Structural testing for static failure, flutter and other scary things

Ground test and flight test methods are described that may be used to highlight potential structural problems that occur on aircraft. Primary interest is focused on light-weight general aviation airplanes. The structural problems described include static strength failure, aileron reversal, static divergence, and flutter. An example of each of the problems is discussed to illustrate how the data acquired during the tests may be used to predict the occurrence of the structural problem. While some rules of thumb for the prediction of structural problems are given the report is not intended to be used explicitly as a structural analysis handbook

Aeroelastic instability stoppers for wind tunnel models

A mechanism for diverting the flow in a wind tunnel from the wing of a tested model is described. The wing is mounted on the wall of a tunnel. A diverter plate is pivotally mounted on the tunnel wall ahead of the model. An actuator fixed to the tunnel is pivotably connected to the diverter plate, by plunger. When the model is about to become unstable during the test the actuator moves the diverter plate from the tunnel wall to divert maintaining stable model conditions. The diverter plate is then retracted to enable normal flow

Effects of angle of attack and vertical fin on transonic flutter characteristics of an arrow-wing configuration

Experimental transonic flutter results are presented for a simplified 1/50 size, aspect ratio 1.77, wind tunnel model of an arrow wing design. Flutter results are presented for two configurations; namely, one with and one without a ventral fin mounted at the 0.694 semispan station. Results are presented for both configurations trimmed to zero lift and in a lifting condition at angles of attack up to 4 deg. The results show that the flutter characteristics of both configurations are similar to those usually observed. Increasing angle of attack reduces the flutter dynamic pressure by a small amount (about 13 percent maximum) for both configurations. The addition of the fin to the basic wing increases the flutter dynamic pressure. Calculated results for both configurations in the nonlifting condition obtained by using subsonic doublet lattice unsteady aerodynamic theory correlate reasonably well with the experimental results. Calculated results for the basic wing obtained by using subsonic kernal function unsteady aerodynamic theory did not agree as well with the experimental data

Dynamic response of a forward-swept-wing model at angles of attack up to 15 deg at a Mach number of 0.8

Root mean square (rms) bending moments for a dynamically scaled, aeroelastic wing of a proposed forward swept wing, flight demonstrator airplane are presented for angles of attack up to 15 deg at a Mach number of 0.8 The 0.6 size semispan model had a leading edge forward sweep of 44 deg and was constructed of composite material. In addition to broad band responses, individual rms responses and total damping ratios are presented for the first two natural modes. The results show that the rms response increases with angle of attack and has a peak value at an angle of attack near 13 deg. In general, the response was characteristic of buffeting and similar to results often observed for aft swept wings. At an angle of attack near 13 deg, however, the response had characteristics associated with approaching a dynamic instability, although no instability was observed over the range of parameters investigated

Wind-tunnel experiments on divergence of forward-swept wings

An experimental study to investigate the aeroelastic behavior of forward-swept wings was conducted in the Langley Transonic Dynamics Tunnel. Seven flat-plate models with varying aspect ratios and wing sweep angles were tested at low speeds in air. Three models having the same planform but different airfoil sections (i.e., flat-plate, conventional, and supercritical) were tested at transonic speeds in Freon 12. Linear analyses were performed to provide predictions to compare with the measured aeroelastic instabilities which include both static divergence and flutter. Six subcritical response testing techniques were formulated and evaluated at transonic speeds for accuracy in predicting static divergence. Two "divergence stoppers" were developed and evaluated for use in protecting the model from structural damage during tests

Recent transonic unsteady pressure measurements at the NASA Langley Research Center

Four semispan wing model configurations were studied in the Transonic Dynamics Tunnel (TDT). The first model had a clipped delta planform with a circular arc airfoil, the second model had a high aspect ratio planform with a supercritical airfoil, the third model has a rectangular planform with a supercritical airfoil and the fourth model had a high aspect ratio planform with a supercritical airfoil. To generate unsteady flow, the first and third models were equipped with pitch oscillation mechanisms and the first, second and fourth models were equipped with control surface oscillation mechanisms. The fourth model was similar in planform and airfoil shape to the second model, but it is the only one of the four models that has an elastic wing structure. The unsteady pressure studies of the four models are described and some typical results for each model are presented. Comparison of selected experimental data with analytical results also are included

Some recent applications of XTRAN3S

A time marching finite difference code, XTRAN3S that solves the three dimensional transonic small perturbation equation for flow over isolated wings was developed. During initial applications of the program, problems were encountered in the prediction of unsteady forces. The use of a revised grid and force calculation scheme improved those predictions. Comparisons are made between predicted and experimental pressure data for a rectangular supercritical wing. Comparisons of steady and unsteady data at M sub infinity = 0.700 show good agreement between calculated and experimental values. A comparison of steady data at M sub infinity 0.825 shows poor agreement between calculations and experiment. Program difficulties were encountered with swept and tapered configurations

Scavenging effects and scattering patterns on porcine carcasses in Eastern Massachusetts

Forensic investigators encountering remains deposited in an outdoor environment face many obstacles, including the scavenging, scattering, and reconcentration of remains by local vertebrate fauna. Scattering rates can vary considerably from region to region, and are highly dependent on the indigenous scavengers present (Haglund et al. 1988; Haglund et al. 1989; Mann et al. 1990; Morton and Lord 2006). In turn, scavenger activity is highly dependent on seasonal changes, rainfall, temperature fluctuations, and environmental stressors such as seasonal resource availability and dietary changes (Brown et al. 2006; Mann et al. 1990; O’Brien et al. 2007). A more thorough knowledge of the variation in scavenging and scattering patterns of the indigenous fauna in different geographical regions would produce a more productive search pattern and increase the recovery rate of scattered remains for those involved in outdoor crime scene investigations. The current study followed and documented the behavior of the indigenous carnivorous birds and mammals, as well as the scattering patterns of these species, in Eastern Massachusetts, using five porcine (Sus scrofa) carcasses. Carcasses were deposited in lightly wooded environments under different depositional settings and tracked by low-light wildlife video cameras and radio transmitter tags attached to the long bones of some of the limbs. The major scavengers of decomposing remains were documented, and the distance and direction of scattered skeletal elements were noted, as well as any secondary depositions. This research was conducted in three phases; the first was a preliminary observation of faunal wildlife and their distribution during the early summer of 2011, followed by one 14-week observation of porcine models during midsummer of 2011 and one 6-week observation of porcine models during late summer and early fall of 2011. Results show that seasonality greatly affects scavenging activity, as carrion deposited in the summer are primarily consumed by the indigenous invertebrate community, causing accelerated decomposition and vertebrate scavenger exclusion. Additionally, though marsupials and avian species fed the longest, coyotes (Canis latrans) produced the most destructive dispersal of carrion. Moreover, although coyotes disarticulated carcasses relatively nearby the original deposition, they sought out outdoor environments that are mostly devoid of human activity to feed upon disarticulated assemblages

An in vitro comparison between two methods of electrical resistance measurement for occlusal caries detection

Because of different measurement techniques and the easier design of the CRM prototype, this in vitro study aimed to compare the diagnostic performance and reproducibility of two electrical methods (Electronic Caries Monitor III, ECM and Cariometer 800, CRM) for occlusal caries detection, and to evaluate the effect of staining/ discoloration of fissures on diagnostic performance. Hundred and seventeen third molars with no apparent occlusal cavitation were selected. Six examiners inspected all specimens independently, using the CRM, and a subgroup of 4 using the ECM. Histological validation using a stereomicroscope was performed after hemisectioning. Intra- and interexaminer reproducibility was assessed by Lin's concordance correlation coefficient (CCC) and Bland and Altman analysis. Diagnostic performance parameters included sensitivity (SE), specificity (SP) and area under the ROC curve (A(z)). The CCC yielded an intra- and interexaminer reproducibility of 0.69/0.62 (ECM) and of 0.79/0.74 (CRM). The mean intra- and interexaminer 95% range of measurements (range between Bland and Altman limits of agreement) given in percentages of the instrument reading were 67%/65% for the ECM and 28%/33% for the CRM. A(z) at the D3-4 level was 0.74 (ECM) and 0.78 (CRM). The CRM showed at least equivalent diagnostic performance to the ECM. However, improvement is still desirable. Diagnostic performance appeared to be enhanced in discolored lesions; however, this may be related to sample lesion distribution characteristics. Copyright (C) 2006 S. Karger AG, Basel

Evaluation of four subcritical response methods for on-line prediction flutter onset in wind-tunnel tests

The methods were evaluated for use in tests where the flutter model is excited solely by airstream turbulence. The methods were: randomdec, power-spectral-density, peak-hold, and cross-spectrum. The test procedure was to maintain a constant Mach number (M) and increase the dynamic pressure (g) in incremental steps. The test Mach numbers were 0.65, 0.75, 0.82, 0.90, and 1.15. The four methods provided damping trends by which the flutter mode could be tracked and extrapolated to a flutter-onset q. A hard flutter point was obtained at M = 0.82. The peak-hold and cross-spectrum methods gave reliable results and could be most readily used for on-line testing. At M = 0.82, a p-k analysis predicted the same flutter mode as the experiment but a 6-percent lower flutter q. At the subcritical dynamic pressures, calculated damping values were appreciably lower than measured data