By Tommy H. Thomason
Friday, July 3, 2015
Call Sign Boron?
A couple of people have asked me about the picture of the VA-55 A-4C above. It was reportedly taken at Danang circa 1967 when the squadron was deployed with Constellation.
Although guesses included a call sign, it was a composite-structure test specimen, installed on a fleet aircraft for a evaluation in operational usage.
From the AIAA paper by A.V. Hawley and M. Ashizawa presented in October 1968 (see HERE for a link to the PDF, which was found by Phil Friddell):
"The (A-4) flap was initially selected as a suitable component for obtaining flight experience with boron filaments. The existing production aluminum flap was redesigned utilizing boron skins supported by a full-depth honeycomb core, while retaining some of the basic component aluminum parts for interchangeability reasons. A second flap design, utilizing graphite as the composite reinforcement and developed in accordance with advanced structural element concepts such as molded graphite parts to replace aluminum rib and hinge fittings was developed. The choice of skin layup and core geometry is explained. It is shown to depend not only on the strength and stability of the skin but also on the temperature and pressure conditions that exist during the cure and secondary bonding. Emphasis is placed on the problems encountered during the design and development phases rather than on those which came to light during the final detailed analysis."
The test specimen was prominently identified, in part because of the health hazards presented by boron fibers when they are burned, and since it was non-standard from a repair standpoint. "Boron" was also a reminder that the component, even damaged, was of interest to the Bureau of Aeronautics and its creators.
Aircraft structure incorporating boron composites were subsequently used in the F-14 among other aircraft.