The Orenda PS.13 Iroquois was an advanced turbojet engine designed for military use. It was developed by the Canadian aircraft engine manufacturer Orenda Engines, a part of the Avro Canada group. Intended for the CF-105 Arrow interceptor, development was cancelled, along with the Arrow, in 1959.
For the CF-105 Arrow project, Avro Canada had originally intended to use one of three different engines, all UK designs: Rolls-Royce RB.106, the Bristol B.0L.4 Olympus, or a license-built version of the Olympus, the Curtiss-Wright J67. The RB.106 and J67 were selected as the primary and backup engines for the new design. However, both the RB.106 and J67 were cancelled during the Arrow’s design phase, too far into the program to select the Olympus. Orenda Engines quickly responded with the PS.13 Iroquois design.
The Iroquois design was based on simplicity and lightness. With this in mind, Orenda pioneered work in the use of titanium in engines, with 20% by weight of the Iroquois (mainly the compressor rotor blades) consisting of this metal. Titanium has light weight, high strength and good temperature and corrosion resistance. It was estimated that the engine would be 850 pounds (386 kg) lighter than if steel had been used. During the early 1950s, this material was in short supply, and the lack of knowledge of its physical properties and fabrication techniques created problems which had to be overcome. It was also very expensive relative to the more common materials such as steel and aluminum.
It was recognized that if the engine parts could be designed with titanium, then the supporting structure could also be lightened due to reduced forces within the engine, with an overall saving in weight. Other parts, such as gearbox casings were made with a magnesium alloy. Inconel was used to make the blades in the low pressure turbine assembly and the metal insulation blanket found at the rear of the engine. This heat resistant nickel-chrome alloy retains its strength at high temperatures and resists oxidation and corrosion. The primary reason for using these advanced metals was to save weight and improve performance, creating an engine with a 5:1 thrust to weight ratio that could produce a sea level dry thrust of 19,250 lb (26,000 lb with afterburner). The design, development and manufacture of such an advanced jet engine was accomplished in an incredibly short time by the Orenda team. The detailed design was completed in May 1954, and the first run was achieved on 15 December 1954. The earlier Orenda 9 had more parts but produced less power. For example, the Orenda 9 weighed 2,560 lb (1,160 kg) and produced 6,355 lb (2,883 kg) static thrust, while the Iroquois weighed 5,900 lb. (2,675 kg) but was reported to have produced 30,000 lb (13,608 kg) static thrust with afterburner for takeoff. (The Orenda did not have an afterburner.)
The Iroquois was one of the most powerful jet engines in the world at its time of introduction, rated at 19,250 lbf (85.6 kN) dry, 25,000 lbf (111 kN) afterburning. It was aerodynamically matched for peak performance at 50,000 feet (15,200 m) altitude and Mach 2 speed.
Wind tunnel tests demonstrated the engine’s successful operation under sustained high inlet temperatures, and the ability to make normal relights up to 60,000 ft (18,290 m), the limit of the wind tunnel in which the tests were conducted. By 1958, the Iroquois had completed more than 5,000 hours of ground running, and many thousands of hours had also been spent testing the engines’ principal components, at the Orenda testing facilities at Nobel, near Parry Sound, Ontario.
In 1956, a U.S. Boeing B-47 Stratojet was loaned to the Royal Canadian Air Force to flight test the Iroquois for use in the CF-105. Canadair, the sub-contractor, attached an Iroquois to the right side of the bomber’s rear fuselage, near the tail, simply because there was no other place to mount it. Designated CL-52 by Canadair, it was a nightmare to fly, since the thrust was asymmetrical; this created great problems for flight control. After the Arrow project was cancelled, the B-47B/CL-52, which had logged about 35 hours of engine flight tests, was returned to the U.S and subsequently scrapped. The CL-52 was the only B-47 used by any foreign service.
After some 7,000 hours of development testing, including tests up to a simulated altitude of 70,000 feet (21,300 m) and a forward speed of Mach 2.3, the program was cancelled, along with the Arrow, on 20 February 1959.
The Canada Aviation and Space Museum in Ottawa houses the nose and cockpit section of Arrow RL 206, along with various wing and fuselage components, and a complete Iroquois-2 engine, Serial Number 117. An example of an Iroquois-1 engine is found at the Canadian Warplane Heritage Museum in Mount Hope, near Hamilton, Ontario. Another Iroquois-2 engine is owned by a private collector in Fort St. John, British Columbia. Since 2011, an Iroquois engine, serial X-116, has been being rebuilt by S & S Turbines in Canada.
Iroquois 2
Type: Twin-spool turbojet
Length: 231 in (590 cm)
Diameter: 42 in (110 cm)
Dry weight: 4,650 lb (2,110 kg)
Compressor: 10-stage split axial flow compressor
Combustors: Annular combustion chamber
Turbine: Single-stage HP, two-stage LP, axial flow
Maximum thrust: 20,000 lbf (89 kN), without afterburning; 30,000 lbf (130 kN), with afterburning
Overall pressure ratio: 8:1
Specific fuel consumption: 0.85 (non-reheat), 1.9 (with reheat)
Thrust-to-weight ratio: 6.45:1 at maximum thrust
