Robert Niewoehner

Use of Piloted Simulation for Evaluation of Abrupt-Wing-Stall Characteristics

A piloted simulation architecture is presented for evaluating uncommanded wing drop due to asymmetric abrupt wing stall for a given aircraft configuration. The architecture incorporates a newly proposed aerodynamic modeling technique that characterizes the wing drop motion as being triggered by aerodynamic stall, modeled by a nonzero basic rolling moment coefficient, and sustained by reduced or propelling roll, modeled via the roll damping derivative. The determination of such derivatives/coefficients from either analytical or experimental methods is not addressed, and the successful identification of such terms, on which any piloted simulation evaluation hinges, remains a topic of research. Models with varying nonzero basic rolling moment coefficients and varying roll damping were inserted into the aerodynamic model and then evaluated by a pilot familiar with wing drop. The pilot assessed the varying models, assigning handling qualities ratings to predeveloped tasks aimed at diagnosing the severity (or absence) of any wing stall characteristics. Tasks included wind-up turns and a closed-loop tracking task in which the pilot tracked a target while flying a drop-prone simulation. The pilot was able to distinguish between satisfactory and unsatisfactory aerodynamic configurations. Pilot ratings and comments, as determined by the lateral aerodynamic model, were generally consistent with the expected handling qualities from flight test.

Integrated Approach to Assessment of Transonic Abrupt Wing Stall for Advanced Aircraft

Abrupt wing stall at transonic flight conditions can result in uncommanded rolling motions that have historically degraded flying qualities, compromised mission performance, and reduced safety of flight for a variety of aircraft. Recently, a U.S. government research program, the Abrupt Wing Stall Program, has advanced the state of the art in detection of abrupt wing stall through computational fluid dynamics, experimental aerodynamics, and flight dynamics. It is therefore essential that these tools be combined into an integrated approach that not only provides for the identification of abrupt wing stall, but also allows for the resulting flight characteristics to be assessed and the risks to the aircraft program be mitigated. The primary means of assessing the flying qualities impacts of transonic abrupt wing stall is through the construction of an aircraft math model that can accurately characterize the dynamic response to abrupt stall. The primary means of mitigating program risks is through the inclusion of free-to-roll wind-tunnel testing in the acquisition plan. Recommendations for assessing transonic abrupt wing stall are presented for the aircraft designer and for the program manager.

Refining Satellite Methods for Pitot-Static Calibration

Nomenclature Fi (x) = error from fit circle to i th data point f, g = generic functions H(x) = optimization cost function h p,c = calibrated pressure altitude h p,i = indicated pressure altitude J (x) = Jacobian matrix pa = ambient pressure ps = (sensed) static pressure Vc = calibrated airspeed Vi = indicated airspeed Vgps = measured groundspeed VT = estimated true airspeed Xi = east–west component of measured ground speed, i th data point Xw = east–west component of estimated wind speed x = estimate state vector Yi = north–south component of measured ground speed, i th data point Yw = north–south component of estimated wind speed hpos = altitude position error p = static source position error Vpos = airspeed position error ψgps = global positioning satellite ground-track azimuth angle ψwind = wind direction

Computational Study of F/A-18 E/F Abrupt Wing Stall in the Approach Configuration

This computational study evaluated lateral instabilities observed during developmental testing of the preproduction F/A-18E/F in the power-approach configuration. These instabilities, described here as abrupt wing stall (AWS), occurred whenever the airplane exceeded 12-deg angle of attack. The AWS was quickly corrected in flight test by the closure of a vent at the wing root, without understanding its physical cause or cure. Computational solutions with both the vent open and closed provide insight into the likely cause of the instability, revealing two distinctive flow topologies. Specifically, all F/A-18 Hornet models depend upon strong vortex flows from the leading-edge extension (LEX) to provide lift at elevated angle of attack. Flow through the open vent displaces the LEX vortex core inboard and up off the wings upper surface. This displacement dramatically weakens the flow stability over the wings entire upper surface. Wind-tunnel studies performed in parallel by another researcher provide quantitative corroboration of the computational solutions. Finally, computational-fluid-dynamics metrics developed within the NASA/Navy/Industry AWS program are applied to determine their validity at this low-speed flight condition and modified to enhance their viability as predictive tools for AWS prone configurations.

F/A-18E/F Super Hornet High-Angle-of-Attack Control Law Development and Testing

The Boeing F/A-18E/F Super Hornet completed the high-angle-of-attack (HiAOA) flight test program in the spring of 1999 as part of the airplanes three-year engineering and manufacturing development flight-test effort. Building on the success of F/A-18 Hornets serving world-wide, the design of the much larger Super Hornet sought to improve on the original Hornets positive attributes and correct those characteristics where 20 years of experience indicated room for improvement. Beginning with the design history and objectives, details of the HiAOA flight control law development and testing are presented, concentrating on those aspects where particular challenges were faced. Successes and failures of the initial design are specifically covered, as well as the refinements necessary to achieve fully the programs design goals.

Pitch Dynamics of Unmanned Aerial Vehicles

Dynamic stability requirements for manned aircraft have been in place for many years. However, we cannot expect stability constraints for UAVs to match those for manned aircraft; and dynamic stability requirements specific to UAVs have not been developed. The boundaries of controllability for both remotely-piloted and auto-piloted aircraft must be established before UAV technology can reach its full potential. The development of dynamic stability requirements specific to UAVs could improve flying qualities and facilitate more efficient UAV designs to meet specific mission requirements. As a first step to developing UAV stability requirements in general, test techniques must be established that will allow the stability characteristics of current UAVs to be quantified. This paper consolidates analytical details associated with procedures that could be used to experimentally determine the pitch stability boundaries for good UAV flying qualities. The procedures require determining only the maneuver margin and pitch radius of gyration and are simple enough to be used in an educational setting where resources are limited. The premise is that these procedures could be applied to UAVs now in use, in order to characterize the longitudinal flying qualities of current aircraft. This is but a stepping stone to the evaluation of candidate metrics for establishing flying-quality constraints for unmanned aircraft.

Effect of propeller torque on minimum-control airspeed

Relations are developed for absolute static minimum-control airspeed, without the bank angle restrictions imposed on manned aircraft by regulatory agencies. Absolute static minimum-control airspeed can be important in the design of modern unmanned aerial vehicles, because autonomous computer controlled flight systems do not impose the same constraints as those imposed by human pilots. It is shown that, for a three-channel unmanned aerial vehicle, absolute static minimum-control airspeed always provides the critical constraint for static minimum-control airspeed. Even for the case of a conventional aircraft configuration with both rudder and ailerons, absolute static minimum-control airspeed can be a critical concern for small high-powered propeller-driven unmanned aerial vehicles.

Use of Piloted Simulation for Evaluation of Abrupt Wing Stall Characteristics (Invited)

A piloted simulation architecture is presented for evaluating uncommanded wing drop due to asymmetric abrupt wing stall for a given aircraft configuration. The architecture incorporates a newly proposed aerodynamic modeling technique that characterizes the wing drop motion as being triggered by aerodynamic stall, modeled by a nonzero basic rolling moment coefficient, and sustained by reduced or propelling roll, modeled via the roll damping derivative. The determination of such derivatives/coefficients from either analytical or experimental methods is not addressed, and the successful identification of such terms, on which any piloted simulation evaluation hinges, remains a topic of research. Models with varying nonzero basic rolling moment coefficients and varying roll damping were inserted into the aerodynamic model and then evaluated by a pilot familiar with wing drop. The pilot assessed the varying models, assigning handling qualities ratings to predeveloped tasks aimed at diagnosing the severity (or absence) of any wing stall characteristics. Tasks included wind-up turns and a closed-loop tracking task in which the pilot tracked a target while flying a drop-prone simulation. The pilot was able to distinguish between satisfactory and unsatisfactory aerodynamic configurations

Comment on "Refining Satellite Methods for Pitot-Static Calibration"

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