Circulation Control airfoils have been demonstrated to provide substantial improvements in lift over conventional airfoils. The General Aviation Circular Control model is an attempt to address some of the concerns of this technique. The primary focus is to substantially reduce the amount of air mass flow by implementing unsteady flow. This paper describes a wind tunnel model that implements unsteady circulation control by pulsing internal pneumatic valves and details some preliminary results from the first test entry.

/pdf/a-wind-tunnel-model-to-explore-unsteady-circulation-control-3qr42ayzce.pdf

A Wind Tunnel Model to Explore Unsteady Circulation Control for General Aviation Applications

Circulation Control technologies have been around for 65 years, and have been successfully demonstrated in laboratories and flight vehicles alike, yet there are few production aircraft flying today that implement these advances. Circulation Control techniques may have been overlooked due to perceived unfavorable trade offs of mass flow, pitching moment, cruise drag, noise, etc. Improvements in certain aspects of Circulation Control technology are the focus of this paper. This report will describe airfoil and blown high lift concepts that also address cruise drag reduction and reductions in mass flow through the use of pulsed pneumatic blowing on a Coanda surface. Pulsed concepts demonstrate significant reductions in mass flow requirements cor Circulation Control, as well as cruise drag concepts that equal or exceed conventional airfoil systems.

Pneumatic Flap Performance for a 2D Circulation Control Airfoil, Steady and Pulsed

The NASA Langley Research Center (LaRC) has been designing strain-gage balances for more than fifty years. These balances have been utilized in Langley's wind tunnels, which span over a wide variety of aerodynamic test regimes, as well as other ground based test facilities and in space flight applications. As a result, the designs encompass a large array of sizes, loads, and environmental effects. Currently Langley has more than 300 balances available for its researchers. This paper will focus on the design concepts for internal sting mounted strain-gage balances. However, these techniques can be applied to all force measurement design applications. Strain-gage balance concepts that have been developed over the years including material selection, sting, model interfaces, measuring, sections, fabrication, strain-gaging and calibration will be discussed.

https://ntrs.nasa.gov/api/citations/19990072772/downloads/19990072772.pdf

NASA LaRC Strain Gage Balance Design Concepts

Experimental design strategies most often involve an initial choice of a classic factorial or response surface design and adapt that design to meet restrictions or unique requirements of the system under study. One such experience is described here, in which the objective was to develop an efficient experimental design strategy that would facilitate building second-order response models with excellent prediction capabilities. In development, careful consideration was paid to the desirable properties of response surface designs. Once developed, the proposed design was evaluated using Monte Carlo simulation to prove the concept, a pilot implementation of the design carried out to evaluate the accuracy of the response models, and a set of validation runs enacted to look for potential weaknesses in the approach. The purpose of the exercise was to develop a procedure to efficiently and effectively calibrate strain-gauge balances to be used in wind tunnel testing. The current calibration testing procedure is based on a time-intensive one-factor-at-a-time method. In this study, response surface methods were used to reduce the number of calibration runs required during the labor-intensive heavy load calibration, to leverage the prediction capabilities of response surface designs, and to provide an estimate of uncertainty for the calibration models. Results of the three-phased approach for design evaluation are presented. The new calibration process will require significantly fewer tests to achieve the same or improved levels of precision in balance calibration. Copyright © 2008 John Wiley & Sons, Ltd.

Adapting second‐order response surface designs to specific needs

UNCERTAINTY ESTIMATES AND PREDICTION INTERVAL DEVELOPMENT FOR INTERNAL STRAIN GAGE BALANCE CALIBRATION SYSTEMS Kenneth G. Toro Old Dominion University, 201-5 Director: Dr. Drew Landman Currently, there is a lack of the use of mathematically rigorous methods to evalu­ ate the performance of multivariate force measurement systems. The specific problem addressed in the research stems from the practical issues faced by test engineers when wind tunnel models with internal strain gage balances are readied for test. Check loads are applied and the question that needs to be answered is whether or not the balance is reading within acceptable limits. These systems tend to be difficult to characterize uncertainty, primarily due to their multivariate nature, but also due to the desire for an estimate on the explanatory variable of the system, instead of the response. This estimation of the explanatory variable is inherent to the calibration problem. For systems that are modeled using non-linear terms, no closed form so­ lution will exist for the explanatory variable. This research details the development of a prediction interval which includes the measurement error in the calibration and check systems. The 20,000 lb. manual stand for calibrating balances used in the National Transonic Facility (NTF) is employed by NASA Langley Research Center and the case study for the work. The uncertainty estimates were developed using the propagation of error method 011 derived physics equations for the system. The uncertainty estimates were integrated into the developed prediction interval, which demonstrated a capture rate of 96% for a trial set of check loads using a 95% level of condence. Comparisons are made to prediction interval capture rates for the Single Vector System using a common set of check loads on an NTF balance.

/pdf/uncertainty-estimates-and-prediction-interval-development-5gkp3r6kp6.pdf

Uncertainty Estimates and Prediction Interval Development for Internal Strain Gage Balance Calibration Systems

An iterative procedure applying matrix methods to accomplish an efficient algorithm for automatic computer reduction of wind-tunnel force-balance data has been developed. Balance equations are expressed in a matrix form that is convenient for storing balance sensitivities and interaction coefficient values for online or offline batch data reduction. The convergence of the iterative values to a unique solution of this system of equations is investigated, and it is shown that for balances which satisfy the criteria discussed, this type of solution does occur. Methods for making sensitivity adjustments and initial load effect considerations in wind-tunnel applications are also discussed, and the logic for determining the convergence accuracy limits for the iterative solution is given. This more efficient data reduction program is compared with the technique presently in use at the NASA Langley Research Center, and computational times on the order of one-third or less are demonstrated by use of this new program.

/pdf/an-efficient-algorithm-using-matrix-methods-to-solve-wind-17o3aoc6zw.pdf

An efficient algorithm using matrix methods to solve wind tunnel force-balance equations

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An efficient algorithm using matrix methods to solve wind tunnel force-balance equations