Francis J. Capone

Free-To-Roll Analysis of Abrupt Wing Stall on Military Aircraft at Transonic Speeds

Transonic free-to-roll and static wind tunnel tests for four military aircraft - the AV-8B, the F/A-18C, the preproduction F/A-18E, and the F-16C - have been analyzed. These tests were conducted in the NASA Langley 16-Foot Transonic Tunnel as a part of the NASA/Navy/Air Force Abrupt Wing Stall Program. The objectives were to evaluate the utility of the free-to-roll test technique as a tool for predicting areas of significant uncommanded lateral motions and for gaining insight into the wing-drop and wing-rock behavior of military aircraft at transonic conditions. The analysis indicated that the free-to-roll results had good agreement with flight data on all four models. A wide range of motions - limit cycle wing rock, occasional and frequent damped wing drop/rock and wing rock divergence - were observed. The analysis shows the effects that the static and dynamic lateral stability can have on the wing drop/rock behavior. In addition, a free-to-roll figure of merit was developed to assist in the interpretation of results and assessment of the severity of the motions.

AWS Figure of Merit (FOM) Developed Parameters from Static, Transonic Model Tests

This paper provides an approach to answer the question of whether one can rely solely on static data taken during a transonic model test to provide the certainty needed that a new aircraft will or will not have Abrupt Wing Stall (AWS) events during its flight operations. By comparing traditional- and alternate-static-Figures of Merit (FOMs) with the Free-To-Roll (FTR) response data, a rational basis for assessing the merits of using standard testing techniques for the prediction of AWS events has been established. Using the FTR response data as a standard, since these results compare well with flight, the conclusion from this study is that neither traditional nor alternate FOMs can be trusted to provide an indication as to whether a configuration will or will not have AWS tendencies. Even though these FOMs may flag features which have a high degree of correlation with the FTR response data, there are as many or more of these FOM flagged features which do not correlate. Thus, one needs to use the FTR rig to assess AWS tendencies on new configurations.

Transonic Free-to-Roll Analysis of Abrupt Wing Stall on Military Aircraft

Transonic free-to-roll and static wind-tunnel tests for four military aircraft-the AV-8B, the F/A-18C, the preproduction F/A-18E, and the F-16C-have been analyzed. These tests were conducted in the NASA Langley 16-Foot Transonic Tunnel as a part of the NASA/Navy/Air Force Abrupt Wing Stall Program. The objectives were to evaluate the utility of the free-to-roll test technique as a tool for predicting areas of significant uncommanded lateral motions and for gaining insight into the wing-drop and wing-rock behavior of military aircraft at transonic conditions. The analysis indicated that the free-to-roll results agreed well with flight data on all four models. A wide range of motions-limit-cycle wing rock, occasional and frequent damped wing drop/rock and wing-rock divergence-were observed

Development of a Free-To-Roll Transonic Test Capability

NASA Langley Research Center, Hampton, VirginiaAIAA-2003-0749ABSTRACTAs part of the NASA/Navy Abrupt Wing Stall Program, a relatively low-cost, rapid-access wind-tunnelfree-to-rollrig was developed. This rig combines the use of conventional models and test apparatuses toevaluate both transonic performance and wing-drop/rock tendencies in a single tunnel entry. A descriptionof the test hardware as well as a description of the experimental procedures is given. The free-to-roll testrig has been used successfully to assess the static and dynamic characteristics of three differentconfigurations--two configurations that exhibit uncommanded lateral motions, (pre-production F/A-18E andAV-8B),and one that did not (F/A-18C).SYMBOLS AND ABBREVIATIONS INTRODUCTIONAWS

Supercirculation Effects Induced by Vectoring a Partial-Span Rectangular Jet

Thrust-induced Supercirculation effects from thrust vectoring have indicated a potential for not only increasing maneuverability of fighter aircraft but also as a means of improving cruise performance. The current study investigated a partial-span rectangular jet-exhaust nozzle located at the wing trailing edge that acts similarly to a jet flap by increasing lift due to Supercirculation. This paper summarizes experimental studies including the effects of nozzle deflection angle, wing camber, and nozzle shape and exit location on lift, drag, and load distributions. The results indicate that significant increases in thrust-induce d lift along with substantial decreases in drag were found. A maximum lift gain factor of 4 was achieved and thrust recovery was maintained to a lift coefficient of 0.50. Of several airfoils considered, the supercritical airfoil exhibited superior performance with respect to both lift augmentation and thrust recovery. Overall performance was maintained to a Mach number of 0.90.

Development of a transonic free-to-roll test capability

As part of the NASA/Navy Abrupt Wing Stall Program, a relatively low-cost, rapid-access, free-to-roll test rig was developed on which conventional high-strength wind-tunnel models can be used to evaluate both transonic performance and wing-drop/rock behavior in a single tunnel entry. The overall objective was to demonstrate the utility of the free-to-roll test technique as a tool for identifying areas of significant uncommanded lateral activity during ground testing and for gaining insight into the wing-drop/rock behavior of military aircraft at transonic conditions. A description of the test hardware as well as a description of the experimental procedures is given. The free-to-roll test rig has been used successfully to assess the static and dynamic characteristics of four different configurations—two configurations that exhibited uncommanded lateral motions inflight (preproduction F/A-18E and AV-8B) and two that did not (F/A-18C, F-16C). Excellent agreement between free-to-roll results and flight was obtained for those configurations where flight data were available.

Review and Recommended Experimental Procedures For Evaluation Of Abrupt Wing Stall Characteristics

Ar eview of the experimental program for four different aircraft configurations conducted as part of the Abrupt Wing Stall Program has been made. Several candidate figures of merit from conventional static-tunnel tests are summarized and correlated with data obtained in unique free-to-roll tests. The conclusion from this study is that these figures of merit can by themselves give some indication as to whether an aircraft would experience uncommanded lateral activity caused by abrupt wing stall. However, no one specific figure of merit consistently flagged a warning of potential lateral activity when actual activity was seen to occur in the free-to-roll experiments. In fact, they yielded as many or more false indications of lateral activity then were seen in the free-to-roll response data. Excellent agreement between free-to-roll results and flight was obtained for those configurations where flight data were available.

Usefulness of Transonic Model Static Data in Predicting Flight Abrupt-Wing-Stall

An approach is provided to answer the question of whether one can rely solely on static data taken during a transonic model test to provide the certainty needed that a new aircraft will or will not have abrupt wing stall (AWS) events during its flight operations. By the comparison of traditional static figures of merit (FOMs) with the free-to-roll (FTR) response data, a rational basis for assessing the merits of using standard testing techniques for the prediction of AWS events has been established. With use of the FTR response data as a standard, because these results compare well with flight, it is concluded that traditional FOMs can not be trusted to provide an indication as to whether a configuration will or will not have AWS tendencies. Even though these FOMs may flag features that have a high degree of correlation with the FTR response data, there are as many or more of these FOM flagged features that do not correlate. Thus, one needs to use the FTR rig to assess AWS tendencies on new configurations

Performance Characteristics of Nonaxisymmetric Nozzles Installed on an F-18 Propulsion Model

The Langley Research Center has conducted an experimental program on a model of the F-18 airplane to determine the performance of nonaxisymmetr ic nozzles relative to the aircrafts baseline axisymmetric nozzle. The performance of a single-expansion ramp and a two-dimensional convergent-div ergent nozzle were compared to the baseline axisymmetric nozzles. The effects of vectoring and reversing were also studied. The results of this investigation indicate that nonaxisymmetric nozzles can be installed on a twin-engine fighter airplane with equal or better performance than axisymmetric nozzles. The nonaxisymmetric nozzles also offer potential for innovative and improved aircraft maneuver through thrust vectoring and reversing.