Prototypes
Summary of progress
The WindFly Rig has been developed through a series of prototypes to the current version which is designed to be mounted in place of an outboard motor on standard 'off the shelf' planing motor boats. This version of the WindFly Rig is currently undergoing sea trials. Perhaps there has been too much focus on applying the WindFly Rig to a planing hull at the expense of achieving earlier success with displacement hulls.
The following have been tested and successfully demonstrated:
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The WindFly Rig causes the kite to act as if the lines are connected to the centre of lateral resistance, eliminating heel.
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Use of a combined keel and rudder system which self adjusts to resist the sideways component of the kite load and eliminates leeway.
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The steering system that uses the same combined keel and rudder elements that are used to balance the sideways component of the kite load.
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The system for controlling the kite in a way that allows control to be maintained as the length of the kite lines is changed.
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The load limiter system which limits the maximum power of the kite - control of the kite is maintained as the kite is depowered.
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The system for raising the foils for access to shallow water
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The quick release system to immediately separate the boat from the kite and WindFly Rig in an emergency.
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The system for mounting the WindFly Rig on the transom of a commercially available 'off the shelf' hull in place of the outboard engine.
The following has been tested and the principle successfully illustrated, however further development is required to achieve reliable operation:
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The system for maintaining a minimum tension in the kite lines, taking in and playing out the kite lines, and storing the kite lines.
The following have not yet been tested
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Operation of the hydrofoil to offset the vertical component of the kite load to achieve reliable planing.
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Automatic control of the kite.
P1 - No heel
To verify that the WindFly Rig can be used to avoid heel a meccano type prototype was built and tested. The prototype had a single drive line, with 2 strands in the biasing arrangement. A counterweight was used to balance the self-weight of the boom.
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The primary aim of the first prototype was to demonstrate:
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That no heeling moment was applied to the prototype when the “kite” lines were pulled perpendicularly to the longitudinal axis of the prototype.
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To demonstrate that (1) is true for all angles of the “kite” lines (i.e. “kite” pulling at any angle above the water surface).
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The prototype was proportioned to take account of the fact that the centre of lateral resistance was at the point where the wheels touch the ground.
Outcomes:
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When the “kite” lines were pulled at right angles to the axis of the prototype the prototype slid sideways across the floor and did not ‘capsize’. This demonstrated that there was no heeling moment applied to the model.
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The 1st prototype demonstrated that (1) is true for all angles of the “kite” lines.
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As the angle of the “kite” lines varied the 1st prototype tracked the movement of the lines so that the line of action continued to pass through the centre of lateral resistance.
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It was noted that tracking was “sticky” when the “kite” lines were at a low angle (close to the “water” surface).
P2 - Flying a kite v1
To prove that a kite can be flown using the WindFly Rig, and to further verify that the WindFly Rig avoids heel, a “static bicycle” prototype was built and tested on shore.
The drive lines and control lines all passed through the biasing arrangement. The biasing arrangement was fixed to the third point of the boom, and each line passed between the boom and the mast 3 times (N = 3). The drive lines terminated at the mast. The control lines extended through the base of the mast so that the kite could be controlled by a crew member in the “cockpit”.
A counterweight was used to balance the self weight of the boom.
The prototype was proportioned to take account of the fact that the centre of lateral resistance was at the point where the wheels touch the ground.
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The primary aims of the second prototype were to demonstrate:
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That a kite could be successfully flown through the WindFly Rig.
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The system for avoiding twisting of the kite lines as a vessel “goes about” or “gybes”.
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To further demonstrate that no heeling moment was applied to the prototype when the kite lines were pulled at in any direction relative to the axis of the prototype.
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The prototype had two wheels arranged one behind the other like a bicycle, this was to provide a “knife” edge support to minimise resistance to heel. The prototype had no steering and therefore had to be anchored – in effect a “static bicycle”.
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Outcomes:
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The prototype successfully demonstrated that a kite can be flown through the WINDFLY Rig and that the WINDFLY Rig tracks the kite so that no heeling moment was applied to the prototype when the kite lines were pulled in any direction relative to the axis of the prototype.
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The prototype successfully demonstrated the method for avoiding twisting of the kite lines as a vessel “goes about” or “gybes”.
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That the system would benefit from a reduction in the number of pulleys and lines running between the boom and the base of the mast. The number of lines and pulley blocks made the system difficult to assemble and increased the risk of line jams.
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That pulley blocks and lines must be more carefully selected to avoid lines jamming in pulley blocks.
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Once again tracking was “sticky” when the kite lines were at a low angle (close to the “water” surface). Occasionally the boom had to be manually nudged before the boom would rise from very low angles to track the kite.
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That it was difficult to maintain control of the kite as the line lengths were altered, as would be required during launch or retrieval of a kite or wing from a boat.
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Item (1) provided proof of the principle on which the WINDFLY Rig is based. The principal objective of the second prototype was achieved.
Item (2) demonstrated the principle underlying management of the control system as the WINDFLY Rig rotates any number of 360 degree rotations or part rotations.
Items (3), (5) and (6) identified areas where development was required.
Item (4) identified that better quality blocks are required.
The theory was developed to address the shortcomings identified by the 2nd prototype. The principal areas of development were:
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An arrangement was developed so that the length of the control lines is automatically adjusted to match the length of the drive line. This simplifies launch and retrieval of a kite / wing.
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The method of using crew lines to adjust the control lines was developed. This allows the kite or wing to be easily controlled as the length of the lines is altered. This makes it practical to launch and retrieve a kite or wing from a boat.
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The theory was developed to take account of friction losses at blocks and bearings and arrangements were developed which make allowance for friction losses at the blocks and bearings.
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The theory was developed to take account of the reduction in the boom raising moment which occurs when the boom is low. This resulted in guidance on maximum practical values for the ratio H/L [(Distance from the pivot pin to the centre of lateral resistance) / (Boom length)].
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Arrangements were developed in which a spring is used to balance the self weight of the boom, instead of a counterweight. This reduces the inertia of the boom and allows the boom to track the kite / wing more rapidly. Replacing the counterweight with a spring also lowers the centre of gravity which improves the stability of the vehicle.
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A quick release system was developed to allow the kite / wing and WindFly Rig to be jettisoned in an emergency.
P3 - Planing trial
A small model was built to test the concept of using a hydrofoil to balance the bow down effect which results from the vertical component of the kite load.
The model was built to represent a hull with the WindFly Rig mounted at the stern above a combined 'keel-rudder'. The hydrofoil was placed at the bow.
Outcomes:
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The model successfully demonstrated that a hydrofoil can be used to offset the 'bow down effect' enabling a hull to plane when pulled using a WindFly Rig mounted on the transom.
Conclusion:
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A hydrofoil should be included to counter the tendency of kite driven boats to drop the bow.
P4 - Crew lines
A version of the WindFly Rig was built incorporating the following developments:
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Crew lines were used to manage the length of the control lines.
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A spring was used to balance the self weight of the boom.
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Only the drive lines passed through the biasing arrangement. A line storage system was provided to play out and draw in the control lines as the drive lines were played out and drawn in. The load in the control lines was transferred to the drive lines before the drive lines entered the biasing arrangement.
The biasing arrangement was fixed to the third point of the boom, and each line passed between the boom and the mast 3 times (N = 3). The drive lines terminated at the mast. The crew lines extended through the base of the mast so that the kite could be controlled by a crew member in the “cockpit”.
The prototype was proportioned to be mounted on a dinghy with the centre of lateral resistance at approximately mid-depth of a keel extending below the hull.
The aims were to demonstrate:
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The use of crew lines to adjust the length of the control lines.
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The use of a spring to balance the self weight of the boom.
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To remove the “sticky” tracking when the kite lines were at a low angle.
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To reduce the number of pulleys in the biasing arrangement.
Outcomes:
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The prototype successfully demonstrated the use of crew lines to manage the length of the control lines.
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The prototype successfully demonstrated the use of a spring to balance the self weight of the boom.
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The prototype successfully demonstrated that by correctly proportioning the length of the boom and mast it is possible to avoid the "sticky" tracking when the kite lines are at a low angle.
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The system for winding the control lines in and playing them out to match changes in the length of the drive lines was successful so long as tension was maintained in all of the lines.
- The system for transferring load from the control lines to the drive lines was successful so long as tension was maintained in all of the lines.
Conclusions
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The final two items listed demonstrated that further work was required on the system for adjusting the length of the control lines as the drive lines are played out and taken in.
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It was decided to proceed and mount this prototype on a boat.
P5 - Mount v1
A plywood dinghy was built with a mount for the WindFly Rig at the stern above the rudder which was intended to operate as a 'keel-rudder' to balance the lateral load of the kite and steer the boat. Manual adjustment of the 'keel-rudder' was required to balance the lateral load of the kite. A fixed hydrofoil was placed at the bow to offset the bow down trim which would result from mounting the WindFly Rig on the stern of the boat.
The aims of the prototype were to demonstrate the use of a kite to drive a boat using the WindFly Rig.
Outcomes:
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The stern mount and bow hydrofoil were found to be unweildy. It was decided that modifications would be required before sea trial commenced.
P6 - Mount v2
The plywood dinghy was modified to provide a forward mount for the WindFly Rig with keels to offset the lateral component of the kite load and a variable incidence hydrofoil directly below the WindFly Rig to offset the variations in trim resulting from the varying vertical component of the kite load.
The aims of the prototype were to demonstrate the use of a kite to drive a boat using the WindFly Rig.
Outcomes:
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It was decided to proceed with sea trials.
Sea trial 1
Outcomes:
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The dinghy floated in calm water: it was decided to proceed with trials in the wind and waves.
Sea trial 2
Outcomes
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The boat was swamped by waves in surf and the hydrofoil was damaged ... I had been doing too much kite surfing to appreciate the size of the waves.
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Sea trials were suspended and trials continued on the beach.
Conclusions:
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A more effective system was of raising the foils in shallow water was needed.
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A more seaworthy boat was needed.
Flying a kite v2
Outcomes:
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Use of crew lines to indirectly manage the length of the control lines to fly the kite was successful.
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Use of a spring to balance the self weight of the boom during kite flight was successful.
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The proportioning of the lengths of the boom and mast to avoid "sticky" tracking when the kite lines are at a low angle was successful.
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During the beach tests the boat heeled away from the kite and towards the wind, demonstrating that the effective point of action of the kite load was below the point at which the hull rested on the beach i.e. the boat responded as if the kite lines were connected to the centre of a keel which extended below the boat.
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A larger kite was then attached ... and during a gust the rig mounting broke.
Conclusions:
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A system of limiting the maximum kite load should be incorporated.