ITW Ultafoil 15: summary of modifications for improved Bft 5 stability
- Bridle length increased to 3.8m
- Centre bridle line reduced by 1cm
- Tail increased to 8.5m
- Vent through put increased by 200%
- Keel vents added
The modifications of the kite as supplied increase the stability of the kite in Bft 5.
Conclusion. Although there are a series of tail modifications to explore I think I can draw some conclusions. Despite its claimed wind range of 5 to 30mph this kite is best flown in lighter winds. It has an inherent instability in gust or turbulent flow which increases with wind-speed. It is very sensitive to side draught and, although it has not inverted in turbulent flow it has displayed alarming weaving culminating in wild swings across the wind in speeds over 15mph. As wind speed picks up this kite requires ever greater space to fly in. At 20- 25mph it is liable to make sudden arcs toward the horizon. (see 0’51”, 1’43” and 2’02” in clip above)
As a light wind kite it is a pleasure to fly with a well balanced pull to lift ratio. It will lift 600g happily in Bft3.
The claim to have ‘updated’ the flowfowm is wide of the mark. Given the flowform patent goes back to 1973 there is nothing of the knowledge gained by KAP fliers over the years built into it. The kite is sold as ‘perfect for KAP’ and yet shows few characteristics desirable in a photographic lifter, it is uncomfortably jittery in the top half of its declared wind range.
The modifications developed by Christian Becot for the Sutton Flowform are effective in reducing the severity of movement in gust and extend the upper wind range of the Ultrafoil 15.
This aerial shot shows just how poor the stock kite (top left) is at keeping a down wind line in Bft5. Wind vector is bottom left to top right in the picture. It is very common for the wind to follow the banks on the washes- did Vermuyden take the dominant wind direction as a cue for the diversion of the Ouse waters?