The end of the second world war saw Germany start a lot of fantastical projects to try and regain air superiority. Among them was the Lippisch P 13a project, which was to use a coal-powered ramjet.
The engine illustration shows the coal basket with a rotation axis perpendicular to the airflow, which increases the risk of coal fragments flying out into the air stream without providing thrust. So I designed a version with an inline basket rotation axis, to mitigate this problem and facilitate the installation of an engine-driven fan allowing for thrust at zero-speed.