Stunt Kites :   Tips and Tricks  

Winter Kite Flying 


 
A collection of some (old-time) cold weather flying posts from alt.rec.kites, assembled in an order that will be easy to follow. In an effort to make the threads easier to read, we have removed the names and headers from the original posts. Don't let winter get you down when you could be flying on a crisp sunny day on a delightful snow covered field.

The Thread :Cooolllddd Kite Flying- Spar Question

>hi!
>Anyone have any points of advice for flying in cold weather??? Do graphite spars get too brittle, or is it just fine?? (I'm living in the icebox of Minnesota ; )

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No problem, the spars will out perform you in cold weather. The rip stop does seem to get a little more vulnerable in temp colder then 15 below. Dress warm and appreciate the no mosquito zone...

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eP2.jpg (12751 bytes)Had the same questions when I had to build some kites for an Antarctic survey: the kites had to be flown in temps below - 40 degrees C. I don't expect it's that cold in Minnesota but here's what I found.
With a lot of help from rec.kiters and testing in a big freezer I came up with the following: Carbon can easily withstand those temps ( source: manufacturer Exel spars ) Spectra or Dyneema only get stronger in low temps ( info from DSM) You have to be careful with molded connectors: Depending on the material they get brittle and tend to break easily when under tension.


The Thread: "Winter Flying"

>A few people lately (I believe it was Marty and Jeff) have been talking about flying in awfully cold conditions. First of all, where are you guys flying that it is so dang cold?! <G>

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I live in DC, where, actually, it's usually not that cold in the winter. I have no problems flying year-round, though there _is_ an occasional weekend when I decide not to bother bundling up too much. But I've even been known to get out in 32F and colder. I love to fly in the snow. The kites are so beautiful against a snowy white backdrop!

>Second, I've wondered what the effects of the cold and wet would be on my kite (during flight). Would it respond differently? Does it get wet from the moisture in the air and a lack of warmth to draw it out?

When it's cold, there tends to be very little moisture in the air, even if the RH (relative humidity), which is the figure given as a percentage which most people think of as just "humidity" is high. RH is a figure that's based on the actual quantity of moisture in the air in relation to the amount of moisture air can hold at the current temperature. If air cools very rapidly, the RH will rise because the amount of moisture in the air isn't changing, but the total amount the air can hold is dropping. In cold winter airs, the humidity is usually low (not as much heat causing water to evaporate into the air, amongst other reasons). So even if the relative humidity is high, it's not the same as high humidity in the summer, because the air holds so much less moisture to begin with.

So unless you're flying in a falling snow, don't expect your kite to pick up any extra moisture than it normally would. In fact, the kite should fly as it always does. I've never noticed graphite getting any more brittle in the cold...I don't break more spars in the winter. I will warn you that if you fly in a perpetually cold area, the ground will probably be harder than you're used to. ;-) Your own reflexes may also be a bit sluggish, so keep that in mind.

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Actually, I intend to try some winter flying. I'm rather excited that it can be done without damage to the kite. I thought for some reason there would be higher moisture or something that might further damage the sail. (Although why I'm worried about winter moisture while I'm systematically dumping my kite now in lakes learning water tip drags, I don't know.. <) It is good to see there is no damage in winter flying, since most of our best
steady wind is found during the winter!

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>Second, I've wondered what the effects of the cold and wet would be on my kite (during flight). Would it respond differently? Does it get wet from >the moisture in the air and a lack of warmth to draw it out?

Winter flying where I live amounts to flying over snow, generally on a frozen lake in temperatures where none of the water is liquid and thus has no tendency to cause problems with lines and kites. The big problem is having enough wind to fly but not so much you turn into an icicle. This is most generally accomplished by restricting flying to the warm winter days (-10C or so).

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Santa <(;)** gave me a Zephyr for Christmas 92 here in South Bend, IN, and I couldn't wait 'till warm weather to fly it. Early in January, an intensely cold but wonderfully windy (25 mph) day presented itself, and I bundled up to fly my new toy on the quad at Note Dame. WOW, what a blast! It was as exhilarating for me as it was incongruous to the occasional passerby bent against the cold. The air was crisp to say the least, and I got my fill of the three reasons I fly--speed, pull, and noise! I stayed out only 15 minutes, though, and learned a few lessons, which I hereby pass on...

1. It's hard to tie knots, clip swivels, and assemble spars with gloves on, or with them off in a freezing wind. I should have done that stuff inside first.

2. I needed some sunglasses or ski goggles. Keeping my eyes open to maintain constant visual contact dried them out in a hurry, caused me to squint from snow reflection, and I ended up alternating one eye at a time to gain relief.

3. Wearing gloves in hand straps, I lost a little bit of touch and control. In high winds like I had, it was not much of a problem, but it would have been in lighter ones, I think.

4. My sneakers did not afford as much traction as in warmer weather. At least two gusts pulled me several feet when I didn't want to. However, with a pair of skis and an open field, this might be great!

As for whether cold weather is tough on a kite, I say "So what?" I intend to fly the last shred of sailcloth out of each of my kites, repairing them as I go, and then buy another to go out and do the same. It's like keeping a sport scar in a garage--it might look great after ten years, but you haven't had any _FUN_ in it!

Anyway, with a little more foresight than I used the first time, there's no reason why winter flying shouldn't be just as enjoyable as the summer.

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I fly through the New England winter. Boston, being on the ocean isn't as cold as parts further inland, but it does get pretty cold during the winter. I'm sure I look pretty funny, all bundled up trying to move a bridle. First you quickly heat up your hands by banging them together or holding a hand warmer, then you quickly remove the heavy gloves, loosen the bridle and maybe move it. Then back to the hand warmer/and or gloves. Repeat until done...

>Second, I've wondered what the effects of the cold and wet would be on my kite (during flight). Would it respond differently? Does it get wet from the moisture in the air and a lack of warmth to draw it out?

Cold has more of an effect than wet. As Jeff mentioned, the air is usually very dry so unless you dunk your kite into the ocean (;-) you don't have to worry about wet. Cold can make vinyl very stiff and brittle. Move the sticks slowly while setting your kite up and taking it down. Some spars are affected by the cold. There was a batch of Easton 3-30's (the spiral wound ones) that would fail when the spiral wound graphite fibers would come unglued from the aluminum tubing at the core.

I used to use rubber tubing in my kites because rubber would remain flexible in the Winter weather.

By far, the biggest problem with flying in the cold is keeping the flyer warm and to prevent frostbite, but we can talk about that when it's the right time of year. (I realize that South of the Equator it's winter right now, but rec.kiters from the south haven't complained, so I assume that they live in moderate climate areas...).

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>I fly in Cold weather, but I always thought carbon spars were more fragile when cold. >Personally I only break spars in wintertime though the snow is quite soft..

My first thought reading this was "I know graphite is used in commercial jets and the planes get rather cold at 37,000 feet" so I checked with my materials expert (who is an aircraft mechanic specializing in repairs of composites in control devices such as ailerons and tabs, and other parts of the wings, and has also worked in a destructive testing lab -- conveniently he's my spouse, Steve).

He concurred, saying he didn't know of any reason that cold should effect carbon/graphite. He also pulled out a chart "Operating Temperature Ranges for Various Classes of Adhesives / Resins" and none of the epoxies showed significant reduction in ultimate tensile strength (the y-axis on the chart; temperature is the x-axis) till approx. -150 to -200 degrees F. (on the high end, the lines *started* to drop in the 150-200 degree range, with a steeper drop above 250).

I asked if making a tube of graphite would change any properties, and the answer was no.

We talked a little about what is carbon fiber and what is graphite, without any conclusion because apparently there isn't consensus on when you stop calling it carbon fiber and start calling it graphite. He doesn't know much about the actual manufacturing process, saying he thought heat and tension were used, which crystallize the carbon fibers (and the more crystallized they are, the stronger and stiffer they are).

This is all rather general, and to really figure out whether cold is affecting the spars, you'd need to do tests. It would help to know exactly what type of carbon/graphite is used (maybe there's something the expert doesn't know :-), what resin, what curing process, etc. Otherwise, maybe all curious rec.kite readers could keep track of what brand/model of spars break and at what temperature, and after next winter, gather statistics.

>Some spars are affected>by the cold. There was a batch of Easton 3-30's (the spiral wound ones) that would fail when the spiral wound graphite fibers would come unglued from the aluminum tubing at the core.

What I learned is that aluminum and graphite have significantly different coefficients of thermal expansion, that is, the pairing of the two materials was most certainly not based on similar expansion properties. If one batch failed, but others didn't, maybe there's a manufacturing problem. The other thing Steve mentioned about alum/graphite is that in additional to graphite's metal-like property regarding conductivity, it is also metal-like regarding corrosion, and alum and graphite are at almost opposite ends of the chart labelled "Electro-Chemical Series for Metals," meaning they are prime candidates for galvanic corrosion (=dissimilar metal corrosion).
So flyers who like to dip their kites into salt water might think about rinsing off spars or painting the ends so the spars are protected from salts which could cause corrosion. I realize none of this is particularly conclusive, but I was curious and thought I'd pass on what I'd learned.

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Several people wrote to comment/ask about the hardness of frozen ground.....so let's try this again. I interpreted Stein's observation to mean that there was lots of soft snow on the ground and that when he crashed, the kite hit the snow but not the ground (which may or may not be frozen) and that he attributed breakage of spars to the air temperature/spar temperature. So I asked more questions:

Q: If you fly over concrete in summer and winter and crash exactly the same way in each season, but the winter temperature is 0 degrees F, will there be a difference in how many spars you break?
A: Steve thought it highly unlikely that the cold temperature would make a difference (that is, never say never).

Q: If you fly in a park (over soil) in summer and winter, and the ground freezes hard in the winter, and you crash exactly the same way each season, will you break more spars in the winter because the ground is harder?
A: He thought so.

None of this addresses some of ideas brought up in other thread on winter flying, such as slower reaction times on the part of cold kite flyers, etc.


The Thread: "all this talk about winter flying"

>I've seen a lot of posts about winter flying, but none ,that I noticed, have really addressed the issue of temperature and the affect it has on the different materials used in the kites.
>So what happens to a carbon spar at 0 C?

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There were some threads on this, though. Although opinions (I can't recall hard facts being mentioned) differ a bit, I think there's little change to the behavior of the frame and or sail. Remember, that 0 degrees C is only defined to be the temperature where H2O changes state. Why should it have an immediate effect on materials? Many of the composite materials' parameters have a quite flat temperature response (i.e. don't change much over a wide range of temperatures).

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Recently I built some kites for a Dutch Antarctic survey team who will use it to bring scientific equipment up. Therefore I did some research. The question was; does everything stay in one piece in minus 35 degrees? I've found that the carbon rods (In my case carbon/polyester) are no problem. "My understanding is that the characteristics of carbon spar in low temperatures depend mostly on the resin used. I discussed about this matter with Exel people a few years ago. They said the sticks will be "better" in low temperatures. Well, Exel is known as the maker of the best (?) cross country ski sticks on the market."



We enjoyed these posts so much that we thought we could add one or two goodies to this winter flying subject. Although all of them are basic, we've seen people have their days cut short by not trying a few of them. So here's our small contribution to the "cold weather flying" section, even if one tip helps you get in another hour of winter flying ...it might be worth the time to read:

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Don't leave your kites in the car after a day of winter flying. Most of us love to get out on those days when the temp just makes it above 0 C (32 F). We have several of these "melt down" days a year and the snow seems to be wet enough to get water into the line and joints of the kite. After the sun goes down and the temps drop drastically, the moisture in your kites and line tends to expand - mixed with joints that are already stiff from the cold......... Take 'em in, dry 'em out - even if you're going back out first thing in the morning.

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Get some "long johns" from a "work warehouse" or similar place that caters to people who spend 9 hours a day working in the cold.

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Use discretion if flying in gusty winds and respect your kite's upper wind limits, try to use the appropriate kite for the kind of wind you are having. An inexpensive wind meter such as the Dwyer Wind Meter is a handy accessory to have until you get the feel of the winter winds.

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The coat or undercoat ... It should have the hood attached. The fabric should run from below your waist , up over the back of your head. The wind will be blowing from behind you and your neck will stay nice and toasty!

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ICE ... the combinations of strong winter winds and a rock hard crash surface can destroy spars with regularity. A flying area where the surface is covered with snow will help to cushion the impact in case of an unexpected landing.

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Take a lawn chair ... No we're not crazy ... If properly dressed, you'll be amazed at how great it is to sit down and watch other flyers, or just delight in the weather. Break out the thermos of hot coffee, soup or hot chocolate ... and enjoy ! You'll be delighted at how much nicer that snow looks when you're not up to your ears in it at the end of your driveway.


Dress warmly, use caution in cold weather and fly year 'round !

 

theGreedyBrain.com