The Benjamin Franklin Kite
What Was The Original Kite Like?
Most school kids have come across references to the Benjamin Franklin kite used in that electricity experiment. But is anything known about the kite itself?
Fortunately for historians, and I use the term very loosely in my case
;-) Mr. Franklin once wrote a letter to a friend, on this topic. Quotes
from this letter may be found in many different places, although the
text is edited just a little for ease of reading.
Here is a typical quote from the letter, which was written by Ben Franklin to Peter Collinson on October 19, 1752...
"Make a small cross of two light strips of cedar, the arms so
long as to reach to the four corners of a large thin silk handkerchief
when extended; tie the corners of the handkerchief to the extremities of
the cross, so you have the body of a kite; which being properly
accommodated with a tail, loop, and string, will rise in the air, like
those made of paper; but this being of silk is fitter to bear the wet
and wind of a thunder gust without tearing. To the top of the upright
stick of the cross is to be fixed a very sharp pointed wire, rising a
foot or more above the wood."
Neatly folded up there in the photo is a modern large silk handkerchief, plain white as was popular in Franklin's day.
The book Benjamin Franklin: An American Life
on Amazon appears to be a very good reference work on the man, judging by the many reviews.
Now, one day I will get my hands on an actual silk handkerchief, not
unlike the one near the quote up there.
Together with some
cedar wood, I intend to re-create a Benjamin Franklin kite and post a photo or 2 of it here, plus some video of the kite flying.
At first reading, I thought the 'loop' Franklin mentions must be a
string around the perimeter of the kite, to which the edges of the
handkerchief are to be attached. But since he has already specified to
"tie the corners" to the cedar wood tips, it seems more likely that
Franklin was referring to a bridle loop tied to the vertical spar.
Almost the last step before being able to go out and fly the kite.
Flying in those conditions simply isn't safe, and it's not even
clear whether Franklin himself actually performed the experiment he
proposed. That is, hand-flying a kite with a wet string in a thunder
storm, complete with key suspended from the hemp line to observe sparks
or feed them to a charge storage device.
Out In The Field
My collection of real-life Diamond kite stories is worth checking out!
Illustrated with photos and videos, of course.
Take a good look at that old art work up there. Franklin
recommended flying the kite from under shelter, such as a verandah or
door-way. The artist seems to have noted this. Also, handkerchiefs are
generally square in shape, unlike a traditional Diamond kite
sail. The artist seems to have got this detail correct too, depicting
the Benjamin Franklin kite as a Diamond with a square sail.
However, the artist has erred in depicting a bridle loop going to each end of the horizontal
spar... On a perfectly square design like the Benjamin Franklin kite,
it just won't fly like that! Instead, the loop should be attached to the
vertical spar, with the flying line attached a lot closer to the nose than the tail of the kite.
Images, or rather images of images or sculptures of Franklin abound. Here's quite a special one, admired by many photographers...
Photo courtesy of Tony.
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Sep 23, 14 01:22 AM
This day's flying had been anticipated for at least a couple of weeks. A 'drag bucket' added to the tail end of the 2m (7ft) span Carbon and Tyvek Diamond was an attempt to raise the upper limit on the flyable wind speed for the kite. From earlier experiences it seems the unmodified Diamond becomes unstable at around 30 kph.
The first flight was done with the drag bucket adjusted for fairly minimal effect. As half expected, the kite soon started to fly way over to the left and right. So, the wind speed up there must be at least 30kph! This was down at Brighton Beach, but all thoughts of doing KAP soon evaporated, due to the high wind speed. Not to mention the turbulence coming from some high buildings directly upwind.
For a second attempt, the Velcro fastener was re-adjusted to considerably open up the intake of the bucket. The bucket being two Tyvek flaps which come together over the tail-most region of the sail. This had an immediate effect. More stability! Unfortunately, the extra drag also helped keep the kite at a lowish line angle in some of the fiercer gusts. Lots of line tension ensued, with a huge amount of distortion apparent in the sail.
At this rate, something was going to break pretty soon, so I struggled to get the kite down to the sand. After shifting the towing point forward by about 3cm (1") the kite seemed a little more comfortable. When the sail of a Diamond distorts badly, it reduces the amount of effective area below the towing point. This is like shifting the towing point back - adding to the problems of too much wind!
And then the inevitable happened. The already broken-and-repaired horizontal ferrule gave way and the kite promptly folded up and sank to the sand. But not before I had carefully observed every second of the kite's struggles, trying to learn more about Diamond kite behavior in high winds.
Just an hour after arriving home, the weather station at the nearby airport was reporting gusts to 50kph! It was less further down the coast, but I suspect the Carbon Diamond felt the brunt of around 40kph for at least a few seconds at a time.
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