ARCHIVED - Flying High After 50,000 Tests

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June 07, 2007— Ottawa, Ontario

A small model of a CF-18 fighter jet drew a big crowd at NRC's Uplands campus in Ottawa on March 15th. The sleek silver model was mounted in the trisonic blowdown wind tunnel, which is housed next door to the much larger low-speed wind tunnel that visitors see on entering the Ottawa airport.

An NRC technician makes final adjustments on the 1/16th scale model of a CF-18 fighter jet in the trisonic blowdown wind tunnel.
An NRC technician makes final adjustments on the 1/16th scale model of a CF-18 fighter jet in the trisonic blowdown wind tunnel.

Dozens of people looked on while the model was buffeted with high force winds for about 20 seconds. The goal was to find out whether two missiles positioned underneath the wings would be subject to dangerous aerodynamic forces when released, or drop safely away from the aircraft.

The experiment was typical except for one thing — it marked the 50,000th test performed in the wind tunnel since it opened in 1963. Dozens of retirees and current staff from the NRC Institute for Aerospace Research (NRC Aerospace) came to celebrate this milestone.

NRC researcher emeritus Lars Ohman pushes the button to start the 50,000th test conducted in the trisonic blowdown wind tunnel since it opened in 1963.
NRC researcher emeritus Lars Ohman pushes the button to start the 50,000th test conducted in the trisonic blowdown wind tunnel since it opened in 1963.

One of the researchers on hand was Lars Ohman, former Laboratory Director, NRC researcher emeritus and one of Canada's foremost authorities on the CF-18. Ohman remembers the early days of wind tunnel tests, when researchers had to manually adjust the instrument dials before each test, and the results came back on chart paper. "Then you used a ruler to measure the output in millimetres," he says. Today, of course, everything is digitized, and computers generate the results automatically.

A luxury for aircraft manufacturers

Known as the 'Cadillac' of wind tunnels when it opened in 1963, the trisonic blowdown wind tunnel was first conceived by the Department of National Defence (DND) as a testing ground for the Avro Arrow interceptor aircraft. "When the Arrow program was scrapped, the tunnel was already being built," says retiree Michael Buckley. Buckley joined NRC as a technician in 1960, the same year that DND handed management of the wind tunnel (then under construction) over to NRC.

In the early years, Canadian universities used the wind tunnel's services the most. "But once we started doing subsonic testing, the commercial work just took off," says Buckley. Boeing, Canadair, de Havilland and other aircraft manufacturers lined up to use NRC's new wind tunnel, and the Canadian Forces came to NRC to test its military aircraft.

Rockets and fallen aircraft

Soon the tunnel was involved in several of Canada's prominent aerospace projects. During the cold war, when communications interference posed a possible security risk, the wind tunnel tested one of the Black Brant rockets being launched to study interference from the Northern Lights. Buckley recalls tests done in the 1960s for the crash position indicator — a system for quickly locating a downed plane. The indicator incorporates a radio transmitter and antenna into a disk that must detach from the aircraft on impact. "We were testing how it would detach," says Buckley. "If this didn't happen correctly, it could damage the plane's tail section, or splinter against it and be destroyed." After testing and design modifications, the crash position indicator went on to improve aviation safety and save lives around the world.

Bigger and better

Upgrades have kept the wind tunnel in high demand over the years. In 1985, the tunnel went through a major overhaul that included installing nine high tech screens to break up the flow of air and reduce turbulence. In 1988, a building addition meant that two projects could be in the setup phase while a third was running in the tunnel. "This really decreased the rigging time to get from one project to another," says Dewart Hennig, who was manager of the wind tunnel when he retired in 1995. The introduction of computers and advances in instrumentation meant that each test yielded far more information. "You can get at least 10 times more data from a test today than we could even 15 years ago," says Hennig.

Today, the wind tunnel is known for its ability to test aircraft at elevated air pressures in order to better simulate reality. "When we increase the density of the air by a factor of four or five, we get a better predictor of what's going to happen in real flight conditions," says technical officer Steve Pynn, who operates the tunnel. "Another one of our strengths is high Mach numbers — we can go as high as Mach 4.5."

Test number 50,000 — like all the tests before it — gave NRC's aerospace clients important data on aircraft performance. In this case, the Canadian Forces learned to predict how their CF-18s will react under real flight conditions — information DND needs to keep its aircraft and pilots safe. After more than 40 years in operation, this enduring facility offers even more value today than when it first opened in 1963.


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