Flying at Supersonic Speed
Sunday, September 17th, 2006This is interesting. Just the other day, I received some photos enclosed in an email describing what an airplane looks like precisely at the point of crossing from subsonic to supersonic speed. These were really great photos.
Ironically, today I was reading chapter 3 in the “Pilot’s Handbook of Aeronautical Knowledge” on aerodynamics and there was a discussion about this very topic. I thought there was an opportunity here…1. To show these great photos, and 2. To explain how this phenomenon happens.
Here goes, right from the book:
“When an airplane flies at subsonic speeds, the air ahead is “warned” of the airplane’s coming by a pressure change transmitted ahead of the airplane at the speed of sound. Because of this warning, the air begins to move aside before the airplane arrives and is prepared to let it pass easily. When the airplane’s speed reaches the speed of sound, the pressure change can no longer warn the air ahead because the airplane is keeping up with its own pressure waves. Rather, the air particles pile up in front of the airplane causing a sharp decrease in the flow velocity directly in front of the airplane with a corresponding increase in air pressure and density.
As the airplane’s speed increases beyond the speed of sound, the pressure and density of the compressed air ahead of it increase, the area of compression extending some distance ahead of the airplane. At some point in the airstream, the air particles are completely undisturbed, having had no advanced warning of the airplane’s approach, and in the next instant the same air particles are forced to undergo sudden and drastic changes in temperature, pressure, density and velocity. The boundary between the undisturbed air and the region of compressed air is called a shock or “compression” wave.”
So there is the boring stuff. Here is the cool stuff…
…and yes, in case you thought it couldn’t be done…a single prop small airplane has broken the sound barrier. Don’t ask me how this was done. Apparently this was a secret project and there were rockets propelling the craft. It is my understanding that this speed would tear the airplane apart, but from the article I read, there were modifications done that would prevent this.
