Complex sentence: It called for a large biplane--that would fit in a shed and so needing folding-wings--to be powered by two Sunbeam engines to carry six bombs and with armour plating to protect crew and engines from rifle-fire from the ground.
Split into simpler sentences: It called for a large biplane--that would fit in a shed and therefore needed folding wings--to be powered by two Sunbeam engines. It was to carry six bombs and have armour plating to protect crew and engines from rifle-fire from the ground.