by Bruce Bowles
Remember the by-gone days of frost shields on car windows? They were installed every fall and removed every spring and they were required by law for winter driving. Did you know that airplanes back in the 1940s and 50s also used frost shields on the cockpit windows? Cabin heat wasn’t as well developed as it is now and there was never enough warm air available to keep the windshield from frosting up. This created problems for pilots that like to see where they were going.
Automotive frost shields worked fairly well on early airplanes as long as the pilot stayed low to the ground and didn’t climb above 4,000 feet. If a pilot flew much above that altitude, the shields would over-inflate and burst at the seam. The difference in air pressure between the inside and outside of the frost shield would cause the seal to fail and the frost shield would frost over rendering it useless.
A Winnipeg company, James B. Carter Ltd, (later Carter Temro and now Phillips & Temro which still has a factory in Winnipeg as one branch of a multinational corporation that makes – among other things – block heaters for cars and trucks) started making frost shields especially for Trans-Canada Air Lines. The secret that made it work was a ‘Z’ shaped seal that ran all the way around the edge of each frost shield. The seal acted like a bellows and enabled the shield to expand and contract with the differing air pressures as the aircraft climbed and descended.
The manufacturing process involved cutting longitudinal slits in a strip of neoprene that ran around the perimeter of the frost shield to create the expandable seal.
This made-in-Winnipeg device, originally used by Trans-Canada Air Lines, was soon used by other airlines such as Northwest Airlines that operated in the frigid cold of winter. A simple piece of plastic – adapted for the rigors of flight and developed in the frosty centre of Canada – made flying safer and more dependable.