1985-04-01

Design and Certification of a Composite Control Surface 850888

A graphite/epoxy composite rudder for the Gulfstream Aerospace G-III executive jet aircraft was designed, tested and certified by the Lockheed-Georgia Company. The design replaces a conventional skin-stiffened aluminum structure, and achieves a 50% increase in acoustic fatigue life with a 22% weight savings. The design incorporates an innovative rib cap design with greatly improved fatigue and damage resistance over conventional composite rib cap designs.Details of the design as well as the FAA certification plan are presented in this paper. The certification plan, based on FAA Advisory Circular No. 20-107 (Reference 1), outlined the design details as well as all requirements for element, component and full-scale testing. Both static and acoustic fatigue element and component tests were conducted, with applied impact damage representive of initially detectable damage levels that could be incurred in the rudder skins. This damage was applied after completion of the required five lifetimes of acoustic fatigue testing; an additional two and one-half lifetimes of damage were then applied at the design noise level. Damage to the static component test article was applied after successful completion of ultimate load conditions in the “as built” configuration; loads well in excess of ultimate were then applied to the component specimen with multiple impact damaged areas.Full-scale testing for the Gulfstream III composite rudder consisted of both static and flight tests. The static test rudder successfully completed ultimate load, damage tolerance and failsafe test conditions. An abbreviated flight flutter program demonstrated that the flutter characteristics of the composite rudder were identical to the previous metal rudder.The G-III composite rudder achieved rate production of five per month at the Charleston, SC, Composite Production Facility of the Lockheed-Georgia Company. Production installation of the rudder was begun in July 1984 on the G-III aircraft.

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