On Monday, January 25, 2021, around 9:30 p.m., residents living southwest of Salt Lake City in Herriman, Utah heard ominous booms and felt their houses shaking. Local Facebook groups lit up with messages such as, "Shaking my house pretty good ..." "Thought it was an earthquake" and "Totally shook our house ..."
For worried residents, the Utah Department of Emergency Management quickly identified the source of the booms and shaking:
Still looking for exact confirmation from the booms, but this is a likely candidate: https://t.co/KHZkI6e9GA— Utah Division of Emergency Management (Utah DEM) (@UtahEmergency) January 26, 2021
Utah is home to the Hill Air Force Base, which is the U.S. Air Force's second-largest base by population and geographical size. Hill is responsible for operating the 2.3-million-acre Utah Test and Training Range located in Utah's west desert. It is the largest block of contiguous, special-use airspace within the continental U.S.
Hill Air Force Base had announced that its 388th Fighter Wing would be conducting night combat training exercises between January 25th and the 29th. In a video posted by the fighter wing, Lt. Col. Yosef Morris said, "Our mission with the F-35s involves deploying the aircraft quickly to anywhere in the world, and then being ready to employ those aircraft in combat very soon after we arrive in theater. So that mission may require us to fly at night.
"As a matter of fact, a way that the aircraft is designed, and many of the missions that we do, we prefer to fly at night in actual combat because it makes us harder to see."
The U.S. Air Force has been conducting supersonic test flights ever since test pilot Chuck Yeager first broke the sound barrier on October 14, 1947. Today, most Air Force fighter aircraft are capable of supersonic speed, and the Air Force requires that whenever possible, supersonic flights take place over open water no closer than 24 km (15 miles) from shore, and that planes be flown above 3 km (10,000 feet). Supersonic flights over land must be above 9 km (30,000 feet), and if flying below that altitude, they must be flown over specially designated areas.
What is a sonic boom?
A sonic boom is caused when an object moves faster than the speed of sound — about 343 meters per second at sea level. Like the waves created by a ship's bow as it moves through the water, an aircraft traveling through the atmosphere produces air pressure waves. When an aircraft exceeds the speed of sound, the pressure waves combine, forming shock waves that travel forward, dropping sonic booms all along the plane's flight path.
For fighter aircraft, the audible "boom" in the sonic boom is concentrated between .1 and 100 Hz and lasts around 100 milliseconds (1/100 of a second). Compare that with the sonic booms lasting 500 milliseconds which were created by the Space Shuttle and the Concorde jetliner.
The sonic boom is greatest in intensity directly under the flight path of the plane, and weakens progressively with greater distance. The ground width of the boom is approximately 1.6 km for every 1,000 feet of altitude, so an aircraft flying supersonically at 30,000 feet will create a boom spanning around 48 km.
Depending on the aircraft's altitude, sonic booms reach the ground between two seconds and 60 seconds after the plane has flown overhead, however, the speed of sound at any altitude is also a function of air temperature. The frigid temperatures at high altitudes bend sound waves upward, so for a sonic boom to reach the ground, an aircraft's speed relative to the ground must be greater than the speed of sound at ground level.
At 30,000 feet, the speed of sound is about 1,078 km per hour, but an aircraft must be traveling at least 1,207 km per hour (Mach 1.12, where Mach 1 equals the speed of sound) for a boom to be heard on the ground. That means that the F-35s flying over Utah must have been really hauling ass.
The F-35 Lightning II
Manufactured by Lockheed Martin along with Northrop Grumman and BAE Systems, the F-35 Lightning II was created to replace the U.S. Air Force's aging fleet of F-16 Fighting Falcons and A-10 Thunderbolt IIs, which have been the U.S.'s primary fighter aircraft for over 20 years.
The F-35 Lightning II is a single-seat, single-engine, all-weather stealth multirole combat aircraft that besides performing strike missions, can also provide electronic warfare and intelligence, surveillance, and reconnaissance.
The plane's development was principally funded by the U.S. with additional funding from NATO, the UK, Italy, Australia, Canada, Norway, Denmark, the Netherlands, and formerly Turkey. The F-35 program is notable for its huge size, complexity, ballooning costs, and delayed deliveries.
There are three variants of the F-35: the conventional takeoff and landing F-35A (CTOL), the short take-off and vertical-landing F-35B (STOVL), and the carrier-based F-35C (CV/CATOBAR). The F-35's engine produces 43,000 lbs. (191273.53 N) of thrust.
The F-35B first entered service with the U.S. Marine Corps in July 2015, followed by the U.S. Air Force F-35A in August 2016, and the U.S. Navy F-35C in February 2019. The F-35 was first used in combat by the Israeli Air Force in 2018.
The F-35 includes the Electro-Optical Distributed Aperture System (DAS), which provides pilots with enhanced missile warning, aircraft warning, and day/night pilot vision. The F-35 is also equipped with the Electro-Optical Targeting System (EOTS), which provides extended range detection and precision targeting against ground targets, along with long-range detection of air-to-air threats.
A helmet-mounted display system provides all the intelligence and targeting information required by the pilot right on the helmet's visor. The F-35 has tactical data links that allow the secure sharing of data amongst pilots and ground-based teams.
Through 2044, the U.S. has plans to buy 2,456 F-35s, and this will represent the bulk of the crewed tactical airpower of the U.S. Air Force, Navy, and Marine Corps for many decades to come. Just hope that the next F-35 combat training exercise doesn't happen over your house.