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Pulqui II No.05

The fifth prototype IAe 33 Pulqui II jet fighter during flight testing.[1]

The FMA IAe 33 Pulqui II was a jet fighter aircraft developed in the late 1940s in Argentina, during the Perón government. It's development was quite problematic and lengthy and it was never ordered into production after the United States offered F-86 Sabres at cut-rate prices in the late 1950s.

HistoryEdit

After the cancellation of the I.Ae. 27 Pulqui I program in 1947, the Aerotechnical Institute (Spanish: Instituto Aerotécnico) continued with its efforts to build a jet fighter. At first attempts were made to improve the earlier aircraft, but these were quickly cancelled when it became apparent that the Pulqui I had little potential for further development. A new design was begun that used the 20.31 kN (4,570 lbf) Rolls-Royce Nene II turbojet engine. In early 1948 they completed a scale model of what they called the IAe-27a Pulqui II with trapezoidal wings swept back at 33° and a NACA 16009 laminar flow airfoil section. A revised model was built later that year with the wings moved to a shoulder-mounted position and the tailplane changed to a T-tail configuration.

Kurt Tank had been hired the previous year to work on a similar project and he adapted his earlier Focke-Wulf Ta 183 Huckebein for the Nene II. The Nene was more powerful than the original Heinkel HeS 011 turbojet, but required a redesigned new fuselage with a larger cross-section due to its use of a centrifugal rather than axial compressor. The two were ordered merged by the director of the Aerotechnical Institute and it was given the designation of IAe 33 Pulqui II. The fuselage of Tank's design was adopted to use the IAe-27a's undercarriage and Tank was appointed project director.

The high-mounted wings were swept back 40°, even more than the Ta 183, and given anhedral. The long fuselage was circular in section with the engine buried inside near the center of gravity. The airframe was finished off with a graceful swept-back T-shaped tail. The pilot sat in a pressurized cockpit under a teardrop canopy. Armament would include four fuselage-mounted 20 mm cannon.

Two gliders, built with the help of Reimar Horten, were used for aerodynamics testing in 1948–49. They revealed significant problems with lateral stability. Modifications were made to the tail to cure this problem and construction began of two airframes, one for static testing and the other for flight testing. The latter was completed in 1950 and made its first flight on 16 June. On the second flight the pilot, ex-Focke-Wulf test pilot Otto Behrens, noticed more lateral stability problems at speeds over 700 km/h (435 mph) and returned to the airfield. He landed at very high speed and the aircraft bounced so hard that he broke the right landing gear. The shock strut in the landing gear had failed so the shock absorber was changed and the height of the front landing gear changed. The leading edge near the wingroot was modified because the wingtip stalled before the root and the rudder was modified in an attempt to solve the lateral instability. The canopy was reinforced with two additional struts and a fairing was installed above the engine exhaust.

These changes required several months and the third flight was not made until 23 October, with Kurt Tank at the controls, to investigate the aircraft's stalling characteristics. It twice stalled before Tank intended, but ballasting the nose cured the problem. The aircraft was demonstrated before President Perón on 8 February 1951 by Tank. Later that year the Argentine Air Force named several of their pilots to fly the new aircraft. The first flight by one of these men was on 31 May 1951 and he noticed severe vibrations around 1,000 kilometres per hour (621 mph) and he soon landed the aircraft. Tank declared the aircraft unserviceable pending an investigation, but this appears to have been overlooked when Captain Vedania Mannuwal took off that afternoon on the aircraft's 28th flight. He was advised not to stress the aircraft as the source of the morning's vibrations had not been discovered, but ignored this advice and began practicing aerobatic maneuvers. During one of these the wing separated from the fuselage and Mannuwal ejected while inverted. The parachute of the Martin-Baker Mk I ejection seat failed to function and Mannuwal was killed. The problem turned out to be defective solder in the joint pin that fastened the wing to the fuselage.

A second prototype was begun immediately afterward and made its first flight on 23 September 1951. A number of changes had been made to rectify faults found in the first prototype. These included a larger rudder to improve lateral stability, a bigger exhaust fairing, unusual Air brake that rotated out from the sides of the fuselage and the canopy was further reinforced. More fuel was carried to extend the range from 2,030 to 3,090 kilometres (1,260 to 1,920 mi). Flight testing continued and the aircraft was supposed to be demonstrated before President Perón on 11 October 1952, but Behrens was killed when his aircraft stalled at low level while practicing his routine two days before the exhibition.

A third prototype was finished in 1953 although it was modified with a stall fence on each wing and four strakes on the rear fuselage to cure the design's deep stall problems at high angles of attack. The cockpit was now pressurized and more fuel was added as well. It made its first flight on 20 August 1953 and began testing the armament in 1954. Tentative plans were made for the manufacture of 100 aircraft, including a version with a radar. However, the departure of Kurt Tank from the program greatly hindered the program. His contract expired in January 1955 and President Perón refused to accept his demand for almost twice as much money.

The sole prototype of the Pulqui II participated in the Revolución Libertadora, a coup d'état against Perón in September 1955. The exact details of its participation are not clear, but it was used against loyalist forces and flew in the victory parade celebrating the success of the coup. The aircraft's oxygen system failed during a long-range demonstration flight in 1956; the semi-unconscious pilot managed to land the fighter, but broke the landing gear and overran the airfield, damaging the aircraft beyond repair.

Shortly afterward an inquiry was made by the Argentine Air Force about building 100 Pulqui IIs. The Fábrica Militar de Aviones replied that ten aircraft could be completed relatively quickly, but that the remainder would take five years to complete. A fourth prototype was ordered in 1957 even though the United States had offered 100 combat-proven F-86 Sabres with Avro Canada Orenda engines. The fourth prototype made its first flight on 28 September 1959 even though the Argentine Government had already accepted an offer of 28 F-86F-40 fighters at a bargain-basement price. Only twelve fights were made by the last Pulqui II before the Sabre's were received in 1960 and the Pulqui was placed into storage. Today, the Pulqui II is preserved at the Argentine Air Force’s Museum in Morón.[2]

ReferencesEdit

  1. Wikimedia
  2. Wikipedia

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