Aerodynamic Effect of Strakes on Two-Dimensional Tail Boom Models of the OH-58A and the OH-58D Helicopters

During hover and low speed flight, helicopters experience significant aerodynamic forces on the tail boom caused by the wake from the main and tail rotors and by crosswinds. These effects were simulated during a study conducted in the Langley 14 by 22 Foot Subsonic Tunnel on a 136 percent scaled 2-D tail boom model with cross sections representative of those on the U.S. Army OH-58A and the OH-58D helicopters. The effects of longitudinal strakes attached to the cross sections were studied. To obtain the aerodynamic forces acting on the cross sections, the flow incidence range on the scaled models was varied from -45 to 90 degrees and the models were tested through a dynamic pressure range of 5 to 15 psf. The results of the OH-58A and the OH-58D configurations show a significant improvement at conditions which represent right sideward flight by reducing the adverse aerodynamic side force when the strakes are installed. These data were used to calculate a change in tail rotor power for the full scale flight vehicle and indicated approx. a 5 to 6 percent average savings in right sideward flight for the critical velocity range of 0 to 30 knots. Increases in the tail boom normal force were noted due to the strakes. The results indicate a potential for reducing the directional control and tail rotor thrust required in the critical hover and right sideward flight speed range with a calculated minimum increase to main rotor power required and an overall net improvement in power of 0.5 percent for both the OH-58A and OH-58D

Helicopter low-speed yaw control

A system for improving yaw control at low speeds consists of one strake placed on the upper portion of the fuselage facing the retreating rotor blade and another strake placed on the lower portion of the fuselage facing the advancing rotor blade. These strakes spoil the airflow on the helicopter tail boom during hover, low speed flight, and right or left sidewards flight so that less side thrust is required from the tail rotor

Two-dimensional aerodynamic characteristics of several polygon-shaped cross-sectional models applicable to helicopter fuselages

A wind-tunnel investigation was conducted to determine 2-D aerodynamic characteristics of nine polygon-shaped models applicable to helicopter fuselages. The models varied from 1/2 to 1/5 scale and were nominally triangular, diamond, and rectangular in shape. Side force and normal force were obtained at increments of angle of flow incidence from -45 to 90 degrees. The data were compared with results from a baseline UH-60 tail-boom cross-section model. The results indicate that the overall shapes of the plots of normal force and side force were similar to the characteristic shape of the baseline data; however, there were important differences in magnitude. At a flow incidence of 0 degrees, larger values of normal force for the polygon models indicate an increase in fuselage down load of 1 to 2.5 percent of main-rotor thrust compared with the baseline value. Also, potential was indicated among some of the configurations to produce high fuselage side forces and yawing moments compared with the baseline model

Development in helicopter tail boom strake applications in the US

The use of a strake or spoiler on a helicopter tail boom to beneficially change helicopter tail boom air loads was suggested in the United States in 1975. The anticipated benefits were a change of tail boom loads to reduce required tail rotor thrust and power and improve directional control. High tail boom air loads experienced by the YAH-64 and described in 1978 led to a wind tunnel investigation of the usefullness of strakes in altering such loads on the AH-64, UH-60, and UH-1 helicopters. The wind tunnel tests of 2-D cross sections of the tail boom of each demonstrated that a strake or strakes would be effective. Several limited test programs with the U.S. Army's OH-58A, AH-64, and UH-60A were conducted which showed the effects of strakes were modest for those helicopters. The most recent flight test program, with a Bell 204B, disclosed that for the 204B the tail boom strake or strakes would provide more than a modest improvement in directional control and reduction in tail rotor power

Seeing Mathematics Through Different Eyes: An Equitable Approach to Use with Prospective Teachers

Teacher educators need to prepare prospective teachers by encouraging them to critically examine their current beliefs about the teaching and learning of mathematics while also providing opportunities for prospective teachers to develop an equity-centered orientation. Attending to these practices in teacher preparation programs may help prospective teachers observe actions that occur in classrooms and determine effective strategies that provide the opportunity to enhance all students’ access to high-quality mathematics instruction. As mathematics teacher educators, we must recognize what prospective teachers attend to as they direct their attention to various classroom events and how they relate the events to broader principles of teaching and learning. In this chapter, we investigate what prospective teachers attend to in a classroom vignette of a student who is above grade level in mathematics and exhibits disruptive behavior during instruction. Keeping everything constant in the vignette except the student’s race and sex, we examined prospective teachers’ responses when the student was an African American male, White male, African American female, and White female. By attending specifically to race and sex, we explored whether prospective teachers demonstrated (1) an equity-centered orientation toward mathematics instruction or (2) deficit views of students based on race, sex, or the intersection of the two. Using a constant comparative method, the data were coded and analyzed using the equity noticing framework. The results indicate that prospective teachers are beginning to attend to cultural influences and their responses reveal differences not only between races but also between males and female

Maths Games: A Universal Design approach to mathematical reasoning

By incorporating math games into the classroom, through the principles of Universal Design teachers are able to address mathematical content, reasoning and problem solving, as well as tailoring games to address students\u27 individual needs

What, how, who: Developing Mathematical Discourse

A collaborative classroom, an open-ended problem, and a what-how-who structure can build students’ reasoning skills and allow teachers to recognize all classroom contributions. With an increased focus on using social discourse to enhance students’ mathematical thinking and reasoning (NCTM 2014, Staples and King 2017), teachers are looking for discussion strategies that encourage middlelevel students to make sense of mathematical concepts. However, structuring these valuable discussions is complex. “Mathematical discourse should build on and honor student thinking, and provide students with opportunities to share ideas, clarify understandings, develop convincing arguments, and advance the mathematical learning of the entire class” (Smith, Steele, and Raith 2017, p. 123). In other words, teachers must carefully consider what tasks provide meaningful opportunities to explore ideas, generate hypotheses, and promote questions within a collaborative environment. Then, teachers need to consider how to structure the activity to encourage discussions and incorporate responses that contribute to understanding specific mathematical objectives. Additionally, teachers must select who will speak to “advance the mathematical storyline of the lesson” (NCTM 2014, p. 30). By intentionally focusing on these elements in mathematics instruction, middle-grades teachers can develop a classroom culture that not only emphasizes sense making but also values the intellectual capacity that students bring to the classroom (Gutiérrez 2013; Lemons-Smith 2008). In this article, we describe how teachers can promote meaningful discussions using the what-how-who structure while giving students opportunities to make sense of mathematical ideas within a social context

Sliding into an equitable lesson

A kindergarten teacher uses Gutierrez\u27s four dimensions of equity to design and facilitate geometry instruction. Equitable instruction is reflected in how students are positioned in the classroom and how their identities evolve through purposeful interactions that value and recognize the intellectual capacity of each student (Gutiérrez 2013; Lemons-Smith 2008). These integral interactions occur when teachers and students exchange problem-solving strategies, discuss relations among various mathematical representations, and listen to the viewpoints of others (NCTM 2000; 2014)

The Institutional Context and Manufacturing Performance: The Case of the U.S. Defense Industrial Network

U.S. manufacturing firms that make sophisticated weapons systems for the Pentagon are subject to an unusual regulatory regime that obligates them to volunteer' information on their business practices to the government and to prime contractors as a condition of their special relationship with the government. Within this organizational community information sharing with and assistance to other firms have come to be viewed as an ordinary obligation - i.e., a condition of citizenship. This cooperative learning environment is indicative of a collaborative manufacturing network that enables member organizations to learn quickly about relevant process technology innovations and to implement them effectively. We find that defense contractors learn about information technology applications more quickly than enterprises outside the network. Moreover, learning advantages are not confined to transactions specific to the Pentagon, but benefit the non-military operations of the networked enterprises as well.