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Rata Jet

Rata Jet kite front view

Rata Jet is a single skin kite descending from NASA parawing (NPW) line. This design attempts to increase single skin kite performance by delaying the point at which nose collapse occurs. This is done by using a RATA (rib angled to airflow) to slow airflow and increase pressure under the nose area.

A view of the front of the kite is on the right side of this page. There are no spars in this design, only flat fabric to fabric sew lines.

Design

Below is the plan for this kite. The small square boxes indicate canopy bridle attachment points. Three dimensional sail shape is controlled by notches in the canopy. The notches in the nose of the kite are in the canopy, not the RATA ribs. The RATA ribs are sewn flat to the kite along the curved line. Unfolding these produces a three dimensional shape in the canopy. Scaling this plan by [grid line = 50cm] gives the specifications listed in the first section.

One "design leap" in this model is the reduced number of LE bridle attachment points in comparison with a standard NPW design. Both notches and increased fabric (described further below) are used in an attempt to reduce the canopy folds which occur at high point loads.

Rata Jet kite plan

CAD code for producing this drawing follow. The points for the notches on the leading edges lie on the circle centered at (5,-3).

; Rata Jet v.1, 2008, Bill Ola Rasmussen
; bridle points
_points 0,0 0.552941,0.771427 1.22857,1.44706 1,0 2,0 2.48,2 _enter
; LE and notches
_lines 2.5,0 0,0 0.538737,0.751589 0.780057,0.578816 0.570193,0.78868 
       1.21132,1.42981 1.42118,1.21994 1.24841,1.46126 2,2 _enter
; nose
_line 2,2 2.5,2
; rata trim line
_line 2,1 2.5,1
; rata sew curve
_circle _3point 2,2 2.48,1 4,2
; (manual step: trim circle to arc between nose and rata trim line)
; bottom of rata
_line 2.48,1 2.48,2
; nose notches
_lines 2.28,2 2.3,1.86 2.32,2 _enter
; TE notches
_lines 0.98,0  1,0.2 1.02,0 _enter
_lines 1.975,0 2,0.3 2.025,0 _enter
; (manual step: reflect around x=2.5)

Two manual steps are indicated in order to keep the code brief.

Differences between this and the original RATA model:

This is RATA iteration #3. The second try did not turn out to be a step forward.

Rata Jet kite side view

Analysis

Looking at the pictures on this page, there are at least three things to note: Rata Jet kite TE view

The above tail view shows the bridling of the kite. Cascaded primaries and secondaries are used for the LE, and just primaries for the TE. Bridle adjustment is done by Prusik knot, as shown on the NPWC 2 Line Bridle page.

Rata Jet kite L/D view

Performance

To the right we see Rata Jet flying quite high up in the window. From the angle of the flying lines, LD appears to be greater than 4! Ok, it looks really nice and is what we are aiming for, but normal flight aspects are not so rosy. At times, the performance of this kite is brilliant. The next moment, an edge will fold and the kite will slide back down in the window.

See a a video of single line flight. It's a 17mb download. A smaller, lower quality version of the video is available on YouTube. Mid video, near apogee, you can see the nose and leading edges folding and unfolding. This indicates that the airflow is switching between splitting just above and just below the leading edge. I believe maximum performance is to be had at a bridle setting where the airflow splits just under the leading edge.

More bridle tuning may be able to fix this spotty behavior. If you also want to work on this, email me and I will give you the latest bridle measurements. Canopy plans are included on this page.

Possible improvements for the next iteration:

Rata Jet is a design which gives glimpses of brilliant performance and deserves further development.

Related pages:
Rata Wing Kite
Lift to Drag Ratio

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©2008 Bill Ola Rasmussen