Unless Boom Supersonic has something up to its sleeve in the form of a contract with an undisclosed engine maker, the US start-up seems to have hit a serious setback. It still hasn’t a confirmed engine and can now exclude Rolls-Royce from the list, after the UK maker confirmed that it is no longer involved in the supersonic airliner project. When will Boom show its engine card? The news was first brought by AINonline on September 6 and later by Aviation Week and FlightGlobal on September 7 and 8. Rolls-Royce hasn’t provided further details about its decision, except for this statement: “We have completed our contract with Boom and delivered various engineering studies for their Overture supersonic program. After careful consideration, Rolls-Royce has determined that the commercial supersonic market is not currently a priority for us and, therefore, will not pursue further work on the program at this time. It has been a pleasure to work with the Boom team and we wish them every success in the future.” Rolls-Royce and Boom announced their collaboration on July 30, 2020. In a statement, Rolls-Royce said back then: “The goal of the new agreement is to work together to identify the propulsion system that would complement Boom’s Overture airframe. The engagement will involve teams from Boom and Rolls-Royce collaborating in engine-airframe matching activities for Boom’s flagship supersonic passenger aircraft, Overture. The teams will also examine certain key aspects of the propulsion system. The teams will investigate whether an existing engine architecture can be adapted for supersonic flight, while Boom’s internal team continues to develop the airframe configuration.” Director of Strategy, Simon Carlisle, said in the statement: “We share a strong interest in supersonic flight and in sustainability strategies for aviation with Boom. We’re now building on our valuable experience in this space as well as our previous work together to further match and refine our engine technology for Boom’s Overture.” A key ingredient was the use of pure sustainable aviation fuel (SAF), which Boom said would get emissions of Overture operations to net zero. No appetite to invest Rolls-Royce hasn’t replied to questions of AirInsight about the extent to which the collaboration had got in the past two years, what engine had been studied, and if the redesign of Overture has anything to do with its decision not to continue. But already at last July’s Farnborough Airshow, there were clear indications that the engine choice was far from confirmed. Rolls-Royce CEO Warren East told TheAirCurrent that his company was unwilling to invest in a dedicated engine for the Overture and that its priority lies within the development of the UltraFan project for commercial engine programs and business jet engines. In other words: Overture’s business case is too small to justify the investment, especially at a time when Rolls-Royce is still trying to recover from the Covid crisis. Analysts weren’t too impressed with its HY1 results recently. Boom CEO Blake Scholl was tightlipped too in Farnborough on the prospect of engine selection, although he said that more announcements were to follow those on new partnerships that were revealed during the airshow. The main topic there was the unveiling of a drasticallly redesigned Overture with a different installation of the four engines. One engine available for Supercruise without afterburner is the GE F414, which will also power NASA's X-59 experimental aircraft. (General Electric) Scholl said that Boom will stick to an engine without afterburner to thrust Overture to Supercruise beyond Mach 1 and up to Mach 1.7. For this, it would need between 15.000 and 20.000 pounds of thrust. One engine that fits that bill is Pratt & Whitney’s F119-PW-100, which is powering the Lockheed F22 Raptor fighter, although at 35.000 pounds of thrust it seems overpowered. General Electric offers the F414 at 22.000 pounds. The F414 is currently available on the F/A-18 Super Hornet and the Saab Gripen JAS39. It has also been selected for NASA’s X-59 QueSST supersonic research project that will study how to reduce the supersonic boom. X-59 is scheduled to start flight tests in 2024. Another engine to offer Supercruise is the Eurojet EJ200 that powers the Eurofighter Typhoon, but offers only 13.000 pounds of power without reheat. Note that Rolls-Royce is a partner of Eurojet, together with MTU Aero Engines, ITP Aero, and Avio Aero. While all three engines would be capable of powering the Overture, they are all jet fighter engines that per definition are loud and thirsty. Even when using precious SAF, this would make the aircraft far from the sustainable SST that Scholl wants many to believe it will be. And he is in for a repetition of Concorde’s history, which was banned from flying over land because of its noise levels and the sonic boom. Again, we don’t know what happens behind the scenes at Boom. Maybe Scholl has a firm commitment from an engine maker and the announcement by Rolls-Royce is nothing to worry about. If he hasn’t, Scholl has to hurry up and get a deal done if he wants to meet his planned first flight in 2026 and entry into service in 2029. So it’s up for Blake Scholl to show his cards soon on the engine choice, or risk that the doubters of Overture will be right.
