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CF-105 Avro Arrow - Technological Developments

One of the key features of the Arrow project --- which also contributed to its end --- was its armament system. This was as ambitious as the Arrow fighter itself. There were numerous problems with the Astra radar and fire control system, designed by RCA-Victor. This was complex and expensive. ASTRA, which had been the most difficult electronic programme undertaken in Canada, was described as an excellent example of integrated production, having been largely US in the opening stages, with a gradual transference of activity to Canada. In addition, a new missile was being developed for the Arrow, and this was a very ambitious one: Sparrow II. In fact, this missile had already been abandoned by the US Navy because it was too ambitious.

The choice of the engines was to be a problem. Originally, the Rolls Royce RB106 engine was chosen, but it was soon recognized that this would not be available. Then the Wright J67 was chosen, but this engine was cancelled in 1955. Finally, it was decided to use an indigenous engine, the Orenda PS-13 Iroquois. Because this engine would not be available for the first prototypes, it was decided to use the Pratt & Whitney J75 to power the Mark 1 prototypes and pre-series aircraft.

All five aircraft were equipped with two Pratt and Whitney J75 engines. A sixth aircraft was produced and ready for roll-out at the time of cancellation on February 20, 1959. This aircraft was equipped with the more powerful Iroquois engine. Sources are in pretty enthusiastic disagreement as to the performance of these engines. The Pratt and Whitney J75 engine is variously reported as having approximately 12,500 lbs, 16,500 lb, or 18,000-lb static thrust and 18,000 lbs, 24,000 lb or 26,000-lb with afterburner. The Iroquois engine is variously reported as having 19,250 lbs, 23,000-lb or 26,000lb static thrust and 25,000 lbs or 30,000-lb with afterburner. Avro gave the static thrust of the J75 in the Arrow Mk. 1 brochure as, "16,500 lb dry, or 24,000 lb with reheat." Some J75s had a higher static thrust rating of up to 26.500 lb with reheat but it appears they were never fitted to the Arrow. The Iroquois was rated at "19,250 lbs dry, 25,000 lbs afterburning" according to Orenda [which became part of Magellan]

It is important to note that the J75 was a production engine and the Iroquois Mk. 2 was still experimental. According to "The Arrow Countdown" by Peter Zuuring page 43, "Charles [Charles Grinyer, VP Engineering at Orenda] said that just before cancellation, the seventh stage compressor rotor was throwing blades without any conclusive solution determined." He paraphrases Mr. Grinyer again later on page 53, "Charles told me that if they had only had one more year on the project, the Iroquois would truly have met its revolutionary goals."

So the J75 was already in production but the Iroquois Mk. 2 was still about a year away. To be fair the Iroquois should not be compared with the Production J75 but with ones that would enter production a year or so after that time. The engines fitted to one Arrow were experimental Iroquois [1] Mk. 2s with solid blades in the hot section. By that time Orenda had already abandoned the Iroquois Mk. 1 with hollow blades in the hot section because of some kind of problems.

The Arrow never flew with the Iroquois because one of the experimental engines had thrown a blade and there was no replacement engine available. At the same time as Orenda was trying to get the Iroquois working properly the company was also talking about a future model called the Iroquois 2 which was to have been capable of 30,000 lb. with reheat. It is unknown how many years it would have taken for Orenda to develop the new engine but it is clear that they were nowhere near entering production with it.

Manufacturing the necessary undercarriage for the Arrow presented a whole range of special problems stemming from weight limitations, the extra stress associated with higher speed landings, and from the fact that the thin wing afforded almost no stowage and the fuselage only a limited amount. The development of the ultra high tensile alloy steel which was found necessary for the relatively slender landing gear was an extremely expensive proposition. The ultimate strength of material ranged from 260,000 to 280,000 pounds per square inch.

The first computers to fly were primitive mechanical devices used to control planes in flight. Airplane and missile designers kept improving these systems, which enabled them to do new things. The German A4 (V-2) rocket of World War II used an early computer control system. The Canadian CF-105 Arrow interceptor airplane, which flew in March 1958, was the first aircraft to use an analog computer not as an autopilot but as a means of improving the flyability of the aircraft. The Arrow's computer was used to reduce the plane's tendency to yaw back and forth in flight.

The initial intention was to use a mechanical control system and couple the remote automatic interception interface to the autopilot. However, the designers discovered a yaw instability that would have required a much larger vertical stabilizer. Their solution was to adopt a dual-channel fly-by-wire system made of analog circuits. At first, the system had no "feel," since control surface motion was a result of stick motion generating an electrical signal, not moving a cable. Eventually Avro had to install springs to provide imitation forces for the pilots. Nevertheless, when it had its first flight on 25 March 1958, fly-by-wire had come to high-performance aircraft, if only to provide a yaw damper extended to three-axis flight control.

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Page last modified: 09-07-2011 02:35:05 ZULU