More profile height causes more lift
A larger height increases the airflow speed over the top surface. That leads
to more lift of the kite. At the point of largest height is the largest lift
related to horizontal line through the kite depending on angle of attack.
Flowforms usually have a larger height as parafoils. So they are more useful
in low wind speed.
Position of maximum height of profile
Different height of profile causes different lift. At the maximum height is
the largest lift. If the maximum height is near to the trailing edge the kite
will fly on a high angle. But the angle of the wind to the kite will be lower
and leads to an unstable flight. If the maximum height is near to the leading
edge the kite will fly with a low angle. The angle of the wind to the kite is
larger and increases the drag on the line. If the flying angle is too low, the
kite tends to swing, but will not collapse.
Air flow holes
The air flow holes on bottom and top side of the kite work in both direction.
They affect the air flow round the profile and change the lift power. That is
a reason, why flowforms have less drag as parafoils. These holes increase the
wind range a little bit and stabilize the kite in gusty winds.
Position of air flow holes on top and bottom side
Usually the air flow holes have a diameter of about 25 percent of chamber width.
They are placed on top surface in a V-shape with the tip towards the leading
edge and on the bottom surface in a V-shape towards the trailing edge.
The lines of the V-shape for the positions of holes of each surface are related to the form of the bottom surface. For the places on the top surface the positions are corrected to the distance of leading edge depending on the shape of the profile. The lines of the V-shape start at about 10 percent of the base line at the leading edge and depending on the shape of trailing edge they end at the trailing edge at about 0 to 20 percent.
Flowforms with 4 chambers may have air flow holes in the same diameter.
Length of bridle lines
To set the length of bridle lines I take 2 or 2.5 times the width of the kite
(or the distance between the outer bridle points). If the bridle lines are
too short, the angle of drag to the surface can deform the kite.
In the same way I set the length of bridle lines for a bridle in more rows. For a large distance of bridle rows a longer line to fix the bridle is nescessary.
Flowforms, which look like molars
The outer profiles are longer as the main profile by a flat course towards
the trailing edge. For these flowforms the maximum height are set towards the
trailing edge (Flowform from the magazine vlieger). It helps to lift the
deformed profile (i.e. the flowforms from the magazine Vlieger). With the
longer profiles the aspect ratio of the kite is changed. The smaller width
causes a stable flight.
How to start large soft kites
Starting soft kites of a size more than about 5sq.m (50sq.ft.) is difficult,
because the chambers have to be filled with air. It is like on hot air balloons,
where you have to fill air through the opening, before you can start.
For an easier launch I fix first a short line at the kite and at the anchor. Now I fill the chambers with air and start the kite. After that start I let out more flying line at the anchor.
Increase of air flow speed
If the air flow increases by more wind speed or a changed height of the profile,
the lift of the kite will increase. The kite have a higher flying angle and the
angle of attack is lower. The air pressure on the upper leading edge increases
and can cause a collapse of the front opening. Than the kite will fall down and
is not able to recover. To work against this behavior with more wind speed the
angle of attack have to be higher (shorter bridle lines at the trailing edge,
load on the trailing edge).
High flight angle causes less stability
If the angle of attack is not corrected in increased air flow the kite flies
unstable with a low angle of attack. To change the angle of attack higher the
back lines of the bridle have to be shorter. For more stable flying is a load
on the trailing edge nescessary.
Load on the trailing edge
Depending on profile shape the lift at the trailing edge is smaller than at
the leading edge. If the lift at the trailing edge is too large a load at the
trailing edge can decrease the lift and stabilize the flight. A load may be
drogues, spinning wheels or tails.
Sewing on spareless kites
It is better to make all the sewing from the leading edge towards the trailing
edge even if it is easier to work in the other direction. All errors will go
towards the trailing edge and will disappear by closing the trailing edge.
Closing the trailing edge is better made by heming than by binding.
Making the keel by more than one piece will help to lead the drag through the flares to the canopy. The sewings are reinforcements and prevent deforming the fabric.
Upscaling/downscaling spareless kites
Thomas Michael Rudolph told me, upscaling or downscaling soft kites in all
dimensions is not possible. The problem is the relation between lift and
stability, which work against. With more lift depending on a larger height,
there is less stability. Larger keels lead not to more stability.
Physics about kites
In the magazine 'Fang den Wind' No. 33/4.95 Thomas Michael Rudolph published
some physical information about kite flying.
(Books)
| [1] | Kites and Windsocks, Jim Rowlands
- Flowform Junior - Flowform - Whale (+ Parafoils) |
| [2] | Kites for everyone, Margaret Greger
- Flowform I - Flowform II |
(Magazines)
| [3] | Kite Lines Vol x/x (Summer 79)
Seite 16: Design Workshop: The flowform kite By Ed Grauel and Margaret Greger |
| [4] | Kite Lines Vol 7/4 (Winter 89/90)
Seite 52: How to make a kite from a parachute How to make a flowform from a parafoil How to stunt your flowform |
| [5] | Vlieger 90/6
de flowform Fred Drexler, Den Haag Herman v. d. Broek, Maarsen Building plan of a flowform with longer profile form towards the trailing edge |
| [6] | Vlieger 93/2
mini flowform Wim Houtman, Den Haag Building plan of a flowform with longer profile form towards the trailing edge |
[ Index ] [ Contents ] [ Top of Page ]
©2015 Harald Prinzler