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Giulio Macchi formed the Macchi aeroplane company in 1912 to build licensed designs from the French manufacturer Nieuport. A lack of landing strips and a plethora of lagoons and anchorages in Eastern Italy promoted the flying boat type. In 1917, Macchi was producing their first original design, the M.5. A flying boat fighter with a speed of 190km/h and highly maneuverable. It was able to compete with landplanes, no mean feat considering the extra drag and weight of the hull. In 1920, the company's name changed to Macchi Aeronautica and they went on to produce improved versions of the M.5 until 1931.

The Schneider Trophy was first competed for in 1913 between France and the USA. Its sponsor, Jacques Schneider intended to stimulate seaplane development by offering a trophy and prize money. The course was 212nm long, with a 2.5nm water navigation part and a 6 hour flotation test. Macchi Aeronautica first won with an new plane, the M.7bis, building on the experience of the M.5, in 1921. It had 250hp for an average speed of 189km/h. After Italy's loss of the trophy in 1922, they regained it in 1926 with another Macchi aircraft, the M.39. Looking far more like a modern aircraft, it was a monoplane with twin floats instead of a hull, both to cut down on drag. Engine power was dramatically increased to 800hp from the Fiat AS.2, and speed rose accordingly to 397km/h. An improved version, the M.52 was raced in 1927 but forced to retire from engine failure. The team continued to be plagued with problems in 1929, both M.67s pulling out leaving a M.52 to take 2nd place. Power had been increased to 1000hp using the AS.3 resulting in 457km/h top speed. The M.52 was clearly dated by this point and preliminary designs began on the competitor for the 1931 race.

Throughout the 1920s, the main designer for Macchi Aeronautica had been Mario Castoldi, now in 1931 the new aircraft was the first to wear his name: the MC.72. Improvements in metallurgy had lead to huge increases in power and the new aircraft was designed around a new 4m long engine, the AS.6, which was not a true “hyper engine” (50kw/L), but produced as much power/litre as the Napier Sabre 10 years later. (The Sabre being one of the most powerful IC engines ever at an eventual 4000hp). The peak output of the AS.6 was 45kW/L (3100hp at 3300rpm), in comparison with the contemporary Pratt&Whitney Twin Wasp's 28kW/L(1200hp). The key to the success was that the AS.6 wasn't an engine at all, it was 2 AS.5 engines mounted together yet completely independently. Both engines drove a single propeller, one clockwise and one anti-clockwise. This was the first example of a contra-rotating propeller and had significant advantages; elimination of torque effects and higher efficiency (About 15% in most attitudes).

Torque effects were a large problem for the Schneider Trophy racers. The huge power of the engines on such a small sized aircraft gave a tendency to cause the right wing to dip in reaction to the clockwise-rotating propeller. The solution was to load the left float heavier with fuel for the engine. For the 1800hp AS.3 engine, the left float was 23% heavier. With the 2650hp engine of the Supermarine S6B, the left float was some 32% heavier. This posed considerable problems when taxiing and when most of the fuel was used. The contra-rotating layout developed by Ing. Serbi reduced the overloading to only 3% with 3100hp. It should be pointed out at this point that the MC.72 was benefiting from being the only Italian entrant and from governmental aid, something the British Supermarine design lacked.

The two AS.5 engines were entirely separate, evidence in the cockpit of two throttles and the remarks “front engine, back engine.” The AS.5 was a 12 cylinder engine, the banks being arranged in a Vee 60° apart. The rear-engine crankshaft was relayed into a gearbox from which a transmission shaft ran through the gap between the cylinders of the front engine to the front engine's gearbox. At this point, the two transmission shafts ran along the same axis, the rear shaft being of smaller diameter and inside the front shaft. The front shaft them turned the rear propeller and the rear shaft turned the front propeller (Fig. 1). Both engines were supercharged (to 1.82bar) by a single centrifugal compressor which was run off the rear engine, there being insufficient space between front and rear engines to mount a second supercharger.

A small radiator for the engine oil was located in a small lip between the two engines on the upper fuselage. Cooling for the AS.6 engine was by evaporative means, another first. This allowed drag to be reduced again, the external radiators being eliminated. They were replaced by large panels covering a large area of the wings, floats and underfuselage. The water coolant through the engine blocks was pressurised, allowing the boiling point to rise above 100° C. Then the superheated water was sprayed into an open tube system inside the aircraft where it rapidly boiled and released its heat. This system allowed for greater streamlining even though it was more complex.


The 1931 Schneider Trophy race was held in The Solent and was the last chance for another country to win back the trophy before Britain could keep it, having won 3 races in a row. The French and Italian entries were not able to ready their aircraft in time so the British Supermarine S.6b was left to compete with a winning speed of 547km/h. The fine tuning of the AS.6 engine proved most problematic for the Italians. The first flight of the MC.72 on 22nd June 1931 was not successful, with the pilot having to land almost immediately due to engine failure. The few flights over the next few months did not improve. One pilot died after crashing on take off, and another died when his MC.72 exploded in flight. More test flights were postponed after this, and bench tests in wind tunnels restarted on the AS.6. A British fuel expert was enrolled in 1932 to help with the problem. A mix of petrol, benzene and alcohol was prepared, allowing 3100 maximum hp or 2500 for endurance running. The final flight of the MC.72, with the only remaining qualified pilot, Francesco Agello was undertaken on 23rd October 1934. Everything went smoothly, with the maximum recorded speed being 709km/h, the world speed record for the time. This speed record for seaplanes was only beaten in 1961 by a turbojet-powered Beriev M10 with a speed of 911km/h, the record for piston-engined seaplanes remaining unbeaten. The remaining MC.72 is preserved at Vigna di Valle museum in Italy.

Full article with pictures here

You recognise that a British fuel expert - 'Rod' Banks - was involved in the development of the fuel for the AS.6 engine.

I think it reasonable to suppose that, with further Government backing for the Schneider Trophy, he would have been working on fuel for the British projects, rather than the Italian world speed record attempt.

So, methinks, 3,100 horsepower might not be attained quite yet, and the M.C. 72 - although certainly a formidable racing plane - would not stand so far above the competition as historical.

Yes, the fuel used was a mixture of petrol, ethanol and benzol. The Rolls-Royce R giving it's top 2300hp on mostly methanol. 3100hp is unlikely because of the preignition problems encountered, but the AS.6 was being bench tested at 2400hp in 1932. The lighter and sweeter crude from Libya would also be better than the 87-oct usually used, but increasing the compression ratio much above 7 would prove difficult. 2400hp-2500hp seems reasonable. Then again, the evaporative cooling system, low-drag airframe and the contra-props still give an advantage. Calculations indicate a speed of 650km/h at sl with 2400hp. An even more conservative 2000hp gives 610km/h. The MC.72 should definitely be superior on taxiing because of the minimal torque effects.

Oh, certainly an exceptional aircraft.

Just not quite so exceptional as historically.