GLASS-OFF IN THE VALLEY:

Flying Humans: An Interview with David Glover (Astrobiology Magazine, Oct 20, 2003)

David Glover is the past President of the United States Hang Gliding Association. He holds a world record for distance hang gliding and has taken more people up for their first flight than almost anyone in the world. Glover is among the fewer than ten tandem hang gliding instructors who have more than 5000 flights with a passenger. Today, there are fewer tandem hang gliding instructors than astronauts. [...]

Flying flexible wing designs has a rich history among forward-thinking planetary explorers. The first flex wing hang glider patent by Dr. Francis Rogallo (NASA Langley wind tunnels, Virginia) dates all the way back to the late forties. Rogallo is considered "The Father of Hang Gliding", and his design is often hailed as a kind of original, not having any model in nature.

In contrast to other flexible aerial devices like parachutes, a load-bearing Rogallo wing produces more lift than drag, though not as much as a conventional wing. But rigid wings could not be folded neatly away when not in use, and they were inherently far heavier. Rogallo first realized what this might mean in 1952, when he chanced across an article on space travel: "with beautiful illustrations depicting rigid-winged gliders mounted on top of huge rockets. I thought that the rigid-winged gliders might better be replaced by vehicles with flexible wings that could be folded into small packages during the launching."

Although the light materials like bamboo and thin, strong cloth have been available for thousands of years, a practical design for human soaring was missing: the dream of foot-launched flight particularly seemed dauntingly difficult. Indeed, the Egyptians had all the items necessary to create a glider capable of carrying a person, but only the latter half of the twentieth century saw the full concept take shape.

As part of its Century of Flight commemoration, Astrobiology Magazine had the opportunity to talk with David Glover about human flight, on the one-hundredth anniversary of the Wright Brothers' famous first lift-off. [...]

AM: What is the moment of 'glass-off', in hang-gliding terminology?

DG: The sun can be down and you still are floating far above the ground. So 'glass-off' denotes an end of the day phenomenon where the latent heat trapped in a valley, usually in front of a mountain, releases a rush of rising air and provides buoyant lift for a pilot.

It is a very descriptive phrase, 'glass-off', because at the end of the day, over a valley, the air can become all lift. It gives the pilot a very smooth ride.

What a lovely phenomenon.

Posted by Orrin Judd at October 26, 2003 6:08 AM