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View Diary: How Airliners Work - Propulsion (191 comments)

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  •  propfans, or unducted fans or ultra-high bypass (3+ / 0-)
    Recommended by:
    BRog, Simplify, basquebob

    Trying to bridge the gap between turbofans and turboprops: get the speed and altitude of a fan jet but the fuel efficiency of a turboprop.  Think of them as an unducted fan: remove the duct and have fewer but thicker blades.  Some versions look more like propellers, others look more like old low-bypass turbofans with blades sticking out.  They work, and they're about 30% more efficient than turbofan engines, but the problem they're running into is noise.  When the tips of your blades are traveling faster than the speed of sound, they spin off lots of little sonic booms.

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