The FMA IAe 33 Pulqui II (in the indigenous language Mapuche, Pulqúi: Arrow)Crowder-Taraborrelli, Tomas F. "Evita in Wonderland: Pulqui and the Workshop of Underdevelopment". CineAction, 22 June 2009. Retrieved 26 April 2010. was a jet fighter aircraft designed by Kurt Tank in the late 1940s in Argentina, under the Perón government, and built by the Fábrica Militar de Aviones (FMA).Green and Pollinger 1955, p. 105.
Embodying many of the design elements of the wartime Focke-Wulf Ta 183, an unrealized fighter project,Meyer 2007, p. 98. the FMA envisioned the IAe 33 Pulqui II as a successor to the postwar Gloster Meteor F4 in service with the Fuerza Aérea Argentina. The Pulqui II's development was comparatively problematic and lengthy, with two of the four prototypes being lost in fatal crashes. Despite one of the prototypes being successfully tested in combat during the 1955 Revolución Libertadora, the political, economic and technical challenges faced by the project meant that the IAe 33 was unable to reach its full potential, and the Argentine government ultimately chose to purchase F-86 Sabres from the United States in lieu of continuing development of the indigenous fighter to production status.Green 1979, p. 304.
Background
In the late 1940s, Argentina benefited from the recruitment of prominent German aerospace scientists and engineers, fleeing Europe following the defeat of the Nazis and seeking sanctuary in Latin America. The first group of these refugees had also included French designer Émile Dewoitine, punished as a collaborator in his homeland, who headed the IAe 27 Pulqui I experimental fighter program with Argentine engineers Juan Ignacio San Martín, Enrique Cardeilhac, Norberto L. Morchio, Humberto Ricciardi, sixteen draftsmen and forty workers."FMA I.Ae.27 Pulqui 1". machtres.com. Retrieved 27 April 2010. The Pulqui I was the first jet aircraft designed and built in Latin America. The prototype made its first flight from the Escuela Militar de Paratroopers (Córdoba) on 9 August 1947, piloted by First Lieutenant Edmundo Osvaldo Weiss.
The experimental plane presented, during the test flights, a series of problems such as the high fuel consumption of the English turbine, which limited its autonomy. This and other factors, plus rapid global advances in aerodynamics (such as swept wings and laminar airfoils, among others), determined that the program was ultimately cancelled. However, the experience gained drove the progress of the national aeronautical industry, which became the eighth in the world to venture into this type of technology and paved the way for more ambitious projects such as the IA-33 Pulqui II.
The Aerotechnical Institute (), under the leadership of Morchio, persevered with its efforts to build a successful indigenous jet fighter and, at first, attempted to modify the earlier aircraft. When it became apparent that the Pulqui I had little potential for further development, the Aerotechnical Institute initiated a new design utilizing the more powerful () Rolls-Royce Nene II turbojet engine. In early 1948, the Institute completed a scale model of what it called the IAe-27a Pulqui II. This design featured trapezoidal wings, swept back at an angle of 33°, and used a NACA 16009 laminar flow airfoil section. A revised model was built later that year with the wings relocated to a shoulder-mounted position and the tailplane changed to a T-tail configuration.Rivas 2008, pp. 166–167.
Kurt Tank Like Dewoitine, German designer Kurt Tank, the former technical director of the Focke-Wulf Flugzeugbau AG, had been hired in 1947 to work on a jet fighter project for Argentina. Tank and 62 of his compatriots at Focke-WulfWilkinson 2010, p. 32. had emigrated to Latin America to restart his career in aerospace ventures.Newton 1992, p. 376. Surreptitiously entering the country with a passport identifying him as Pedro Matthies, he found a warm welcome and did not maintain the subterfuge of a secret identity. Along with his former employees, he was instrumental in the evolution of the Instituto Aerotécnico into Argentina's military aircraft factory, the Fábrica Militar de Aviones at Córdoba."Argentina: Old Hands, New Directions". Time. 23 October 1950. Tank was both an engineer as well as a test pilot, who had designed the Fw 190 fighter, but his design team had also been responsible for the Focke-Wulf Ta 183,Schick and Meyer 1997, pp. 146–147. an unbuilt project that had won the 1945 German Emergency Fighter Competition. The diminutive, swept-wing, jet-powered Ta 183, designed by Focke-Wulf engineer/designer Hans Multhopp, had only reached the stage of wind tunnel studies before the German surrender.Myhra 1999, p. 4.
Design and development
After his appointment as project director for a new indigenous fighter program, Tank adapted the basic Ta 183 airframe for the Nene II engine, resulting in a new design that bore only a passing resemblance to its forebear. The Nene was larger, heavier and more powerful than the Heinkel HeS 011 turbojet that had been planned for use in the Ta 183, and therefore required a new, redesigned fuselage with a larger cross-section primarily due to the Nene's centrifugal compressor rather than the HeS 011's axial compressor design.
Due to the similarity of the IAe-27a and Tank's redesign of the Ta 183, Juan Ignacio San Martín, the director of the Institute merged the two parallel projects as the IAe 33 Pulqui II. The fuselage of Tank's design was further adapted to use the IAe-27a's undercarriage.Rivas 2008, p. 167. The shoulder-mounted wings were swept back 40°, an even greater sweep angle than that of the Ta 183,Waligorski, Martin. "Pulqui: Argentina's Jet Adventure" . Camouflage & Markings: IPMS Stockholm, 22 September 2006. Retrieved 27 April 2010. and given a small amount of anhedral. Comparable to the Ta 183's engine placement, the Nene engine was situated aft of the cockpit, near the center of gravity with engine maintenance and service facilitated through the removal of the tail section. The airframe featured a graceful, 50° swept-back T-shaped empennage and a pressurized cockpit topped by a clear bubble-type canopy, faired into the dorsal fuselage. Armor was provided around the cockpit and a bulletproof windscreen was incorporated.Donald 1997, p. 384. Fuel capacity was initially 1,250 L (275 Imp. gal.) internally and 800 L (176 Imp. gal.) in the wings. Armament was planned to include four 20 mm cannon, a pair mounted in a staggered, near-ventral position along each side of the fuselage slightly set back from the jet intake.Rivas 2008, pp. 167–168.
Testing and evaluation To prove the soundness of the IAe 33 design, two gliders built under contract by another expatriate, Reimar Horten, were constructed and used for aerodynamics testing in 1948–1949, including flights by Tank himself. These tests revealed significant problems with lateral stability, resulting in modifications to the tail to address this problem before construction began on two prototype airframes. Due to the lack of modern machinery, the all-metal fabrication relied heavily on handcrafting, and fabricating the prototypes was a labor-intensive procedure. President Perón envisioned that a benefit of setting up an aviation factory in Argentina would be to introduce production standards comparable to world-class manufacturing facilities. However, Tank realized that production tools and jigs were not feasible at this stage and relied instead on essentially hand-built examples.Rathkolb 2004, p. 220. The first airframe (No. 01) reserved for static testing, was subsequently destroyed during the tests.Paul 1960, p. 145.
The first of the "flying" IAe 33 prototypes, (No. 02) built in 1950, completed its maiden flight on 27 June of that year, with Captain Edmundo Weiss at the controls. On the second flight, ex-Focke-Wulf test pilot Otto Behrens encountered severe lateral stability problems at speeds over and returned to the airfield as a precaution. Landing at very high speed, the aircraft bounced with sufficient force to cause the right main undercarriage strut to fail. During repairs to the aircraft, in order to rectify the "tricky" landing characteristics, the front undercarriage strut was increased in length, which served to alter the angle of incidence of the aircraft, while the shock absorbers were adjusted to have a greater "throw". Although insufficient for the aircraft to be considered docile, the modifications improved the takeoff, landing and low-speed characteristics of the IAe 33. More serious aerodynamic problems persisted, stemming from tip stall— in which the wingtip stalled before the wingroot resulting in an unpredictable "rolling moment"— leading to a change in the wing leading edge near the wingroot, while the rudder was modified in an attempt to resolve the interminable lateral instability issues. In addition, the canopy was reinforced with two external frames and a small fairing was installed above the engine exhaust.Rivas 2008, p. 168.
Tank, himself a capable development test pilot,Wilkinson 2010, p. 24. took over the test program to investigate the aircraft's stalling characteristics, although the requisite airframe changes took several months to complete, with the Pulqui II N. 02(m) so modified not able to undertake its third proving flight until 23 October. During the ensuing high-altitude test, on two successive occasions, the IAe 33 stalled inadvertently, although Tank had sufficient height at 9,000 m for recovery. Adding ballast to the nose of the aircraft cured the problem. On 8 February 1951, Tank publicly demonstrated the IAe 33 before Perón at the Aeroparque Jorge Newbery in Buenos Aires. The audience included government officials, legislators, the military attaches of foreign embassies, and a large crowd of spectators. Both the IAe 27 Pulqui I and IAe 33 Pulqui II flew during the demonstration.Moyano, Miguel Angel. "El Proycto 'Pulqui': Propaganda peronista de la epoca". (Project 'Pulqui': Peronist propaganda of the time) lucheyvuelve.com. Retrieved 26 April 2010.
With the successful completion of the proving test flights, the Argentine Air Force requested a pre-production order of 12 IAe 33 aircraft. In 1951, the air force established a team of service pilots to test fly the new aircraft in a series of acceptance flights. The first flight by Commander Soto on 31 May 1951 revealed severe vibration at about . Tank declared the sole prototype unserviceable pending an investigation into the problem, although this stricture appears to have been overlooked and the prototype continued to fly. On the eve of its 28th flight, Captain Vedania Mannuwal, assigned to the test program, was advised not to stress the aircraft, as the source of the vibrations experienced during the previous flight in the morning had not been discovered. Determined to "better" his team leader's recent performance, however, he ignored the precautions and began practising aerobatic maneuvers near Córdoba during his afternoon flight. Consequently, in a high g-force turn, the wing separated from the fuselage due to a structural failure. After struggling with the Martin-Baker Mk I ejection seat, Mannuwal ejected at low altitude while the aircraft was inverted, but his parachute did not fully deploy and he was killed. The defect in the Pulqui II was traced to faulty welding of the joint pin that fastened the wing to the fuselage. Welding had been necessitated by the lack of modern forging and pressing equipment in Argentina.Rivas 2008, pp. 168–169.