The world's largest airship has been unveiled, as the enormous Pathfinder 1 begins its first round of flight tests. Measuring 400 ft (121.9 metres) in length, this gargantuan blimp is nearly twice the length of a Boeing 747-8 quadjet, the world's longest aircraft. The blimp uses approximately one million cubic feet of helium and 12 electric motors to achieve vertical take-off and speeds of up to 75mph (120km/h). The vast airship has been created by LTA Research, a company backed by Google co-founder Sergey Brin. Its creators say that craft like this could one day reduce the carbon footprint of...