By Alberto Casirati v. Verdi 12 24052 Azzano S. Paolo (BG) Italy

Behind Piaggio, the last aquaplaning of my S 65...

One of the very first men to study the topic of hydroplane tabs in depth was Ing. Giovanni Pegna, who previously had many interesting and intense experiences in various fields of aeronautical engineering.

Ing. Pegna developed a study on hydroplane tabs for high speed flying boats. He decided to do that after careful examination of the ways in which speed gains for those machines had been obtained; in fact, he noted that improvements had been mostly achieved by increasing engine power, while just a few studies aimed at decisive reduction of drag factors had been carried out. His studies were therefore aimed not only at improving aerodynamic qualities, but also at the total elimination of some drag factors. The most important amongst the latter was the presence of the floats, which were responsible for wasting the highest percentage of available power. Hydroplane tabs could solve the problem. Theoretically, the solution appeared exciting, and very elegant, but many uncertainties needed to be solved. Nothing similar had been attempted before, so that there were no previous experiences to learn from. In addition, there was not much time available for experimental work, because of the delivery date imposed by thé ministerial contest issued for the 1929 Schneider Trophy Race.

Scale model of the Pc.7 in the Piaggio model collection of its aircraft

Hydroplane tabs were to be used as takeoff devices; this meant that the following conditions had to be met:

- the fuselage had to be waterproof, so that it could act as the hull;

- a waterscrew had to be installed, in order to make the aircraft gain speed while still on the water; the tabs would allow the hull to rise from the water once a certain speed was reached and then power would be diverted to the airscrew for takeoff;

- a choice had to be made as far as the powerplant was concerned: it was possible to install two différent engines (one for the waterscrew and one for the airscrew) or to adopt a single unit, equipped with a diverting device; the latter solution was chosen and the resulting difficulties prevented flight testing the prototype;

- the adoption of a very long engine shaft and of reduction grears.

The use of hydroplane tabs could give advantages like much reduced total frontal area and overall smaller dimensions, so that higher speeds could be achieved with the same available power. The airplane would also have preserved all the advantages of flying boats as far as takeoff and landing were concerned.

All of the main difficulties were solved in theory, but a prolonged series of experiments was needed to make theoretical solutions work in practice. This prevented the machine being ready for the 1929 Schneider Trophy Race, although early floating trials, carried out by test pilot Dal Molin, gave good results. Other difficulties, and the resulting costs, caused the abandonment of the project.

The Piaggio Pegna Pc.7 was a monoplane with elliptical wings. Its fuselage had a hull shape and three tabs were fixed to the hull, one under the tail surfaces and two under the engine. Power was to be supplied by the Isotta Fraschini inline, vee 800 hp engine, placed just before the wing leading edge. Cooling was achieved by means of radiant surfaces placed on the wing upper surfaces, while the oil cooling device and air intakes for the carburetors were placed on the forward fuselage sides. The airplane had a long nose, and this immediately earned it the nickname of `Pinocchio'.

Technical data: Wing span 6.70 m, length, 8.86 m, height 2.45 m, wing area 9.83 sq.m, empty weight 1,406 kg, loaded weight 1,686 kg, and maximum theoretical speed 600 km/h.

1988 Schneider Cup

Although the Piaggio Pegna Pc.7 never flew the design and concept were fully vindicated in 1988 when an R/C model of the PC.7 flew and won the tenth Schneider Cup event for models, held at Lake Varese, Italy in October. Built by Alain Vassel, the model Pc.7 was launched, the waterscrew was started, the plane lifted itself from the water on its tabs, the propeller was engaged and the little Pc.7 took off from the lake. It flew the five required laps, becoming the fastest and the winner of the event, landed on the lake, touching down five times, and taxied to the shore.

Alain Vassel's beautiful R/C model of the Piaggio Pegna Pc.7 bright red with upper wing copper, ailerons and wing tips aluminium

The Pc.7 in flight and its way to victory during the Schneider Cup

The beautiful red bird landing on the lake after its five lap flight

Among the other fifteen entrants in 1988 were models of the Sopwith Tabloid which won the 1914 Schneider Trophy Race, the Macchi M-7 which won the 1921 race, the Macchi M-33 which was third in 1925, the Supermarine S.5 which won the 1927 event, the SIAI SM-65 pusher-puller, twin boom seaplane built for the 1929 race but which crashed on landing in January 1930 killing Dal Molin who was the pilot, and the Fiat C.29 built for the 1931 Schneider.

Another participant at the 1988 Schneider Cup event was this model of the Sopwith Tabloid

Red with aluminum cowl and top decking model of the 1931 Fiat C.29, with the Macchi M-33 model just behind it

Sky Ways N° 16 october 1990

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