Tessalit - Gao - Niamey - Fort Lamy - Bangui - Bumba - Stanleyville - Kigali - Bujumbura - Elizabethville and onward through Ndola in Northern Rhodesia (now called Zambia) and four further stops to Tananarive.
Of course it suited the French to force SABENA to route via Oran where there were fewer passengers than in Algiers and of course the S.73 service from Brussels to Paris fed the alternative and shorter Air Afrique service to the Belgian Empire. Imperialism was a dirty game.
It is not possible to understand the nature of 1930s airline flying, or the Savoia Marchetti S.73 in particular, without simulating operations to and from places like Elizabethville (now Lubumbashi) in real weather, (real temperatures), using realistic flight dynamics and realistic RDF = GPS radio navigation procedures.
Many airliners and military aircraft designed and produced in Europe were not in the least intended for use in Europe. They were designed to operate in the hinterland of the European Empires which have become the third world. They were bush planes intended to operate from some of the worst, hottest, highest, roughest, bush country on the planet. The S.73 was no exception.
SABENA could not participate on the collaborative route to the Congo basin until they increased capacity by taking delivery of the S.73 from February 1935. Once the S.73 took over the Imperial Route from October 1936 it was obvious that it was very superior to the competing Bloch 120. Air Afrique operated the French Imperial service to Madagascar, through the Belgian Congo, in its own name and livery from September 1937 using the Bloch 120 until France and Belgium were both invaded by Germany in May 1940 suddenly terminating all such services.
Which brings us neatly to military usage of the S.73, and its twin brother the S.M.81 bomber, all of which were subsequently converted to military transports, which then hardly differed from the original S.73.
Thus far I have gone out of my way to demonstrate how English language sources, whether first published in Britain or the United States, deliberately diminish the status of Italian Aviation. We must now come to terms with the opposite situation. The Italian fascist state censored the Italian media and required them to convey various ideas about the status of Italian aviation to exaggerate the extent to which Italian aviation relied only upon Italian products. That propaganda is also widely repeated within the many different Boys Book of Wonderplanes and then plagiarised all over the web.
This part of our story must also begin before the First World War and then move to Bristol in England, and then to Paris, before returning to Italy.
The Radial engine was invented by the Italian engineer Anzani before the First World War. It was soon eclipsed by the literally revolutionary Rotary engine invented by the French Seguin brothers. They set up a company called Gnome to manufacture their rotary engines which were soon widely copied via licences or just piracy.
One competitor who copied the Seguins Rotary engine was Le Rhone. Anzani responded by inventing the two row radial, but he never really solved the problems of cooling the rear row of cylinders and he soon discontinued production of two row radials. By 1918 the British engineer Bentley had created a rotary engine that produced 242hp continuously at sea level. The gyroscopic forces of these revolving engines were now so great, and so difficult to control, that no more powerful rotary engine could even be contemplated.
The Holy Grail pursued by the international aero engine industry was the *reliable* two row radial, but first the world needed a better single row radial to replace the reliable single row pre WW1 Anzani.
This was soon invented by the British engineer Fedden who led the new aero engine design team, which included 31 other engineers, at Bristol. He called his new 9 cylinder radial the Jupiter. It was soon being produced under licence in seventeen nations and powered over 260 different types of aircraft in the 1920s and 1930s.
This was an interesting development since Bristol had managed to design only one good aeroplane, the Bristol Fighter, and had no reputation or prior experience of aero engine development and manufacture at all! Over in Paris Gnome and Le Rhone had plenty of both but no product to manufacture. The first step was for Gnome to make a takeover bid for Le Rhone creating Gnome et Rhone and then for Gnome et Rhone to enter into a secretive arrangement with Bristol.
That 'arrangement' would be one of the most controversial in aviation history. Much of it was always secret. Bristol regarded it as a technology transfer and licensing deal whilst Gnome et Rhone regarded it as a Euro collaborative project akin to the modern Airbus concern in which they would have equal rights going forward. Three Bristol engineers moved to Gnome et Rhone in Paris where parallel development of the Jupiter soon proceeded.
Meanwhile Fedden and his team in Bristol created two new engines that used shortened Jupiter cylinders. The first with only seven shortened cylinders for use in commercial aircraft they called the Titan. The one with nine shortened cylinders for use in fighters they called the Mercury. The shortened cylinders of the Mercury reduced its frontal area and profile drag, but it had to run at higher rpm, or employ a more powerful supercharger, to match the power of the Jupiter.
Further development of the original Jupiter engine slowly became neglected with all new improvements being incorporated into the Mercury. These were then suddenly incorporated into the Jupiter, at which point it became the Pegasus. All four engines in this family had many parts and maintenance procedures in common. Over in Paris the engineers from Bristol, Gnome, and Le Rhone put their heads together and soon began to make many minor improvements to this Jupiter family without altering the basic design.
Also in France the Farman brothers now invented and patented a superior airscrew reduction gear mechanism. Gnome et Rhone licensed it from Farman, but at first Bristol did not.
Based on their version of the arrangement that Bristol had entered into Gnome et Rhone now began to manufacture the slightly modified Mercury with Farman patent airscrew drive as the Gnome et Rhone GR9 Mistral and ceased paying royalties to Bristol even though over 90% of the parts were manufactured from Bristol drawings. Gnome et Rhone then began manufacture of the 7 cylinder Bristol Titan with the same modifications applied using the brand name GR7 Titan, again claiming that it was a different engine and refusing to pay royalties to Bristol.
However the real goal in both Bristol and Paris was still the Holy Grail, which was a reliable two row radial. In 1928 the three teams of engineers in Paris cracked it and what might logically have been called the Twin Titan was actually branded the GR14 Mistral Major. Gnome et Rhone now claimed that this engine was exclusively theirs and that Bristol had no right to build it. This caused the final breakdown in the arrangement. The three engineers from Bristol returned to Bristol where in due course they all joined the board and helped Bristol to bring assorted law suits against Gnome et Rhone for hardware piracy. However Bristol failed to put the world beating Mistral Major into production in England, suggesting that they gave some credence to the claims made by Gnome et Rhone concerning the nature of the secret arrangement.
After studying the Mistral Major for four years Pratt & Whitney would create a competing two row 14 cylinder radial that did not infringe either Bristol or Gnome et Rhone patents. The Twin Wasp dates from 1932, but in some ways it remained inferior to the 9 cylinder Wright Cyclone until the end of the 1930s.
It is impossible to understand the S.73 airliner and its twin brother the S.M.81 bomber transport without first understanding the above and I will now explain why.
The S.73 and the S.M.81 shared a single prototype which the many Boys Book of Wonderplanes will inform us was powered by Piaggio P.X Stella engines. In a sense this is true, but the information that was withheld by the Italian censor is that the Piaggio P.X is nothing more than the Gnome Rhone GR9 Mistral manufactured under licence.
That common prototype, and the next four aircraft from the S.73/S.M.81 production line, then pass to SABENA. From then onwards SABENA sourced more powerful replacement GR9Kfr Mistral engines and spares from Gnome et Rhone in Paris.
You will recall that in early 1935 SABENA wanted Mistral engines because they were designed to run on airline grade 76 Octane AVGAS. Now it is time to grasp that in early 1935 the Regia Aeronautica had exactly the same requirement. Italy had not yet procured adequate stocks of military grade AVGAS from the few superpowers which could sell it to them, or withhold it. In addition Italy was at war in Ethiopia and needed to base modern heavy bombers inland from the coast of Africa in places where it was not possible to supply both adequate stocks of military grade fuel and airline grade fuel.
The S.M.81 bombers destined for service in Italian East Africa would all be powered by Mistral/Mercury engines, built by Piaggio, requiring only airline grade AVGAS. We must now think of those initial production S.M.81s as the S.M.81-I.
When the first S.M.81-I rolled off the Savoia production line Savoia had not yet begun licensed production of the Hamilton Standard 'Hydromatic' two pitch airscrew. When they did it would of course be refered to as a Savoia two pitch airscrew. The Piaggio P.X Stella (actually Mistral) engines in the earliest S.M.81-Is would have to drive four blade fixed pitch screws. The engine that powered them would however benefit from a much more powerful Bristol Mercury supercharger than the Gnome Rhone Mistral supercharger fitted to the more powerful GR9Kfr in the SABENA S.73s.
The TOGA rating of the Piaggio P.X/R.C.35 Stella = Mistral with a late model Mercury supercharger was 650hp at 3500 metres. Italian built engines are easy to decode, R = airscrew reduction gear, C = Compressed and 35 = 3500 metres rated altitude. This Piaggio version of the Mistral/Mercury engine was highly optimised for use from the Eritrean highlands, over the Ethiopian highlands and it would only ever be based in Eritrea and Ethiopia.
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
Scenele (now called Chinile) but we must use Dire Dawa in FS9.
Once Savoia began series manufacture of the Hamilton Standard two pitch screw it was fitted to the Piaggio manufactured Mistral to create what we should think of as the S.M.81-II. Maybe the first thirty or forty S.M.81s had four blade fixed pitch screws and were S.M.81-Is. The rest were S.M.81-IIs with three blade variable pitch (v/p) screws. Both types served only at the East African bases indicated above.
Now remember that that there was no point manufacturing S.73s with Cyclone engines until the Italian Empire had adequate stocks of military grade 87 Octane, (supplied one way or another by the Soviet Union), all round the coast of its African colonies. Once that was true, and adequate supplies of military grade AVGAS were also present at a few locations in Italy, the Regia Aeronautica could order into production a variety of S.M.81 with superior engines that used 87 Octane AVGAS to generate TOGA power. We should call this the S.M.81-III.
So it came to pass that Alfa Romeo now obtained a licence from Bristol to build the Bristol Pegasus under licence as the Alfa Romeo 125 and 126. These Alfa Romeo engines had many of their parts in common with the Piaggio P.X because both were varieties of Bristol Jupiter. The only significant difference was in the length of the cylinders and the manifold pressure to which they could be boosted by a supercharger. High compression requires high octane AVGAS however the high compression arises.
The Pegasus engined S.M.81-IIIs all had Savoia two pitch screws. Unusually they were intended for use in Europe not Africa, but as we shall see the S.M.81-III soon wound up flying combat missions from Africa against Europe anyway.
The licence obtained from Bristol, (in return for Imperial Airways gaining the right to overfly Italy), included the right for Alfa Romeo to produce the very latest two speed Bristol Mercury supercharger. This was very advanced technology compared to the Gnome Rhone superchargers being built under licence by Piaggio intended for use in military aircraft using airline grade 76 Octane fuel, or even the General Electric superchargers on the Cyclone engines being imported from the United States for use in the Cants and Savoias of Ala Littoria which required military grade fuel.
In England Bristol were not yet using powerful Mercury two speed superchargers with Pegasus engines. It was this combination pioneered by Alfa Romeo in 1936 for the S.M.81-III that would cause Bristol to eventually do the same, but not until 1938. The Anglophone authors of the many different examples of the Boys Book of Wonderplanes, will quickly misinform us that the Italians could screw up British engines too. They will often report the Alfa 126/R.C.10 as a 680hp engine!
The Alfa Romeo 126/R.C.10 was actually TOGA rated 850hp and actually for odd reasons at 1150 metres rather than 1000.
Of course by now there was a better engine even than the Bristol Pegasus. The Holy Grail of aero engine design had been discovered in Paris in the form of the GR14 Mistral Major, yet another variety of the same Bristol Jupiter engine.
So naturally it came to pass that Issota Fraschini sought and obtained a licence from Gnome et Rhone to manufacture the GR14K Mistral Major in Italy to power what we should think of as the S.M.81-IV. This version was intended for use only from Tripoli, Benghazi, and El Adem, (just south of Tobruk), all in Libya.
El Adem is now called Gamel Abd El Nasser (by Microsoft).
The S.M.81-IV was far more powerful than the other varieties of S.73 and S.M.81. This allowed it to fly at higher weights, carry more fuel, and bomb more distant targets with the same bomb load. It could also sustain longer maritime patrols. S.M.81-IVs, originally with engines purchased from Gnome et Rhone deployed to their combat bases in Libya from December 1936 onwards. As Libya was overrun by the British Army in 1943 these aircraft retreated to Lampedusa, then Pantalleria, and finally to Palermo and Catania. None seem to have survived the allied invasion of Sicily.
Of course the Anglophone Boys Book of Wonderplanes will quickly misinform us that the clueless Italians could screw up French engines too. When the magnificent GR14K, the Holy Grail of aero engines, was deployed by Italy it is often reported as a 650hp engine.
In reality the Isotta Fraschini 140/R.C.40 Mistral Major was TOGA rated at 860hp!
It had many parts in common with the Piaggio and the Alfa Romeo and like them it drove a Savoia (Hamilton Standard) two pitch screw, via a Farman reduction gear box. It would have been utterly stupid of the Regia Aeronautica to deploy four varieties of S.M.81s with three entirely different engines at the same time, and so the Anglophone Boys Book of Wonderplanes reports that they did just that. Of course they didnt. Just as the Bristol Mercury engines of the Blenheim are closely related to the Bristol Pegasus engines of the Hampden and Wellington, so the Piaggio, Alfa Romeo and Issotta Fraschini engines are closely related, have common maintenance procedures, and many parts in common.
Of course both the British Government and the French Government cried crocodile tears over the plight of the poor Ethiopians, and not long after more crocodile tears over the plight of the poor Spanish, but they signed the end user certificates for the licensing agreements for military use eagerly enough and added the royalties paid by the fascists to the Imperial National Product of Britain and France.
Imperialism was a dirty game.
In 1936 the Spanish Fascist Party under the leadership of General Franco lost the Spanish general election. They immediately staged a coup, but at first they were weak because most of the Spanish Army was in Africa imposing the will of Spain upon its colonies. Once the Spanish Civil War was underway Franco was soon receiving covert and overt aid from Mussolini. Similar aid to rid Europe of the Asiatic Bolshevik Insurgency would later be provided by Hitler who had become Chancellor of Germany in 1933.
In July 1936 a squadron of Regia Aeronautica S.M.81-III bombers with Alfa Romeo 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.
All bar half a dozen S.M.81-IIs supplied as transports, used during the Spanish Civil War, required military grade 87 octane fuel. Mussolini was consequently obliged to supply limited quantities of military grade AVGAS to Franco. The first Italian military AVGAS tanker didnt dock in Spanish Morocco until August and combat operations 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. Italy suddenly found itself with many new logistic problems in the Spanish Empire. 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 Spnaish 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. This Spanish name was later also adopted by Italian aircrew, but was never official, and it isnt even Italian.
About sixty five S.M.81-IIIs 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.
In August 1937 Franco had created a new fascist airline which he called Iberia. At first he welcomed investment and technical help from both Lufthansa and Ala Littoria. Soon two ex Ala Littoria S.73s were among the earliest equipment of Iberia. I have no certain knowledge of the routes which they flew for Iberia, but I believe they were based in Seville and since they were highly optimised for operation from African bush strips it seems likely that they served Spanish Africa, though other aircraft including ex Lufthansa Junkers Ju52/3ms would also have flown African services for Iberia.
I believe Iberia routed to Rabat from Seville and then onward to Casablanca, Marrakech, and Sidi Ifni. Then onwards again to the Spanish Canary Islands, (especially Tenerife and Gran Canaria), which lay west of Sidi Ifni, or further down the coast into the Spanish Sahara terminating at Villa Cisneros, (now called Dakhla).
Avio Linee Italiane, a Fiat subsidiary, and the only Italian airline to survive the creation of Ala Littoria as the 'chosen instrument' of the state, purchased powerful Alfa Romeo engined S.73s, including I-SAUL, for use on its network in 1937. Their trunk route appears to have been Turin - Milan - Venice, though they had other internal services and a Milan - Munich - Berlin international service. Milan - Paris was added after delivery of the S.73s. However it fell to Ala Littoria to serve Eastern Europe. Consequently Ala Littoria now acquired half a dozen 'economy models' of the S.73 with low powered Piaggio engines to fly the two routes Rome - Venice - Trieste - Klagenfurt - Bratislava - Prague and Rome - Venice - Trieste - Belgrade - Bucharest.
Despite its huge size, from late 1940, the S.M.81 was adopted by the Regia Aeronautica as an instrument rating trainer and was used to teach IFR procedures that were a new concept in the Regia Aeronautica. Very oddly the Scuola Volo Senza Visibilita was in the Alps at Porta Littoria (now called La Thuile, but Turin must be used within FS9). Instrument training in such difficult terrain and weather was certainly an interesting choice. These S.M.81 trainers had no armament and closely resembled the S.73.
During 1936-37 Piaggio engined S.M.81-IIs 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.
I believe several squadrons of S.M.81s, with different engines, formed at Vicenza in turn before deploying to Africa. This may have been true of the other locations above. 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.
Nevertheless understanding this complicated family of Savoia aircraft requires us to grasp that they were African bush planes of the 1930s, not European airliners and heavy bombers of the 1940s. They should not be compared with the aircraft of the 1940s, or aircraft designed to operate from nice cool, long, flat, grass airports, let alone airports with hard runways. They must be understood within the context of their real timeline and the hostile African highland and jungle bush environment they were designed to match.
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 the S.M.81-I and S.M.81-II 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-I 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.
When Germany invaded Belgium in May 1940 seven SABENA S.73 airliners made their way to London where they were quickly requisitioned and operated by 24 Sqn and 271 Sqn RAF, alongside their normal equipment, probably both based at Hendon in north London during May and June 1940. Hendon now houses the RAF museum, but is no longer an airfield. It can be replicated in FS9 using nearby Elstree (EGTR) which is about the right size for a 1940 RAF transport base. OO-AGL passed to 271 Sqn.
At first the RAF used their Mistral powered S.73s to supply the RAF squadrons supporting the British Expeditionary Force in Northern France and Belgium with operations into all relevant continental airfields, but following the collapse of French morale on their southern flank the BEF were soon retreating to Dunkerque.
The RAF S.73s now flew round the clock evacuating the RAF personnel and equipment they had just supplied. OO-AGS was shot down over Belgium whilst serving with 271 Sqn RAF in June 1940. I believe the six survivors then all passed to 271 Sqn and moved to that squadrons main base which was Doncaster.
From there 271 Sqn provided the airlift capability for RAF Fighter Command during station relocation which was a common event just before the Battle of Britain which was about to begin. However the probability that RAF operated S.73s would be lost to friendly fire once the Battle of Britain got underway was so great that they were placed in reserve and in practice were never needed again. 271 Sqns main equipment throughout this period had been the Handley Page Sparrow.
Italy bided its time until French morale collapsed and then declared war on both Britain and France in June 1940. Imperialism was a dirty game. 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. This obviously terminated the Ala Littoria Linea Imperiale.
A little over a month after the RAF had requisitioned seven SABENA S.73s the Regia Aeronautica requisitioned thirteen belonging to Ala Littoria. I-ASTI is likely to have been one of them. Serving with 605 and 606 Sqns of the Regia Aeronautica these now supplied the Italian Army in Libya via Benghazi and later Tripoli. Italian forces in Eritrea, Ethiopia and Somalia could no longer be reached by air on a regular basis.
By the summer of 1941 more and more S.M.81 bombers were being converted to transports and joining the S.73s in air supply duties. Some of the S.73s and a larger number of 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 S.M.81 bomber-transport always had a troop 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.
The two S.M.81s allocated to Mussolini and the King of Italy at the end of 1936 were also based near Rome, though the wartime airfield no longer exists, so we should probably use Viterbo in FS9 to simulate S.M.81 armed VIP transport missions.
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 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 Stormi typically had 24 aircraft so thats 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. A few of the requisitioned Ala Littoria S.73s and S.M.81 transports now maintained a military air bridge;
Lecce - Tirana - Bucharest - Odessa - Donetsk
These aircraft may have been based in Bucharest which as we shall see later was also the southern terminus of the Lufthansa S.73 service from Prague at that time.
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. 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 Pantellaria. 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 a handful of either type 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 *bomber* 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 missions 1936-1942. Until mid 1943 less than a quarter of Regia Aeronautica S.M.81 bomber or transport aircraft were based in Italy and by then only remnants remained.
Regia Aeronautica 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 with the Italian flag under the cockpit. They were based at Bergamo. In January 1944 these moved briefly to 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 Goslar south east of Hannover. 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. In Europe they belong on airfields the size of Elstree and Drutte. Better still use them from modern high altitude African bush strips to understand their aerodynamics and their power dynamics. Some SABENA S.73s were captured by Vichy French forces in the French African colonies in 1940, but oddly they seem to have made no use of them, perhaps they were handed over to Italy.
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 Mistral powered S.M.81-II and although many nations desired heavy bomber capability the S.M.81-II was too lacking in performance compared to the latest airliners with American engines, such as I-ASTI, 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.
The bombs were loaded vertically into the bomb bay, nose down. They tumbled badly after release. All of 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 Lancia turret more than doubling the firepower of the dorsal turret.
During 1937 one other airline had purchased the S.73. That was CSA (Ceskoslovenska Statni Aerolinie) who operated five S.73s from 1937 to about 1943. Just as the Bristol Pegasus was built under licence in Italy by Alfa Romeo so it was built under licence in Czechoslovakia by Walter. However since Czeckoslovakia like Belgium had no access to military grade AVGAS Walter manufactured the Pegasus II.M2 which ran on airline grade fuel. It was TOGA rated 620hp at 600 metres.
Thus the CSA S.73s were the least powerful variety of this interesting family of airliners and military transports by a large margin. However they did not need to cope with the hot and high bush strips of Africa. Rated power of the Walter Pegasus engines was 580hp, only 20hp less than the GR9Kfr Mistral used by SABENA and the climb and cruise ratings would each have been down by about 20hp (=< 5%) compared to the SABENA aircraft.
Whilst these things do not really convert in a truly linear fashion simply subtracting 0.33 Ata from each Mistral power setting (bar TOGA) specified in the supplied SABENA handling notes will replicate operation of the Pegasus II.M2 by CSA in Eastern Europe well enough. When simulating CSA procedures climb should be conducted at 0.867 Ata, econ cruise at 0.6 Ata, and so on. Performance and mission profiles will self adjust.
A CSA take off must be simulated with the engines throttled to 0.95 Ata against the brakes, before brake release, to replicate the lower TOGA power of the Walter manufactured Pegasus II.M2 compared to the GR9Kfr in the SABENA version whose air file we should use.
Now we must remember that the major Czechoslovak airline before WW2 was CLS. They held the really lucrative route licences. CSA was only allowed the route licences that CLS did not want extending to the less lucrative east. I believe the five CSA S.73s flew the following two services;
Prague - Vienna - Zagreb - Bucharest
and
Prague - Warsaw - Moscow
Most of these stages allowed (far) fewer than 18 passengers.
The assets and aircraft of CSA were seized by the German government and handed over to Lufthansa after the invasion of Czechoslovakia, but they continued to fly the same two routes.
So by the end of 1945 all the S.73s had gone and 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/R.C.34 Pegasus. All had been relegated to transport duties six years earlier. They didnt last much longer.
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.
I have supplied on screen and separate printable handling notes elsewhere in this package.
Finally a quick comparison of the four types of S.73 supplied in this package.
Early 1935 - SABENA launch customer model - 3 x 770hp Mistral medium superchargers - quite good all round, but best at nothing. Low profit margins. Quite good for use in both Europe and Africa.
Late 1935 - Ala Littoria Flagship model - 3 x 875hp modest superchargers, but only with military fuel. The fastest variant. However with airline grade fuel less powerful than the earlier SABENA aircraft and a waste of money if used without access to military fuel. Highly optimised for the Italian colonies in Africa at any price.
1936 - Ala Littoria economy model - 3 x 650hp Piaggio very powerful superchargers. Not capable of using very short runways, very slow at low levels, but quite fast at high levels. Offered the best profit margin. Optimised for Europe. The easiest to fly within its engine and aerodynamic limits.
1937 - ALI - 3 x 850hp Alfa Romeo very weak superchargers - almost as good as the Cyclone variant for STOL performance despite using airline grade fuel, but only from low altitude runways. Capable of cruising fast, but not economical, and poor performance from high altitude runways. Optimised for Europe.
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.
