The biggest delta made from this template has a 20 foot wing span (6.1m). Deltas of roughly 6 foot span and smaller can require some extra material added to the trailing edges in the form of a flap or "apron" (best done at the layout stage), and for spans in the region of 4 foot this should be cut into a fringe with cuts at intervals of an inch to an inch and a quarter, to the depth of the line marked S/2 on the drawing below.
|"An eighth of an inch makes all the difference."|
|-the late Doug Hagaman|
|N||nose angle||S||nominal span||C||length at centerline|
|F||length of fin||D||depth of fin||B||towing point position|
|LE||length of leading edge (ref)||L||nominal length of wing spars||SA||spreader strut attachment point|
|· Nominal means measurements are marked on the initial fabric layout prior to cutting, and not after construction.
· The plan view shows sleeves and wing tips as finished.
· Sleeve width is optional, but about 4x the diameter of the leading edge spars is recommended.
· The grain direction on fins can be parallel to the edges, or perpendicular to the center spine, but in the latter case the fin edges need to have extra reinforcing strips (tabling or seam binding) in line with the edges to prevent undo stretching.
· Although the wing tip point is off the kite in the drawing, before cutting it will be on the kite material, located by the primary dimensions C and S/2.
Note also that Tan N/2 = S/2 divided by C.
Use these proportions
|S/2||1.0 to 1.1C||L||0.75 LE||to SA||7/9L|
A rough guide to hardwood wing spars and spines is to use 1/16" of diameter for each 2 feet of span, and use the next size up for spreaders. Fiberglass equivalents are approximately: 1/8"(3mm) wood=3mm fiberglass, 3/16"(5mm) wood=4mm fiberglass; 1/4"(6mm) wood=5mm fiberglass; 5/16"(8mm) wood~=1/4"(6.35mm) fiberglass, but not quite - scale a 5/16"(8mm) wood kite down by around 92.5% to make one in 1/4"(6.35mm) fiberglass.
The maximum length of 1/8"(3mm) diameter wood spars should be about 24"(61cm); 3/16"(5mm) about 36"(91.5cm); 1/4"(6mm) about 48"(1.22m). The maximum lengths are for light wind versions.
Average spar lengths for normal flying would be something like 34"(86cm) for 3/16"(5mm) wood or 4mm fiberglass; 36 to 41"(91 to 104cm) for 1/4"(6mm) wood or 5mm fiberglass, with 39"(99cm) normal for 95 to 98 degree nose angles. For 5/16"(8mm) Ramin, 52 to 60"(1.32 to 1.52m) works, with 54"(1.37m) normal, 60"(1.52m) for light winds.
1. Cut out the two wing halves together, one on top of the other as shown.
Grain: Although I generally prefer the fabric grain in line with the centerline, parallel to the trailing edge, on some designs it is aligned with the leading edges instead, as on my Whirlwind and Wildcard. This is not, however, recommended for stretchy fabric.
1a. Cut the fin allowing for a hem and with a "B" mark on the centerline (long) side. Fins are easier to hem with the grain parallel to the edges. Double-stitch hems wider than about ¼inch (6mm).
Fin grain: If making the fin with the grain perpendicular to the center spine, the edges will stretch because they are cut on the bias, that is, across the grain of the fabric, unless they have extra reinforcing. A narrow strip of ripstop cut along with the grain can be placed inside or outside a single-fold hem and sewn in along with the hem.
2. Mark center sleeve sewing line at 4x the diameter of the spine material from the cut edge. Similarly draw lines showing where the wing sleeves will be folded to, for a 4x spar diameter finished width. Mark spreader attachment point, towing point position, spar ends (adding extra length at least equal to spar diameter).
3. Make reinforcing tapes for both ends of the wing spars, nose and tail ends of the center sleeve, and a towing point tape. Ripstop folded 3 or 4 times is fine for small kites, and made double thick (two layers) for medium sizes.
4. Similarly, make up some spreader strut pockets. At 4x the width of the strut, the foldover at each end is less than or equal to, but not more than, the width. Make sure they're long enough; they can be trimmed after they've been sewn on.
5. Glue the tapes for the wing spar top end reinforcements in position, and make certain your original spar end lines are visible for when you sew.
6. Sew the wing sleeves, leaving a space at the tips for spars to be inserted.
7. Sew the two wing halves together along the line drawn in step 2. Glue on the nose tape.
8. Hem the fin and sew it into the center sleeve aligning the "B" marks. Sew the row nearest the stitching already there first, starting from the "B" mark and running to either end of the sleeve. With that row done, glue on the tail tape. Leaving a gap for the spine at the rear/bottom end, sew the final outer row of center sleeve stitching. Finish sewing the tail tape on, not forgetting to leave the opening for the spine.
9. Glue the towing point tape on with it pointing to the "B" mark on the centerline. Glue on the wingtip tapes. Mark the positions for the spreader pockets, perpendicular to the centerline, and draw lines twice-the-spar-diameter in from the leading edge across each pocket position, parallel to LE, to mark the sewing line for the gap for the spars. Glue the pockets on and draw the line across each showing the gap. Sew all on, remembering to leave appropriate gaps for inserting frame parts.
10. Fit a spine, just tight enough to give a gentle curve. Make sure the two wing spars flex exactly equally (by hand) and install as a symmetrically matched pair (eyeball them). Spines are the same diameter as the wing spars (or their wood equivalent).
11. Fit a spreader so that when the kite is held upside down by its towing point the off-clearance or gap between kite and strut is 0.12 to 0.16 of the distance measured along LE from the nose to the spreader pocket mark. 0.14 is normal; 0.12 is tighter, for light wind efficiency; 0.16 is for fresh breeze kites. Spreaders are one size thicker than spines.
NOTE: don't sew back and forth with tiny stitches at crucial stress points (especially) as this merely produces a closely packed row of perforations through all layers substantially weakening them all.
There aren't many things that can go wrong if the sequence of steps is followed. Symmetry should "fall out" at the end, and the kite ought to fly and handle very well.
As a final check, suspend the kite by the fin without the spreader to make sure the two wing tips are exactly equal. If the wing spars have been checked for matching flex, the kite should fly. If it happens to be too stiff, it can be difficult to launch, but may fly well once up above ground winds.
If it twirls then it is too stiff or the spreader could be too tight. Either try some smaller diameter wing spars, or move the spreader pockets towards the nose, or shorten the spreader if it needs it.
If it's very bendy it might be okay for light wind flying, but avoid gusts.
If the spreader is too heavy, some kites may tend to dive in gusts, but that's not always the cause of dives. If the spreader is bendy, the kite will feel mushy and unresponsive, however, some smaller ones with bendy, say, fiberglass spreaders can fly in a wider range of winds, albeit at lower flying angle - works best on small kites.
Most problems should be eliminated in advance while making the kite, simply by working with diligence, care and attention at each stage of the construction.