Which type of kite is better for low wind conditions: LEI or foil?

In summary, there is an ongoing debate in the Kitesurfing world about the aerodynamics of LEI (leading edge inflatable) kites and Foil kites. LEI kites have large inflatable 'bladders' that keep the shape and float, while foil kites are closed cell RAM air parachutes with twin skin and lots of bridles. The argument is that some believe foil kites are better in low wind due to being lighter and having a higher aspect ratio, while others argue that LEIs are better due to less drag. The simplified analysis of lift and drag equations is inconclusive, and wind tunnels are often used for a more accurate evaluation.
  • #1
Marshall10488
9
0
just wanted to say hi first as this is my first post.
I will explain the story...
There is an ongowing debate within the Kitesurfing world regarding the aerodynamics of LEI (leading edge inflateable) kites and Foil (like RAM aim parachutes) kites.

LEI Kites:
They have large inflateable 'bladders' that keep the shape of the kite and also make it float. they are single skin and the foil shape comes from the leading edge's cylndrical shape. They have only a few 'bridle' lines on the leading edge with a thickness of about 3-5mm. very curved shape so projected area is not same as surface area
http://www.boardlife.sk/userfiles/16-North_Rebel_2007_12m2_a_North_Rebel_2008_10m2.JPG.311008_122249_11.JPG
some links to LEI companies
http://www.northkites.com/public/content/index_eng.html"
http://www.naishkites.com/en/index.html"

Foil kites:
closed cell RAM air parachutes. twin skin. lots of bridles, the majority of which are about 1-2mm. then some 3-5mm and 2 5-8mm. very flat so projected area is close to surface area. very light.
http://www.flysurfer.com/gallery2_code/d/141624-2/SPEED3+Deluxe+mit+Bridles.png
main water re-launchable foil company
http://www.flysurfer.com"

Ok so the argument is that some beleave that foil kites are better in low wind as they are lighter, tend to have a higher AR. Others that LEIs are better as less drag etc.
My thinking is: Lift needed to fly it L=ma
Lα1/M
Lα V[squared]
Lα Lift coefficient
L α Area

But i need to add in the drag equation so lift needed to fly:
l=ma + 0.5 Cd ρ V[squared] a (don't know if this is right)
so by equating i get that the velocity to beed gravity and drag
v=Root[(2ma)/(ρ(Cl Ak-Cd Ab)
Where Cl is lift coefficent
Ak is area of kite
Ab is area of bridles
Cd is drag coefficient

knowing that Cl = [2(pi)(AoA)]/[1+(2pi)/AR]
AoA= Angle of attack
AR = Aspect ratio
is there another equation for Cd without simply just rearaging the drag equation?
anyone who knows more about parachute/kite physics/fluid dynamics have a definitive answer to this discussion?
Thanks
Ben
 
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  • #2
Those are cool!

I suspect your simplified analysis is not worth doing; those look like very complicated shapes (you must consider the full 3-D problem) and the wind conditions are highly variable in time. Wind tunnels are used for a reason.
 
  • #3
i'm not looking for exact just estimate, to prove either way. the big problem i have is the drag from the bridles due to harmonics.
 

1. What is fluid dynamics?

Fluid dynamics is the study of the motion of fluids (liquids and gases) and the forces that act on them. It involves the analysis of how fluids flow and interact with their surroundings.

2. How does a kite fly using fluid dynamics?

A kite flies by using the principles of fluid dynamics, specifically lift and drag. The shape of the kite, along with the angle of attack and the speed of the air passing over the kite, create lift which allows the kite to stay airborne. The tail of the kite helps to stabilize its flight by providing drag.

3. What factors affect the flight of a kite using fluid dynamics?

The shape and design of the kite, the wind speed and direction, the angle of attack (the angle between the kite and the wind), and the weight and balance of the kite all play a role in its flight using fluid dynamics.

4. What is the Bernoulli's principle and how does it relate to fluid dynamics?

Bernoulli's principle states that as the speed of a fluid (such as air) increases, its pressure decreases. This principle is important in understanding how lift is created in a kite as the air passing over the curved surface of the kite moves faster, creating an area of low pressure above the kite and an area of high pressure below it, resulting in lift.

5. How can fluid dynamics be applied to other areas of science and technology?

Fluid dynamics has a wide range of applications, including in the design of airplanes, cars, and boats. It is also used in the study of ocean currents, weather patterns, and blood flow in the human body. In addition, fluid dynamics plays a crucial role in many engineering and manufacturing processes, such as in the production of wind turbines and power plants.

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