Banners are towed with a single line trailing from the plane.
source: © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)
How can they guarantee the banner is vertical and not upside down?
Banners are towed with a single line trailing from the plane.
source: © Raimond Spekking / CC BY-SA 4.0 (via Wikimedia Commons)
How can they guarantee the banner is vertical and not upside down?
The tow line has the "Y" connection to a pipe/rod along the leading edge of the banner. This keeps the leading edge perpendicular to the tow direction. The bottom end of the pipe/rod is weighted so that once in the air gravity will rotate the banner to the vertical.
From wikipedia:
There usually are three lines to the actual towing line. The top one is shortest so that the center of gravity will be below the center of the boom. This to ensure that the message will hang vertical. In addition, often the bottom will be fitted with a weight.