The Boom SST engine problem, Part 4

By Bjorn Fehrm

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Introduction

December 15, 2016, ©. Leeham Co: In our article series around the engine for a Boom SST, we established the thrust requirements for the engines in Part 3.

To fulfill these requirements, we have now designed four different engines. Three are of the type that Boom says it is considering, an engine that is based on an existing core.

Figure 1. Boom Technologies Boom Mach 2.2 45 seat airliner. Source: Boom.

We based these around a military core with the right characteristics for a low-to-medium bypass SST engine. The fourth engine is a custom-designed straight turbojet, very similar to the engine that propelled the only operational SST, the Concorde.

We will use the reference turbojet to understand the difference to a turbofan in this application and why the selection of an engine for a SST follows different rules than for a normal airliner.

Summary:

  • Supersonic flight requires engines with low frontal areas and low mass flows.
  • Should the engine be designed as for a normal airliner, the inlet drag would be prohibitive.
  • The engine also must have a low pressure ratio core; otherwise the energy of the fuel is wasted on non-productive work.

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