N161-003 TITLE: Aerial Refueling Tanker and Receiver Aerodynamic Interaction Modeling and Simulation

TECHNOLOGY AREA(S): Air Platform

ACQUISITION PROGRAM: PMA 268 Unmanned Combat Air System Demonstration Program

OBJECTIVE: Develop a modeling and simulation (M&S) approach and toolset to calculate the incremental forces and moments on the receiver aircraft due to tanker wake during aerial refueling operations.

DESCRIPTION: The Navy continues to invest in the development of tactical Unmanned Air System (UAS) capabilities. One important area of investment seeks to extend the range and endurance of tactical UAS aircraft through Autonomous Aerial Refueling (AAR). As part of the Navy�s Unmanned Combat Air System (UCAS) demonstration program, the X-47B completed an AAR demonstration in a limited envelope using the Omega B707 tanker aircraft. Similarly, future UAS programs will have requirements for AAR capabilities. Currently, the Navy does not have sufficient aerial refueling simulation capabilities which apply a tanker�s wake to a receiver�s six-degree-of-freedom (6DOF) flight dynamic simulation. Tanker wakes are known to strongly influence the dynamics of the receiver aircraft particularly when close to engaging the refueling basket. While 6DOF modeling and simulation (M&S) has proven a valuable resource in most phases of a mission, the lack of high fidelity AAR M&S can cause unplanned flight control software redesign, limited flight envelopes, and additional flight test requirements. Though vortex lattice methods have previously been used to calculate wake impact on the receiver at the center of gravity, an improved simulation approach is needed to better capture the wake effect over the entire receiver planform. In most fixed-wing aerodynamic models, forces and moments are calculated via lookup tables that use the air mass properties (e.g. angle of attack, sideslip, etc.) at a single reference point (e.g. center of gravity) on the aircraft body. As a result, simply applying a tanker flow field at the reference point provides only a first order estimate of the tanker�s wake effects on the receiver. This approach also does not incorporate moment effects beyond empirically based estimates.

An M&S approach and toolset that calculates the incremental forces and moments of the receiver aircraft due to tanker wake during aerial refueling operations is desired. The toolset should be capable of easily integrating with existing Navy fixed-wing 6DOF aircraft simulations (both realtime and offline), including the CASTLE® simulation architecture. The CASTLE® equations of motion are driven by aircraft body axis forces and moments and include existing variables for accepting external forces and moments. It is anticipated that the communication between CASTLE® and the toolset would be accomplished using a network protocol such as User Datagram Protocol (UDP). CASTLE® documentation and software will be provided during Phase I or Phase II as required and determined by the Navy. Inputs to the toolset may be as simple as the relative position between the aircraft and the tanker/receiver geometry data. Outputs should include receiver incremental forces and moments. The toolset should also allow an externally generated flow field to serve as an input, vice an internally generated tanker wake. In this case, the outputs should still include receiver incremental forces and moments. Possible approaches to this problem may include using vortex lattice, free wake, and/or Computational Fluid Dynamics (CFD) methods, however others will be considered.

PHASE I: Develop a M&S approach and toolset and assess feasibility to calculate the incremental forces and moments of the receiver aircraft due to tanker wake during aerial refueling operations. A key component of this phase includes choosing an approach to calculate the incremental forces and moments of the receiver aircraft based on the non-uniform flow field behind the tanker. Consideration should be given to how the method could be integrated into the CASTLE® architecture.

PHASE II: Develop a prototype toolset that calculates the incremental forces and moments of the receiver aircraft due to tanker wake during aerial refueling operations. This toolset should be capable of demonstrating that the 6DOF simulation response of a receiver aircraft yields the expected response. Validation with other sources of information, including flight test data (to be provided by the government early in Phase II efforts), is desired. The model/toolset shall be delivered to the Navy to demonstrate its capability at the end of the phase II effort.

PHASE III DUAL USE APPLICATIONS: Finalize and transition the M&S toolset to future Navy and commercial development programs, such as UCLASS, to assist in the development of aerial refueling flight control laws, predicting performance, and reducing flight test requirements. Validate with additional sources as required. The toolset developed under this SBIR is relevant in applications beyond aerial refueling. The underlying technologies can be used with traditional 6DOF fixed-wing aircraft simulations to incorporate the 6DOF effects of complex flow fields. Other applications include ship airwake integration and aircraft wake effects in terminal flight phases. The toolset may be useful in studies involving the Federal Aviation Administration (FAA) wake separation standards of departing and landing aircraft.

REFERENCES:

1. Dogan, Atilla, Sriram Venkataramanan, and William Blake. "Modeling of Aerodynamic Coupling between Aircraft in Close Proximity", Journal of Aircraft, Vol. 42, No. 4 (2005), pp. 941-955. Retrieved from: http://arc.aiaa.org/doi/abs/10.2514/1.7579

2. Saban, Deborah and James Whidborne. "Modeling of Wake Vortex Effects for Unmanned Air Vehicle Simulations", Proceedings of the AIAA Atmospheric Flight Mechanics Conference, AIAA Modeling and Simulation Technologies Conference, August 2009, AIAA paper 2009-5686.

3. Dogan, Atilla, Timothy A. Lewis, and William Blake. "Flight Data Analysis and Simulation of Wind Effects During Aerial Refueling", Journal of Aircraft, Vol. 45, No. 6 (2008), pp. 2036-2048. Retrieved from: http://arc.aiaa.org/doi/abs/10.2514/1.36797

KEYWORDS: Modeling And Simulation; Autonomous Aerial Refueling; Unmanned Air Vehicle; tanker wake; tanker downwash; 6DOF simulation

TPOC-1: 301-995-2038

TPOC-2: 301-757-2035

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