Today in Aviation History: First Flight of the Stipa-Caproni

On October 7, 1932, the Stipa-Caproni took its first flight, a flight of a revolutionary idea that was forever going to alter modern aviation. This is a story of a prototype that was never mass-produced but still became a marvel that was studied across several nations for its incredible design. In the early 1930s, as aviation required more efficient propulsion systems, Luigi Stipa, with his expertise in aerodynamic efficiency and propeller performance, came up with a “intubed propeller” concept. This concept featured a hollow, barrel-shaped fuselage housing the engine and propeller within itself, acting like a single ducted fan. Now, this might sound familiar, as this very idea that was born in Italy was an inspiration for modern-day jet propulsion.

The Italian Progettare

Stipa’s design of the aircraft involved a magnificent application of Bernoulli’s principle. He envisioned the fuselage as a tapered duct housing the engine and the propeller. This duct acted as a venturi tube, compressing the airflow from the propeller and engine exhaust before it exited the outlet at the trailing edge. The unique cylindrical design of the fuselage allowed for a streamlined profile and reduced drag, increasing the overall efficiency. Stipa then worked with the Engineering Division of the Italian Ministry of Air Force, studying the idea mathematically. During these years, he concluded that the inner surface of the venturi tube needed an airfoil shape to achieve the greatest efficiency. He also studied and determined the best rate of revolution of the propeller and the most efficient distance between the leading edge of the duct and the propeller. After spending years refining his idea, he finally petitioned the Italian government to manufacture a prototype aircraft for his design. The contract for building Stipa’s design was given to Caproni in 1932, as the Italian government was seeking ways to showcase Italian aviation technology.

Fasi della costruzione della carlinga dello Stipa Caproni 06

Fasi della costruzione della carlinga dello Stipa Caproni 07

The Prototype

With the combined efforts of Stipa and Caproni, the resulting aircraft was a barrel-like, short and fat monoplane with a mid-wing. The fuselage was mainly composed of wood and was open at both ends to form the tapered duct. The elliptical wings passed through this duct with the engine nacelle inside it. The duct, as predicted by Stipa, had a profile similar to that of the airfoil, with a fairly small rudder and elevators mounted on the trailing edge of the duct. This design allowed the ducted propeller wash to flow directly over the mounted controls as it exited the fuselage to improve handling.

Stipa Caproni 2 — 3/4 view of the prototype

The engine was powered by the 120-horsepower (89 kW) de Havilland Gipsy III, which was mounted within the duct behind it at the midpoint of the fuselage. Additionally, the aircraft had low, fixed, spatted main landing gear and a tailwheel with twin open cockpits. The Stipa-Caproni prototype proudly showcased its Italian origin in a blue-and-cream color used on racing aircraft of the day, with Italian flag colors painted on the rudder.

The Maiden Flight

After spending a valuable amount of time on intricate details, the Stipa-Caproni prototype took its first flight on October 7, 1932, with test pilot Domenico Antonini. The flight went successfully, showcasing that the intubed propeller design indeed increased the engine’s efficiency, as Stipa had researched. Moreover, even the airfoil shape of the duct interior proved to be an effectual idea as it provided the aircraft with additional lift, a very low landing speed of 42mph, and a higher rate of climb.

1280px Stipa Caproni in volo — The Stipa-Caproni in flight. Photo from the book L’uomo e l’aria – L’aeronautica vol. II Editore F. Vallardi 1939

The placement of the rudder and elevators at the trailing edge of the tube gave the aircraft efficient handling characteristics, making it very stable in flight. The Stipa-Caproni was also strikingly quieter than conventional aircraft of the time. Unfortunately, despite its experimental success, the aircraft has some deal-breaking drawbacks. These drawbacks included the intubate propeller design, which induced so much aerodynamic drag, and also the aircraft’s top speed proved to be only 81 mph. Thus, the benefits in engine efficiency were canceled out.

Every End is a Beginning

Since the airplane did not perform better than the existing conventional designs, the Italian Air Force made the harsh decision to cancel any further development on the aircraft. Hence, no further prototypes were built, and the aircraft never entered mass production. However, the test flights of the Stipa-Caproni shined so bright that it reached France, Germany, Italy, and the UK and to the National Advisory Committee for Aeronautics in the United States. It caught their academic interests, and Stipa’s work was studied for inspiration across the globe. Various countries like France and Germany designed aircraft influenced by Stipa’s design, especially the German Heinkel “T” fighter of 1940.

The legacy of the Stipa-Caproni lives on through modern tributes like the 3/5-scale replica built by Lynette Zuccoli and Aerotec Queensland in Australia. Powered by an Italian Simonini racing engine, this carefully crafted replica successfully took to the skies in October 2001. Piloted by Bryce Wolff, the aircraft managed to replicate the stability and performance described by Italian test pilots nearly 70 years earlier. Though its flying days may be over, the replica now sits on display at Toowoomba City Aerodrome in Australia, a testament to Luigi Stipa’s visionary design and the ongoing fascination with this pioneering aircraft. It reminds us of the spirit of innovation and how the Stipa-Caproni, despite its unconventional appearance, contributed to the evolution of modern jet propulsion.

Today in Aviation History is a series highlighting the achievements, innovations, and milestones that have shaped the skies. All the previous anniversaries are available HERE.

Haritima Maurya

"Haritima Maurya, pen name, ""Another Stardust,"" has been passionate about writing since her school days and later began sharing her work online in 2019. She was drawn to writing because of her love for reading, being starstruck by the art of expression and how someone can make you see and feel things exclusive to their experience. She wanted to be able to do that herself and share her mind with world cause she believes while we co exist in this beautiful world least we can do is share our little worlds within.

As a commercial pilot, Haritima balances her passion for aviation with her love for storytelling. She believes that, much like flying, writing offers a perspective beyond the ordinary, offering a bridge between individual experiences and collective understanding.

Through her work, ""Another Stardust"" aims to capture the nuances of life, giving voice to moments that resonate universally. "

Today in Aviation History: First Flight of the Stipa-Caproni