Peter Blackmore and I are looking at the ‘soft’ kite options including modification of existing designs. There are occasions when soft kites have a clear advantage in deployment, they pack small and are not fragile in the way sparred kites are. Having spent yesterday struggling in Bft 2 to raise a camera for more than a few minutes with a Sutton FF30 and Explorer 2.7 I have to accept the soft kites are a compromise between utility and wind range. Get one in a good matched wind-speed and they are the best thing in the sky, get it wrong and you either have a fight on your hands to get it back or the sickening drop of a collapsed wing.
Flying a powerful kite in a stop start light wind is a nervous experience, even more so with a camera hanging off the line. Midsummer Common Cambridge is often tricky for kites as it sits on the valley floor, it has the advantage of being fairly quiet ( you get the bothersome dog now and again) and if a camera can be raised plenty of interesting detail may fall under the lens.
I’m looking for the best of what I can only describe as ‘imperfect devices’ which are characterised by poor adaption to variable to wind speed (wind range) and difficult wind shadow launch behaviour.
After months of patient work the best off-the-shelf soft lifter for stronger winds is the KAPfoil 1.6, next in lighter winds, is the Explorer 2.7. The variables explored with soft kites:
- Angle of attack (AoA)
- Cell wall venting
- Cell mouth profile
- Wide or tall aspect
- Keel size and Becot ‘window’ mods
- Trailing edge vent
- Tail and drogue
- Pull and recovery method.
What we learned by observation of the 3 off the shelf designs and various adaptions from them:
- Weaving can be cured by tail vents or a towed tail/drouge.
- A drogue works only if correctly sized and flown at the correct distance
- A train of drogues is a good substitute for a tail
- Deep keels may not be necessary (the Becot ‘window’ demonstrates this)
- Cell mouth is usually square
- A flat camber to the top chord skin is as effective as a curved one
- A thin chord creates more pull that a deep one
- 1.6 or 1.5m sq is a good size for Bft 4 and 5
- 2.7 sqm is just big enough for Bft2
- Wider than tall aspect flies steeper than the opposite
- A flat angle of attack reduces pull but is unstable in higher wind speeds
- Cell wall vents don’t seem to do much
- The rake of the top leading edge over the bottom (usually 30 deg) may be varied
- Taller than wide aspect needs venting in top and bottom skins
- Wide aspect needs a Y line and tail/drogue to reduce yawing.
The big disappointment was the Merry designed Ultrafoil 1.5 which needed a great deal of modification to be stable in Bft 5 and even then was a handful.
In Bft 5 the KAPfoil 1.6 is in a class of its own, the Explorer 1.6 does well in Bft 4 but ultimately is pushed over by increasing wind speeds, the KAPfoil is not. The only serious drawback with the KAPfoil is its powerful pull requiring careful handling in recovery. It requires a tail and is thoughtfully supplied with one of adequate length for Bft 4, doubling the tail for Bft 5 is helpful.
The Air Affairs Sutton FF30 is still the best light wind lifter with a wide wind range but sadly no longer made. Ivo van Olmen’s Explorer 2.7 is a good replacement flying at a shallower angle than the Hatboro wonder. It can collapse in lull, and needs careful attention to keep aloft in very light conditions, a sparred kite can glide and pull up but a flowform can only work if kept pressurised with constant line tension, not easy in a confined space. Even a modest 300g Filalu rig comes down quick when the wind dies. The rig weight gets a parachute effect from the flowform but the sink rate means running backwards to keep it from dragging into the ground.
The Explorer2.7 is workable in Bft 2 but hastly line hauling was needed when lull killed the lift.Even with very little height a montage of the scene below is possible. Things got a bit scary as the wind dropped…
I can honestly say the 8’or 9’Delta and 8’Rok out perform soft kites for KAP. Today conditions are much the same and a DL R8 launched easily and hauled not one, but 2 cameras aloft for an hour.
The softs win for travel, but at a price of light wind performance and careful recovery technique.