Effect of Control Surface Damage and External Defects on System Flight Dynamics

TECH FOCUS AREAS: Directed Energy; General Warfighting Requirements (GWR) TECHNOLOGY AREAS: Air Platform OBJECTIVE: Develop a flight dynamics model capable of assessing the impact of externally generated defects in the outer mold line or control surfaces on the overall flight stability for high-speed aircraft and missiles. DESCRIPTION: Defects on the outer mold or control surfaces of a high-speed system may lead to flight instability. Understanding the extent to which these defects alter system performance, dynamics, and controllability is crucial to system design. For the purposes of this topic, both the aerodynamic performance and flight dynamics of aircraft and highly maneuverable missile systems are of interest. Aerodynamic performance is typically described using static quantities such as the lift and drag coefficient. Flight dynamics are generally described in terms of aerodynamic stability derivatives, which includes terms that are both static and dynamic in nature. Accurate computation of the aerodynamic coefficients and full set of stability derivatives is essential to meeting the topic objectives, to include derivatives related to control surface actuation. Computational methods to assess aero-mechanics and flight dynamics include panel-based methods and volume-based computational fluid dynamics (CFD). Panel methods allow fairly rapid parametric variation of airframe properties and are computationally efficient and accurate for typical aircraft configurations but are not designed to represent fine-scale details such as surface defects and the mathematical formulations are likely incapable of doing so. CFD models the aircraft geometry in much finer detail but incurs a significantly higher modeling and computational cost due to the higher fidelity involved. Additionally, most CFD formulations are led for either steady-state or time-domain solutions which can provide static aerodynamic characteristics but do not directly yield the dynamic stability derivatives required for accurate flight dynamic assessment. To address these shortcomings, responses to this topic should propose a method computing the aerodynamic coefficients along with the static and dynamic stability derivatives of an aircraft subjected to parametric variations (size, shape, location, etc.) of one or more external defects. The method should enable the parametric alterations to be modeled in a reasonably automated manner requiring minimal analyst input. The method should correctly account for propulsive effects on the flowfield and aircraft flight dynamics, along with the potential to model damage to control surfaces and the associated impacts on vehicle control. Near-term applications are focused on the low-speed flight regime, but the method should be applicable at high subsonic and supersonic speeds as well. Although accurate aeromechanical modeling of the external defects is the primary goal, priority should also be given to developing a computationally efficient method that can feasibly simulate large numbers of parametric variations without requiring excessive schedule or computational resources. Candidate numerical methods which may fulfill the criteria include, but are not limited to, the use of alternatives to traditional CFD such as Lagrangian vortex methods [1], application of system identification procedures within a time-domain CFD solver [2] or use of frequency-domain CFD to directly compute stability derivatives [3]. PHASE I: Develop a simple prototype model or demonstrate the numerical strategy for computation of aerodynamic coefficients, stability derivatives, and a corresponding flight dynamics model. Using a notional test case, derive these parameters using a high-fidelity baseline (e.g., time-domain CFD results) to be used as a verification dataset. PHASE II: Define a user-focused workflow to enable efficient definition of parametric defect sets, calculation of aerodynamic derivatives, and demonstration of defect impact on flight dynamics. Mature the prototype into a functional tool, to include a graphical interface and user documentation. Validate flight dynamic calculations using either wind tunnel or free-flight testing of a scaled model vehicle. PHASE III DUAL USE APPLICATIONS: Unify the method with external solvers capable of computing realistic defect geometry. Investigate enhancements to computational efficiency to broaden the range of configurations which can be considered on a given schedule. Extend the method to account for aeroelastic effects and weakening of the underlying substructure to enable a larger range of system effects to be considered. NOTES: The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the proposed tasks intended for accomplishment by the FN(s) in accordance with section 5.4.c.(8) of the Announcement and within the AF Component-specific instructions. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws. Please direct questions to the Air Force SBIR/STTR Help Desk: usaf.team@afsbirsttr.us REFERENCES: [1] Cottet, G. H., & Koumoutsakos, P. D. (2000). Vortex methods: theory and practice (Vol. 8). Cambridge: Cambridge university press; [2] Allen, J., & Ghoreyshi, M. (2018). Forced motions design for aerodynamic identification and modeling of a generic missile configuration. Aerospace Science and Technology, 77, 742-754; [3] Jacobson, K., Stanford, B., Wood, S., & Anderson, W. K. (2020). Flutter Analysis with Stabilized Finite Elements based on the Linearized Frequency-domain Approach. In AIAA Scitech 2020 Forum (p. 0403). KEYWORDS: Computational fluid dynamics; high speed flow; panel methods; flight dynamics; flight stability; surface defects; aerodynamics, aircraft; missiles