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Author Topic: Center T  (Read 1415 times)
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cojack_2107
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« on: July 15, 2010, 06:01 AM »

Hi guys...im new n realli curious... the center T for stunt kites r often internal ferrule... but after i build my kite... i kept breakin 2 carbon tube when using internal ferrule... Cry i used 7cm graphite rod..

Guys i nid suggestion... some help?
« Last Edit: July 15, 2010, 06:15 AM by cojack_2107 » Logged
Will Sturdy
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« Reply #1 on: July 15, 2010, 07:05 AM »

What type of spars are you breaking?

I'd use a longer ferrule. For lower spreaders I use a 4" (~10 cm) ferrule. This spreads loads more Make sure it is centered in the center tee - The spar you glue it into won't have half of the ferrule in it. Using R-sky center tees, I insert 1.75" into one end and glue it. The CT is .5", so there is 1.75" left to slip into the opposing spreader. Do make sure it is glued well - if it slips, that can be an issue.

Make sure it is the proper size - if the ferrule is not a snug fit, all of the force is on the tip of the spar and tip of the ferrule, which concentrates stress and can cause breakage.

Sand both ends of the ferrule down some so there is no ridge. The ridge puts lots of stress on a small area, which is not good

Make sure the spreaders are strong enough. What size/design/weight kite is this?

Is the bridle properly tuned? If the inhaul is too long, that can put lots of force on the center tee as it will flex more there since there's lots of force and little support. One way to reduce this is by attaching a line between the ends of the standoffs to prevent the spreader from bowing much.
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cojack_2107
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« Reply #2 on: July 15, 2010, 07:17 AM »

Its my DIY kite 'orange' from Simo Sivonen.. i guess the size of the ferrule is an issue..its abit loose.. for the tube.. thank you so much for the info.. it helps alot!!.. Thanks once again
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mikenchico
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« Reply #3 on: July 15, 2010, 07:29 AM »

Are these Pultruded Graphite Spars? If so they do not work well with an internal ferrule, pultruded spars should only be used with an external ferrule. GWTW doesn't show any externals that would fit 7mm spars though.

Your option if you can't find an external would be to re-inforce the rod in some manner, thread wrapping with epoxy is the prefered method.

 
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cojack_2107
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« Reply #4 on: July 15, 2010, 07:35 AM »

Yes its a pultruded graphite...hmm... so after i some thread wrappin..i can use internal ferrule?? or still external??
how do i really thread wrap it?? closely together or leave a few inch??
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Will Sturdy
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« Reply #5 on: July 15, 2010, 07:49 AM »

What I've done when thread wrapping for reinforcment is wrap thread tightly in a spiral about 1/8 apart a few inches past where it's needed, secure it, and then spiral in the opposite direction back so it gets a diamond type look to it. Soak all the threads in epoxy or CA to get them to stay put.
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mikenchico
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« Reply #6 on: July 15, 2010, 08:02 AM »

After wrapping you may get away with an internal, your only option once wrapped.

The problem is with pultruded rods all the graphite fibers are aligned down the rod length so splitting forces from the inside are all directed at the epoxy matrix, the weaker part of the rod. On wrapped tubes the fibers run at very slight angles but enough to avoid splitting from the enternal force. Pultruded tubes are pretty reliable with crushing forces which is the dominte force an external ferrule imparts.

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ko
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« Reply #7 on: July 15, 2010, 03:51 PM »

my 2 cents? well your going to get it anyway! get hold of are host and order rods and ferules  that will work for you  steve@gwtwkites.com
« Last Edit: July 15, 2010, 10:12 PM by ko » Logged

have fun kurt
JimB
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« Reply #8 on: July 15, 2010, 09:25 PM »

When working with pultruded spars what you want to do is use external ferrules for the leading edges and an external ferrule for the spreaders at the center tee.

You also want to load the spreader ends of the lower spreaders with either Micro Carbon or Fiberglass.

« Last Edit: July 15, 2010, 09:27 PM by JimB » Logged
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