Observations of Severe In-Flight Environments on Airplane Composite Structural Components

An investigation of the effects of severe in-flight weather environments on composite structures has been conducted as part of the NASA-Langley Research Center Storm Hazards Program. The on-going program uses an extensively-instrumented F-106B airplane to make thurderstorm penetrations. The vertical fin cap was chosen for the experimental composite structure because of the likelihood of lightning strike attachments and the ease of component replacement. Three components were flown and investigated. The first was the U.S. Air Force production glass/epoxy fin cap which was flame-sprayed by NASA with aluminum for lightning protection. The second fin cap was fabricated with Kevlar/epoxy fabric skins and used an aluminized glass cloth for lightning protection. The third fin cap was fabricated with graphite/epoxy fabric skins with no lightning protection. All three components were exposed to high rain rates and direct lightning strikes. The effects of the flight environments on the components were monitored visually and areas of interest photographed. The performance of the three fin caps and any required repairs are reported herein.