PropCart: STEM for Aviation and Windpower

Julian Earwaker
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引用次数: 0

Abstract

PropCart is a three wheeled model vehicle with a variable pitch pusher propeller and rubber band motor. This paper presents the construction and testing of this vehicle as a platform for teaching concepts of linear and rotational mechanics, and elementary aerodynamics of airfoils applied in aircraft and wind turbines. Building and testing the vehicle is proposed as a 12th Grade STEM project: SCIENCE component: Physics; Linear and Rotational Mechanics with practical determination of basic and derived quantities in particular uniformly accelerated motion. TECHNOLOGY component: Design and construction of the vehicle. ENGINEERING component (overlapping technology): Measurement of thrust of the propeller at different setting angles using video data of propeller angular velocity and cart linear velocity; enabling determination of relative wind and angle of attack, calculation of Reynolds number and identifying stall angle without the use of a wind tunnel. MATHEMATICS component: Data analysis using Excel. A teaching course based mainly on the Khan academy physics programme is provided to support concepts used in the propeller cart project. PropCart is based on a four wheeled vehicle with fixed pitch propeller, devised by David Newton (1999). A redesigned three wheel vehicle with a variable pitch propeller was used in a practical project in a 12 week introductory engineering course at the University of Canterbury (2002) for 15 Petronas students. 12 students completed the project: Test videos for each student were taken in PAL format at 25fps for time intervals of 1–2 seconds for propeller setting angles of 15, 30 and 45 degrees; with student choice of the number of rubber bands used and the number of windup turns. Readings of linear and angular motion were taken with software which could select frame by frame display. Linear and angular displacement against time were plotted against time and time squared. Separate experiments were conducted on the performance of the propeller with the cart fixed with motor axis normal to an annular scale graduated in degrees. The propeller using 2 rubber bands was wound up by 30 turns for each test. Setting angles from 0 to 90 degrees were used. Graphs of angular displacement against time were compared over one second and plotted on a common time axis for setting angles 0 to 90 degrees. The graphs show that stalling occurs at angles greater than 15 degrees. Cart linear motion and propeller angular velocity within a one second time interval were related. Angular velocity of the propeller against time was a piecewise function: At low setting angles near 15 degrees tending to an acceleration sub-function followed by a constant velocity sub-function the latter giving constant thrust and constant linear acceleration of the cart. The angular displacement against time squared graph showed non uniform decreasing acceleration, with the rate of decrease increasing with time squared due to drag; further supported by the test results of the linear motion of the students’ vehicles. A large number of activities are detailed for the teaching of linear and rotational mechanics. For example, the rotational inertia of the propeller can be determined by mounting it as a compound pendulum; this activity importantly uses the parallel axis theorem. Taking the propeller blade as a flat plate airfoil: The relative air flow at mid span can be determined as falling along the resultant of air relative to the cart and air relative to the reference point on the blade: Enabling the determination of flow angle and angle of attack for a given setting angle. A parallel linkage with adjustable link lengths was developed for measuring setting angle by reflecting a laser beam off mirror foil on the blades, this is briefly discussed.
PropCart:航空和风能的STEM
PropCart是一种三轮模型车,具有可变螺距推进螺旋桨和橡皮筋电机。本文介绍了该飞行器的建造和测试,作为线性和旋转力学概念的教学平台,以及应用于飞机和风力涡轮机的翼型的基本空气动力学。建造和测试车辆被提议作为12年级的STEM项目:科学部分:物理;线性和旋转力学,特别是均匀加速运动的基本量和推导量的实际测定。技术部分:车辆的设计和制造。工程组件(重叠技术):利用螺旋桨角速度和车线速度的视频数据测量螺旋桨在不同设置角度下的推力;可以在不使用风洞的情况下确定相对风向和迎角,计算雷诺数和识别失速角。数学部分:使用Excel进行数据分析。一个主要基于可汗学院物理课程的教学课程提供了支持螺旋桨车项目中使用的概念。PropCart是基于固定螺距螺旋桨的四轮车辆,由David Newton(1999)设计。2002年,在坎特伯雷大学为15名马来西亚国家石油公司学生开设的为期12周的工程入门课程中,一辆重新设计的带有可变螺距螺旋桨的三轮汽车被用于一个实际项目。12名学生完成项目:每个学生的测试视频为PAL格式,25fps,时间间隔为1-2秒,螺旋桨设置角度为15、30、45度;由学生自行选择使用的橡皮筋数目及上发条的转数。采用可逐帧显示的软件对直线运动和角运动进行读取。线性位移和角位移随时间的变化随时间和时间的平方而变化。对小车与电机轴垂直于环形刻度刻度固定时的螺旋桨性能进行了单独试验。使用2根橡皮筋的螺旋桨每次上30圈。设置角度从0到90度。角位移随时间变化的图形在一秒钟内进行比较,并绘制在一个共同的时间轴上,设置角度为0到90度。图表显示,失速发生在大于15度的角度。在一秒的时间间隔内,计算了船的直线运动和螺旋桨角速度。螺旋桨对时间的角速度是一个分段函数:在接近15度的低设置角趋向于一个加速度子函数,然后是一个恒定的速度子函数,后者给予恒定的推力和恒定的直线加速度。角位移随时间的平方曲线显示加速度不均匀减小,由于阻力的作用,减小的速率随时间的平方而增大;由学生车辆直线运动的测试结果进一步支持。在线性力学和旋转力学的教学中详细介绍了大量的活动。例如,螺旋桨的转动惯量可以通过将其安装为复摆来确定;这个活动重要地使用了平行轴定理。将螺旋桨叶片作为平板翼型:跨中相对气流可以确定为沿相对于车的空气和相对于叶片上参考点的空气的结果下降:可以确定给定设置角的气流角和攻角。研制了一种连杆长度可调的平行连杆,通过反射激光束在叶片上的反射来测量设置角,并对其进行了简要讨论。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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