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Evaluation of Unsteady Loading on Store Trajectories


OBJECTIVE: To develop and demonstrate an accurate method of screening aircraft/store combinations for store trajectory deviations. DESCRIPTION: Current aircraft operated by the US and our allies employ weapons bays for internal carriage of highly sophisticated weapons. These internal weapons bays present significant challenges for carriage and safe release of weapons due to their inherent unsteady flow character (fluctuating surface pressures). This combined with weapon design trends toward reduced stability are increasing the possibility that localized unsteady pressure induced loading could influence store separation trajectories. To date this phenomena has not been reported during flight testing because it is simply too expensive to perform repeated drops at release conditions of interest. The current risk reduction exercises typically use time averaged"steady"aerodynamic loads generated either computationally or in small scale wind tunnel tests to approximate the bay aerodynamic effects. With sufficient store ejection forces the aerodynamics are dominated and this approach appears to be sufficient; however sophisticated electronics and smaller weapons can be sensitive to these large ejection loads. The goal of this effort is to provide a reasonable (duration of weeks not months) method of screening aircraft/weapons combinations for this unsteady influence. The ability to identify the portion of the flight envelop which is likely to produce trajectory variations is critical to developing the store certification plan. The ideal model would be able to give a flight envelop with areas of potential difficulty flagged for further analysis. This capability is sought for any aircraft bay environment/store combination of interest to the Air Force. Development of a method that could quantify the frequency and magnitude of the aircraft bay aerodynamics coupled with the store stability/flight characteristics which would allow rapid assessment model development will be considered. Identification of the appropriate aircraft flow parameters and the store stability parameters to consider for the model is left to the proposer. This model would help to screen configurations that need to be modeled using CFD, wind tunnel testing, and/or flight testing. PHASE I: Define a plan to develop, identify critical parameters, and clearly demonstrate the proposed methods are capable of characterization of both bay unsteadiness and store susceptibility to it. Prepare a Phase II plan to populate the required data and implement the model. PHASE II: Implement the model and produce a database to support identified Air Force aircraft and stores. Aerodynamic parameters will need to be produced either via CFD analysis or wind tunnel testing. Demonstration and documentation of the model and installation on a standalone government computer system is required. PHASE III: Include fighter/attack aircraft, bomber, and unmanned aircraft that carry weapons or fuel tanks internally. May include a method of correlating unsteady aerodynamic loading on aircraft landing gear to the landing gear bay acoustics. REFERENCES: 1. Johnson, R., Stanek, M. and Grove , J."Store Separation Trajectory Deviations due to Unsteady Weapons Bay Aerodynamics,"AIAA-2008-188, 46th AIAA Aerospace Sciences Meeting and Exhibit, Reno, Nevada, Jan. 7-10, 2008. 2. Roughen, K., Wang, X., Bendiksen, O., and Baker, M."A System for Simulation of Store Separation Including Unsteady Effects,"AIAA-2009-549, 47th AIAA Aerospace Sciences Meeting, Orlando, Florida, Jan. 5-8, 2009. 3.Westmoreland, S.,"Trajectory Variation Due to an Unsteady Flow-Field,"AIAA 2009-550, 47th AIAA Aerospace Sciences Meeting, Orlando, Florida, Jan. 5-8, 2009. 4. Roughen, K., Gariffo, J., Hammerand, D., and Roberts, R."Estimation of Unsteady Loading for Sting Mounted Wind Tunnel Models,"AIAA 2011-1941,52nd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference, 19th AIAA/ASME/AHS Adaptive Structures Conference, Denver, Colorado, April 4 7, 2011. 5. Neal Kraft, N."Non-Repeatability of Store Separation Trajectories from Internal Weapon Bays Due to Unsteady Cavity Flow Effects - Lessons Learned from a 2D Investigation,"AIAA-2011-1238, 49th AIAA Aerospace Sciences Meeting and Aerospace Exposition, Orlando, Florida, Jan. 4-7, 2011.
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