Understanding operation of the Savoia Marchetti S.M.79
During the 1930s Italy was heavily dependent on the licensed manufacture of collaborative Bristol and Gnome Rhone aero engines driving Hamilton Standard airscrews and Farman airscrew reduction gear also built under licence. The S.M.79-M is no different. The engine in this version is a tried and tested, easy to maintain, willing to suffer abuse, low powered variant of the Bristol Pegasus. The supercharger seems to be licensed copy of that normally employed with the Bristol Mercury. The engine and supercharger combination is inferior to that in the Bristol Blenheim I, which had entered service with the RAF a few weeks earlier, but 50% extra power from a third engine delivers excellent high altitude performance. On the other hand the Hamilton Standard airscrews manufactured under licence by Alfa Romeo are advanced technology and superior to anything available in Britain.
The S.M.79 has a tiny wing to maximise cruising velocity with low power deployed at high altitude. Consequently it requires more lift augmentation devices than any comparable aircraft. It has Handley Page patent automatic slats from the engines outboard to the wing tip. These give the S.M.79 a very low stalling speed, but associated with a very high stalling angle.
Consequently the S.M.79 required full span Fairey patent camber changing gear with drooping ailerons all along the trailing edge to reduce pitch at low IAS. It is safe to touch down at speeds as low as 110 KmIAS without risk of violent tail strike. However view over the nose cowl is quite poor even at modest angles of attack and so nailing Vref is more important than usual. Arriving over the airfield boundary at less than Vref (135 KmIAS at 20,000lbs) will place the aircraft so nose up that visual contact with the touchdown zone may be lost causing undershoot or loss of directional control. If we cannot nail Vref then we should arrive a little faster, never a little slower. Remember landings should be made with no bombs remaining and normally with less than 20% fuel remaining. The SM79 will survive a landing at any weight, but successful high weight landings require more skill.
The drum brakes are weak, subject to fading, and due to the need to approach unusually fast, compared to rotation speed, the landing roll with max braking is about 30% longer than the take off roll. Nevertheless this is almost a STOL bush plane compatible with short and hot bush strips across the deserts of North Africa.
Taxi slowly. Use differential braking in lieu of differential power. View ahead is very poor due to the central engine and cowl. Follow the edge of taxiways and runways looking left and down from the VC. Line up on a runway using the same method. Taxi slowly enough to retain control in an aircraft whose ground handling characteristics were very poor by modern standards. There is a tailwheel lock, but with correct technique the tailwheel won't be on the ground for long during the take off roll. Make sure the lock is disengaged when you taxi.
The camber changing gear will not *travel* with excessive profile drag (IAS) applied. Once locked it will withstand higher drag, but we should avoid applying it anyway. The flying controls are manual with no power assistance. We will be handling a ten ton truck manually with only thin air for traction. The real aircraft had more stages of wing camber change than are provided in this release, but we have the important settings.
The whole idea of this aeroplane is to cruise fast, at high altitude, in thin air, using very little power (fuel burn per hour). Design cruise power and economical cruise power hardly differ. Design cruise altitude is 6Km with either power setting. Max cruise is an irrelevant concept in this aircraft. If we need to increase fuel burn to prevent fuel exhaustion when battling a severe headwind we may employ any power setting up to rated power. If we use rated power at other times we will quickly exhaust the fuel. See on screen (html) handling notes. The txt version of the handling notes is for printing.
Published time to height figures for this aircraft assume both no auxiliary fuel and use of rated power for climb, which was permitted, but was not the norm, since it squandered fuel and combat radius. Operating the S.M.79 is all about conserving fuel to maximise combat radius, and maximising cruising velocity by cruising higher than other medium bombers of 1937. The ability to cruise any bomber at 200 KTAS with any bombload was quite exceptional in 1937.
Real aircraft are not operated at random altitudes. Choosing the correct altitude for cruising is a key captaincy decision in any aircraft. If we apply economical cruise power at 6000 metres when operating a Savoia S.M.79-M bomber our mean cruising velocity will be 185 KTAS, using 600 pounds of AVGAS per hour (PPH), but if we make the mistake of cruising an S.M.79M at 1000 metres, using the same power settings, our mean cruising velocity will fall to 164 KTAS.
If we try to fly the sortie at 185 KTAS at 1000 metres we will run out of fuel. We would need to increase fuel burn by 25% to 750 PPH to fly the same sortie at 185 KTAS at 1000 metres instead of 6000 metres. Our range would be reduced by 25%!
After Italy declared war on Britain in June 1940 sinking British merchant and naval shipping became a high priority for the Regia Aeronautica. New more powerful versions of the S.M.79 were produced as dedicated torpedo bombers (S.M.79 Bis/N) and some existing S.M.79-Ms were given dual capability. The torpedo was mounted to port inducing substantial roll and yaw. I have not introduced that problem by default. If you wish to cope with that problem move the default bombload one foot to the left in the aircraft.cfg.
Nor have I varied the warload for the two standard S.M.79-M missions. The design bombload was 1000 Kg whilst the single standard Italian air droppable torpedo and its mounting hardly weighed any less. The extra drag of the torpedo mounting and the torpedo will be present if you load them with the spoiler key. When you launch the torpedo (again with the spoiler key), only the drag of the torpedo crutch will remain. You really can launch the torpedo in FS9. Just don't expect it to run.
Whilst the drag of the torpedo will be deducted automatically, to remove its weight, or the weight of the internal bombload, we must open the FS9 payload menu and set the warload to zero. The advanced technology torpedo was launched from an altitude of 100 metres with almost no restriction on launch velocity, (up to 290 KmIAS). This advanced Italian air launched torpedo was also normally employed by the Luftwaffe and Kriegsmarine once it was available.
Over short ranges the S.M.79-M could carry 5 x 550lb (250Kg) bombs or 12 x 220lb (100Kg) bombs, but if you choose to alter the default payload to represent that short range bombload you must remove fuel to exactly offset the extra bombload. These changes should always be made using the FS9 fuel and payload menu, not the aircraft.cfg.
The defensive armament and systems of the S.M.79-M were poor and crude compared to the earlier S.M.81 heavy bomber. The conversion from the original S.M.79-P airliner was half hearted. Over Spain a dedicated hatch gunner was considered obligatory. He had a single 7.7mm WW1 surplus Lewis gun on a Scarf ring which he could fire to either beam, but later the uselessness of that armament was better understood and the S.M.79-M later flew with only four crew and hatches closed to improve performance.
The co-pilot / navigator was also the bomb aimer, (American = bombardier). He occupied the gondola during the bomb run. He was also the camera operator during recce missions. The captain had a fixed forward firing Breda-SAFAT 12.7mm gun which was of little practical use. The wireless operator could deploy a second Breda-SAFAT 12.7mm gun situated at the rear of the dorsal hump. This open position was wind blasted, very cold, and had a poor field of fire. If the flight engineer moved to the gondola whilst en route he could deploy a third Breda-SAFAT 12.7mm gun which had a very limited field of fire behind and below. The old Lewis 7.7mm was substituted by two Breda-SAFAT 7.7mm guns. The S.M.79M was very much a 'schnell bomber'. It relied on its exceptionally high cruising velocity and high design cruising altitude to evade interception in the days before radar.
Although this aircraft, which deployed in 1937, was exceptionally fast, and had a variety of advanced systems no one considered the need for airframe de-icing. This aircraft has only carb heat and pitot heat. It will ice up fast in bad weather, especially at northern latitudes. The only remedy is to exit icing conditions and hope. If you use it where it was not designed to be used, you may pay the price.
When Italy entered WW2 in June 1940 S.M.79s were based at the following locations;
Pisa
Viterbo
Rome (Ciampino)
Rome (Orvieto)
Villacidro (Sardinia)
Decimomannu (Sardinia)
Comiso (Sicily)
Sciacca (Sicily)
Catania (Sicily)
Castelvetrano (Sicily)
Gela (Sicily)
Benghazi (Libya)
El Adem (Libya) = Gamel Abd el Nasser in FS9
Triploi (Libya)
Bir el Bhera (Libya)
Just over a quarter of the available S.M.79s were based in mainland Italy but some of those soon deployed to Rhodes (in the Dodecanese islands.
The S.M.79 operated by day and by night and in bad weather. Sometimes it needed to maintain radio silence. If not it operated exactly like a European airliner of the same date. The way it should be navigated in FS9 hardly differs anyway since with, or without, radio silence we must consult the running navigation plot (FS9 GPS) every so many minutes to calculate and then set our assigned heading on the gyro comparison compass.
The pioneer phase of aviation history gave way to the vintage phase of aviation with the arrival of highly trained and qualified wireless operators (wireless telegraphers), and highly trained and qualified navigators who joined the flight deck crew, and sometimes displaced pilots as captain of the aircraft.
When we use any flight simulator we must always act as both pilot flying and aircraft captain. Performing other crew roles is optional. The bearings supplied to the qualified WTO or RO were plotted on a chart by a qualified navigator. Ideally three bearings from different D/F operators in sequence were used to triangulate present (actually recent) position. Just as in a surface ship the navigator then instructed the helmsman what heading to steer based on where the vessel was believed to have been a few minutes earlier.
Conducting a GPS navigated flight using Marconi + Adcock technology during the vintage phase of aviation history only requires self disciplined use of the default FS9 GPS.
1) The GPS window must be 'popped up' only at substantial intervals during cruise; perhaps every 10th minute for a short haul flight, or every 30th minute for a long haul flight.
2) Once every such position update interval, a course correction not exceeding five degrees, and always rounded to five degrees, is made after using the GPS to establish whether the flight is currently left or right of flight plan track due to wind drift and any other cumulative navigation errors, (that we have perpetrated).
What we will be simulating using intermittent course changes and headings, which will be wrong by up to four degrees 80% of the time, is the error that arose from the manual plotting delay and the bearing errors inherent in using HFDF as the contemporary GPS system at extended range.
In the real Savoia Marchetti S.M.79 pilot not flying (PNF) was the navigator. He maintained the GPS plot on his lap. Every ten or thirty minutes he worked out whether the bomber was left or right of flight plan track and if necessary assigned a different heading to pilot flying (PF). In many vintage airliners the comparison gyro compass was placed where PNF could update the assigned heading for PF.
FS9 users may have come to think of the comparison gyro compass as part of a vintage era autopilot, and it may be, but that is not its primary use. The assigned heading is always bugged, (usually by PNF), and equality maintained by PF. In FS9 we must play both roles. Only every ten or thirty minutes we must pop up the GPS window and determine whether we are converging with flight plan track. If not we bug a heading five degrees more convergent with flight plan track and then we fly it. Whether or not we intend to use an autopilot to maintain the assigned heading. An AP is a luxury in any vintage bomber. A gyro comparison compass is not.
We never bug a heading that is not divisible by five and we never attempt to navigate direct to anywhere many miles ahead. We always bug and then fly a heading that converges with our flight plan track. Unless of course our current bugged heading is holding flight plan track exactly in the current crosswind. If we are using real weather, that happy co-incidence will never last for long.
We use the panel clock to time our GPS updates. Updating late is OK, but allowing ourselves to update at intervals of less than 10 minutes, or allowing continuous display of the GPS is cheating. Vintage era GPS did not have that continuous and instant update capability.
By 1937 many bombers, including the Savoia Marchetti S.M.79 had combined gyroscopic compasses and course deviation monitors. In some, including the S.M.79M these were already combined within a wing levelling autopilot which drove the rudder trim tab when activated. It is important to understand however that the assigned heading was always bugged whether or not the wing leveller was going to be used. The heading assigned by the navigator was dialled into the assigned heading monitor on the upper scale of the captain's gyro compass. The actual heading revolved below. As pilot flying we must always keep them superimposed, but after dialling current and assigned heading into the comparison compass we actually do that using the heading deviation compass above.
Today in the 21st century pilot flying is assigned headings by qualified radar controllers looking at a radar plan position indicator (RPPI). In the vintage era he was instead assigned headings by a navigator looking at a GPS display which he was updating manually. It makes no difference at all to us as pilot flying in FS9, or to us as the aircraft captain in FS9, who mandates the assigned heading, or whether they are aboard the aircraft. Actually it makes no difference in real life either.
Today a GPS can update the aircraft plot in less than a second. In 1937 it took a few minutes to use GPS signals to update the GPS plot in an ocean liner, a battleship, or an aircraft with the relevant crew complement and H/F wireless transceiver. Using GPS to simulate the vintage phase of aviation is entirely realistic. Most FS9 users fail to deploy GPS correctly during military simulation of the vintage phase of aviation.
All complex Italian aircraft of this period had a gyro comparison compass and loosely associated 'autopilot' system similar to those in use in Germany. Some of these have been explained correctly in other FS9 releases and some have been 'faked'. Nothing we encounter here is fake and that requires us to understand how to use the five different compasses in the S.M.79 correctly.
The magnetic compass is top centre. Directly underneath is a gyro repeater compass. Now locate the gyro comparison compass between the altimeter and the artificial horizon on the captain's panel. It has two rotating drums, one above the other. The lower drum is controlled with the left hand knob. It must be set equal to the magnetic compass as frequently as may be necessary so that it displays current magnetic heading. This lower drum also drives the gyro repeater compass under the magnetic compass. They are in fact slaved to one another so that the co-pilot can adjust the main comparison compass lower drum which is in front of the captain using the control under the repeater compass.
The upper drum of the gyro comparison compass, (in front of the captain), is set with the right hand knob. It must be set to the assigned heading deduced from the GPS (see above).
The internal gyroscopes of the captain's comparison compass then compare the two headings and drive the heading deviation compass situated above the comparison compass. Every time our assigned heading changes (perhaps only every ten or thirty minutes whilst en route, we must make fine adjustments of the difficult to read 'gyro comparison compass', but in between we use the easy to read and interpret 'heading deviation compass' above.
None of that has anything to do with whether the aircraft even has an autopilot (AP) or whether the AP fitted will cope with what we are trying to achieve by way of 4D navigation. None of those instruments is an AP or even part of an AP.
These aircraft do have an automatic pilot (AP) of sorts. The 'Corretore Autodirezionale' is a primitive device of limited capability. It can hold assigned headings and little more. To do this it senses the gyroscopes of the captain's gyro comparison compass and if the actual heading deviates even a little from assigned heading it uses the rudder to maintain course with many 'very little and often changes'. It can be used to make *small* heading changes, by slight variation of the assigned heading on the upper drum of the captain's comparison compass, but since it has no control over pitch status changes of pitch may be induced as the rudder attempts to roll the aircraft to a new assigned heading.
The 'Corretore Autodirezionale' master switch is bottom right of the captain's panel, next to the fuel (benzina) contents gauge. The normal procedure is that we first set current magnetic heading on either lower drum, (main or repeater), then the assigned heading on the upper drum of the captain's gyro comparison compass, then we manually achieve zero deviation on the deviation compass above flying manually, then (maybe) we turn on the 'Corretore Autodirezionale' if the assigned heading is expected to endure long enough to make using the AP worthwhile.
The 'AP' has no control over pitch. The aircraft can be pitched with elevator or power when the AP is on. In real life it could be rolled with aileron against the rudder inputs of the AP, but FS9 will not allow that. There is an AP connected warning light beside the deviation compass. Be warned this system has been misrepresented in some other FS9 releases and you may need to relearn its usage before operating the S.M.79.
In the vintage era of aviation there were no mandatory arrival and approach procedures published by a federal agency via an arrival and approach plate. The key flight planning decision was always voluntary placement of top of descent (TOD) to terminate the limit of the GPS component of the vintage phase flight. We must descend through cloud somewhere that does not risk collision with terrain in the descent. We must plan and then vertically limit the descent accordingly.
In general the present day federally mandated procedure is just an amalgam of the prior employer mandated procedures many of which date back to the 1930s. They are the same thing really, so if a current NDB arrival and approach procedure is available for download, it should be downloaded and followed. Even if it appears that a modern STAR has no relevance to vintage bomber operation in the 1930s it probably does. The current approach plate is always relevant. It tells us what our minimum descent altitude must be in FS9 since we must avoid masts present in FS9 whether or not they were present in the 1930s and 1940s.
The rules for planning top of descent are therefore those explained in Part 3 of the original Propliner Tutorial available from Calclassic.com even though it addressed only flight in the later Classic phase of aviation history.
In FS9 we will use GPS to navigate the Savoia S.M.79 as explained above until it is time to descend. Then we will switch to terminal guidance using the goniometer.
When instruments such as the goniometer first appeared they were often installed in front of only one pilot. In this aircraft the radiogoniometrico is right of the co-pilotÂ’s artificial horizon. When the time comes to fly the arrival and the approach we must slide ourselves across from the captain's seat, (real life eyepoint and eyeline), to the co-pilot's seat, (real life eyepoint and eyeline), using the keyboard (CTRL + SHIFT + ENTER). We will then normally fly the arrival, approach, and right hand landing pattern from the right hand seat, having flown the rest of the flight from the left hand seat, so that our virtual co-pilot could act as pilot not flying and navigator to update the GPS.
However once the captain, who has become pilot not flying, announces that he can see the airfield he may also decide to carry out the circuit and landing. If we wish to fly a left hand pattern we can simply slide back to the captain's real eyepoint and eyeline using CTRL + SHIFT + BACKSPACE.
A tutorial concerning use of goniometers is provided within the Savoia Marchetti S.73 (version 2) release by Stefano Meneghini available from SurClaro.com and elsewhere. It is not repeated here, but the ability to comply is required to recover the S.M.79 safely to base in limited visibility or low cloud. Procurement and practice is advised. Of course the Savoia S.M.79 in this release can be used in lieu of the Savoia S.73 cited in the original tutorial.
This S.M.79M release also provides a Lorenz Beam and co-located DME receiver to the right of the pitot heat switches on the co-pilot's panel. The S.M.79M would not have had this luxury when first delivered, but Lorenz Beam receivers would have been standard equipment in later versions and all versions of the S.M.79 use the same Virtual Cockpit. The Lorenz Beam receiver tutorial is again within the Savoia S.73 V2 release and is not repeated within this S.M.79 release, even though the exercises can be flown just as easily using the S.M.79M. The tutorial features SABENA S.73 approaches to Oostende in Belgium. Whilst the S.M.79M did not deploy to Belgium in real life, that was only because the Regia Aeronautica decided to deploy the Fiat B.R.20 to Belgium to bomb England during the Battle of Britain instead.
It would be a crying shame not to fly the Virtual cockpit environment of the S.M.79 from both real life eyepoints and eyelines. The dual VFR and IFR functionality of the supplied Virtual Cockpit, from each real life eyepoint and eyeline, is one of the strengths of this remarkable freeware release to which my contribution was quite slight.
