Geometry Project - Kite Shapes

by Jayden
(Oklahoma City, OK, USA)


Both a square and rhomboid (diagonal) kite are perpendicular to the wind. They both have effective areas. What shapes would those be? And whats the difference from the effective areas?

And where on a box kite would I tie string to get the greatest effective area?


After a little research I was able to figure out what you are actually asking :-) I believe you are enquiring about differences between the traditional square Box kite and the slighly flattened version called the Rhomboid kite?

The geometry question only makes sense if the Rhomboid kite is just the Box kite with the bracing cross-pieces changed in length. To put it in a non-mathematical way, imagine the square Box kite is 'squashed' so the cells look diamond-shaped instead of square. Of course, both kites have exactly the same amount of sail area.

The question states that both kite designs are placed perpendicular to the wind. Let us imagine that they are sitting on their tail ends on the ground too, and being held there, ready to launch. Just down-wind of the kites is a large smooth wall. It is night time and the kite-flier, way upwind, is shining a very bright light towards the kites. CASTING SHADOWS ON THE WALL.

These shadows can represent the effective areas of the kites. Both shadows will show 2 rectangles for each kite. An upper and a lower one, corresponding to the upper and lower cells of the kites.

But look - the Rhomboid kite is casting wider shadows than the Box kite! Since the heights of all the shadows are the same, what does that mean? It means the Rhomboid has a larger effective area than the Box, despite having the same amount of sail material covering it. If it is stopping more light from hitting the wall, it must also be a bigger obstacle for the air flowing around it!

If you did a little trigonometry, you could calculate the exact difference in effective area between the 2 kites. Ask another question if you would like that explained in detail. Of course, kites cannot fly perpendicular to the wind, so in real life the effective areas are smaller.

I hope all this helps to make the concept of 'effective area' a little clearer.

Regarding the last part of your question, about getting the largest effective area for a box kite... You would tie the string to the exact middle of one of the long main spars. But of course, the kite wouldn't fly! You could perhaps toss it out the back of a drag racer as an air-brake ;-)

One more comment... It's funny that the Rhomboid Kite has that name, since technically the cell shape is a Rhombus. That is, a shape with all 4 sides of equal length. A Rhomboid is the more general case where adjacent sides are of unequal length. That is, 2 sides have one length and the other 2 sides have another length.

Click here to post comments

Join in and write your own page! It's easy to do. How? Simply click here to return to About Kites.

FREE E-Book!

I'm referring to Simplest Dowel Kites, my popular kite-making download. It's a printable PDF file. Make a diamond, delta or sled. Each kite is capable of flying hundreds of feet up for hours on end.

Could you do me just a small favor though?

Please sign up for my free monthly publication, "Tethered Flying". No other emails will be sent, and your details are safe with me. You need to be at least 16 years old. There's...

  • A huge "photo of the month" (via a link)
  • 3 "tips of the month" (one each for beginners, parents and the more experienced)
  • A "flight report of the month" (selected from my own flying logs)

Back to top of page

Need winders, reels, flying line?

We earn a small commission if you click the following link and buy something. The item does not cost you any more, since we are an "affiliate" of Amazon.

Click here to buy anything you need. Just use the Search box in there if you need different weights or lengths of line, for example.

P.S. Keep an eye out for books by kite author Glenn Davison, a prominent kite person in the USA.

What's New!

  1. Tiny light wind newspaper kites

    Jul 09, 20 08:25 PM

    As a child (around 6) one of my parent's friends with children near my age took us outside and taught us how to make the smallest of light-wind kites from

    Read More

Wind Speeds

Light Air
1-5 km/h
1-3 mph
1-3 knots
Beaufort 1

Light breeze
6–11 km/h
4–7 mph
4–6 knots
Beaufort 2

Gentle ...
12–19 km/h
8–12 mph
7–10 knots
Beaufort 3

Moderate ...
20–28 km/h
13–18 mph
11–16 knots
Beaufort 4

Fresh ...
29–38 km/h
19–24 mph
17–21 knots
Beaufort 5

Strong ...
39–49 km/h
25–31 mph
22–27 knots
Beaufort 6

High Wind
50-61 km/h
32-38 mph
28-33 knots
Beaufort 7

Like/share this site...

Like/share this page...