Understanding the sonic boom

We love jet fighters, their power, their speed, and their agility. When we were kids, what impressed us most at jet-fighter-rides.com was and still is the sonic boom. Although when flying at or over the speed of sound one does not feel anything, the boom the aircraft produces is very impressive. It feels like engineering vs forces of nature, and this is also why we like it so much. For once, man has been able to understand and dominate nature on this one.

So here is a little word about the sonic boom.

The sonic boom is a sound associated with the shockwave created by the supersonic flight of an aircraft. The boom generates tremendous amounts of energy, sounding much like an explosion, hence the “boom”. When an object – like a jet fighter - passes through the air, it creates a series of pressure waves in front of it and behind it. These waves travel at the speed of sound, and as the speed of the object increases, the waves are forced together, or compressed, because they cannot “get out of the way” of each other, eventually merging into a single shock wave at the speed of sound. This critical speed is known as Mach 1 and is approximately 1,225 kilometers per hour (761 mph) at sea level at room temperature. In smooth flight, the shock wave starts at the nose of the aircraft and ends at the tail. Because directions around the aircraft’s direction of travel are equivalent, the shock forms a Mach cone with the aircraft at its tip.

The power, or volume, of the shock wave is dependent on the quantity of air that is being accelerated, and thus the size and shape of the aircraft. As the aircraft increases speed the shocks grow “tighter” around the craft and do not become much “louder”. At very high speeds and altitudes the Mach cone does not intersect the ground and no boom is heard. The “length” of the boom from front to back is dependent on the length of the aircraft to a factor of 3:2. Longer aircraft therefore “spread out” their booms more than smaller ones, which leads to a less powerful boom which has a less “spread out” boom. The sound of the boom also depends on the distance between the aircraft and the observer.

sonic boom

A sonic boom is usually heard as a deep double “boom” as the aircraft is usually some distance away. Depending on the aircraft’s altitude, sonic booms reach the ground two to 60 seconds after flyover. However, not all booms are heard at ground level. The speed of sound at any altitude is a function of air temperature. A decrease or increase in temperature results in a corresponding decrease or increase in sound speed. Therefore, the more a plane flies high, the less you are likely to here the boom.

Can the sonic boom destroy buildings and other things on the ground ? Not really, but chances are it will annoy many people on the ground. The sonic boom creates pressure, measurable in pounds per square foot. A fighter jet flying at high altitude will generate less pressure on the ground as the shock wave’s intensity reduces through the air before reaching the ground. If flying at low altitude, the pressure is greater. To give you an example, SR71 flying at 80,000 feet at Mach 3 generates only 0.9 pounds per square foot. Concorde when flying – sic – at 52,000ft at Mach 2 was generating 1.94 pounds per square foot. The main reason Concorde was not authorized to fly at supersonic speed was not because of fear it would break all the windows, but primarily because of the noise.

Is it possible to find jet fighter rides going at Mach speed ? YES my friends. As of today you can fly the Mig 29 Fulcrum in Russia to the edge of space, reaching Mach 2 as you near an altitude of 65,000ft. You can also try out the supersonic and aerobatic Mig 29 flight which will get you at Mach 1.1 and then enjoy some aerobatics. The Electric Lightning in Cape Town can do that as well but it is currently undergoing maintenance. The Starfighter in Florida will also get you to the speed of sound.

You can find additional information on the sonic boom on Wikipedia.