Luigi Stipa
Encyclopedia
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.
, Italy
in 1900. He left school to serve in the Italian Army
's Bersaglieri Corps during World War I
. After the war, he earned academic degree
s in aeronautical engineering, hydraulic engineering
and civil engineering
. He went to work for the Italian Air Ministry, where he rose to the position of general inspector of the Engineering Division of the Regia Aeronautica
(Italian Royal Air Force).
—in accordance with Bernoulli's principle
—a fluid's velocity increases as the diameter of a tube it is passing through decreases, Stipa believed that the same principle could be applied to air flow to make an aircraft's engine
more efficient by directing its propeller-wash through a venturi tube in a design he termed an "intubed propeller." In his concept, the fuselage
of a single-engined airplane designed around an intubed propeller would be constructed as a tube, with the propeller and engine nacelle inside the tube, and therefore within the fuselage. The propeller would be of the same diameter as the tube, and its slipstream would exit the tube via the opening at the tube's trailing edge at the rear of the fuselage.
Stipa spent years studying the idea mathematically
, eventually determing 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. He appears to have intended the intubed propeller for use in large, multi-engine, flying wing
aircraft—for which he produced several designs—but saw the construction of an experimental single-engine prototype
aircraft as the first step in proving the concept.
Stipa published his ideas in the Italian aviation journal Rivista Aeronautica ("Aeronautical Review"), then asked the Air Ministry to build a prototype
aircraft to prove his concept. Eager for propaganda opportunities to highlight Italian achievements in technology to the world, and particularly interested in aviation advances, the Italian Fascist
government approved of the venture, and contracted with the Caproni
Aviation Corporation to build the prototype in 1932.
, first flew on October 7, 1932. Remarkably ungainly in appearance, the plane nonetheless proved Stipa's concept in that its intubed propeller increased its engine's efficiency, and the airfoil shape of the tube gave it an improved rate of climb compared to conventional aircraft of similar engine power and wing loading
. The Stipa-Caproni also had a very low landing speed and was much quieter than conventional aircraft. Its rudder
and elevators
were mounted in the propeller's slipstream in the opening at the trailing edge of the tube in order to improve handling, and this configuration gave the aircraft handling characteristics that it made it very stable in flight.
The Stipa-Caproni's great drawback was that the intubed propeller design created so much aerodynamic drag that most of the design's benefits in efficiency were negated by the drag. However, Stipa viewed the Stipa-Caproni as a mere testbed
, and probably did not believe that the intubed propeller's aerodynamic drag problem would be significant in the various large, multi-engined flying wing aircraft he had designed.
After the Caproni company completed initial testing of the Stipa-Caproni, the Regia Aeronautica took control of it and conducted a brief series of additional tests, but did not develop it further because the Stipa-Caproni offered no performance improvement over aircraft of conventional design.
, Italy, and the United States
, and his work was published in France
, Germany, Italy, the United Kingdom
, and the United States, where the National Advisory Committee for Aeronautics
studied it. The Regia Aeronauticas tests also sparked academic interest in the intubed propeller.
France in the 1930s based its ANF- Mureaux BN.4 advanced night bomber
design on a multi-engine intubed-propeller Stipa design, although the BN.4 was cancelled in 1936 before the first aircraft could be built. In Germany in 1934, Ludwig Kort designed the Kort nozzle
, a ducted fan
similar to Stipa's intubed propeller and still in use, and the German Heinkel T fighter design bore a similarity to Stipa's concepts. In Italy, none of Stipa's flying wing designs with intubed propellers ever were built, but the Caproni Campini N.1, an experimental but impractical advanced derivative of the intubed propeller idea powered by a motorjet
, appeared in 1940.
Stipa himself believed that he deserved the credit for inventing the jet engine
via his intubed propeller design, and claimed that the pulse jet engine
the Germans employed on the V-1 flying bomb
of World War II
violated his intubed propeller patent in Germany, although the pulse-jet engine was not in fact closely related to his ideas.
Stipa died in 1992, embittered over never having received what he viewed as his just recognition for inventing the jet engine. Some aviation historians do at least partially agree with Stipa, noting that the modern turbofan engine has features which show it to be the descendant of his intubed propeller concept.
Early life and career
Stipa was born in Ascoli PicenoAscoli Piceno
Ascoli Piceno is a town and comune in the Marche region of Italy, capital of the province of the same name. Its population is c. 51,400.-Geography:...
, Italy
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...
in 1900. He left school to serve in the Italian Army
Italian Army
The Italian Army is the ground defence force of the Italian Armed Forces. It is all-volunteer force of active-duty personnel, numbering 108,355 in 2010. Its best-known combat vehicles are the Dardo infantry fighting vehicle, the Centauro tank destroyer and the Ariete tank, and among its aircraft...
's Bersaglieri Corps during World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
. After the war, he earned academic degree
Academic degree
An academic degree is a position and title within a college or university that is usually awarded in recognition of the recipient having either satisfactorily completed a prescribed course of study or having conducted a scholarly endeavour deemed worthy of his or her admission to the degree...
s in aeronautical engineering, hydraulic engineering
Hydraulic engineering
This article is about civil engineering. For the mechanical engineering discipline see Hydraulic machineryHydraulic engineering as a sub-discipline of civil engineering is concerned with the flow and conveyance of fluids, principally water and sewage. One feature of these systems is the extensive...
and civil engineering
Civil engineering
Civil engineering is a professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including works like roads, bridges, canals, dams, and buildings...
. He went to work for the Italian Air Ministry, where he rose to the position of general inspector of the Engineering Division of 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).
The intubed propeller
In the 1920s, Stipa applied his study of hydraulic engineering to develop a theory of how to make aircraft more efficient as they traveled through the air. Noting that in fluid dynamicsFluid dynamics
In physics, fluid dynamics is a sub-discipline of fluid mechanics that deals with fluid flow—the natural science of fluids in motion. It has several subdisciplines itself, including aerodynamics and hydrodynamics...
—in accordance with 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...
—a fluid's velocity increases as the diameter of a tube it is passing through decreases, Stipa believed that the same principle could be applied to air flow to make an aircraft's 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...
more efficient by directing its propeller-wash through a venturi tube in a design he termed an "intubed propeller." In his concept, the 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...
of a single-engined airplane designed around an intubed propeller would be constructed as a tube, with the propeller and engine nacelle inside the tube, and therefore within the fuselage. The propeller would be of the same diameter as the tube, and its slipstream would exit the tube via the opening at the tube's trailing edge at the rear of the fuselage.
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...
, eventually determing 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. He appears to have intended the intubed propeller for 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—for which he produced several designs—but saw the construction of an experimental single-engine prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
aircraft as the first step in proving the concept.
Stipa published his ideas in the Italian aviation journal Rivista Aeronautica ("Aeronautical Review"), then asked the Air Ministry to build a prototype
Prototype
A prototype is an early sample or model built to test a concept or process or to act as a thing to be replicated or learned from.The word prototype derives from the Greek πρωτότυπον , "primitive form", neutral of πρωτότυπος , "original, primitive", from πρῶτος , "first" and τύπος ,...
aircraft to prove his concept. Eager for propaganda opportunities to highlight Italian achievements in technology to the world, and particularly interested in aviation advances, 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 approved of the venture, and contracted with 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....
Aviation Corporation to build the prototype in 1932.
The Stipa-Caproni
The prototype, named the Stipa-CaproniStipa-Caproni
The Stipa-Caproni, also generally called the Caproni Stipa, was an experimental Italian aircraft designed in 1932 by Luigi Stipa 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...
, first flew on October 7, 1932. Remarkably ungainly in appearance, the plane nonetheless proved Stipa's concept in that its intubed propeller increased its engine's efficiency, and the airfoil shape of the tube gave it an improved rate of climb compared to conventional aircraft of similar engine 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 Stipa-Caproni also had a very low landing speed and was much quieter than conventional aircraft. Its 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 in the propeller's slipstream in the opening at the trailing edge of the tube in order to improve handling, and this configuration gave the aircraft handling characteristics that it made it very stable in flight.
The Stipa-Caproni's great drawback was that the intubed propeller design created so much aerodynamic drag that most of the design's benefits in efficiency were negated by the drag. However, Stipa viewed the Stipa-Caproni as a mere testbed
Testbed
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...
, and probably did not believe that the intubed propeller's aerodynamic drag problem would be significant in the various large, multi-engined flying wing aircraft he had designed.
After the Caproni company completed initial testing of the Stipa-Caproni, the Regia Aeronautica took control of it and conducted a brief series of additional tests, but did not develop it further because the Stipa-Caproni offered no performance improvement over aircraft of conventional design.
Stipa's later work and influence
Despite the lack of Regia Aeronautica interest in developing the intubed propeller concept further, the Italian government publicized the success of Stipa's idea. Stipa patented the intubed propeller in 1938 in GermanyGermany
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...
, Italy, and the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, and his work was published in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, Germany, Italy, 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 the United States, where 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...
studied it. The Regia Aeronauticas tests also sparked academic interest in the intubed propeller.
France in the 1930s based its ANF- Mureaux BN.4 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:...
design on a multi-engine intubed-propeller Stipa design, although the BN.4 was cancelled in 1936 before the first aircraft could be built. In Germany in 1934, Ludwig Kort designed 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....
, a 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...
similar to Stipa's intubed propeller and still in use, and the German Heinkel T fighter design bore a similarity to Stipa's concepts. In Italy, none of Stipa's flying wing designs with intubed propellers ever were built, but the Caproni Campini N.1, an experimental but impractical advanced derivative of the intubed propeller idea powered by a 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 :...
, appeared in 1940.
Stipa himself believed that he deserved the credit for inventing the jet engine
Jet 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...
via his intubed propeller design, and claimed that the pulse jet engine
Pulse jet engine
A pulse jet engine is a type of jet engine in which combustion occurs in pulses. Pulsejet engines can be made with few or no moving parts, and are capable of running statically....
the Germans employed on 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....
of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
violated his intubed propeller patent in Germany, although the pulse-jet engine was not in fact closely related to his ideas.
Stipa died in 1992, embittered over never having received what he viewed as his just recognition for inventing the jet engine. Some aviation historians do at least partially agree with Stipa, noting that the modern turbofan engine has features which show it to be the descendant of his intubed propeller concept.