A New Tack

by popular demand i'm going to switch gears and jump right into designing and creating kites.
i'm going to suggest designs, try them and see if they work. you're welcome to try them also. i've sort of been trying to wing it on a theoretical model for how kites work. this approach is difficult for me and boring for a lot of readers. so, lets have some fun and get out the paper and string.

I'm Still Here

i'm thinking hard on the best aerodynamic model for kite design. so far i've decided to model flow lines across the contoured surface of a kite. this would be a lot simpler if i was using a 3D CAD package, but it's really a challenge using AutoSketch. i would recommend that you use CAD for your kite designs. TurbCad 2D/3D Deluxe seems to be a good choice. personally, I plan to use TurboCad Pro when i upgrade my system.

Bernoulli's Equation

i have given some examples. i think it is
appropriate to explain the principle that explains
how kites fly.
that is, Bernoulli's equation ( a statement of energy conservation
along the streamline of a fluid ).

m*g*h + (1/2) * (d*v^2 )+ p*(Vol1) = m*g*H + (1/2)*(dV^2) + P*(Vol2)

m*g*h and m*g*H represent gravitational potential and are equal so they can be eliminated
so:

(1/2)*(d*v^2) + p*(Vol1) = (1/2) (d*V^2) + P*(Vol2)

(1/2)*(d*v^2)-(1/2)*(d*V^2) = P*(Vol2) - p*(Vol1)

(1/2)*d*(v^2-V^2) = Vol(P-p)

d = density of air
v = initial velocity of air
V = velocity of air after it contacts the kite surface

we are going to assume that the volume of the air remains the same so

Vol = Vol1 = Vol2
p = pressure of air before it reaches the kite surface
P = pressure of air at the kite surface

we are interested in (P-p)

if the surface brings the velocity of air to a completely
perpendicular to the wind surface:
V = 0 -- that is capital V

and

(1/2) (d*v^2)= Vol*(P-p)

or, the difference in pressure DP = (P-p) is proportional to (1/2)(d*v^2)

though there is no complete analytical solution for all
shapes and orientations of surfaces, i am going to
use this equation as a starting point in the
calculations to come.

Dihedrals -- Symmetry and Stability

think about how the dihedral in the diagram enhances the stability of a kite. the keel produced by the two angled faces makes the kite track straight in the wind. solving for the effective area of the dihedral is simple trigonometry A'= cos@*2*A. this of course assumes that the keel between the faces is perpendicular to the wind. there are other ways of improving kite stability but this may be the most common application.