1. Introduction

After reading some plans of flowforms, I wondered about the leading edge of the keels of some flowforms and the different form of the profile. Than I was interested in more information of these kites for comparison. All datas of flowforms I could get, I scaled to a specific size to compare them directly.

In the beginning all sketches for the comparison were made by hand. So the comparison has faults by drawing and reading datas out of the sketches. With the second edition the specific datas for the comparison were calculated from the given information out of the existing plans.

Some people had problems with making and flying flowforms and they asked me, which flowform will be the best one to build. It is not my goal to say that flowform is good and that flowform is bad. This comparison should be seen as an overview over available flowforms (ready made and as plans) with some technical information and my points of view.

2. Definitions

Leading edge
The front edge towards the wind is called leading edge. Spareless kites have an upper leading edge on the top side (towards the sky) and a lower leading edge on the bottom side (towards the earth).

Trailing edge
The rear edge opposite to the wind is called trailing edge. Flowforms have straight or curved trailing edges with a center opening (jet chute). sein.

angle of attack
The angle of attack describes the direction of the wind to the lower surface of the kite. At a low angle of attack (0 degrees to the surface) the wind has low resistance. Drag and lift are small. At a high angle of attack (90 degrees to the surface) the wind hit directly the lower surface of the kite. There is the highest resistance but no lift. Only between these extreme angles there is lift by deflection of the wind. Therefore the highest lift is at an angle of attack of 45 degrees.

angle of drag
The angle of drag describes the direction of the flying line to the lower surface of the kite. The difference between angle of attack and angle of drag is about the flying angle of the kite at the ground.

Aspect Ratio
The relation between width and average length of the profile is called aspect ratio. With an aspect ratio lower than 1 the width of the kite is smaller as the length. With an aspect ratio of 1 the length and width have the same value. An aspect ratio larger than 1 means the width of the kite is larger as the length. There are three ranges for aspect ratio:

LAR Low Aspect Ratio Aspect Ratio is smaller as 1
MAR Medium Aspect Ratio Aspect Ratio is between 1 and 6
HAR High Aspect Ratio Aspect Ratio ist larger as 6
(Is not used for kites.)

Jet chute
The center opening at the trailing edge of flowforms is called jet chute. With air flow out of this opening the flying of the kite is more stable.

Air flow holes
Flowforms have holes on the lower and upper surface to compensate the internal pressure. Most times the holes are placed in a V-shape. On the upper surface the tip of th V is placed near the leading edge and on the lower surface the tip of the V is placed near the trailing edge. The air flows in both direction and affects the lift and the stability.

Spareless kites have holes on the inner rib to compensate the different pressure of the chambers. They work on start and in gusty wind for a equal pressure in all chambers.

Compound Bridle
If the kite has more as one row of bridle lines it is easier to set the angle of attack by a compound bridle instead of fixing all lines to the tow point of the flying line. All bridle lines of one row lead to one ring. From these rings lead a help line to the fixing point. The corect length of the bridle lines is set one time. The change of the flying angle is made by checking the length of the help lines in an easy way.

3. Differences Flowform/Parafoil

Height of the profile
A flowform has more height placed near the leading edge as a parafoil. An exception are the parafoils from Jim Rowlands. Even the profiles of his flowforms look different as other flowforms.

Air entry
The flowform has a larger height of air entry, which are most larger than 50 percent of the height of the profile. The height of air entry on parafoils are smaller as 50 percent of the maximum height. The angle of air entry is on flowforms higher than on parafoils.

Air flow holes
A parafoil has no air flow holes on lower and upper surface. The vents on the inner rib are smaller as the vents of flowforms.

Type of keels
Usually keels are placed on every second rib of flowform and parafoil. The flowform uses keels made of one piece and a parafoil have more pieces for the keel. The keels of flowforms are larger than the keels of parafoils.

Type of bridles
Most flowforms have only on row of bridle lines, which are placed below the leading edge of the lower surface. The bridles of most parafoils are made by 2 or 3 rows.

Trailing edge
The center chambers of flowforms are opend at the trailing edge (jet chute) for stabilisation. The trailing edges of parafoils are straight and all chambers are closed. Most flowforms have curved trailing edges, which are realized by cutting the center ribs or by longer outer ribs.

Aspect Ratio
Most flowforms have an aspect ratio smaller than one. Some flowforms have a changed aspect ratio depending on the curved trailing edge. The larger parafoils have an aspect ratio larger than one. Smaller parafoils can have an aspect ratio smaller than one.

Flying capabilities
Parafoils can fly very unstable over a wide area of the flying field. They have a lot of drag on the flying line at a high flying angle. For stabilisation a drogue is nearly allways nescessary. Flowforms have not so much drag on the flying line and fly more stable as parafoils. Some flowforms fly even in very low wind speed.

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