Unducted fan engines.

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This was copied from Facebook.

 

This (unducted fan) concept has been explored before. I am not exactly thrilled about not having a cowling to protect the fuselage from flying projectiles when blades let go. Anyway progress is now largely dictated by climate change and economics.

When an aircraft engine's bypass ratio is 15 or 16, the benefits of a large fan are wiped out by the additional drag created by a very big duct.   The current bypass ratio on jet engines is at 11 to 12, so the end  of large increases in bypass ratio  is close.

Turboprops have bypass ratios of 50-100  although the propulsion airflow is less clearly defined for propellers than for fans and propeller airflow is slower than the airflow from turbofan nozzles.

An open fan design can easily take the bypass ratio up to 60. This would likley mean significant fuel burn advantages

A bypass ratio is a key measure of the efficiency and performance of jet engines, referring to the ratio of air bypassing the engine core versus air passing through it.

Airbus has said test flights of a demonstrator of the “open fan” engine would take place on a modified A380 towards the end of this decade.

Tests will determine what powers the next generation of single-aisle aircraft that will succeed the A320 aircraft when they come on the market towards the end of the 2030s.

Airbus hopes that the new engine configuration will contribute to an expected 20 to 30 per cent fuel efficiency improvement compared with existing models. Current types use “ducted fan” engines, where the fans are enclosed within a casing.

 

 

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Even my xair has an unducted fan