Certification Issues Relating to ABDR

New tactical air vehicles are normally designed to be ballistically survivable on the modern battlefield by incorporating active and passive signature reduction and ballistic damage tolerance features. A large percentage of these air vehicles return from combat missions with various levels of combat damage or may suffer from ballistic threads while on ground. Maximum air vehicle fleet availability is essential during surge operations; therefore, quick assessment and repair of the damage are necessary. Since certification of the platform as a system is covered for peacetime operations, qualified methods for assessment of damage and repair of structures / components together with tools and additional training for repair crews are required to achieve adequate risk / safety levels during combat operations 1.0 INTRODUCTION The constant demand for improved performance in the development of new fighter / transport aircraft required reduced structural weight limits and has led to new design techniques, among them increased utilization of advanced fibre reinforced materials or advanced metal alloys with higher material allowables for the load carrying structures. Although the trend for composites in structural applications in percent of structural weight will show an asymtotic amount of approx. 30% in future, (Fig. 1.0-1), the wetted area will be made almost exclusively from thermoset composites like CFRP, which is used in most cases as a combination of a high strength/modulus carbon fibre and a hot curing thermoset resin. A high percentage of modern fighter aircraft's exterior surface is covered with composite skins (Fig. 1.0-2), including fuselage, wings, horizontal and vertical stabilizer (e.g. for the Eurofighter about 70%). All of this graphite epoxy skin surface is load carrying, most of it primary structure. Metal designs also increased not only in individual part size, but also in the integration of structural elements, i.e. machined stiffened skins or bulkheads With the structural requirement of high mechanical loads for the primary load pathes in combination with local load introductions and stability criteria, the result is very often either thin-walled stiffened skin design and/or sandwich structures. The large amount of integrated structural elements with reduced number of fasteners dictate the requirement for maintainability and repairability of these elements, especially under the consideration of part costs and assembly effort. Maintainability aspects are partly covered due to the damage tolerant design approach, in general today's composite structures are designed using a "Limited Fibre Strain Approach" at ultimate design loadcases, where the reduced material allowables account for a low energy impact damage level, ,that can be sustained without compromising structural strength over the entire life of the aircraft. For metal parts the Report Documentation Page Form Approved OMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE MAY 2010 2. REPORT TYPE N/A 3. DATES COVERED 4. TITLE AND SUBTITLE Certification Issues Relating to ABDR 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) EADS Military Air Systems Rechliner Strasse D-85077 Manching 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S) 11. SPONSOR/MONITOR’S REPORT NUMBER(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 13. SUPPLEMENTARY NOTES See also ADA564486. Battle Damage Repair Techniques and Procedures on Air Vehicles Lessons Learned and Prospects. RTO-EN-AVT-156 14. ABSTRACT New tactical air vehicles are normally designed to be ballistically survivable on the modern battlefield by incorporating active and passive signature reduction and ballistic damage tolerance features. A large percentage of these air vehicles return from combat missions with various levels of combat damage or may suffer from ballistic threads while on ground. Maximum air vehicle fleet availability is essential during surge operations; therefore, quick assessment and repair of the damage are necessary. Since certification of the platform as a system is covered for peacetime operations, qualified methods for assessment of damage and repair of structures / components together with tools and additional training for repair crews are required to achieve adequate risk / safety levels during combat operations 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT SAR 18. NUMBER OF PAGES 18 19a. NAME OF RESPONSIBLE PERSON a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 Certification Issues Relating to ABDR 14 2 RTO-EN-AVT-156 working stress levels are chosen to accommodate safe fatigue lifes at stress riser locations, covering to some extent also possible local repairs due to maintenance / operational damage during service However, damages exceeding these limits should not lead to the need of immediate replacement of parts or extensive A/C-downtime for disassembly, autoclave repair, reinstallation and inspection. The alternative of designing most components as fully exchangeable between A/C's is also limited, therefore the "Repair on Aircraft" capability for the structure becomes an important part of the maintenance concept for highly integrated structures, that need to be considered during design and qualification phases. Some of this inherent tolerance to damage can also be utilized for ABDR purpose, given that the individual damage state is substantiated and the remaining capability can be qualified. 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 1955 196