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By Bill Upton

All images accompanying this article are via the author's collection unless attributed otherwise.

Part 2: CL-41 Prototype No.1

The CL-41 design reflected in the detailed, full-scale mockup was well received by all interested parties. Very few critical comments emerged from the engineering mockup review due in part to the RCAF Directorate of Training’s Jet Trainer Liaison Committee having worked closely with the Canadair design team and Canadair test pilot Ian MacTavish in the final overall aircraft layout. Canadair and the Canadian government funded the manufacture of two prototypes, along with several airframes destined for static and fatigue testing. A small, dedicated design team produced them in a hand built, "Skunk Works", fashion.

Places, Powerplants, and Prototypes
The basic configuration of the new trainer had been finalized by August 1957, and by November 1957 construction of the two prototypes, using shop-aid type tooling, commenced at Canadair’s somewhat secretive Plant 4 facility. Originally the home of the Curtiss-Reid Aircraft factory, and later, the Canadian Car & Foundry (CC&F) Aircraft Division, where the first prototype Burnelli CBY-3 Loadmaster, CF-BEL, was built and flown from in July 1945, these facilities later became home to Canadair’s Missiles & Systems Division. The classified Velvet Glove and Sparrow II air-to-air missiles were developed and tested here, for use with the RCAF’s interceptors. At least four Avro CF-100 Canucks were based at these facilities during the course of the missile programmes.

As an aside, the historical Plant 4 complex was eventually demolished in 1994 to make way for an encroaching housing project and golf course. Fellow retired Canadair employee and CAHS author Wayne Saunders and I had the original Curtiss-Reid Aircraft Limited stone plaque above the main entrance photographed, carefully removed, and preserved for posterity at a local aviation museum.

The completion date for the two airframes was originally set for November 1958, with the first flight planned for early 1959. However, numerous problems with engine availability meant that the scheduled first flight would be seriously delayed.

Five examples of a new generation of compact turbojet engines in the 2,000 lb (907 kg) thrust range had been investigated by Canadair for possible use in the new trainer. These were the Armstrong-Siddeley Viper ASV11, the Continental Gabizo, the Rolls Royce RB.108, the General Electric MX-2273 (later to become the J85), and the Fairchild J83-R-1. The CL-41 airframe had been designed from the outset to permit, without any structural modifications, the widest possible choice of engines.

Initially the RB.108 was the preferred choice, albeit this engine was a first generation lift-engine concept, with the alternate being the J83 to satisfy British and US criteria. Later, emphasis shifted to the use of the Fairchild engine, and studies were made to optimize the airframe design around this power plant. Final selection of the J83 in 1958 for installation in the prototypes proved improvident, as the USAF soon withdrew its backing for this engine in the aftermath of the cancellation of the unmanned Fairchild SM-73 Bull Goose long-range decoy missile project, for which it was originally intended. This unforeseen event left the two completed prototype airframes idle at Canadair, awaiting an alternate available power plant.

Ultimately, a loan arrangement was quickly worked out with Pratt & Whitney in Hartford, Connecticut, to make the first installation of its new lightweight JT12 turbojet engine in the CL-41 prototypes. This engine, originally called the DS-3J, had been under development for a forecasted small jet engine market for executive aircraft, and soon was chosen to power the Lockheed JetStar and the North American T-39 Sabreliner.

The engines for the CL-41 prototypes were built in Hartford; however Pratt & Whitney Canada, located in nearby Longueuil, Quebec, had performed much of the initial design and testing. There were hopes that this Canadian designed and built trainer/power plant combination would result in a long production partnership. However, politics came into play to the extent that such a result could not be realized.

With little fanfare, the first prototype aircraft was rolled out in early 1959 to perform some ground-based, non-destructive tests. During these tests, the forward fuselage of prototype No 2 had been mated to the rear fuselage of prototype No 1. Similarly, the forward section of prototype No 1 was attached to the rear section of prototype No 2 complete with the under-tail attachment bracket for the spin chute and associated release cable. For this aircraft, the civil / military registration would follow that assigned to the forward fuselage / cockpit assembly.

In May 1959, a trial installation of the complete JT12A-1 prototype engine mockup into the first prototype’s airframe proved satisfactory. It was deemed necessary to confirm the design layout of the aircraft’s internal structure prior to the acceptance of an actual engine. These first form and fit checks paved the way for the employment of the flight rated engine. Soon thereafter the prototype aircraft / engine combo began a thorough ground and flight test and evaluation programme from Canadair’s Cartierville facilities.

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First Flight and Evaluations
The first of the newly developed JT12 engines, cleared for ground run purposes only, was installed in the airframe on 18 September 1959. Initial ground run engine tests were performed in what was colloquially called “the pit” at Canadair’s Plant 2 complex. The engine, weighing only 430 lb (195 kg), was derated by controlling the fuel flow via mechanical throttle stopping from 2,900 lb (1,315 kg) static thrust in order to achieve better fuel consumption to improve range, reliability and overhaul life. During one of these ground test runs, a technician monitoring the aircraft walked next to the intake and items from his pocket were sucked in, damaging the engine. Apparently, at the time, the FOD screens had been retracted for some reason. This event necessitated an engine change, delaying the first flight attempt.

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Finally, following a series of successful engine runs in December with the second delivered JT12, all was ready for the premiere flight of Canadair’s first original aircraft design. Bearing civil experimental registration CF-LTW-X, the CL-41 prototype was first flown by project pilot Ian MacTavish on 13 January 1960, powered by the new Canadian designed Pratt & Whitney JTC12A-2 axial-flow turbojet, with 2,400 lb (1,089 kg) static thrust, which was also making its first flight as a prototype engine. The aircraft responded remarkably well as MacTavish took it up to 15,000 ft (4,572 m) altitude, and to a speed of 278 knots (515 km/h / 320 mph), during its 1 hour and 10 minute maiden flight around the Montreal area. A second flight was conducted with the aircraft on 25 January. MacTavish had company on this flight, with a flight test engineer joining him to monitor test instrumentation and record data, as had also been the case on the first taxi runs in December.

Speed trials were conducted at nearby St. Hubert airport, which afforded a longer runway and was less densely populated compared to the immediate Cartierville environs. Four series of cold weather, and trailing static ‘bird’ flight tests were conducted in Prince Edward Island during late February 1961.

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An official RCAF survey team, made up of one pilot from the Central Flying School and two from the Air Training Requirements and Directorate of Air Training, AFHQ, gave the CL-41 prototype preliminary flight evaluations during a week-long workout in March 1960. Only 30 flight hours had been accumulated on the airframe by this time. This evaluation almost didn’t come about as originally planned. The day prior to the RCAF evaluation team’s arrival, a test flight of the aircraft was made to ensure that all was in order, and somehow during the flight the canopy was accidentally jettisoned. The “topless” CL-41 immediately returned to Cartierville Airport, and was landed successfully, with the crew of MacTavish and flight test engineer Colin Harcourt quite chilled but none the worse for wear. With daylight fading rapidly, a team of Canadair employees went up in a chartered aircraft to search the test area for the missing canopy. Then from a glint of reflected sunlight on the snow, they spotted it lying in a farmer’s field. It was found to be relatively intact with minor damage to a couple of defrosting pipes, all of which was easily repaired following its recovery back to Canadair. The canopy was reinstalled and the aircraft was ready by the next morning for the RCAF evaluation. All who flew it were suitably impressed with the new aircraft’s performance and handling. This was the final trainer in a series of international aircraft types from the United Kingdom, France, and the United States previously evaluated by this survey team.

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Some of the tests conducted with the CL-41 prototype aircraft went somewhat beyond the typical scope of ground-based and flight-related testing.

In April 1959, Canadair began investigations into branching out from pure aircraft and tracked vehicle products and entering the field of design, engineering, and manufacturing of architectural structures due to the rapidly expanding building programme then underway in Eastern Canada. Thus was born the Architectural Products Division, later to be formally named Canarch Limited. This new division was initially asked to bid on the exterior aluminum curtain wall construction of Montreal’s new Place Ville Marie (PVM) high rise office building. They lost that contract, but soon put in a bid and won the contract to supply the exterior curtain walls of the 34-story CIL House (named after owners, Canadian Industries Limited) , also located in downtown Montreal. This project was assigned the Canadair model number CL-92.

Canadair’s Experimental Engineering Department performed the necessary stress and structural material strength calculations. Of note was the architectural design requirement to dynamically test the single pane glazing design with actual wind and rain loads imparted upon it, and it was also necessary to prove that it would be suitable for the harsh summer and winter weather conditions of the region.

At Canadair’s Plant 4 facility, where the Missiles and Systems Division was located, a representative test specimen panel of three modules was erected on the exterior facade of Building 409 along with a simulated interior office area of the planned building. The office area was set up with heating and air conditioning systems precisely controlling the temperature, humidity, and airflow.

A preliminary series of dynamic wind tests was conducted on the specimen using the Trans-Canada Air Lines Merlin engine test vehicle, affectionately known as “Oscar”, on short-term loan from nearby Dorval Airport. The vehicle was backed up next to the building and the Merlin’s propeller wash was concentrated across the three modules. As the latter months of 1960 approached, colder weather provided the need to test the specimen with higher velocity airflow that could not be met with Oscar. That was when the CL-41 aircraft design made its contribution to the CL-92 architectural design.

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This excerpt is part of a series published in the CAHS Journal about the development of the Tutor. The full article, in Volume 52, Number 2, is available to CAHS members. For more information on CAHS membership, please go to