By Jonny Lupsha, Wondrium Staff Writer
A new Russian weapon, the Avangard, travels 27 times the speed of sound, AP News reported recently. Fired from a ballistic missile, it also has groundbreaking maneuverability, making it harder to track. Breaking the sound barrier back in 1947 was a feat of technology and aviation.
According to the AP article, Russian President Vladimir Putin “described the Avangard hypersonic glide vehicle as a technological breakthrough comparable to the 1957 Soviet launch of the first satellite.” With regard to its functionality, “The Avangard is launched atop an intercontinental ballistic missile, but unlike a regular missile warhead that follows a predictable path after separation, it can make sharp maneuvers in the atmosphere en route to target, making it much harder to intercept.” This latest step in weapons technology can be traced back to breaking the sound barrier.
Problems of the Sound Barrier
Before the National Advisory Committee for Aeronautics—or NACA, the predecessor to NASA—could break the sound barrier, they first had to run into it.
“Before, during, and after World War II, there was a widespread perception that aeronautics faced a so-called sound barrier at speeds around 767 miles per hour, also known as Mach 1,” said Dr. James W. Gregory, Professor of Mechanical and Aerospace Engineering at The Ohio State University. “It was as if there [were] some kind of inherent physical limit, a literal sound barrier, that prevented flight near or at the speed of sound.”
Dr. Gregory said that the sound barrier presented three major obstacles for piloted aircraft. Around Mach 0.8, lift began to decrease. At the same time, drag began to increase considerably. Third, pilots faced a major reduction in flight controls.
So how would aviators even learn to break through it?
Solutions to the Sound Barrier
“The breakthrough came when NACA built special transonic wind tunnels so study the phenomena happening at transonic speeds—and what they found was startling,” Dr. Gregory said. “When the airspeed increased above a certain threshold, shock waves began to form on the wing, and as the velocity of the wind continued to increase, the strength of the shock increased, and its location on the wing changed.”
One of the biggest ideas for reducing the drag on an airplane involved “swept wings,” which are angled somewhat backwards or forwards from the body of the plane instead of sticking out horizontally.
“This idea was first presented by Adolf Busemann at the 1935 invitation-only Volta Conference,” Dr. Gregory said. “He proposed an idea stating that compressibility effects on a wing were due to the Mach number of the flow perpendicular to the leading edge. So, if the wing were swept back, the component of flow velocity parallel to the leading edge would not have an impact, leaving only the component perpendicular to the leading edge to affect the wave drag.”
In other words, when planes reached high speeds with perpendicular wings, air rushed into them with such force along their wingspans that it slowed them down. If the wings angled back along their wingspan, those same air molecules would have an easier time moving along the wings rather than only being forced over or under them.
With the use of transonic wind tunnels for observation, the discovery of the sound barrier, and the implementation of swept wings, it wasn’t long before Chuck Yeager broke Mach 1 in the Bell X-1 aircraft over the Mojave Desert in October 1947—and others followed suit. Nowadays, every major commercial airliner uses jet engines and swept wings to transport its passengers.
Dr. James W. Gregory contributed to this article. Dr. Gregory is Professor of Mechanical and Aerospace Engineering at The Ohio State University. He received a bachelor of science degree in Aerospace Engineering from Georgia Tech and a doctorate in Aeronautics and Astronautics from Purdue University.