Boom Symphony

The Boom Symphony is a two-spoolmedium-bypassturbofan engine under development for use on Overture. The engine is designed to produce 35,000 pounds (160 kN) of thrust at takeoff and sustain Overture supercruise at Mach 1.7, and burn sustainable aviation fuel exclusively. Development of the engine will be conducted in partnership with Kratos subsidiary Florida Turbine Technologies for engine design, General Electric subsidiary GE Additive for additive manufacturing consulting, and StandardAero for maintenance. Boom aims for initial production of the engine to begin in 2024 at the Overture factory at Greensboro, North Carolina.

Development

Background

Boom intends to use moderate-bypass turbofans which can achieve supercruise (supersonic flight without afterburners) and will not have them fitted. Concorde's Rolls-Royce/Snecma Olympus could sustain supercruise, but required afterburners for takeoff and transonic acceleration. Although improved over afterburning, supercruise still creates more noise for worse fuel consumption compared with a modern subsonic wide-body aircraft. A supersonic aircraft is estimated to burn at least three times as much fuel per passenger as a subsonic aircraft.

The only current supersonic engines available are jet fighter engines, which have neither the fuel economy nor the reliability required for commercial aviation. Boom propose a modified version of an existing turbofan engine design, although it will come with higher maintenance costs. An engine was to have been selected in 2018, being either a derivative of a commercial engine or a clean-sheet design. Developing the engine around an existing commercial engine core, with a new low-pressure spool, is preferred over a clean-sheet design.

A 55-seat model was to have been powered by three 15,000–20,000 lbf (67–89 kN) engines without afterburners, with shorter maintenance intervals than subsonic jets.

Larger diameter fans have higher cruise thrust requirements for a higher fuel-burn and lower range, but are preferred due to their higher bypass and lower take-off noise. It is unlikely to be a modified military engine, due to export controls. Intake compression would need a low-pressure core, and derivatives of existing 3–4:1 bypass-ratio turbofans are a compromise between takeoff noise and wave drag, with a good fuel efficiency. Dave Richardson, of Lockheed Martin's Skunk Works, noted that suitable engines with low overall pressure ratio are scarce. Development of 1950s–1960s engines like the GE J79, GE YJ93, GE4, PW J58 or Rolls-Royce Olympus ended when higher efficiency was pursued, and subsequent advances in materials science for much hotter cores are not optimized for long supersonic endurance. Current engines are even less suitable than the PW JT8D or GE J79.

The high development costs render new low-bypass-ratio turbofans unlikely. As of November 2016, no engine manufacturer could develop such an engine based on sales of only 10 units. In July 2020, the company entered into an agreement with Rolls-Royce to collaborate on engine management. Having delivered their findings, Rolls-Royce are not pursuing the market any further.

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Symphony
Type	Medium-bypass turbofan
National origin	United States
Manufacturer	Boom Supersonic
Major applications	Overture

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