New Tech Kites

kchunks · Posted: Fri May 12, 2006 3:36 pm Post subject: Kites 201 help

I figure I am beyond a 101 course so I am calling it 201. I have a few questions that pertain to kites in general, not just stuff by NTK.

What does an 8' stunt kite do or not do that seems to make it more desirable than a smaller one? Is it just that it flys a little slower and is that always the case?

What is so great about polyester and why is it more expensive? There is a tent manufacturer that used mostly polyester but has now abandoned it for nylon like all other tent companies. Their logic was that it (polyester)didn't fade, didn't stretch when wet (not a big deal for kites I presume), and didn't degrade like nylon when exposed to UV. Nylon is a stronger material initially, but it loses about 70% of that after the first 100 hours of UV exposure. Regardless, a polyester tent did not cost any more than a similar nylon tent.

What is a pultruded frame exactly? Does it just have the bulky ferrules?

What are the pros and cons of a carbon vs fiberglass frame?

What is the difference between an active and a three point bridle? It seems that they are both adjustable.

What is this "pitchy" flying that I am hearing about?

Apparently the difference between a sled and a parafoil is that sleds have spars and parafoils don't. Is the skyhook just a parafoil with a built in tail? What makes flowforms so special? Is any one style better for hoisting laundry than another?

Flight school tells us not to fly near traffic. How near? There a some major streets that run by the parks where I like to fly my stunt kites. Is it due to distracting the drivers or more just in case something happens the kite doesn't end up in the road? (Granted, one place where I fly, if the lines broke and the kite went towards the road it would get eaten by power lines first.

That about does it for now.
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Kevin

Albert · Wind Seeker Joined: 18 Apr 2006 Posts: 9

Well, it looks like you're a little ahead of me here, Kevin, but I'll add what I can.

I'm wondering about polyester versus nylon too. I think all you said is true, except UV strength loss in nylon may be a litle high. There may be a few other considerations, like abrasion resistence and strechiness. Even if nylon has an initially stronger tensile strength, if it stretches more it may distribute stresses on the frame better and yield a stronger kite. This is pure speculation on my part. However, I find it interesting that all parachutes I know of are made of nylon, not polyester. I also find it interesting that kites aren't using the Zero-P (zero porosity) fabric that parachutes have been for a while now. It made a HUGE difference in parachute performance. You might want to check out www.paragear.com if you're interested in the parachute side of things.

I think this site will help answer some of your questions about pultruded graphite, fiberglass,etc.:
http://www.woolmer.co.uk/tech.html

In short, fiberglass is cheaper and more flexible. Graphite has a higher strength to weight ratio and is stiffer. Speaking of tents, note that all I know of use fiberglass or aluminum poles, not graphite. Graphite is strong, but stiff. It will break before it bends much. I think that's part of the wrapped and tapered tubes thing. It allows the small end to flex more, which in turn could let something like a wing tip to flex more. Sort of variable geometry, like moving the ailerons on a plane. In addition to lowering weight, it can strengthen the end that gets the most stress, for example the lower spreader at the center tee. An anchor point for a flexible member is a natural stress riser. All my 5mm pultruded lower spreaders have broken at the center tee, this is to be expected. Tapering the rod on that end spreads the bend out and lowers the stress at the tee. Its sort of like the double butted tubing that has been used in higher end bicycles for years. Note that my suggestion of inserting a short piece of 3mm solid carbon rod in the end of 5mm pultruded tube in a previous post essentially does the same thing.

I've been studying bridles some too. Adjustments really do make a difference on my Pyro XS. If you want the straight scoop, I suggest the man as far as I know invented the active bridle:
http://www.andywardley.com/kites/bridle/index.html

I've been studying it, but haven't tried it. It could take a lot of trial and error. So far its not high on my prioity list while I just try to master the basics. Maybe someday. One thing I would like to see however, is an easier way to adjust the bridle I have. It takes some finess with a tight radius bridle line larks head knot. Its just not easy to do in the field accurately, at least for me yet. What we need here is a gadget to make it easy for everybody. I thought about something like a cord lock, you know those barrel shaped gadgets with a plunger you push to adjust the hood on your parka or a stuff bag. The ones I have are made for cord, not kite line and don't hold.

As far as the pitchy stuff goes, I think its rotating the kite nose to tail. Think airplane terms, and I haven't got anywhere near that yet. So factor that in when you consider my comments. An Axle, my one and only trick so far, is a yaw trick, rotating wing to wing. My Pyro XS seems pretty balanced, it will float rather than glide nose or tail first. I just can't get that sucker on its back. I'm starting to experiment with tail weights now. Three 1/4" nuts on the spine at the tail seem to have helped. Hey it was a cheap experiment. Now I'm thinking of wrapping some lead free solid core solder around the spine next.

Sorry, I can't help much with your other questions. Maybe some others will chime in.

Albert

kchunks · Posted: Mon May 15, 2006 1:02 pm Post subject:

Thanks for the reply, Albert. I am curious to see what Chris has to say on some of this. The nylon uv degredation is what a materials science engineer that worked part time at the storetold me when the polyester tents come out. I actually think he told me that it degrades 75%, but I was being conservative as it has been a while. I imagine that improvements have been made across the board. I am curious about that nylon; I wonder if my Ozone foil is made out of the non-porous stuff. We'll see what the authorities have to say on the rest of the matter.
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Kevin

Chris · Posted: Tue May 16, 2006 2:16 pm Post subject: Re: Kites 201 help

Chris · Posted: Tue May 16, 2006 5:20 pm Post subject:

More information about wrapped tubes from Marieanne Trennepohl at SkyShark:

Wrapped tubes are made by hand using pre-preg carbon cloth which varies by content of carbon, modulus and resin. By adding plys or layers we are changing the weight and strength of the tube. These layers of cloth are cut to exact size and are then wrapped around a specific size mandrel at a certain place on the mandrel . The mandrels with the wrapped material are now placed in a machine that spins the mandrel and tapes the tube with a cellophane looking material that compresses and wraps the material. This is what gives the spiral effect you see on the tubes. This is also the cause for friction and wear on bridle lines. The tubes are then placed in a oven to bake (cure) for a certain amount of time. Then they go into a machine that breaks the mandrel loose from the tube. They then strip the cello material off the tube and cut it to length. If we are making any of the new Black Diamond series tubes we are then putting the tubes in a centerless sanding machine that very precisely takes off the ridges left by the binding process to make the tubes smooth. We then paint the tubes with a special clear-coat paint and bake them once again to harden the paint. The tube is then printed to identify it. I hope this gives you a better idea of what goes into making one of our tubes.
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"Fly a kite for a child and you entertain them for the day. Teach a child to fly a kite and you entertain them for life."

kchunks · Posted: Tue May 16, 2006 5:45 pm Post subject:

Chris, thanks for the replies. It would really take some doing to get my kite onto the road (if there were a problem), but I do understand how it could be a distraction. I agree, I think that tent manufacturers are using a thicker polyester. Thanks for all of the clarifications.
_________________
Kevin