Background
Many projects have been carried out in Europe as well as in other countries, addressing the large supersonic transport aircraft market. None has already emerged due to the difficulty to overcome the economic and environmental issues. But beyond the current market for small subsonic aircraft there is a substantial segment of customers interested in flight time being reduced by 20 to 50% as compared with current subsonic business aircraft on distances over 6500km which is the minimum required for transatlantic flights.

Updated Project objectives
The stopping issues are strongly alleviated by reducing the size. The HISAC project aims therefore at establishing the technical feasibility of an environmentally compliant small size supersonic transport aircraft (S4TA), through a MultiDisciplinary Optimisation (MDO) approach and focused technological improvements.
The first general objective is to identify the characteristics of aircraft that could meet prospective environmental requirements, namely:

• reduction of external noise by 8dB cumulative margin re ICAO Chapter 4,
  
• NOx emissions: less than 5g per kg fuel burnt in the long term, 10g in the medium term,
  
• emissions at landing and take-off comparable to those of a subsonic aircraft,
  
• reduction of the sonic boom signature overland, while offering attractive performance for the customer:
  
• time reduction from 20% to 50% compared to current aircraft,
  
• range at least transatlantic,
  
• operation from small airports,
  
• cabin suitable for 8 to 16 passengers.

The second objective is to provide policy makers with a set of recommendations for future environmental regulations which could reasonably be met with an optimised S4TA.

As a third objective, HISAC will provide progress on critical elementary technologies and associated design and optimisation multidisciplinary methods as well as a plan for further research.
The three main objectives of the project are illustrated in the following chart and quantified in the following table:

Description of the work

Based on their experience, the HISAC partners have chosen the following avenue:

• Translation of the environmental objectives into quantified design criteria for community noise, atmospheric emissions, sonic boom, applicable to an S4TA;
  Adaptation of numerical models and tools essential to the multidisciplinary design process; emphasis will be put on noise, emissions, sonic boom, engine and aerodynamics, as well on MDO process itself;
  
• Development and validation of the most critical engine and airframe technologies; technologies considered will be variable cycle and nozzle noise reduction for engine, forced laminar flow, high lift devices and variable geometry wing for airframe; mixer-ejector nozzles will be designed and tested for a better assessment of this engine technology;
  
• Establishment of rules and methods to solve key integration issues; for this purpose specific shape design work, supported by wind tunnel tests, will be performed, focusing on engine integration (compromise between low noise and low drag), boom minimisation, and maximisation of laminar boundary layer; specific airworthiness issues will also be overviewed in order to identify the key points of the future specific conditions for certification;
  
• Application of MDO methods, using the results of the above, to obtain:
  
  • aircraft specifications compliant with environmental objectives; to explore the broadest range of concepts and address all design and environmental issues, the work will be shared between the partners with the constitution of three aircraft configuration teams;
    
  • quantified trade-offs between aircraft performance and environmental constraints
  
  

Expected achievements

HISAC will provide:

• achievable specifications for an environmentally compliant and economically viable small size supersonic transport aircraft
• recommendations for future supersonic environmental regulations (community noise, emissions, sonic boom) enabling technologies, and a road-map for their further maturation and validation, up to a future Proof Of Concept