Stipa-Caproni
Encyclopedia
The Stipa-Caproni, also generally called the Caproni Stipa, was an experimental Italian
aircraft designed in 1932 by Luigi Stipa
(1900–1992) and built by Caproni
. It featured a hollow, barrel-shaped fuselage
with the engine
and propeller
completely enclosed by the fuselage—in essence, the whole fuselage was a single ducted fan
. Although the Regia Aeronautica
(Italian Royal Air Force) was not interested in pursuing development of the Stipa-Caproni, its design was an important step in the development of jet propulsion
.O.E. Lancaster, High Speed Aerodynamics and Jet Propulsion. Vol. XII: Jet Propulsion Engines, Princeton 1959 claims that "The Stipa Aero plane built by Caproni in 1932 should be classified as a Jet Aircraft. The Stipa Aero plane can be considered as a predecessor of the Jet Aircraft of today."
s; in fact, after having patented his design in Italy, Germany
, and the United States
in 1938, Stipa became convinced that German rocket
and jet technology (especially the V-1 flying bomb
) was using his patented invention without giving proper credit. Stipas basic idea—which he called the "intubed propeller"—was to mount the engine and propeller inside a fuselage that itself formed a tapered duct, or venturi tube, and compressed the propeller's airflow and the engine exhaust before it exited the duct at the trailing edge of the aircraft, essentially applying Bernoulli's principle
of fluid movements to make the aircraft's engine more efficient.
Stipa spent years studying the idea mathematically
while working in the Engineering Division of the Italian Air Ministry, eventually determining that the venturi tube's inner surface needed to be shaped like an airfoil
in order to achieve the greatest efficiency. He also determined the optimum shape of the propeller, the most efficient distance between the leading edge of the tube and the propeller, and the best rate of revolution of the propeller. Finally, he petitioned the Italian Fascist
government to produce a prototype aircraft. The government, seeking to showcase Italian technological achievement—particularly in aviation—contracted the Caproni
company to construct the aircraft in 1932.
The resulting aircraft—a midwing monoplane of mostly wooden construction dubbed the Stipa-Caproni or Caproni Stipa—was strikingly ungainly in appearance. The fuselage was a barrel-like tube, short and fat, open at both ends to form the tapered duct, with twin open cockpits in tandem mounted in a hump on top of it. The wings were elliptical and passed through the duct and the engine nacelle
inside it. The duct itself had a profile similar to that of the airfoils, allowing the fuselage to provide the airplane with additional lift
, and a fairly small rudder
and elevators
were mounted on the trailing edge of the duct, allowing the ducted propeller wash to flow directly over them as it exited the fuselage to improve handling. The propeller was mounted inside the fuselage tube, flush with the leading edge of the fuselage, and the 120-horsepower
de Havilland
Gipsy III engine that powered it was mounted within the duct behind it at the mid-point of the fuselage. The aircraft had low, fixed, spatted main landing gear and a tailwheel, making it look as if it was squatting when on the ground. It was painted in a blue-and-cream scheme of the type used on racing aircraft of the day, and its rudder bore the colors of the Italian flag.
company test pilot Domenico Antonini at the controls. Initial testing showed that the "intubed propeller" design did increase the engine's efficiency as Stipa had calculated, and the additional lift provided by the airfoil shape of the interior of the duct itself allowed a very low landing speed of only 68 km/h (42 mph) and assisted the Stipa-Caproni in achieving a higher rate of climb than other aircraft with similar power and wing loading
. The placement of the rudder and elevators in the exhaust from the propeller wash at the trailing edge of the tube gave the aircraft handling characteristics that made it very stable in flight, although they later were enlarged to further improve the plane's handling characteristics. The Stipa-Caproni proved to be noticeably quieter than conventional aircraft of the time. Unfortunately, the "intubed propeller" design also induced so much aerodynamic drag that the benefits in engine efficiency were cancelled out, and the aircraft's top speed proved to be only 131 km/h (81 mph).
When Caproni had completed initial testing, the Regia Aeronautica took control of the plane and transferred it to Guidonia Montecelio
for a brief series of further test flights. All test pilots reported that the plane was extremely stable in flight, to the point where it was difficult to change course; test pilots were also astounded by the very low landing speed and the consequently very short landing run.
As the plane did not perform noticeably better than conventional aircraft designs, the Regia Aeronautica decided to cancel further development. No further prototypes were built.
—instead envisioning its use in large, multi-engine flying wing
aircraft he had been designing in which the aerodynamic drag properties would not be significant, and the Italian government publicized the Stipa-Caproni's design as an example of Italian aviation technology prowess. None of Stipa's flying-wing aircraft designs were built, but experiences collected with the Stipa-Caproni did become an important influence in the development of the motorjet
-powered Caproni Campini N.1.
The test flights of the Stipa-Caproni also sparked much academic interest, and resulted in Stipa's work being studied in France, Germany, Italy, and the United Kingdom
, and by the National Advisory Committee for Aeronautics
in the United States
. France designed—but never constructed—an advanced night bomber
based on a Luigi Stipa design in the mid-1930s, and various aircraft designs such as the German Heinkel T fighter of 1940 are thought to have incorporated some of Stipa's ideas as demonstrated by the Stipa-Caproni.
The Kort nozzle
ducted fan of today—designed in Germany in 1934—uses many of Stipa's principles, and the modern turbofan engine is thought by some aviation historians to be a descendant of the "intubed propeller" demonstrated in the Stipa-Caproni.
, Lynette Zuccoli and Aerotect Queensland designed a 3/5-scale replica of the Stipa-Caproni, accurate even in terms of paint scheme and markings, powered by an Italian Simonini racing engine. They built it in 1998 and in October 2001 succeeded in making two directional test flights with it with Bryce Wolff at the controls. Each flight covered about 600 meters (660 yards) and reached an altitude of approximately 6 meters (20 feet), with Wolff reporting that the replica was very stable in flight and performed much as the Italian test pilots reported that the original aircraft had 69 years to the month earlier. The replica may never have flown again, and apparently now is on static display in Australia.
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
aircraft designed in 1932 by Luigi Stipa
Luigi Stipa
Luigi Stipa was an Italian aeronautical, hydraulic, and civil engineer and aircraft designer who invented the "intubed propeller" for aircraft, a concept that some aviation historians view as the predecessor of the turbofan engine....
(1900–1992) and built by Caproni
Caproni
thumb|right|300px|[[Caproni Ca.316]] seaplane at its moorings.Caproni was an Italian aircraft manufacturer founded in 1908 by Giovanni Battista "Gianni" Caproni....
. It featured a hollow, barrel-shaped fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
with the engine
Aircraft engine
An aircraft engine is the component of the propulsion system for an aircraft that generates mechanical power. Aircraft engines are almost always either lightweight piston engines or gas turbines...
and propeller
Propeller (aircraft)
Aircraft propellers or airscrews convert rotary motion from piston engines or turboprops to provide propulsive force. They may be fixed or variable pitch. Early aircraft propellers were carved by hand from solid or laminated wood with later propellers being constructed from metal...
completely enclosed by the fuselage—in essence, the whole fuselage was a single ducted fan
Ducted fan
A ducted fan is a propulsion arrangement whereby a fan, which is a type of propeller, is mounted within a cylindrical shroud or duct. The duct reduces losses in thrust from the tip vortices of the fan, and varying the cross-section of the duct allows the designer to advantageously affect the...
. Although the Regia Aeronautica
Regia Aeronautica
The Italian Royal Air Force was the name of the air force of the Kingdom of Italy. It was established as a service independent of the Royal Italian Army from 1923 until 1946...
(Italian Royal Air Force) was not interested in pursuing development of the Stipa-Caproni, its design was an important step in the development of jet propulsion
Jet propulsion
Jet propulsion is motion produced by passing a jet of fluid in the opposite direction to the direction of motion. By conservation of momentum, the moving body is propelled in the opposite direction to the jet....
.O.E. Lancaster, High Speed Aerodynamics and Jet Propulsion. Vol. XII: Jet Propulsion Engines, Princeton 1959 claims that "The Stipa Aero plane built by Caproni in 1932 should be classified as a Jet Aircraft. The Stipa Aero plane can be considered as a predecessor of the Jet Aircraft of today."
Stipa's design
The design of the Stipa-Caproni was very similar to that of modern jet engineJet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s; in fact, after having patented his design in Italy, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
in 1938, Stipa became convinced that German rocket
Rocket
A rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
and jet technology (especially the V-1 flying bomb
V-1 flying bomb
The V-1 flying bomb, also known as the Buzz Bomb or Doodlebug, was an early pulse-jet-powered predecessor of the cruise missile....
) was using his patented invention without giving proper credit. Stipas basic idea—which he called the "intubed propeller"—was to mount the engine and propeller inside a fuselage that itself formed a tapered duct, or venturi tube, and compressed the propeller's airflow and the engine exhaust before it exited the duct at the trailing edge of the aircraft, essentially applying Bernoulli's principle
Bernoulli's principle
In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy...
of fluid movements to make the aircraft's engine more efficient.
Stipa spent years studying the idea mathematically
Mathematics
Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...
while working in the Engineering Division of the Italian Air Ministry, eventually determining that the venturi tube's inner surface needed to be shaped like an airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
in order to achieve the greatest efficiency. He also determined the optimum shape of the propeller, the most efficient distance between the leading edge of the tube and the propeller, and the best rate of revolution of the propeller. Finally, he petitioned the Italian Fascist
Italian Fascism
Italian Fascism also known as Fascism with a capital "F" refers to the original fascist ideology in Italy. This ideology is associated with the National Fascist Party which under Benito Mussolini ruled the Kingdom of Italy from 1922 until 1943, the Republican Fascist Party which ruled the Italian...
government to produce a prototype aircraft. The government, seeking to showcase Italian technological achievement—particularly in aviation—contracted the Caproni
Caproni
thumb|right|300px|[[Caproni Ca.316]] seaplane at its moorings.Caproni was an Italian aircraft manufacturer founded in 1908 by Giovanni Battista "Gianni" Caproni....
company to construct the aircraft in 1932.
The resulting aircraft—a midwing monoplane of mostly wooden construction dubbed the Stipa-Caproni or Caproni Stipa—was strikingly ungainly in appearance. The fuselage was a barrel-like tube, short and fat, open at both ends to form the tapered duct, with twin open cockpits in tandem mounted in a hump on top of it. The wings were elliptical and passed through the duct and the engine nacelle
Nacelle
The nacelle is a cover housing that holds engines, fuel, or equipment on an aircraft. In some cases—for instance in the typical "Farman" type "pusher" aircraft, or the World War II-era P-38 Lightning—an aircraft's cockpit may also be housed in a nacelle, which essentially fills the...
inside it. The duct itself had a profile similar to that of the airfoils, allowing the fuselage to provide the airplane with additional lift
Lift (force)
A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...
, and a fairly small rudder
Rudder
A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...
and elevators
Elevator (aircraft)
Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...
were mounted on the trailing edge of the duct, allowing the ducted propeller wash to flow directly over them as it exited the fuselage to improve handling. The propeller was mounted inside the fuselage tube, flush with the leading edge of the fuselage, and the 120-horsepower
Horsepower
Horsepower is the name of several units of measurement of power. The most common definitions equal between 735.5 and 750 watts.Horsepower was originally defined to compare the output of steam engines with the power of draft horses in continuous operation. The unit was widely adopted to measure the...
de Havilland
De Havilland
The de Havilland Aircraft Company was a British aviation manufacturer founded in 1920 when Airco, of which Geoffrey de Havilland had been chief designer, was sold to BSA by the owner George Holt Thomas. De Havilland then set up a company under his name in September of that year at Stag Lane...
Gipsy III engine that powered it was mounted within the duct behind it at the mid-point of the fuselage. The aircraft had low, fixed, spatted main landing gear and a tailwheel, making it look as if it was squatting when on the ground. It was painted in a blue-and-cream scheme of the type used on racing aircraft of the day, and its rudder bore the colors of the Italian flag.
Test flights
The Stipa-Caproni first flew on 7 October 1932 with CaproniCaproni
thumb|right|300px|[[Caproni Ca.316]] seaplane at its moorings.Caproni was an Italian aircraft manufacturer founded in 1908 by Giovanni Battista "Gianni" Caproni....
company test pilot Domenico Antonini at the controls. Initial testing showed that the "intubed propeller" design did increase the engine's efficiency as Stipa had calculated, and the additional lift provided by the airfoil shape of the interior of the duct itself allowed a very low landing speed of only 68 km/h (42 mph) and assisted the Stipa-Caproni in achieving a higher rate of climb than other aircraft with similar power and wing loading
Wing loading
In aerodynamics, wing loading is the loaded weight of the aircraft divided by the area of the wing. The faster an aircraft flies, the more lift is produced by each unit area of wing, so a smaller wing can carry the same weight in level flight, operating at a higher wing loading. Correspondingly,...
. The placement of the rudder and elevators in the exhaust from the propeller wash at the trailing edge of the tube gave the aircraft handling characteristics that made it very stable in flight, although they later were enlarged to further improve the plane's handling characteristics. The Stipa-Caproni proved to be noticeably quieter than conventional aircraft of the time. Unfortunately, the "intubed propeller" design also induced so much aerodynamic drag that the benefits in engine efficiency were cancelled out, and the aircraft's top speed proved to be only 131 km/h (81 mph).
When Caproni had completed initial testing, the Regia Aeronautica took control of the plane and transferred it to Guidonia Montecelio
Guidonia Montecelio
Guidonia Montecelio is a town and comune in the province of Rome, Lazio, central Italy.- Geography :The community of Guidonia Montecelio lies to the north-east of Rome, some kilometres from the Grande Raccordo Anulare - a ring-shaped motorway which forms a circle around the capital...
for a brief series of further test flights. All test pilots reported that the plane was extremely stable in flight, to the point where it was difficult to change course; test pilots were also astounded by the very low landing speed and the consequently very short landing run.
As the plane did not perform noticeably better than conventional aircraft designs, the Regia Aeronautica decided to cancel further development. No further prototypes were built.
Influence
Stipa himself never had intended his "intubed propeller" to be employed on single-engine aircraft like the Caproni-Stipa—which he viewed merely as a testbedTestbed
A testbed is a platform for experimentation of large development projects. Testbeds allow for rigorous, transparent, and replicable testing of scientific theories, computational tools, and new technologies.The term is used across many disciplines to describe a development environment that is...
—instead envisioning its use in large, multi-engine flying wing
Flying wing
A flying wing is a tailless fixed-wing aircraft which has no definite fuselage, with most of the crew, payload and equipment being housed inside the main wing structure....
aircraft he had been designing in which the aerodynamic drag properties would not be significant, and the Italian government publicized the Stipa-Caproni's design as an example of Italian aviation technology prowess. None of Stipa's flying-wing aircraft designs were built, but experiences collected with the Stipa-Caproni did become an important influence in the development of the motorjet
Motorjet
A motorjet is a rudimentary type of jet engine which is sometimes referred to as thermojet, a term now commonly used to describe a particular and completely unrelated pulsejet design.- Design :...
-powered Caproni Campini N.1.
The test flights of the Stipa-Caproni also sparked much academic interest, and resulted in Stipa's work being studied in France, Germany, Italy, and the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
, and by the National Advisory Committee for Aeronautics
National Advisory Committee for Aeronautics
The National Advisory Committee for Aeronautics was a U.S. federal agency founded on March 3, 1915 to undertake, promote, and institutionalize aeronautical research. On October 1, 1958 the agency was dissolved, and its assets and personnel transferred to the newly created National Aeronautics and...
in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
. France designed—but never constructed—an advanced night bomber
Bomber
A bomber is a military aircraft designed to attack ground and sea targets, by dropping bombs on them, or – in recent years – by launching cruise missiles at them.-Classifications of bombers:...
based on a Luigi Stipa design in the mid-1930s, and various aircraft designs such as the German Heinkel T fighter of 1940 are thought to have incorporated some of Stipa's ideas as demonstrated by the Stipa-Caproni.
The Kort nozzle
Kort nozzle
The Kort nozzle is a shrouded, ducted propeller assembly for marine propulsion. The hydrodynamic design of the shroud, which is shaped like a foil, offers advantages for certain conditions over bare propellers....
ducted fan of today—designed in Germany in 1934—uses many of Stipa's principles, and the modern turbofan engine is thought by some aviation historians to be a descendant of the "intubed propeller" demonstrated in the Stipa-Caproni.
Replica
In AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Lynette Zuccoli and Aerotect Queensland designed a 3/5-scale replica of the Stipa-Caproni, accurate even in terms of paint scheme and markings, powered by an Italian Simonini racing engine. They built it in 1998 and in October 2001 succeeded in making two directional test flights with it with Bryce Wolff at the controls. Each flight covered about 600 meters (660 yards) and reached an altitude of approximately 6 meters (20 feet), with Wolff reporting that the replica was very stable in flight and performed much as the Italian test pilots reported that the original aircraft had 69 years to the month earlier. The replica may never have flown again, and apparently now is on static display in Australia.
Specifications (original Stipa-Caproni)
Sources
- Guttman, Robert. "Caproni Flying Barrel: Luigi Stipa Claimed His 'Intubed Propeller' Was the Ancestor of the Jet Engine." Aviation History. March 2010. ISSN 1076-8858.
- Thompson, Jonathan W. Italian Civil and Military Aircraft, 1930-1945, Aero Publishers, 1963