Probabilistic fatigue methodology for six nines reliability

Fleet readiness and flight safety strongly depend on the degree of reliability that can be designed into rotorcraft flight critical components. The current U.S. Army fatigue life specification for new rotorcraft is the so-called six nines reliability, or a probability of failure of one in a million. The progress of a round robin which was established by the American Helicopter Society (AHS) Subcommittee for Fatigue and Damage Tolerance is reviewed to investigate reliability-based fatigue methodology. The participants in this cooperative effort are in the U.S. Army Aviation Systems Command (AVSCOM) and the rotorcraft industry. One phase of the joint activity examined fatigue reliability under uniquely defined conditions for which only one answer was correct. The other phases were set up to learn how the different industry methods in defining fatigue strength affected the mean fatigue life and reliability calculations. Hence, constant amplitude and spectrum fatigue test data were provided so that each participant could perform their standard fatigue life analysis. As a result of this round robin, the probabilistic logic which includes both fatigue strength and spectrum loading variability in developing a consistant reliability analysis was established. In this first study, the reliability analysis was limited to the linear cumulative damage approach. However, it is expected that superior fatigue life prediction methods will ultimately be developed through this open AHS forum. To that end, these preliminary results were useful in identifying some topics for additional study

The NASA supercritical-wing technology

A number of high aspect ratio supercritical wings in combination with a representative wide body type fuselage were tested in the Langley 8 foot transonic pressure tunnel. The wing parameters investigated include aspect ratio, sweep, thickness to chord ratio, and camber. Subsequent to these initial series of tests, a particular wing configuration was selected for further study and development. Tests on the selected wing involved the incorporation of a larger inboard trailing edge extension, an inboard leading edge extension, and flow through nacelles. Range factors for the various supercritical wing configurations are compared with those for a reference wide body transport configuration

Cold-air study of the effect on turbine stator blade aerodynamic performance of coolant ejection from various trailing-edge slot geometries. 1: Experimental results

Trailing-edge slot configurations were investigated in a two-dimensional cascade of turbine stator blades. The trailing-edge slots were incorporated into blades with round trailing edges. The five blade configurations investigated included blades with two different trailing-edge thicknesses and four different slot widths. The results of the investigation showed that there was, in general, a significant increase in primary-air efficiency due to the coolant flow, the increase varying with slot configuration. For the five configurations tested, the average percent change in primary-air efficiency per percent coolant flow varied almost linearly from zero to about 1.4 percent over a range of coolant- to primary-air exit-velocity ratios between 0 and 1.2. However, for different configurations there was considerable deviation from the average values in the lower range of exit velocity ratios

Application of antiresonance theory to helicopters

Antiresonance theory is the principle underlying nonresonant nodes in a structure, and covers both nonresonant nodes occurring naturally and those introduced by devices such as dynamic absorbers and antiresonant isolators. The dynamic antiresonant vibration isolator (DAVI) and the nodale module are examples of the applications of transfer antiresonances. It is shown that antiresonances are eigenvalues, and that they can be determined by matrix iteration. Applications of antiresonance theory to helicopter engineering problems, using the antiresonant eigenvalue equation are suggested

Evaluation of installed performance of a wing-tip-mounted pusher turboprop on a semispan wing

An exploratory investigation has been conducted at the Langley Research Center to determine the effect of a wing-tip-mounted pusher turboprop on the aerodynamic characteristics of a semispan wing. Tests were conducted on a semispan model with an upswept, untapered wing and an airdriven motor that powered an SR-2 high-speed propeller located on the tip of the wing as a pusher propeller. All tests were conducted at a Mach number of 0.70 over an angle-of-attack range from approximately -2 to 4 deg at a Reynolds number of 3.82 x 10 to the 6th based on the wing reference chord of 13 in. The data indicate that, as a result of locating the propeller behind the wing trailing edge at the wing tip in the crossflow of the wing-tip vortex, it is possible to improve propeller performance and simultaneously reduce the lift-induced drag

An evaluation of a constrained test method for obtaining free body responses

A method for obtaining free body responses from dynamic tests on a constrained structure is investigated for practical feasibility. The method is based on the principle that a constrained structure can be considered to be a free body acted upon by multiple forces which include the forces of constraint. By measuring these forces and by exciting the structure so as to develop linearly independent sets of forces, the response of the free body to one force at a time can be computed. Techniques for producing these independent forces are discussed. The development of the theory, computer simulations of tests of representative aerospace vehicles (including experimental error), and a description and listing of the computer programs developed are included. The procedure appears to be a practical method for obtaining in-flight characteristics of such vehicles

At the Heart of the Classroom: Teachers\u27 Experience of the Suffering and Success of Students for Whom They Care

The core of teaching is the relationship of care between the student and the teacher. A community can be created in the classroom that honors and respects the inherent worth of each individual and through such mutual respect students and teachers can experience success. The suffering and the successes that teachers experience are central to the way they care for their students. There is currently a great deal of focus on education and schooling in the United States and generally this focus ignores the necessity and vitality of the relationship of care. Teachers must daily support and care for students who have great struggles and great triumphs. In my dissertation, I will explore the nature of the experience of these teachers as they work with students who experience suffering and success. I will identify the themes of their experience using a hermeneutic phenomenological methodology based on the work of Max Van Manen. This dissertation is essentially a philosophical examination of the nature of teachers’ care for students and how they manifest the experience of suffering and success of those students. Therefore it is a deeply phenomenological work, bound not by the empirical, but by the life- worlds of the participants and of the author. The electronic version of this Dissertation is at OhioLink ETD Center, www.ohiolink.edu/et

At the Heart of the Classroom: Teachers\u27 Experience of the Suffering and Success of Students for Whom They Care

The core of teaching is the relationship of care between the student and the teacher. A community can be created in the classroom that honors and respects the inherent worth of each individual and through such mutual respect students and teachers can experience success. The suffering and the successes that teachers experience are central to the way they care for their students. There is currently a great deal of focus on education and schooling in the United States and generally this focus ignores the necessity and vitality of the relationship of care. Teachers must daily support and care for students who have great struggles and great triumphs. In my dissertation, I will explore the nature of the experience of these teachers as they work with students who experience suffering and success. I will identify the themes of their experience using a hermeneutic phenomenological methodology based on the work of Max Van Manen. This dissertation is essentially a philosophical examination of the nature of teachers’ care for students and how they manifest the experience of suffering and success of those students. Therefore it is a deeply phenomenological work, bound not by the empirical, but by the life- worlds of the participants and of the author. The electronic version of this Dissertation is at OhioLink ETD Center, www.ohiolink.edu/et