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Why is the Reaction Engines Limited SABRE (Synergistic Air-Breathing Rocket Engine) curved along it's length?

SABRE Engine Diagram

    Illustration of the SABRE engine with the pre-cooler heat exchanger highlighted in blue. Credit: REL/Adrian Mann

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    $\begingroup$ Because the acronym wouldn't be half as cool if it weren't, obviously. :-) $\endgroup$ Nov 4, 2015 at 0:00
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    $\begingroup$ I like that picture. It looks like a cutaway drawing of a Flash Gordon spaceship. $\endgroup$ Nov 4, 2015 at 3:27

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According to Mark Hempsell, formerly Future Programmes Director at Reaction Engines Ltd., now CEO of Hempsell Astronautics Ltd., explaining the reason for SABRE's curved nacelle over at NasaSpaceFlight.com forum:

Why a Curved nacelle? – the most frequently asked technical question. The answer is: the air intake on the front of the nacelle needs to point directly into the incoming airflow whereas SKYLON’s wings and body need to fly with an angle of incidence to create lift, so the intake points down by 7 degrees to account for this. The rocket thrust chambers in the back of nacelle need to point through the centre of mass of the vehicle so are angled down; again by 7 degrees but it is a coincidence the angle is the same.

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    $\begingroup$ I've read the explanation but don't yet understand it or see what is unique about Sabre that lead to this design solution. Are there any similar concepts in other existing systems jet aircraft/ramjets/missiles with aerofoils? $\endgroup$
    – Puffin
    Mar 15, 2016 at 15:16
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    $\begingroup$ It's the Skylon design that has the curved nacelle, it is not required by SABRE, but can be accommodated by it. It's not seen in other systems because other hypersonic craft with subsonic air breathing engines don't fly at as high an Angle of attack, and have the engines aligned with the centre of mass. $\endgroup$
    – user20636
    Aug 9, 2017 at 17:10

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