Introduction
Airframe Designs was tasked by Tenencia Aerospace Design to assist with design and the certification of an upgraded avionics system for many Dassault Falcon 50 special mission aircraft.
This upgrade involved installation of a low profile GPS and antennas to the fuselage and engine nacelles. The objective was to make the upgrades compliant to the elected civilian certification basis of FAR-29 up to Amendment 34 in accordance with the type Certificate Data Sheet. This would then be reviewed and approved by the foreign Military Aviation Authority (MAA).
Returning Original Strength
When dealing with the removal of material from principal structural elements (PSEs) is to “Return Original Strength” sometimes called the “Zero Margin” approach. This approach is also utilised within structural repairs but is only applicable for static strength substantiation. Fatigue and Damage Tolerance is an entirely different story!
The method involves comparing the original repair region x-section (original area) to the modified x-section including the effect of the doubler reinforcement, with an example calculation to the left.
Material Strength Analysis
Once the area gained is understood, the stress across the reinforced region is determined by assuming the original pre-modified structure has a reserve factor of 1 and experiences stress levels up to the material ultimate strength. By adding more material to the doubler then is lost, the overall stress across the post-modified region is lowered. This is due to the antenna feed through penetrations.
Joint Strength Analysis
Once the stress across the modified region has been established, the load being transferred to the repair doubler by the riveted joints can be determined as a function of area gained and modified stress. The total load then can be shared between the number of effective rivets considering both longitudinal and circumferential loading directions.
Conclusion
Through structural analysis and design, AFD showcased a high level of skill and experience, delivering a high standard for the customer. Click the link to read the full case study.
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