By Bjorn Fehrm

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Introduction

December 19, 2016, ©. Leeham Co: It's time to round off our article series around the engine for a Supersonic Transport Aircraft (SST). The series was triggered by Boom Technologies’ plans to launch a business class-only SST with Virgin Atlantic signing up to buy the aircraft if Boom succeeds.

Our initial articles described the problems involved in making a Mach 2 SST. We singled out the engine with nacelle as the most difficult challenge.

Figure 1. Boom Technologies' Mach 2.2 airliner with 45 business seats. Source: Boom.

Subsequent articles focused how to select an engine for such an aircraft. The requirements are pretty unique and forces design choices which are contrary to a normal airliner engine.

Today, the words "low bypass ratio" and "low overall pressure ratio" are nonexistent in engine OEMs' brochures. Yet this is what we need for our SST. Having covered the cruise phase in Part 4, we now close with take-off/landing and what else to think of when propelling an SST.

Summary:

• An SST aircraft needs low bypass engines with a low overall pressure ratio. This is contrary to all normal airliners' needs.
• The engines need to be housed in nacelles with variable inlets and outlets.
• As a consequence, a configuration with three engines is questionable. A two engine layout would be more optimal.