Complex sentence: It was powered by a Hirth HM 504 air-cooled, four cylinder, inverted inline engine, which was totally enclosed with the flat sided fuselage with no side-scoops for cooling air, an arrangement which lead to overheating.
Split into simpler sentences: It was powered by a engine Hirth HM 504 air-cooled, four cylinder, inverted inline engine. The engine was totally enclosed with the flat sided fuselage, with no side-scoops for cooling air, an arrangement which lead to overheating.