Dynamic Wind Tunnel Balance

The Air Force is interested in the measurement of high frequency loads on small store models inside and near weapons bay cavities in a wind tunnel. The flow environment can be very dynamic because of the presence of an unsteady shear layer outside of the weapons bay cavity. There is interest in measuring those loads at a high frequency in order to determine the time-dependent response of the model at a given freestream condition. Wind tunnel testing of aerodynamic models is typically accomplished by using a 6-component internal strain-gauge balance; however, current balances are not capable of resolving the loads at frequencies of interest because of the structural vibrations of the system, physical limitation of strain-gage output capability, and/or other potential limitations. Although wind tunnel balances are usually stiff, because of the model support requirements and other elements, it can be difficult to avoid oscillatory movements of the model resulting from the dynamic nature of the flow environment. Those vibrations induce inertial forces and moments on the balance and model and can have a negative impact on the accuracy of the measurements. The natural frequency of the model, balance, and sting may be in the same or lower frequency range as the loads of interest, making it difficult to separate the aerodynamic loads from the structural vibrational loads measured by the balance. The primary interest is in measuring the loads on a store model inside and outside of a weapons bay in a wind tunnel facility. The measurement system would notionally be applied to a 1/15th scale store model (approximately 5-10 inches long and 0.33 to 0.46 inches in diameter) in a 4x4 foot wind tunnel test section for two-body testing in which a store model can be remotely moved relative to a parent vehicle model. The system should measure dynamic loads on the store due in part to the oscillatory pressure (aero-acoustically driven) loads in the cavity and be able to resolve the amplitude and frequency of those loads over a short measurement period. The model/measurement system/sting frequency response must be distinctly separate from the aerodynamic frequencies of interest and the aerodynamic loads of interest must be able to be adequately resolved. This is a Request for Information (RFI) only, as defined in FAR 15.201(e), to obtain pricing, delivery, capabilities, and other market information for planning purposes. This RFI shall not be construed as a formal solicitation or an obligation on the part of the Government to acquire any product or service.