Do you know what the first commercial transport to break Mach 1 was? It wasn't the Concorde or the Tu-144, it was the Douglas DC-8, which on August 21, 1961 broke the sound barrier in a shallow dive.
Bombardier just broke the sound barrier as a part of its certification tests for its Global 8000 business jet. (paid subscription required)
It was an uneventful flight, and they got the data that they needed, and any pilot who tries this during ordinary flight should have his license pulled:
As Bombardier continues certification tests of the extended-range Global 8000, company test pilots have provided new details of the unusual supersonic flight-test campaign conducted last year off the California coast.
Flight testing for the fastest and longest-range purpose-built business jet is being conducted using FTV-5, a development Global 7500 aircraft on which the new variant is based. Tests at supersonic speeds were required as part of plans to certificate the Global 8000 with a maximum Mach operating speed (MMO) of Mach 0.94, versus the Global 7500’s top speed of Mach 0.925.
Bombardier’s high-speed test campaign culminated in May 2021 when FTV-5 repeatedly achieved supersonic speed in shallow dives, reaching Mach 1.015 off California’s Pacific coast. The tests marked the fastest flight of a civil aircraft since the retirement of the Anglo-French Concorde and the first transport category aircraft to fly supersonically with sustainable aviation fuel.
Describing details of the test and lessons learned, Ed Grabman, senior technical authority for the Bombardier Flight Test Center and an engineering test pilot, said envelope expansion was undertaken because certification requirements require a minimum margin between the maximum cruise speed and the maximum dive speed. “So, while the speed increase was not particularly large the regulations would require us to demonstrate that the aircraft is safe at supersonic speeds. And keep in mind [that] while this is a transonic jet, initially there's never been any plan to test it above Mach 1.”………
As part of preparations for the flights a complete systems analysis was conducted to understand the effects as the aircraft went supersonic. As a result, the standard air data system was augmented with an experimental air data system, which consisted of a nose-mounted miniboom and a trailing cone on the empennage—the latter for measuring accurate free-stream static pressure.
Flying outside the envelope protection of its fly-by-wire (FBW) flight control system, the crew resorted to operating the aircraft in direct mode instead of the standard normal mode. For testing aeroelastic excitation the high rates of descent and short time on condition meant that the usual external aerodynamic vane system could not be used for testing frequency sweeps and dwells. “So we went ‘old school’ and used stick wraps and control pulses for the excitation, but instead of the pilot making the inputs they were actuated by the flight test injection system [(FTI)],” said Grabman, who added that this capability was embedded within the FBW system.
In addition to the technical issues, there were also significant regulatory issues:
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Testing was conducted in restricted air space off the coast from Vandenberg Space Force Base. “There were some test area constraints,” says Jeff Karnes, principal engineering test pilot at Bombardier. “We had to stay greater than 12 mi. offshore, and we couldn't be pointed at land when we did the supersonic dives because of the shockwave. We also had to stay within 90 nm of our telemetry trailer, which was located at Santa Maria Airport,” he says. For safety, the aircraft was fitted with a high-speed recovery chute on a tail-mounted mortar and was provisioned with two inflight emergency egress doors, one at the bottom of the aircraft around midfuselage and the other located in the cargo bay, which was modified with a hydraulic ram door opening device. The crew also wore life vests and parachutes. A NASA-operated Boeing F/A-18 was used as the chase aircraft.
It would have been fascinating to be on those flights.
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