Larger feathers could have increased lift incrementally, until sustained flight was gradually achieved.

较大的羽毛可以逐渐增加升力，直到逐渐实现持续的飞行。

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But how does NASA plan to get the scramjet to the supersonic speeds necessary for sustained flight?

不过，太空署要如何使得超燃冲压发动机进入持续飞行需要的超音速呢？

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In 2005, the 9th prototype achieved sustained flight times, laying the foundation for a viable and successful pre-production prototype to be developed.

在2005年，第九原型实现持续飞行时间，为建立一个可行的和成功的前生产原型开发。

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This flight was important for a number of reasons, but in no small part because it represented the first controlled, sustained flight complete with human-powered takeoff.

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Everything that is required to support sustained combat flight operations is available in a single mobile package.

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That, and improving efficiency really made human powered-flight move from sustained hops and skips to the international crossings of the Albatross.

ENGADGET: The Highs and Lows of Human-Powered Flight Alt