23 October 1934: At Lago di Garda, Brescia, Italy, Warrant Officer Francesco Agello, Regia Aeronautica, set a Fédération Aéronautique Internationale (FAI) World Record for Speed Over a 3 Kilometer Course when he flew the Macchi Aeronautica M.C. 72 float plane, serial number MM 181, to an average speed of 709.21 kilometers per hour (440.68 miles per hour).¹
A contemporary news article described the event:
FLYING the Machi-Castoldi 72 seaplane (3,000 h.p. special 24-cyl. Fiat) at Lake Garda on Tuesday of last week, Warrant-Officer Francesco Agello, of the Italian Royal Air Force, raised his own world’s air speed record by putting up a mean speed (subject to homologation) of 709.202 km./hr. (440.677 m.p.h.) for the usual four flights. His previous record stood at 682.403 km./hr. (423.76 m.p.h.)
The weather conditions under which the attempts were made were ideal, there being just sufficient breeze to take the glassiness off the water, so assisting the takeoff. Temperature was suitable, and the air was free from bumps.
Just before 3 p.m. Agello took off and made four runs over the three-kilometre course, clocking as follows:—
[Direction] Secs. km./hr. m.p.h
North-South 15 29/100 705.882 438.614
South-North 15 19.2/100 710.433 441.423
North-South 15 18.1/100 711.462 442.081
South-North 15 23.4/100 709.034 440.738
After the successful attempt a banquet was held in the Officers’ Mess at Desenzano in Agello’s honour. The speeds were announced, and Col. Bernasconi, who is in command of the High-speed Flight, stated that Signor Mussolini had honoured Warrant-Officer Agello by promoting him to a full lieutenant.
Only a few modifications had been made to the Macchi-Castoldi since the previous attempt, chief among them being the substitution of wooden floats for the metal ones previously used.
As is well known. the most interesting feature of the machine is the extremely unconventional power-unit, the Fiat A.S.6. The problem of frontal area for such a powerful unit as was specified was solved by placing the twenty-four cylinders (totalling in capacity over fifty litres) in two rows, forming a 60 deg. “vee,” and further, arranging them in two mechanically independent groups.
Each group has its own crank shaft, but a single crank case is used for both. The crank shafts, which rotate in opposite directions, are coupled in the centre by spur-gear reduction units, which drive two airscrew shafts. One of these shafts is hollow, and the other operates within it. The two shafts run forward through the “vee” of the front unit, and each carries an airscrew; so that there are two of the latter, close together, but revolving in opposite directions.
Each engine unit has independent camshafts (two per engine), water pump and dual Marelli magnetos, but a common induction system is used, an eight-jet carburetter being mounted behind the rear unit and mixture being drawn from it passed to the cylinders by a supercharger geared up to 20,000 r.p.m. An interesting point is that this supercharger absorbs 200 h.p., and, since it is driven by the rear engine, the blades of the front airscrew (which the rear engine drives) are given different inclination to correct for the slight difference in power.
The power units develop 3,000 h.p. at 3,200 r.p.m., and weighs 2,045lb., giving a weight per h.p. of 0.706lb. The all-up weight of the machine, with pilot and full tanks, is 6,670lb.
British equipment figured in the success, for Castrol oil and K.L.G. plugs were used.
— FLIGHT, The Aircraft Engineer and Airships, No. 1349, Vol. XXVI, November 1, 1934, at Page 1152.
The Macchi-Castoldi M.C.72 was designed by Mario Castoldi for Aeronautica Macchi. It was a single-place, single-engine, low-wing monoplane float plane constructed of wood and metal. It was 8.32 meters (27 feet, 3.5 inches) long with a wingspan of 9.48 meters (31 feet, 1.25 inches) and height of 3.30 meters (10.83 feet). The M.C.72 had an empty weight of 2,505 kilograms (5,512 pounds), loaded weight of 2,907 kilograms (6,409 pounds) and maximum takeoff weight of 3,031 kilograms (6,669 pounds).
It was powered by a 50.256 liter (3,067 cubic inch) liquid-cooled, supercharged Fiat S.p.A. AS.6 24-cylinder 60° dual overhead cam (DOHC) V-24 engine with 4 valves per cylinder. The engine produced 3,100 horsepower at 3,300 r.p.m. and drove two counter-rotating metal two-bladed fixed pitch propellers with a diameter of 8 feet (2.56 meters). The counter-rotating blades cancelled the torque effect of the engine.
Surface radiators were placed on top of each wing and surface oil coolers on the floats.
Five Macchi M.C.72 float planes had been built for the 1931 Schneider Trophy race, but problems with the Fiat AS.6 engine, which was essentially two AS.5 V-12s assembled back-to-back, prevented them from competing.
Four test pilots, including Francesco Agello, had been selected to fly the airplanes for speed record attempts. Two were killed while testing the M.C.72, and the third died when another airplane crashed. The cause of the accidents were explosions within the engines’ intake tract. Though they ran perfectly on test stands, in flight, they began to backfire, then explode.
It was discovered by Rod Banks, a British engineer who had been called in to develop a special high-octane fuel, that the Fiat engineers had overlooked the ram effect of the 400 mile per hour slipstream. This caused the fuel mixture to become too lean, resulting in predetonation and backfiring. A modification was made to the intake and the problem was resolved.
Francesco Agello was twice awarded the Henry De La Vaulx Medal by the Fédération Aéronautique Internationale, and also awarded the Medaglia d’oro al valore aeronautico. In part, his citation read, “A high speed pilot of exceptional courage and, after competition in difficult and dangerous test flights during the development of the fastest seaplane in the world, twice he conquered the absolute world speed record.”
Captain Agello was killed in a mid-air collision, 26 November 1942, while testing a Macchi C.202 Fogore fighter.
¹ FAI Record File Number 4497
© 2016, Bryan R. Swopesby