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.
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.
Vents
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.
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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