Fiberglass rods are found in the great majority of affordable sparred kites. But you know me, this is not just a dry technical discussion of kite construction! I have done a spot of research, to uncover just a few extra snippets of interesting info.
The low cost of fiberglass keeps fancier alternatives like carbon fiber or graphite from dominating the manufacturing and sales of kite spar material.
Carbon fiber is wonderfully light, stiff and strong. As it eventually gets cheaper, I suppose it could even become the 'bamboo' of the 21st Century, as far as kite making is concerned!
But for now, fiberglass is cheaper, with very respectable properties for making things that fly.
Now to mention a couple of kites constructed with fiberglass spars, that we have flown.
We had a Windjam Delta a few years ago, a mid-sized typical store-bought kind of design. There it is in the photo over there...
This Delta flew straight, and had a reasonable wind range. Not to mention a nice high line angle. We eventually lost it, but that's another story.
Point is, a modern rip-stop nylon kite with fiberglass spars is very durable and reliable in good flying conditions. Some designs are better fliers than others. Rods made from fiberglass bend and can take quite some punishment, like careless handling during transport. Or an inexperienced flier managing to smack it nose-first into hard ground!
Some time ago our family visited Singapore and it was there that I flew my brother-in-law's Light-Wind Eagle. That's it in the photo. True to its name, this fiberglass-sparred Bird kite did a very good job of staying up in quite light air.
It's hard to describe the exact configuration of this design without having it here right now to look at. Suffice to say, the long bowed fiberglass spreader kept the very realistic wings outstretched.
At the crowded park where we flew, we spotted one or 2 other identical Eagles. Hey, if you can't fly like a bird, why not fly one on the end of a string!
The 2 most important parameters of spar materials are weight and stiffness. The size, sail shape and desired wind-range of a kite determine the stiffness needed. From there, the lighter the better, although the very lightest spar materials will also make your wallet lighter...
The nice thing about man-made materials like fiberglass or graphite is the great homogeneity of the rods. This means weight and stiffness are very uniform along the entire length of such a spar. Unlike a typical length of wooden dowel from the local hardware store! Pro kite-makers select dowel carefully, making sure stiffness is very similar on both sides of the kite.
Personally, I like to file away some wood to bring a newly constructed kite into perfect trim!
While on the topic of rods, I should mention hollowed-out rods or tubes. These represent a further weight-saving for a given strength or stiffness. But solid rods are fine for small to medium sized designs. However, they are much heavier than wooden dowels of the same diameter.
Companies that manufacture rods from fiberglass don't just sell to kite people of course. Just about every application that requires a flexible rod now has something already available in fiberglass. Beach tents, golfing flag-poles, you name it! In fact, some of these have actually ended up in large home-made kites. For example, fishing rods.