To prevent the need for drive train design and manufacturing that was determined to be outside the scope of this project, a base drive train was selected from an off-the-shelf product to be used for the ETOP. The product that was selected was the Syma S107G RC Helicopter which is a small, coaxial vehicle with a rotor diameter of less than 0.3 meters. The thrust capabilities of the system were experimentally quantified and the flight stability characteristics of the vehicle when tethered were experimentally observed according to the following flight test setup.

Multiple tests were performed, each resulting in the same unstable flight characteristics for the tethered vehicle. The instability is explained by the vehicle’s inability to resolve the tension force in the tether resolving in an overturning moment induced about the center of gravity (CG) of the vehicle, according to the following diagram.

Multiple prototypes were designed, manufactured, and flight tested in order to test the viability of a passive stabilization method for a tethered, coaxial vehicle. The design includes three components, as shown in the image below.

This structural system redirects the line of action of the tether tension force to act through the CG of the vehicle, thereby resolving the overturning moment acting on the vehicle. This system preserves the vertical thrust produced by the vehicle which allows the vehicle to maintain its altitude while flight stability is reestablished through the mitigation of the tether force. This behavior is shown in the image below.

Multiple prototypes were created and flight tested to determine their flight characteristics with a focus on flight stability. A comprehensive summary of the three prototypes tested is given with important features of each prototype listed.

Prototype 1

     -     Establish viable ring stabilization system

     -     Test tethered vehicle performance

Prototype 2

     -     Test different pinning locations to improve vehicle stability

     -     Refine structural design for lower weight

Prototype 3

     -     Implement new, more robust drive train

     -     Implement optimal pinning location as determined by Prototype 2 testing

     -     Implement in-line fuselage design

Flight testing was performed on the final vehicle to validate stable flight characteristics with the tether installed.

A ground station is required to allow the user to control the vehicle and deliver power to the vehicle via the tether. The ground station was developed to contain the power supply for the vehicle, allowing the vehicle to be lower weight while ensuring long endurance capabilities. User controls are contained within the ground station as well as a battery power level indicator and screen to present images captured by the ETOP. The ground station prototype is shown in the image below.