Predictor of Aircraft Structural Loads Due to Buffet
Navy SBIR 2019.2 - Topic N192-058
NAVAIR - Ms. Donna Attick - [email protected]
Opens: May 31, 2019 - Closes: July 1, 2019 (8:00 PM ET)
TECHNOLOGY AREA(S): Air Platform
ACQUISITION PROGRAM: PMA290 Maritime Surveillance Aircraft
OBJECTIVE: Develop an innovative loads prediction methodology that combines analytical and test-derived data models and utilizes aircraft state variables along with existing aircraft instrumentation data to predict airframe structural loads due to buffet for in-service fixed wing aircraft.
DESCRIPTION: Buffet is a complex load source characterized by random pressure oscillations on aircraft structure caused by unsteady airflow. A variety of flight conditions and aircraft configurations can lead to buffet loading events. Turbulent flow, normal shocks, and stall can cause flow to separate from the wing, possibly leading to a buffet response in the wing itself, the fuselage and the empennage as unsteady flow excites a dynamic response from these surfaces. Due to its dynamic nature, buffet loads have historically been difficult to numerically model due to the complex structural and aerodynamic non-linearities. Buffet is highly dependent on aircraft geometry; flow can separate from aircraft wings or can be affected by external structures such as weapons bay doors, antennae, and weapons stores, causing the turbulent flow to impinge structures in its wake. Given this, buffet load analysis is usually updated via flight test-based regression methods such as peak-valley tables and Mach number-dynamic pressure usage data; however, these methods rely heavily on flight test data, can be limited in the number of aircraft configurations and flight conditions that are flown, or are overly conservative due to the particular method’s
approach. This can lead to unknowns in the magnitude and duration of buffet loading for points in the flight envelope resulting in unknown fatigue damage on the aircraft.
Buffet events during flight impart load cycles that can provide significant structural fatigue damage depending upon the buffet type, intensity, frequency, content of the excitation, and duration [Ref 10]. In some cases, short excursions into buffet have rapidly reduced a significant portion of the structural life of an aircraft component. As service life extension programs seek to continually increase the longevity and capability of in-service aircraft, the ability to accurately predict the loads due to buffet (and as a result, track structural fatigue damage due to buffet) becomes increasingly relevant to maintaining fleet readiness. Aircraft structural fatigue damage is essential in the determination of required aircraft maintenance activities and, ultimately, when to retire the aircraft.
An innovative methodology is desired that can take advantage of modeling (e.g., aerodynamic and structural models) and instrumented test data to accurately predict structural buffet loads for the P-8A aircraft. The approach should be able to address non-linear aircraft structural response and aerodynamic excitation. Models should be validated and agree with flight, ground, and vibration test data provided by the Government.
PHASE I: Develop an innovative technique to predict structural loads due to buffet for in-service P-8A aircraft that is based upon analytical and test-derived data models that utilize aircraft state variables and existing P-8A instrumentation data to be provided by the Government during Phase I. Demonstrate feasibility of the developed approach through initial predictions and comparisons to available flight test data. The Phase I effort will include prototype plans to be developed under Phase II.
PHASE II: Develop a robust architecture to predict aircraft structural loads due to buffet for in-service aircraft. Validate predictions with existing flight test data to be provided by the Government. Fully develop this model for application to flight test data sets or dedicated future testing on an aircraft.
PHASE III DUAL USE APPLICATIONS: Perform final testing on and integrate this technology into the P-8A aircraft platform. Commercial aircraft, such as the Boeing 737 family, would benefit from the developed technology. The private sector could use the technology to improve aircraft buffet models and individualized fatigue tracking of commercial aircraft.
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KEYWORDS: Buffet Loads; Aerodynamics; Structures; Fatigue Damage; Aircraft Tracking; Modeling