Arc
From KiteWiki
An Arc or Twinskin is a particular design of depower kite pioneered by Peter Lynn.
Contents |
Design
The design is basically a long rectangular aerofoil shaped wing without bridles, but with rigid spars between the leading edge and trailing edge at the wing tips. In flight, the kite forms an arc shape with a fair amount of the surface actually vertical at either side, hence the name.
The main lines connect to the front of the kite, and the steering lines (or back lines) to the back. The steering lines connect to the control bar ends and the main lines go to a trim strap that connects via a depower rope to the chicken loop which is hooked into the flier's harness. An Arc or Twinskin therefore has to be flown with a harness to take advantage of the depower available, but can be flown unhooked by the more experienced rider.
A particular feature of Arcs is that when flown, the air inside them is sealed in by a clever arrangement of one way flap valves. This also means that unlike fixed bridle foils they need to be inflated before being launched.
Inflation
Inflation is achieved via a wide zipped opening that is held open into the wind until kite is fully inflated, then fastened before launch. The internal pressure holds the kites shape, which replaces the bridles. This design makes the kites very resistant when hit by gusts as the kites retain their shape well, but can open up at the tips to allow the gust to be absorbed. In the same conditions, a fixed bridle or depower foil would catch the gust and loft you or cause you to let go. If you manage to hold on the kite can still become unstable and tuck or luff, which can cause problems if kite falls back into power zone.
Auto Zenith
Another benefit of the later arcs is the Auto Zenith feature. Simply put, when you are hooked in, you can let go of the bar, and the kite will automatically find it's way back up to the zenith, i.e. above your head. This is the safe zone, and it means that if you have fallen or taken your eye off the kite, it will not suddenly shoot into the powerzone, but will gently drift up to safety.
One note of caution with auto zenith, if you unhook (on purpose or accidently) and let go of your kite, it will fly on its own. The bar will give enough weight under the kite to allow it to auto zenith, and if the wind picks up, the kite will fly away (not crumple and fall like a fixed bridle or depower kites). You will therefore need a leash to attach to the chicken loop, but make sure that the leash has a safety quick release.
Launching/Landing
You will need to learn a new technique for launching/landing arcs.
Launching
Once you have opened out the kite with the underside facing up, place the spars in the wingtips, put the tip that the safety is attached to upwind (in the direction the wind is coming from) fold the tip over slightly and weigh it down (with a sandbag, pebbles or a full litre bottle), open up the inflation zip at this end, attach lines as directed. When the kite is fully inflated it should look like a pump up matress. The more you inflate it, the easier it will be to launch, remembering that nderinflation is the main cause of dangerous bowties (and an uncontrollable kite).
Close zipper and go to the bar, hook in your safety leash and chicken loop, depower the trimmer, make sure that loose lines are not tangled around your feet and whilst the lines are still slack, walk round to about 45+ degrees between your kite and the wind. The leading edge of kite should be further away and trailing edge closer to you. Walk away from your kite, as the downwind tip raises it will catch the wind and kite will roll up into the wind quite quickly. Be prepared for kite to pull, but you will need to make some input by pulling on the bar and steering to take it to the edge of the wind window. The pull on the bar should slow the kite and hold it's shape as it completly inflates. Hold the kite at the edge until it feels responsive to your input, then guide it up zenith.
Landing
Landing is best done with a helper, depower the kite and take it down to the edge of the wind, get helper to grab the spar on bottom tip, as they grab it run toward them so rest of kite flags out downwind, then you can either undo the deflate zip and fold the kite to roll it up, or if you are taking a short rest, put the kite down in the launch position ready for next flight. Make sure safety is pulled when the kite is down and that it is secured on kite stake or similar, in case the wind picks up and shifts the kite.
If you are alone or have no competetant helpers, you can either, if wind is light, grab the rear lines and reverse the kite down. This can be dangerous if the wind picks up because the kite is in the power zone and is capable of massive pull. The other way is to take the kite to the edge of the wind window, and then pull the safety, this can look quite scary, but the kite will flap about and slowly move round until it is in front of you.
It is possible to pull the safety while kite is above you. This may stop the bar from flying too far up the lines, but may also cause tangles as the kite comes down. Once the kite is down, secure the safety leash, then secure the kite.
External links
http://www.peterlynnproducts.com/pdf/tsman.pdf - The original Peter Lynn twinskin manual.
