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Scaled Paraglider Testbed Project

Project Background

        The Scaled Paraglider Testbed project is intended to serve as an unmanned platform for testing paraglider airfoils. Current certification standards require human pilots to induce a variety of common failure modes in untested airfoils to evaluate performance and safety. This process can be very dangerous for pilots, and also produce subjective and inconsistent data.By utilizing a mechanical system for testing and gathering telemetry data, testing standards can be altered to represent a more objective, repeatable, and safe metric.

        Paragliders are a type of aircraft that incorporate the use of a collapsible fabric wing sewn with interconnected cell that inflate in flight to become a rigid airfoil. Unlike other types of aircraft, paraglider pilots sit suspended in a harness beneath the wing, using a number of lines connected to the wing at different locations to control both orientation and speed. The two most commonly used control methods are brake line actuation and pilot weight shifting. In flight, the brake lines can be pulled to drag down the trailing edge of the wing, inducing drag and slowing down the system; however, when there is an uneven amount of drag on the wing by pulling one just one brake line, a combined yaw and roll motion is induced. A pilot shifting their weight inside the harness will cause an uneven distribution of line tension on one side of the system, effectively inducing a tilting motion that is an isolated roll maneuver. This technique, while less infuential for direction control, can be utilized by advanced pilots to perform loops in the air known as wingovers. 

         Since testing with full-sized wings is prohibitively expensive, our project will develop the specifications of a smaller-scale, but more affordable RC-paraglider wing with a flight dynamic and performance similar to that of the most common full-sized hobbyist models. In addition, existing autonomous paraglider models and applications use primarily brake-line actuation in order to accomplish combined banking and turning maneuvers, neglecting to simulate the effect of a pilot's weight-shifting movements in the generation of isolated roll maneuvers. As such, our sponsor has tasked us with developing and validating the performance of a scaled paraglider system that emphasizes the use of a weight-shifting mechanism to generate rolling maneuvers in addition to the more traditional brake line actuation. 

Objectives

• 1. Design and manufacture a weight-shifting mechanism to actuate a method for controlling the roll of the system.

  2. Integrate closed-loop control algorithms into the weight shifting mechanism 

  3. Develop a geometrically-scaled paraglider wing simulator to test the performance of our weight shifting mechanism

  4. Integrate the weight shifting mechanism into a frame to be mounted onto the wing simulator. 

  5. Validate systems performance with control inputs using recorded data from the microcontroller and pre-programmed flight maneuvers.

Process: 

Selection and Scaling of Paraglider Wing

        Because the penultimate objective of the project is to design a system compatible with virtually any existing or developing paraglider canopy, the first step was to decide upon a set of physical design parameters that already exist in industry with the two most important criteria for selection being aspect ratio and overall carrying capacity. Wings with a lower aspect ratio closer are less prone to wing collapse in flight at the cost of being less agile and responsive to pilot inputs, making it ideal for beginners and the overall design of our system. A larger carrying capacity translates into greater freedom in the selection of components and materials for the platform. We decided to model our system after the Opale Oxy 5.0, (seen above) which has the below features:

• Supplier: Opale Paramodels

• Model: Oxy 5.0

• Wing Span: 5.0m

• Aspect Ratio: 5.1

• Flight Weight: 20kg

• Market Value: $600

Weight Shifting Mechanism Design:

        Our design focused on the application of a pulley-driven linear slider supported on two linear rods. This configuration was favorable above other designs due to the analysis of possible failure modes while in flight. In particular, special consideration was given to the case of 90 degrees of roll in which the amount of torque necessary for the stepper motor to generate is maximized for any given design. Lever arm designs must always operate at maximum torque, whereas the torque required by linear sliders is primarily a function of the radius of the driving pulley. As the latter would theoretically be smaller at our scale of application, it would result in smaller and more cost efficient electronics purchases down the line.

Selection of Sensor Package:

     For our project, we decided on the Texas Instruments BeagleBone Blue microcontroller. Another crucial aspect of the project in addition to control of the system's actuation is the ability to accurately and reliably record data. As such, we selected a controller that most effeciently fulfilled our needs of both position sensing as well as motor control. The BeagleBone Blue has the following benefits:

• 9-axis IMU (accelerometer, gyroscope, mangetometer) for orientation feedback

• Multi-threading capability for simultaneous control of the brake lines and the weight-shifting mechanism

• Existing RoboticsCape Library for servo and motor control

Mass Analysis

        Our overall system dynamics can be modeled similarly to a pendulum whose position with respect to the rest angle within the system is a function of the displacement issued to the linear slider as seen in the picture above. Derived using the conventional equation for center of mass and the above diagram, the resultant roll angle is given by:

System Operation: