Foil or parafoil kites are well represented in kite sports. For an AWE use, these (and not only) kites could be assimilated to blades for rotary AWES. Two main wing designs are used: closed cell and open cell.
Closed cell vs. open cell foil kites
Closed cell and open cell foil kites share a bridle system and have a similar internal structure created with the cloth battens that hold the top canopy to the lower canopy.
The difference between an open and closed cell foil is whether or not the leading edge of the kite is open so you can see the individual cells of the kite.
A closed cell foil has the front of the kite closed off and has a series of baffle ports that allow air into the kite. When the kite is leading edge down in the water the baffle ports are closed off on the inside of the kite with flaps of fabric. This allows the foil kite to be relaunched off of the water. They are commonly used for kitesurfing.
A open cell foil kite has openings on the front of the kite. These will fill the kite with water when it is crashed. They can also be “over-inflated” with excess pressure when gusts are encountered then partially collapse when the gust dissipates. They are commonly used for snowboarding and landboarding.
Advantages of foil kites
- Very good for light wind conditions
- Very good upwind capability
- Fast kite speed
- Stable and predictable in the air
- Compact (packed) compared to an inflatable kite of the same power
- Easy for a novice person to assist with landing (given appropriate instructions)
- No pump is required
- Generate more power than inflatable kites (e.g. a 10m foil can have same power as 14m inflatable)
- Quick to launch (if no tangles)
Disadvantages of foil kites
- Complex bridle system that can get tangled
- No flotation - the kite can sink if it is crashed onto water (don’t crash it!). Closed cell foil kites do float for a while.
- Some older models can be difficult to use - e.g. wingtips fold
- Less durable than an inflatable kite - more prone to damage from hard crashes
Some comments mention some closed cell foil kites.
Technical specifications of Flysurfer VMG:
It looks like SkySails uses closed cell kites.
Does anyone know if this (closed or open cell) affects the lift to drag ratio and lift coefficient depending on angle of attack?