Survival kite

Posted by: Tjin

Survival kite - 06/15/02 11:28 AM

i found this "survival kite" on the web , they say that this is kite a great locator for SAR units and is visible on radar and bla bla bla, but is it ? i mean a kite with only 160 feet of line doesnt come high enough to be visible for radar, so is this another commercial attemt to sell junk or does it actually works ?
Posted by: aardwolfe

Re: Survival kite - 06/15/02 06:11 PM

I don't see where on the website it says it only comes with 160 feet of cord, but you could easily supplement that. Even if you couldn't, I just did a quick back-of-the-envelope calculation. Assuming your 160 feet of cord went out at a 45 degree angle, the kite will be about 113 feet above the surface. Let's say it's not that high; make it 90+ feet to equal 30 metres above the surface. How far away can it be seen by an observer on the ground? If my arithmetic is correct, it would be about 20 kilometres (12 miles). The same arithmetic shows that a 6' tall person would be able to see about 5 kilometres (3 miles) to the horizon. So the kite would increase your range by a factor of 4, which isn't bad. Even more important, the total surface area from which you could be detected would increase by a factor of 16. <br><br>(The math isn't difficult if you understand the theorem of Pythagoras for finding the lengths of the sides on a right triangle, a^2 + b^2 = h^2. One side of the triangle, a is the radius of the earth; the hypotenuse h, or long side, is the radius of the earth plus the height of the kite above the earth. The remaining side, b, is the distance from the kite to the horizon, ie. the distance from which it could be seen by an observer on the ground.)<br><br>From Paul Tawrell's "Camping and Wilderness Survival", p.91, there is a formula for doing this. Take the square root of the height above sea level in feet (it's in the section on water travel/Ocean Navigation), If the kite is 100 feet above sea level, then the square root would be 10. Multiply this by 1.15 to get the distance in miles to the horizon. So according to this formula, a kite 100 feet above sea level would be visible from 11.5 miles away. Otoh, if you were 9 feet tall, your hat would only be visible from 3.45 miles away. :-) For a 6' tall person, the horizon is 2.8 miles away. (Which is pretty close to my calculation of 5 km.) <br><br>For those who are interested, a good rule of thumb is that 100 km/hr = 60 mph, and the metre was originally defined to be 1/10,000,000 of the distance from the equator to the North Pole; Hence, the circumference of the Earth is 40,000 kilometres. <br><br>"It's not the bullet with your name on it you have to worry about; it's the piece of shrapnel addressed to 'Occupant'."
Posted by: Chris Kavanaugh

Re: Survival kite - 06/15/02 07:41 PM

Aardwolf did a spendid job of explaining the long range benefits. Let me point out another factor, wave action. We memorized the Beaufort scale to determine wind velocity on the surface. 0 is "sea like a mirror" My chief had us stare at a toilet. "That is sea like a mirror, gentlemen, and flushing same, that is reality." 160' in a rolling sea is a tremendous advantage. Sometimes a rescue unit can be literally on top of a survivor before spotting them. The kite is made of metalized Mylar, same stuff as the birthday balloons. Yes, it is radar reflective.
Posted by: Anonymous

Re: Survival kite - 06/16/02 07:47 PM

A kite is a great idea. It would be easy to make a kite yourself from a piece of a mylar space blanket, some duct tape and string, which could all be parts of a mini-kit. The snag is the sticks. The comercial kite gets around this problem by making their kite inflatable.<br><br>It seems that there is a lot of room for some clever inventiveness here.