NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Bubble sextant in U-2
From: Paul Hirose
Date: 2013 Jan 11, 16:20 -0800
From: Paul Hirose
Date: 2013 Jan 11, 16:20 -0800
One of the most unusual sextants was operated by U-2 pilots. It's described in the 1959 flight handbook now online at the CIA. This sextant was an optical system installed in the airframe. It viewed the sky through a glass dome ahead of the cockpit. An optical train brought the 15° field of view to a display which looked like a 6 inch radar scope at top center on the instrument panel. An eyepiece wouldn't have been practical for viewing through the faceplate of a pressure suit helmet. Except for electric illumination, the sextant was totally mechanical. Azimuth and elevation were visible in the display. A clockwork integrator accumulated an average for up to two minutes. The sextant was fixed to the airframe; the manual says, "if the bubble is far off it may indicate that the aircraft is not on a straight and level course." Although it was only necessary to bring the body and bubble together, best accuracy was attained if this occurred near the center of the display. The display was shared with the drift sight, which was similar to the periscopic drift meter on transports and bombers of that era. A pull knob switched the view from one to the other. Other navigation equipment included Doppler radar connected to an ASN-6 dead reckoning computer, MA-1 gyro stabilized flux valve compass, and an ARN-6 radio direction finder. https://www.cia.gov/news-information/featured-story-archive/2012-featured-story-archive/pilot-honored-for-bravery.html (link to manual at bottom of page) --