MOBILITY ENGINEERING Produced by SAE Media Group
MOBILITY ENGINEERING
Magazines
Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Magazine cover

Current Issue

Archives

Influence of Leading-Edge Oscillatory Blowing on Time-Accurate Dynamic Store Separation

Developing an understanding of, and potentially controlling, pitch bifurcation of a store release from an aircraft during flight could improve weapons delivery.

Increasing the operational efficiency of weapons employed in hostile environments is a high priority of the United States Air Force (USAF). In recent history, the USAF has made a move to smaller and internally stored weapons, especially for fighter aircraft. Maintaining a low radar cross section signature, and thus a low observable air vehicle, is desirable so the aircraft is less detectable by the enemy.

Modified SUU-41 pod used for the weapons cavity acoustics store separation apparatus.

An internal weapons bay has a reduced load out but yields a low observable profile (reduced radar cross section). Also, aircraft can carry a greater number of weapons if the weapons are smaller, increasing the quantity of targets that can be engaged per sortie. The newer attack aircraft in the United States, such as the P-8A, F-22 and, most recently, the F-35, employ weapons delivery from bomb bays. The effects of this design element have not been fully explored and the impact on weapon release can sometimes be challenging to predict. Thus, it is important to understand the sensitivity of the flow field effects on the internally loaded weapon within a few feet from the carriage.

When using an internal weapons bay, several issues arise with the weapon release. The aeroacoustic environment formed by the cavity is unsteady. The mission stores are subject to this unsteady flow and strong acoustic loads. The unsteadiness originates from the presence of a self-reinforced acoustic resonance phenomenon in conjunction with a robust free shear layer instability. Pressure fluctuations and acoustic resonance that stem from this unsteady flow can impart high dynamic loads on the weapon stores while in motion. These dynamic loads can also fatigue the cavity structure as well as impact the release trajectory from aircraft bays.

Unsteady and unsuppressed pressure levels reach up to 180 dB and can lead to structural fatigue of bulkheads and even failure of weapon components. Strong acoustic resonance can, in dramatic cases, lead to instant changes in direction of normal forces from ‘in to’ to ‘out of’ the weapons bay; this is called “pitch bifurcation”. In general, it is possible that strongly time-dependent flow might affect mission store release. For smaller and lighter weapons, this could impact its safe release and effectiveness.

The time-dependency of cavity flow is a matter of concern for current data acquisition. Since typical wind tunnel data consists of time averaged store loads, common store separation analysis cannot detect a sensitivity to timing of the store release. Also, the workload and cost associated with a specific project increase dramatically for the testing of multiple configurations. Mitigation of the workload and cost can be accomplished with the implementation of dynamic wind tunnel testing which also provides time-accurate data. Previous research conducted in the Air Force Institute of Technology, AFIT, low-speed wind tunnel emphasized the importance of collecting such data in order to characterize the dynamic loads during mission store release.

The goal of this research was to support the static and dynamic characterization and the time-accurate dynamic load data acquisition in a low-speed wind tunnel. Oscillatory blowing was applied at the leading edge to emulate, to an extent, the strong time-dependent flow in a transonic environment, where Rossiter tones prevail. Both static and dynamic testing data in the AFIT low-speed wind tunnel were collected at speeds of 60, 100, and 120 mph, with different model sizes and angles of attack, to produce time-accurate force and moment measurements. Actuation of the Linear Motor Apparatus (LMA) accomplished a vertical store release trajectory. The data was analyzed to determine the nature of the effects of strong oscillatory flow of load profiles as the store progresses through the free shear layer.

This work was done by Ryan G. Saunders for the Air Force Institute of Technology. AFRL-0277

Topics:
Aeronautics Aerospace Aircraft Aviation Data Acquisition Data Acquisition Data management Defense Defense industry Electronic equipment Military aircraft Military vehicles and equipment Motors & Drives Munitions Radar Technical review Test & Measurement Vehicles Wind tunnel tests
This Brief includes a Technical Support Package (TSP).
Document cover
Influence of Leading-Edge Oscillatory Blowing on Time-Accurate Dynamic Store Separation

(reference AFRL-0277) is currently available for download from the TSP library.

Don't have an account?

More From SAE Media Group

    Magazine cover
    Aerospace & Defense Technology Magazine

    This article first appeared in the October, 2019 issue of Aerospace & Defense Technology Magazine (Vol. 4 No. 6).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document is a thesis by 2d Lt Ryan G. Saunders, titled "Influence of Leading Edge Oscillatory Blowing on Time-Accurate Dynamic Store Separation." It investigates the aerodynamic effects of leading-edge oscillatory blowing on the separation of stores (such as missiles or fuel tanks) from an aircraft, particularly focusing on the dynamics involved in this process.

    The thesis begins with an introduction that outlines the background and motivation for the research, emphasizing the importance of understanding store separation dynamics for improving aircraft performance and safety. The problem statement identifies gaps in existing research regarding the influence of oscillatory blowing on separation behavior.

    The methodology section details the experimental setup, which includes the use of the Air Force Institute of Technology (AFIT) wind tunnel and a linear motion apparatus designed to simulate the conditions of store separation. The document describes the design of the experimental models and the configurations used during testing, as well as the motor control system that facilitates precise control over the blowing mechanisms.

    Results from the experiments are summarized, highlighting key findings related to the effects of leading-edge blowing on the aerodynamic forces experienced during store separation. The significance of the research is discussed, noting its potential contributions to the field of aerospace engineering, particularly in enhancing the understanding of flow dynamics and improving store separation techniques.

    The conclusions and recommendations section provides insights into the implications of the findings, suggesting areas for future research and testing to further explore the effects of oscillatory blowing. Appendices include test matrices, additional experimental data, code used for analysis, and drawings of the models employed in the experiments.

    Overall, the thesis presents a comprehensive study that combines theoretical analysis with practical experimentation, aiming to advance knowledge in the field of dynamic store separation and its applications in military and civilian aviation. The work acknowledges the contributions of various individuals and organizations that supported the research, underscoring the collaborative nature of scientific inquiry.

    Top Stories

    INSIDERRF & Microwave Electronics

    Feature Image FAA to Replace Aging Network of Ground-Based Radars

    PodcastsDefense

    Feature Image A New Additive Manufacturing Accelerator for the U.S. Navy in Guam

    NewsSoftware

    Feature Image Rewriting the Engineer’s Playbook: What OEMs Must Do to Spin the AI Flywheel

    Road ReadyPower

    Feature Image 2026 Toyota RAV4 Review: All Hybrid, All the Time

    INSIDERDefense

    Feature Image F-22 Pilot Controls Drone With Tablet

    INSIDERRF & Microwave Electronics

    Feature Image L3Harris Starts Low Rate Production Of New F-16 Viper Shield

    Webcasts