Everyone knows how the Citroen 2CV and Visa twins have been used for many single seater aircraft. This larger GS / Super Ami engine is a seventies flat air cooled four cylinder engine in the 1 litre class and could be an upgrade to two seaters with somewhat similar tech still. Interestingly, it has two overhead camshafts driven by toothed belts, and a single valve driving enclosure on both sides. I don't know if this means that it was designed for higher revs, meaning possible problems in aircraft use. Citroën GS + GSA boxer engine Comments?