America by Air: Gliding Through Boulder

Editor’s Note: This article previously appeared in a different format as part of The Atlantic’s Notes section, retired in 2021.
Eric ZImmerman

Our aerial feature gets a new kind of craft:

Not sure if I’ve missed it, but with all the piston, turbo, jet, land, and seaplane [and blimp! and paraglider! and helicopter! and skyscraper!] photos, I don’t think I've seen one from a glider! Here’s one I took a few years ago over Boulder, Colorado, on aerotow behind a Super Cub on a winter afternoon. Note the critical instrument visible on the right: the humble yaw string.

What’s a yaw string?

Also known as a slip string, it’s a simple device for indicating a slip or skid in an aircraft in flight. It performs the same function as the slip-skid indicator ball, but is more sensitive, and does not require the pilot to look down at the instrument panel.[1] Technically, it measures sideslip angle, not yaw angle,[2] but this indicates how the aircraft must be yawed to return the sideslip angle to zero. It is typically constructed from a short piece or tuft of yarn placed in the free air stream where it is visible to the pilot.[3]

The yaw string is considered a primary flight reference instrument on gliders, which must be flown with near zero sideslip angle to reduce drag as much as possible. It is valued for its high sensitivity, and the fact that it is presented in a head-up display. Even the most sophisticated modern racing sailplanes are fitted with yaw strings by their pilots, who reference them constantly throughout the flight.