I Learned About Flying From That - Supersonic Flight VFC General Manager
GM Corner
BGen (Ret’d) GCP Matte, CD, PhD I’ve been asked on numerous occasions to relate my experiences beyond Mach 1, in part based on the story I shared at last year’s Wings Awards Banquet about flying supersonic at 100’ AGL. In fact, many if not most of the non-aviators that I took up for a backseat ride in the CF-18 asked to experience breaking the sound barrier. Spoiler alert… for most it was a non-event as they didn’t feel a thing, so I had to direct their eyes to the Mach meter so that they could see for themselves that they were hurtling through the sky faster than the speed of sound. I can understand the allure. Prior to Chuck Yeager’s flight in the Bell X-1 on 26 April 1948, many believed that supersonic flight was impossible, and to this day only a limited number of people (astronauts, fighter pilots, Concorde passengers, etc.) have exceeded the speed of sound. The reason for this belief was the underlying physics. While air is far less dense than water or hydraulic fluid, it too can be compressed to the point of incompressibility…a barrier that would destroy any plane that attempted to pass through it. However, the growing knowledge of aerodynamics and experimentations with aircraft designs made the impossible possible. But this also depends on the conditions. At higher
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altitudes the air is far less dense than at sea level. When Yeager broke the sound barrier for the first time, it was in the stratosphere at 45,000’ MSL. At lower altitudes, the air becomes increasingly dense, and the “experience” of going supersonic is much different. Violent might be one of several adjectives that I would use, having once taken the CF-18 supersonic at 100’ AGL (approximately 2000’ MSL) over the Cold Lake Air Weapons Range (CLAWR). While the CF-18 was designed for supersonic flight, with an upper limit of Mach 1.8 (which I explored on a separate occasion), my flight that day in May 1988 was an experience that I would never forget, nor repeat! To put things in perspective, the speed of sound (aka Mach 1) at 2000’ MSL on a standard day (15 degrees Celsius) is about 1100 feet per second, or 760 miles per hour. By way of a comparison, driving down the Pat Bay Highway at 122 kilometers per hour would equate to 76 miles per hour…one tenth the speed of sound. As you might imagine, as one gets closer and closer to the earth’s surface the speed rush seems to increase exponentially. Flying supersonic at 100 feet above the treetops feels VERY fast. Naturally, the margin of error for a slight dip from level flight is razor thin, so it’s important to
focus on maintaining level flight and avoiding the treetops. To fly faster than the speed of sound at low altitude, I started at about 20,000’ MSL where it’s easier for the Hornet to go super. I then pushed the nose over and dove towards the earth in full afterburner while maintaining about 1.1 Mach, as I was concerned that I might slow back into the transonic regime as the air density increased. My plan worked! I carefully pulled out of my steep descent as I transitioned below 1000’ AGL while remaining supersonic. With great care, I leveled out at 100’ AGL (about 70’ AGL on my radar altimeter, given the trees). Fortunately, the terrain is relatively flat in the weapons range, so level flight was relatively easy to maintain… if it wasn’t for the thermals as my flight path criss-crossed over the cold water of the various lakes and the warmer land. While the total duration of my “experience” at low level only lasted about 45 seconds that was as long as I could stand it, as I thought that at any moment the plane might suddenly disintegrate out from under me due to the stress on the fuselage, wings and twin vertical stabilators. As I said earlier, “violent” is probably the best adjective I could use to describe the experience. In addition to potential airframe
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