[MOCs] Schneider Trophy - The Italian Triplets (Piaggio-Pegna P.7 / Savoia S.65 / Macchi-Castoldi MC.72)

Hod Carrier · April 14

<-- Supermarine S.6B (Calshot 1931)

The most successful designs throughout the history of the Schneider Trophy were of conventional design, and the Macchi designs, penned by Mario Castoldi, exemplified this approach. Given how far aviation technology was being pushed, simplicity in design allied with sound engineering was how races were won. That said, it is likely that no nation involved with the contest innovated more than Italy, especially during the latter half of the 1920s.

Piaggio-Pegna P.7

Giovanni Pegna was a designer who was clearly in a hurry for the future to arrive. He seemed to be completely unconstrained by convention and willing to push technology beyond its capabilities at the time, such as his 1917 idea for an aircraft capable of stratospheric flight.

The Schneider Trophy exercised a huge degree of fascination for Pegna who penned quite a few designs for racers that never made it off the page. What was clear from all of them was that he had a good understanding of the principles of streamlining and its importance for high-speed flight, but what made them so challenging was the degree of impracticality they exhibited. The only one of his Schneider Trophy designs to be constructed was the Piaggio-Pegna P.7.

In essence, the Piaggio-Pegna P.7 was a new take on the flying boat. The aircraft had a fully watertight hull and would sit up to its wings on the water. Where it differed from other seaplanes is that it was much more streamlined than either a conventional flying boat, with its separate hull and engine nacelle, or a floatplane. Instead, the P.7 made use of hydrofoils.

Looking more like something from last week rather than the 1920’s, the P.7 had a slender fuselage and comparatively small elliptical wings. Three hydrofoils were provided, one under the tail ahead of a boat rudder, and two on outriggers. Power for the P.7 was provided by an Isotta-Fraschini 12-cylinder vee engine producing 970hp mounted amidships. This engine drove both the conventional aircraft propellor at the front of the aircraft and a high-speed boat propellor under the tail through a series of clutches that would be engaged and disengaged by the pilot.

As there would not be enough clearance for the aircraft propellor when the P.7 was at rest on the water, this would be held horizontally by a shaft brake while disengaged from the engine. The idea was that the P.7 would start and be accelerated through the water using the boat propellor until it had reached the speed where it had been lifted clear of the water on its hydrofoils. Once there was enough clearance to divert drive, the pilot would operate a series of levers in the cockpit to engage the propellor, allowing the aircraft to continue to accelerate to take-off speed.

Only a single P.7 was completed and was delivered to Desenzano on Lake Garda for evaluation, where the only pilot willing to try it was W.O. Tommaso Dal Molin. One disadvantage of the design immediately became clear, as the aircraft sat very low in the water. This may have been fine on a fairly smooth lake but it may have been more of a problem on the open sea where the Schneider Trophy trials usually took place. Waterproofing the P.7 would have been crucial to prevent it being swamped in a swell.

A somewhat larger issue is that the P.7 never achieved flight. Part of the reason is that the mechanism for diverting the drive was too complicated. Operating the clutches correctly in a coordinated manner to manage the engine revolutions while controlling the aircraft would have required the pilot to have had three hands. This was probably for the best, as alighting the P.7 is likely to have been hazardous in the extreme as it probably could only have been achieved with the engine stopped to prevent the propellor striking the water.

Image from Piaggio P.7 / Piaggio-Pegna Pc 7 Schneider Racer | Old Machine Press

Savoia S.65

Designed by Alessandro Marchetti, the Savoia S.65 was a somewhat unconventional twin-engine aircraft. Like the Piaggio-Pegna P.7, it was intended that the S.65 would compete for the Schneider Trophy in 1929, but technical problems prevented it from coming to the start line. However, the Italian team still brought the S.65 with them to Calshot where it was displayed to give the British something to think about.

The Savoia S.65 was distinctive in that both engines were contained in a central nacelle in a “push-pull” configuration, with the pilot sandwiched between them. The tailplane and rudder were supported on booms and strut-braced to the very long slender floats. The engines were a pair of Isotta-Fraschini Asso 12-cylinder vee engines rated at 1,050hp each. Confidence in the design was high and it was believed that it would be faster than the Supermarine S.6.

The location of the cockpit of the S.65 and its position between the two engines meant that it was incredibly cramped and not suitable for every pilot. Indeed, the only pilot on the Italian team small enough to fit was W.O. Tommaso Dal Molin. Some accounts record that he had to dispense with a parachute to make sure that he would fit, although attempting to bail out of the S.65 would have been highly risky given the hazard posed by the rear propellor.

The S.65 was dogged by problems with fuel starvation and overheating, especially for the rear engine. It was also found that the cockpit would fill with exhaust fumes, but this was cured by moving the exhaust ports from the top of the engine to the sides. However, by the time these issues had been rectified the window had closed on its participation. The S.65 was also fitted with an enlarged tail fin and rudder to try and remedy longitudinal control issues.

Development work continued until early 1930 when the S.65 crashed on a test flight. The aircraft pitched up steeply after take-off, stalled and crashed into the lake, killing Dal Molin. The aircraft sank immediately and it was more than a week before it, and the body of Dal Molin, could be recovered.

Image from Savoia-Marchetti S.65 Schneider Racer | Old Machine Press

Macchi-Castoldi MC.72

At the conclusion of the of the 1929 Schneider Trophy race at Calshot, Italian Air Minister, Gen. Italo Balbo, declared “We have obtained the results we expected, but we have now finished playing our part as sportsmen. Tomorrow our work as competitors will begin.” Italy had suffered two defeats but clearly considered themselves capable of beating Britain and were determined to get back to winning ways. Rather than trying to develop multiple types as before, all energy would be focused on one all-conquering design.

This design would be the Macchi-Castoldi MC.72, the ultimate expression of Mario Castoldi’s seaplane racer design. The heart of the MC.72 was the monstrous FIAT AS.6 engine, a huge 24-cylinder vee engine producing 2,500hp which measured 11 feet in length. It was essentially a pair of AS.5 12-cylinder engines mounted back-to-back on a shared crankcase, each driving one half of a counter-rotating propellor through co-axial driveshafts.

The use of a counter-rotating propellor was primarily to aid take-off by cancelling out the problem of torque reaction, something that had plagued the high-powered seaplanes entered into the Schneider Trophy for years. The inertia of the engine and propellor as it was spun in one direction would result in the rest of the aircraft attempting to spin in the opposite direction, in accordance with Newton’s Third Law of Motion. This afflicted floatplanes in particular, because this interaction of forces could result in one float being driven under the water during take-off, causing a huge amount of hydrodynamic drag. It was not uncommon for Schneider Trophy racers to make uncontrollable arcs on the water and fail to “unstick”. The most common solutions were to address the buoyancy of the aircraft by making one float slightly larger than the other or by rebalancing the fuel load to lighten whichever float was prone to submersion. Other techniques included taking-off at an angle to the wind until enough speed had been gained to start hydroplaning, by which time the aircraft would have turned itself into the wind. However, the configuration of the FIAT AS.6 cancelled out torque reaction at source making take-offs much safer.

The prodigious power and clever configuration of the FIAT AS.6 would be the MC.72’s greatest strengths, but it would also be its Achilles Heel. One of the disadvantages of such a massive engine was how to dissipate the huge amount of heat it generated. As well as the usual wing surface radiators, the requirements for engine cooling meant that the MC.72 was also provided with radiators on the fuselage flanks, the floats and the float struts. It was also a difficult engine to set-up and was a constant source of trouble to the Italian team.

The first of a total of five aircraft was built and delivered to the Italian team at Desenzano for testing, but problems with the engine immediately became evident. The two halves of the AS.6 engine were not linked and, with the rear 12-cylinders also driving the supercharger for the whole engine, the two propellors did not always rotate at the same speed. In addition to this, the engine suffered with carburettor issues and would backfire violently in flight, which cut short the first flight of the MC.72 in the hands of Lt. Giovanni Monti. This would be an enduring problem with the FIAT AS.6 engine. On a later test flight, Monti overflew the engineers on the ground so that they could hear its irregular firing. As they listened and watched, the aircraft suddenly pitched upwards before diving into the lake, causing Monti’s death. An investigation concluded that a bearing had failed in the co-axial driveshafts causing the two propellors to touch.

Similar engine-related problems were encountered with the second MC.72, raising doubts as to whether it would be ready to compete for the 1931 Schneider Trophy. In the end the decision to withdraw from the contest had to be taken but, despite this, Italy was not going to give up and allow the British to have everything their own way.

The potential of the MC.72 was already evident and so, two days before Britain would win the Schneider Trophy, an attempt would be made on the world air speed record. Sadly, the attempt ended in tragedy. While making a high-speed run, the aircraft flew into rising ground without any attempt to deviate and was destroyed. The official investigation found that the engine had back-fired violently into the carburettor air intake setting fire to the gravity fuel tank just behind it and incapacitating its pilot, Lt. Stanislao Bellini.

With the conclusion of the Schneider Trophy series, Italy invited British petrochemical engineer Rod Banks to help solve the problems afflicting the FIAT AS.6. Banks had been involved with the development of the Rolls-Royce R engine that had powered the Supermarine S.6 series and had been responsible for formulating the special fuels that they ran on. He was surprised to find that ground testing of the engine had not been done in a way that replicated flight conditions, as Rolls-Royce had. He persuaded FIAT to install a wind tunnel and then formulated a special fuel for the engine and set about dealing with the big engine’s carburetion problems.

With the fuelling problems fixed and the engine now producing 3,000hp, the MC.72 could finally show its full potential. In April 1933, with W.O. Francesco Agello at the controls, the MC.72 set a world air speed record of 423.82mph. This was raised to 440.68mph by Agello in the MC.72 in October of the following year, a record that still stands today for the fastest piston-engine seaplane.

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