8 Foot Barn Door Kite
by Bill Freeman
I have decided to build an 8 foot barn door kite. (I recently built your 48 inch with great success.) I will be using Dacron for the sail. I have found a place where I can order solid fiberglass rods in 96 inch lengths.
My question is: what diameter solid fiberglass rod would be required in order to assure a sturdy framework for a kite this size? I would only fly this kite in light winds, but I realize gusts happen and I want to be sure the framework could handle them. The ones I have been looking at are 0.187 inches in diameter - would this be adequate? I haven't been able to find any specifications for rod diameter used in barn door kite frameworks anywhere. Thanks in advance for any info.
Glad to hear of the Dowel Barn Door success! The extra rigidity of the 3-way frame is a bonus in higher wind strengths. Although I don't work with fiberglass myself, a little research turned up some helpful info. It appears that solid fiberglass rod is considerably heavier than the same diameter dowel and it is not as stiff. This is not good for performance. Particularly for constructing a light wind kite as you intend to do.
Given that you use the same or slightly larger diameter fiberglass than the dowel spec, the extra weight would mean the big Barn Door would need a few extra mph of wind speed to fly. It would be less stable, and would experience more bending towards the top of its wind range. Considering that the Barn Door is relatively stiff anyway, this might not be a huge problem though.
I think the kite would fly, but you would get far more satisfaction from it if you went with better spar material. Here are some options...
- Just scale up the dimensions and stick with wooden dowel. Brass or copper tubing can be used to join sections if necessary. Followed by some winds of tape to keep the join together and help prevent splintering under stress. Alternatively, check out the 2-Skewer Barn Door plans and do something similar with short lengths of dowel at the joins. This approach doesn't add a single item to your materials list!
- Fiberglass tubing is both lighter and stiffer than solid fiberglass. It generally weighs about the same as wooden dowel of the same diameter. However, it's likely you will have to join sections together to make up the required length. Also, the tips can be rather abrasive and should be capped so they don't damage the sail pockets and corner straps. A bit of sanding, followed by a few winds of insulation tape would help here.
- Carbon or Graphite tubes are not as expensive as they used to be. But being even stiffer than fiberglass tubes, you might not be able to put much bow into the horizontal spar!
Personally, I'd lean towards good old wooden dowel! Double your existing kite and double your success...
Go to kitebuilder.com, click on Kitebuilding supplies
then click on the category FRAMEWORK
for plenty of spar materials available online.