Ph.D. Defense

Jiacheng Xie
(Advisor: Prof. Dimitri N. Mavris)

Incorporating Airworthiness Certification Requirements into
Unconventional Transport Aircraft Conceptual Design and Optimization

Wednesday, April 5
9:00 a.m. EDT
Weber Space Science and Technology Building, Room 304
Zoom: https://gatech.zoom.us/j/99681067398?pwd=MjZCSjFybHp4NFNHRUZOekxqNkcxUT09

Abstract
In response to future environmental design goals, novel aircraft configurations and propulsion architectures have emerged in recent years. While these revolutionary technologies are anticipated to improve aircraft aerodynamic and propulsive efficiencies, their implementation is impeded by certification challenges. Type certification, a mandatory process ensuring the safety of a new type of aircraft before it enters commercial service, is costly, time-consuming, and fraught with uncertainties due to the intensive analyses, experiments, and flight tests required to demonstrate compliance with airworthiness regulations. Unconventional aircraft, with their unique flight characteristics, can make the certification process even more complex and risky compared to conventional counterparts.

This dissertation aims to develop a methodology to explicitly incorporate the airworthiness certification requirements from Title 14 of Code of Federal Regulations Part 25 Subpart B Flight and Subpart C Structure into unconventional aircraft conceptual design and optimization. The first research area focuses on the development of certification analysis capabilities to determine design candidates' compliance with certification rules using limited design knowledge during the conceptual design stage. Two certification analysis tools are created for this purpose, converting performance and structural certification rules into quantitative analysis functions. These tools are validated using a conventional aircraft model calibrated based on the ATR 42 aircraft and applied to an unconventional aircraft model calibrated based on NASA's PEGASUS concept to demonstrate their capabilities.

The second research area focuses on incorporating certification constraints into the design space exploration for unconventional aircraft conceptual design. A certification-driven design framework is created by integrating the established certification analysis capabilities with disciplinary analysis tools. Using the design framework, multidisciplinary design space exploration studies are performed for the ATR 42 and the PEGASUS aircraft. The results show that certification constraints have a greater impact on the optimal performance of unconventional aircraft design candidates compared to conventional designs and the simplified constraints commonly used in traditional conceptual design practices are not sufficient to capture the criticality of certification constraints for unconventional aircraft.

The third research area examines the level of confidence afforded by the certification analysis by quantifying the impact of uncertainties. Epistemic uncertainties arising from modeling errors and technological uncertainties are quantified through a series of multiplicative factors applied to intermediate disciplinary variables. Aleatory uncertainties due to irreducible noise factors are represented by the loading errors and wind velocities added to flight dynamics simulations. The quantification study shows that two types of uncertainties can affect the aircraft dynamic responses in flight test simulations, thus compromising certification compliance. By incorporating robustness as a design metric in the optimization process, the negative impact of uncertainties can be effectively mitigated.

Finally, a certification-driven design methodology is established and compared against the design methodologies currently used for unconventional aircraft conceptual design. The results demonstrate the superiority of the proposed methodology over existing conceptual design approaches in generating optimal and robust conceptual designs for unconventional aircraft.

Committee

• Prof. Dimitri N. Mavris – School of Aerospace Engineering (advisor)
• Prof. Daniel P. Schrage – School of Aerospace Engineering
• Prof. Brian J. German – School of Aerospace Engineering
• Dr. Evan D. Harrison – School of Aerospace Engineering
• Dr. Nicholas K. Borer – NASA Langley Research Center