Lighter than air, or near lighter than air vehicles? (Maybe only when lower than 1000' or something?) http://video.nationalgeographic.com/video/i-didnt-know-t

Lighter than air, or near lighter than air vehicles? (Maybe only when lower than 1000' or something?) http://video.nationalgeographic.com/video/i-didnt-know-that/idkt-balloon-lift http://video.nationalgeographic.com/video/i-didnt-know-that/...