Analysis of information sources in references of the Wikipedia article "Bell 47" in Vietnamese language version.
I thought the bubble was a great idea, and we tried it. It consisted of taking a large sheet of Plexiglas, and a plywood form, cut for the final dimension for the outside of the bubble, then heating the Plexiglas, putting it under the plywood form, letting air pressure come up through the middle, and it would blow just like a soap bubble. And, then we had a gauge saying how far to blow, and when it reached that point, we turned off the air pressure.
