Project summary

The research done in this project is about the introduction and airworthiness of cruiser-feeder concepts of operations for civil aircraft. Cruiser-feeder concepts of operations are investigated as a promising pioneering idea enabling energy efficient air transport of the future. The soundness of cruiser-feeder concepts of operations for civil aircraft has been under investigation in the RECREATE project for 36 months. A concept with fuel transfer from feeder to cruiser, and a concept with payload transfer between feeder aircraft and a nuclear propelled cruiser have been studied extensively. For the latter nuclear cruiser concept, it is concluded that neither airworthiness nor acceptance of the idea by the general public is within sight. However, for the concept with fuel transfer from feeder to cruiser (civil air-to-air refuelling operations), the results of our collaborative research indicate a fuel burn reduction potential on isolated aircraft level between 11% and 23 % for a typical 6000 nautical miles flight with a payload of 250 passengers. It is remarked that the lower bond of this reduction potential is usually considered as large in the aerospace industry.

The most important outcome of the RECREATE research is that a clear route has been mapped out on how cruiser-feeder operations (as a concept to reduce fuel burn) could ever comply with airworthiness requirements for civil aircraft. It is proposed to follow an approach similar to certifying for automatic landing systems as specified for All Weather Operations. In line with the corresponding Acceptable Means of Compliance, the performance of the aerial refueling system may be demonstrated through simulations using a model of the system, validated by flight tests. Corner stones of the project for generating all the new data are the optimized cruiser and feeder conceptual and preliminary designs which have been made and refined in two design iterations. These designs are based on separately formulated airworthy operational concepts.

A crucial outcome of the project is the clear vision on the route towards full automation of the whole refuelling phase. Based on the automation concepts chosen and the detailed models created, demonstrations of the performance of the aerial refueling system have been made. The same models have been used in a coupled cruiser – feeder flight simulation experiment involving commercial aviation pilots, to investigate human factors of cruiser-feeder concepts of operations for civil aircraft. From the initial flight simulation experiment, safe refuelling operations are judged as feasible by the pilots involved.

Finally, a surprizing outcome of the project is the result of the benefits study. Benefits in terms of fuel burn reduction or economic benefits have been studied on an integrated air transport level, accounting for realistic fleet and traffic. Unlike our anticipation at the start of the research, not only fuel burn reduction but also cost reduction seems to be feasible.