טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentYehuda Shafir
SubjectFlight Mechanics of Wind-Surfing Kite
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Iosilevskii Gil
Full Thesis textFull thesis text - English Version


Abstract

Following its invention in the late 1980s, windsurfing kite has become a popular sport and the kite itself has been developed to a high performance, agile, user friendly product. Yet, development methods used over the years were mostly trial and error, not scientific. Existing studies analyzed the kite's longitudinal stability, performance, and trajectory optimization for power generation, but not handling qualities. There is an evident lack of literature regarding theoretical models that capture the Kite's lateral dynamics in response to lateral control and that could be used to upgrade design and enhance performance.

This study addresses this gap. Specifically, the study deals with the aerodynamic mechanism of the kite's control:

?         How pulling the control lines is translated into dynamic forces on the kite?

?         What are the dynamic characteristics of "successful" kite?

?         What determines the characteristic time scales of the kite motion?

?         What combinations of the kite’s parameters render "desirable" handling qualities for the kite-surfers? 

To this end, a synthetic environment was created, providing a common basis for kites’ evaluation.  It included a solver of the pertinent equations of motion (EOM), an adaptive aerodynamic model, and a user interface, allowing for an easy definition of the kite geometry and its deformation under control input.

The aerodynamic model was based on an asymptotic lifting line theory, which combined simplicity - needed for its efficient implementation in the EOM solver - with acceptable accuracy.  The model was validated using a wind-tunnel model of a kite. 

 By systematically “flying” different kite shapes in different maneuvers, the synthetic environment allowed to relate the kite's geometrical and structural characteristics with its motion characteristics. It allowed identifying the control mechanisms of the kite and its basic eigen-modes. It also made possible to relate surfers' common terminology of the kite handling with the evaluated parameters. 

It was found that twisting the kite structure renders much bigger control authority than bending it. It was found that a kite is laterally unstable, with a diverging mode similar to the spiral mode of airplanes.  The relation between kite’s geometry and its handling qualities were identified.