Design and build your own

Dan Leigh Standard Delta

N	= nose angle	S	= nominal span	C	= length at centerline
F	= length of fin	D	= depth of fin	B	= towing point position
L.E.	= length of leading edge (ref)	L	= nominal length of wing spars
S.A.	= spreader strut attachment point

Nominal means measurements with respect to the wing tip point as marked on the initial fabric layout prior to cutting. The plan shows finished sleeves and wing tips, so this point is off the kite in the picture, but, before cutting, the primary dimensions C and S/2 locate this point.
Note also that Tan N/2 = S/2 over C.

Use these proportions

S/2	= 1.0 to 1.1C	L	= 0.75 L.E.	to S.A.	= 7/9L
F	= 0.75C	D	= 0.33 S/2	B	= 0.5C*

* This does not apply to scalloped, clipped wing, or extended keel deltas. Use 0.5 for small kites. For bigger ones a range of 0.50 to 0.375 is possible, gradually increasing toward the 0.375 limit as the kites are scaled up. The 0.50 position remains the optimum, while for stronger winds the towing point may be positioned further forward anywhere within the specified range.

Rough Guide

Before you begin

Read the section on frame specifications first, because your starting point is the length of the wing spars, and this depends on the material used.

Frame Specifications:

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 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.

Construction steps

1. Cut out the two wing halves together, one on top of the other as shown. Cut the fin allowing for a hem and with a "B" mark on the centerline (long) side. It's easier to hem with the grain parallel to the edges.

Option: Although I generally prefer the grain parallel to the trailing edge, in line with the centerline, on some designs it is aligned with the leading edges instead - not recommended for stretchy fabric.

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 4x is fine for small kites.

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.
Finished pocket

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, 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 edge across each pocket position, parallel to L.E., to show 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 gap between kite and strut is 0.12 to 0.16 of the distance measured along L.E. 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.

Testing

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 will be difficult to launch but may fly well once up a ways.
If it twirls then it is too stiff. Either try some smaller diameter wing spars or move the spreader pockets towards the nose.

If it's very bendy it'll be fine for light wind flying, but avoid gusts.
If it leans to one side first swap the wing spars left to right and vice-versa. If it leans to the opposite side, then re-check the wing spars for equal flex. If instead it still leans to the same side, then something's wrong with the fabric symmetry - the wings are either skewed somehow, or else there is an unevenness in the weave of one kind or another. It might be best in this case to try sewing a flap along the trailing edge.
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 will fly in a wider range of winds, albeit at lower flying angle.

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