Kite Making - The Airbra part 2

Assembling the Kite

AirbraNow I had the sail in 4 sections the next stage was to stitch the 4 section together to get the whole sail. However this was also a decision point. One of the outstanding things was the fundamental question of:

Was the Airbow sail 3D or flat?

By this I mean is the 3D shape made just by the spars, or is the sail actually shaped in some way to aid the 3D shape? Up to this point I had assumed a flat shape, but after further thought and discussion with others I decided that the main verticals were curved (although you can't tell from the various Airbow photos).

I then amended the cardboard templates to curve the seams - I removed approximately 1 cm from each side of the seam edge and stitched it together. However I reckoned that the central seem (where the 2 sail halves meet) would be OK straight.

Whilst I was at it I put a slight curve in the leading edges - about 1cm in the middle of each leading edge - then did the double rolled seam. It seemed obvious that I should do the leading edge seams before stitching the 4 parts together.

Once stitched together I could see some accuracy problems - I was slightly out in either my stitching or marking the panels from the card template - as the kite sail wasn't properly symmetrical. But as it was only a little bit out I decided not to worry about it.

The last thing on the sail was to stitch Dacron reinforcement bits onto all the tips (where the spars would attach to the sail).

The Spars

I wondered about what to do with the spars for the Airbra - I knew from the Airbow website that the central spar was 8mm and was custom Skyshark. My first thought was to make one out of 'normal' 8mm carbon tubing from Decathlon (which in fact I did buy), along with standard 4mm carbon for the verticals and the standoffs. Then it occurred to me that I could reuse the spars from my old Revolution EXP which I wasn't using anymore - at least until I have seen how the Airbra works out. The EXP spars were themselves 8mm wrapped carbon, so were at least similar to the official Airbow spars (but I guess not as stiff or strong).

I then made both the 4mm (for the verticals) and 8mm (for the central horizontal spine & the short central vertical) spar end caps out of plastic tubing bought from B&Q, flattened one end a little bit by heating the plastic (to prevent the spar from being driven though the cap), and drilled a small hole for the sail attachment line.

The scary moment was using the soldering iron to melt the holes in the sail in order to attach the end caps - but thankfully this passed off without any problem! I could then use short loops of bridle line to connect the end caps to the sail (4x 4mm verticals, 2 x 8mm vertical and 2 x 8mm central spine).

The next problem was exactly how to fashion the standoff fittings (the ones that connect the 4mm verticals spars to the 8mm central 'spine' & push out the surface of the kite). My local kite shop didn't have 8mm/4mm stand off fittings needed so I was left with trying to make some. Again I turned to my trusty B&Q plastic tubing - this time I cut about 4 cm of the 8mm internal diameter plastic and flattened about 2cm of it. This gave me enough surface to drill a 8mm hole through it so I could fit the Revolution spar through it. I then glued the smaller diameter plastic tube (about 2cm in length) in the open end to reduce the diameter to something line 4mm.

In this way I was able to assemble the whole frame. The Airbra was (at last) beginning to take shape!

The Bridle

At first I thought that the Airbow didn't actually have a bridle - i.e. the flying lines attach directly to the kite at the tips of the vertical spars. However on closer inspection of published photos of the Airbow in flight it became apparent that there was in fact a bridle, and quite a complicated one at that!

Using a mixture of cheap braided nylon line (from B&Q) and left over 'proper' bridle line I knocked up something that looked about right. Basically I connected the top and bottom of each vertical spar, with a loop near the top and another loop near the bottom to attach my flying lines. Each side's bridle was then connected in the middle by a line - but as I had no idea on how slack or tight this connecting line should be I tied it with a slip knot so it could be adjusted when it got it's first test flight.

My thinking was this: if I did away with the bridle and (as I first thought) attached the flying lines to the top of the vertical spars, then a lot of strain would be on the vertical spars - and therefore a greater possibility of breaking them. So I needed the bridle to distribute the strain more efficiently over the frame of the carbon. Am I right? No idea - but it sounds good!

In the end it looked OK, but only time would tell if what I had guessed would actually be OK.........