I found some video which about how to relunch 5th line kite.
In this video, it says I have to keep the tense on 5th line in order to increase the AOA of kite, and pull the turn line(back line). but one of my friend said the 5th line just help me lay down the C kite on the water, and make it easier to go to the relunch position(the edge of wind window).
So I am very confuse right now. Should I keep the tense of 5th line and also pull the turn line, or just olny pull the turn line?
I was wondering could any one tell me how to relunch a C kite?(The kites I am using are Touch and JN PD3)

here is the video I found.

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You need to play the lines (fifth line and rear lines) like a puppeteer. You should go into shallow water on a low wind day and just practice pulling on the fifth line just enought to get the kite to start to fall onto its back, and then grab a rear line and get the feel of how hard to pull and when to ease up, etc. If you do that for an hour or so, it will be obvious to you, what everyone is trying to describe.

I've been flying Torches for a few years. Kite LE down relaunch:

Pull in 5th line to get kite to tilt. You need to pull in quite a bit of 5th line, 2-3 arms length.
Do not let kite roll fully onto its back, aim for about 45 degrees.
Pull on one side of the bar.
Kite will start to move round.
As it starts to relaunch start letting out 5th line.
On windy days you can keep a bit of 5th held in to depower the kite as it goes up.

If kite is fully on its back then it can be a PITB to relaunch which is why I ride suicide when unhooking, Torches have more than enough depower.

In answer to your question yep keep 5th line tense, you hold the kite in the tilt position using the 5th line, the wingtips will catch the wind and it'll move round to relaunch position

Thanks you guys give me very useful advise, I will try your way next time.

cheers~~

if you have a modern c kite don't worry too much about this, you can just pull a rear line to relaunch it unless the wind is really light

when i use the JN PD3, sometimes i can just pull the rear line to relaunch(the leading edge is on the water). but in some case, even i pull the rear line quite hard, the kite still sticks on the power zone and doesn't want to move to the edge of wind window.
So, I think in this case, I may have to pull the 5th line to let the kite lay down a bit, make it easier to move to the relaunch position?