A shark that was never allowed to bite: Piaggio Pegna PC.7 racing plane

Attention: I will reveal a few things about the Piaggio Pegna PC.7 right at the beginning, which, for the sake of suspense and to keep the reader interested, I should like to present at the end. Why am I doing this? It's easy to explain: the following three questions are bound to arise in view of this unusual model!

• Question number one: “Fiction or reality: was this plane really ever built?”
• Question number two: “Was this aircraft actually tested in real life?”
• Question number three: “Has this plane ever flown?”

The shortest answer to these three questions is: “Yes, yes and no”.
Of course, this does not reveal anything important about this amazing concept and the aircraft developed from it, but rather gives rise to further questions!

Anyone who thinks that the proverbial crazy loner was at work here is mistaken: the official starting point for the development of the PC. 7 was a commission from the Italian Ministry of Aviation to develop a racing seaplane to take part in the Schneider Trophy in 1929. This commission was not given to just anyone, but brought one of the most recognized personalities in the Italian aviation industry into play: Giovanni Pegna, head of the development department at Piaggio at the time, had a solid amount of experience in aircraft construction in general and in the development of seaplanes in particular. The aircraft manufacturer Piaggio, on the other hand, was known at the time for large and mostly multi-engine designs and would go on to develop a series of remarkable bombers and transport aircraft.

Question number 1: Fiction or reality: was this aircraft really ever built? About the design and construction of the Piaggio Pegna PC.7

After intensive investigations, some of which were carried out experimentally in water tanks and others on the design tables, Giovanni Pegna came up with a highly innovative proposal for the required new racing aircraft, which immediately convinced the Ministry of Aviation: in March 1928, Piaggio was commissioned to build two aircraft with the designations MM126 and MM127. The designation “PC. 7” referred on the one hand, as was customary in Italy, to Pegna's name as the responsible designer and to the manufacturer Piaggio, and on the other hand the following ‘C' stood for ‘Corsa' and thus designated the field of application of the planned design as a racing machine.

With his unusual approach to a “racing boat airplane”, Giovanni Pegna believed he was advancing a topic that was becoming increasingly apparent as a problem with the racing seaplanes of the day: the floats and the necessary struts limited the maximum speeds that could be achieved. The alternative of a flying boat, with its voluminous hull cross-section, also restricted the performance that could be achieved. Pegna's approach was to keep the cross-section of the aircraft as small as possible by submerging the entire fuselage almost completely so that it could be used as a buoyancy chamber. This meant that floats could be completely dispensed with. The high-set wings of the shoulder deck would rest on the surface of the water and stabilize the aircraft.

In order to get the construction, which was largely under water, moving, a propeller was installed in the stern, which was driven by the 800 hp Isotta Fraschini Asso 500 V-12 in-line engine via a remote shaft. If the PC.7 picked up enough speed, it would rise out of the water on its two hydrofoils until the two-blade propeller - held horizontally by an automatic system until then - came free of the water. Once this state was reached, the screw was to be disengaged and the propeller engaged so that its enormous tractive force could take over the propulsion. In this way, the machine would quickly build up the necessary speed to take off - and subsequently win almost every race! Because one thing seemed to be a predictable fact: the aerodynamically slim and floatless shape, combined with the tremendous power of the high-bred in-line engine, would push into previously unattainable speed ranges: a top speed of a highly respectable 600 km/h was calculated for the Piaggio Pegna PC.7!

The water landing was to take place at a still rapid 165 km/h. Before the hydrofoils were allowed to touch the water surface, however, the propeller had to be successively slowed down in flight so that it could then be fixed in a horizontal position again by the automatic system. This was undoubtedly a delicate procedure, which - lucky for us? - never had to be tested in reality.

The hull of the Piaggio Pegna PC.7 was made of two layers of plywood, with a waterproof membrane glued between these layers to ensure that the hull remained watertight. The wings, tail unit, the rudder system under the stern and the construction of the two hydrofoils at the bow and the one under the stern were also made of wood. The fuel tank was installed in the middle of the fuselage between the IF Asso 500 in-line engine and the narrow cockpit at wing height.

Special attention had to be paid to the design as a “submersible”: the exhaust system was located on the upper side, while the carburetor intake opening was closed by a rubberized cover during take-off and landing. This was automatically pressed against the opening during the corresponding flight phases to keep it watertight. The wingspan of 6.6 m with a length of 8.86 m was typically short for a racing aircraft; fully loaded, however, the PC.7 weighed 1686 kg (empty weight 1416 kg)

Was this airplane actually tested in real life? Did it ever fly? The testing of the Piaggio Pegna PC.7

The flight tests took place with the MM126 from October 1929 in Desenzano on Lake Garda. However, a glance at this date also makes one thing clear: the PC.7 had narrowly missed the Schneider Trophy held in September of that year. The “roll” tests were nevertheless carried out with interest, although the lengthy search for a pilot from Reparto Alta Velocità (RAV) who was actually willing to test this unusual construction may also have contributed to this delay. In the end, however, a test pilot was found in Tommaso Dal Molin who was prepared to embark on this unusual adventure. The RAV had been founded in 1928 as an organization with an exclusive group of test pilots to research high-speed flight and at the same time prepare for successful participation in the Schneider Trophy races. It had a counterpart in the “High Speed Flight” of the British.

Dal Molin actually managed to accelerate the MM126 in the water until the propeller was far enough away from the water to engage it - but it was not to be: Water had penetrated the hull in the meantime and made the coupling between the main shaft and the stern propeller so slippery that its performance dropped off. It also became apparent that the PC.7 was becoming worryingly unstable while sailing on the hydrofoils and could hardly be kept on course.

During the subsequent attempts to repair the clutch, the compact design of the fuselage without maintenance hatches proved to be a decisive obstacle: in order to access the defective coupling, it would have been necessary to completely rebuild the fuselage. However, as both Piaggio and the Ministry of Aviation were already beginning to lose interest in the concept at this point, the MM126 was stored in Desenzano for the time being, ultimately, as it turned out, without ever being repaired or made airworthy again. After a few years, the airframe, which was already desolate at the time, was dismantled.
In the meantime, the second PC.7 MM127 had been taken to Guidonia Montecelio near Rome. Here, speed tests were carried out for some time in a large water tank, although the focus was already on researching the hydrofoils. To all appearances, no flight tests were carried out with the second PC.7. The aircraft, which was stored soon afterwards, was destroyed in an air raid in 1944.

Kit and building process:

Piaggio-Pegna PC.7 from AMP in 1:48
Even if no original of this spectacular experimental machine has survived, it seems that enough stories and materials have remained to persuade the manufacturer AMP to bring a wonderfully designed plastic kit of this aircraft rarity onto the market a few years ago. A highly welcome development that few would have expected until 2019!

Anyone who has already had the pleasure of holding an AMP kit in their hands will not be surprised by the contents of the “Piaggio-Pegna PC.7 Schneider Trophy series”/ No. 48011 kit: accurately fitting plastic parts with an eye for fine details are supplemented by a small etched parts board on which the harness and the simple instrument panel can be found. The fine slats of the surface vaporization, which can be found on large areas of the wings and fuselage, are reproduced precisely and finely structured. AMP also managed to package the kit in such a way that no damage was found on these sensitive parts.

The construction itself was not difficult and can be carried out quickly and without detours. As you know, there is always a little room for modifications: since the hydrofoils were to be glued to the fuselage with a narrow end face, I wanted to improve their stability. With four small holes and just as many metal pins glued into them, I calmed my gut feeling that there could be trouble ahead. This is a low-cost measure that I would recommend, in retrospect. The only thing I added were the exhaust pipes protruding from the top. These are not available as components, but because they contribute significantly to the appearance, I improvised them with cable insulation of a suitable size.

I would like to recommend this kit with conviction. AMP offers a well-made kit of a rare (water) bird to anyone who enjoys and has an appreciation for such unusual models!

An addendum: after modeling friends and myself came to the conclusion that the shapes of the PC.7 are amazingly similar to a shark, I tried to express this whimsical idea with two drawings. I take the liberty of attaching these pictures.

28 additional images. Click to enlarge.