Aktivwaage

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Dieser Artikel basiert auf Ausführungen von Andy Wardley.

Herzlichen Dank an Michael Hildebrandt, dessen Übersetzung hier verwendet werden darf.

Einleitung

Die Aktiv-Waage ist eine neue Arte der dynamischen Waage für zweileinige Drachen. Diese Schrift führt die Aktiv-Waage ein, beschreibt die Konstruktion und Unterschiede im Vergleich zur statischen Waage und diskutiert die verbesserten Flugeigenschaften eines mit der Aktiv-Waage ausgerüsteten Drachen.

Zusammenfassend:

  • größerer Windbereich
  • vergrößertes Windfenster
  • gleichmäßigenre Geschwindigkeit durch das gesamte Windfenster
  • verbesserter Geradeausflug
  • weichere Drehungen mit bessere Kontrolle über die Anzahl der Drehungen
  • verbesserte Kontrolle im Stall, Slide, Tip Stand
  • weichere Einleitung in und aus Tricks heraus
  • positive Eigenschaften für Fades und Flic-Flacs
  • Drachen bleibt in nahezu jeder Position kontrollierbar

Statische Waage

Abb. 1

Betrachten wir als erstes die klassische statische Waage, wie in Abb. 1 zu sehen. Drei Waageleinen laufen auf einen zum Drachen fixen Punkt zu. Dieser Punkt ist der Zugpunkt, von dem üblicherweise ein weiterer kurzer Schenkel zur Brefestigung der Flugschnüre abgeht (grün gezeichnet)

Die meisten zweileinigen Drachen erlauben in gewissen Grenzen eine Verstellung der Waage indem die relativen Längen der Waageschenkel gekürzt oder verlängert und dadurch die Flugeigenschaften des Drachen verändert werden. Im allgemeinen ruft eine Verschiebung des Zugpunktes relativ zum Drachen folgende Änderungen im Flugverhalten hervor:

Zugpunkt in Richtung Drachennase verschieben
Drachen spricht bei leichtem Wind besser an, kann aber überfliegen und übersteuert in höheren Winden. Die Präzision wird meist verbessert, oft ist es aber so das der Drachen übermäßig sensibel wird und nach hoher Präzision in Steuerung und Ausführung von Tricks verlangt. Stalls sind schwierig beizubehalten aufgrund des verbesserten Steigverhalten des Drachen.
Zugpunkt von der Drachennase wegschieben
Das Handling bei höheren Windgeschwindigkeiten wird verbessert, bei leichterem Wind verschlechtert, da der Auftrieb geringer wird. Diese Einstellung verbessetr das Halten von Stalls, aber die straffere und schnellere Drehneigung kann in Stalls ein Kippeln sowie die Möglichkeit in Kurven eher zu übersteuern hervorrufen. Das "lockere" Gefühl trägt zu einem weicheren und mehr verzeihendem Ansprechverhalten für Tricks bei.
Zugpunkt in Richtung Leitkante schieben
Der Drachen hat ein schnelleres, stärker ansprechendes Drehverhalten, neigt aber zum wackeln im Geradeausflug und Übersteuern in Drehungen.
Zugpunkt wird in Richtung Mittelkreuz bewegt
Der Drachen ist spurtreuer und das Eckenverhalten wird knackiger, weiche Drehungen werden schwieriger.

Verschiedene Positionen haben ihre Vor- und Nachteile und jede Position ist ein Abwägen zwischen den verschiedenen Charakteristiken.


Die Aktiv-Waage

Abb. 2
Abb. 3
Abb. 4
Abb. 5

Das eigentliche Prinzip jeder dynamischen Waage ist ein Zugpunkt der sich relativ zum Drachen bewegen kann. Die Aktiv-Waage ermöglicht dieses mit zwei zusätzlichen Schenkeln die ihr die notwendige Bewegung in der gewünschten Richtung erlauben und dabei das Optimum an verschiedenen Waagepositionen für unterschiedliche Bedingungen, Positionen, Manövern und Tricks.

Wie bei dynamischen Waagen üblich, erlaubt die Aktiv-Waage eine Bewegung des Zugpunktes bei der alle Waageschenkel straff sind. Das ist notwendig für optimale Kontrolle des Drachen und für optimales Ansprchverhalten auf jegliche Zugbewegung des Piloten. Für eine Bewegung des Zugpunktes an einer statischen Waage muß ein oder mehrere Schenkel spannungsfrei sein. Der Konstruktionsvorteil der Aktiv-Waage ist, so viel Bewegung wie nötig zu erlauben um das Flugverhalten zu verbessern und dabei die Waage in Form und Spannung zu behalten.

Der erste zusätzliche Schenkel ist der Stabilisator, rot gezeichnet zu sehen in Abb. 2. Er stellt eine Verbindung zwischen zwischen oberem und den unteren Schenkeln her.

Der zweite zusätzliche Schenkel, der "Aktivator", rot in Abb. 3 gezeichnet, verbindet die inneren und oberen Schenkel und zieht sie etwas zusammen.

Stabilisator Bewegung Abb. 4 zeigt den Effekt des Stabilisators in der Bewegung des Zugpunktes in Richtung Leitkante oder Kielstab. Die Auswirkungen sind folgende:

  • Wenn der Drachen sich im Geradeausflug befindet ist der Druck auf beiden Flugleinen in etwa gleich (wenn die Häde des Piloten in gleicher Höhe gehalten werden). In diesem Stadium bewikt die Aktiv-Waage eine Bewegung der Zugpunkte in Richtung Kielstab. Dabei erhöht sich die Präzision im Geradeausflug.
  • Wenn der Pilot eine Leine zieht oder drückt um eine Drehung auszuführen wird der jeweilige Zugpunkt sich in Richtung Leitkante bewegen. Dabei erhöht sich die Drehfreudigkeit des Drachen.
  • Die Art der Drehungen des Drachen kann sehr differenziert ausgeführt werden. Ein leichter Druck der Leine erzeugt einen langsamen Flug in einem Kreibogen, während das andere Extrem, ein harter Zug einer Leine, einen sehr schnellen und Engen Spin erzeugt.

Activator Bewegung Abb. 5 zeigt die Auswirkungen des Aktivators auf den Anstellwinkel des Drachen indem der Zugpunkt sich auf und ab bewegt.

  • Wenn der Druck auf dem Segel gering ist bewegt sich der Zugpunkt nach oben, dei Drachennase wird zum Piloten geneigt. Das verbessert das Ansprechverhalten bei leichtem Wind und am Rand des Windfensters.
  • Wenn der Druck im Segel zunimmt bewegt sich der Zugpunkt nach unten, die Nase bewegt sich etwas vom Piloten weg. Dadurch wird der Drachen in höheren Windgeschwindigkeiten gebremst und man hat eine bessere Kontrolle in der Mitte des Windfensters. Böen werden durch dieses Verhalten "geschluckt", der Drachen fliegt sich dann weicher.
  • Die Effekte, die hier beschrieben sind, geben dem Drachen ein größeres Windfenster und erlauben einen Flug mit konstanter Geschwindigkeit durch den gesamten Bereich und unter wechselnden Windbedingungen.

Diese beiden Effekte in Verbindung mit der Aktiv-Waage geben dem Drachen eine höhere Präzision, verbesserten Geradeausflug, weichere Drehungen, vergrößerte Windbereiche und Windfenster und eine konstantere Geschwindigkeit. Es ist der Vorteil der Kombination verschiedener Waageeinstellungen ohne irgendwelche Nachteile zu bekommen. Des Weiteren erfolgen diese Einstellungen automatisch unmittelbar auf Windeinwirkung oder durch Leinendruck. Eine manuelle Waageeinstellung entfällt dadurch.


Benefits for Freestyle and Trick Flying

The Active Bridle has shown itself to not only be well adapted to improving the precision, wind range and smoothness of the kite, but also to greatly increasing the kite's ability to perform advanced freestyle and trick flying maneuvers. This is perhaps the most significant achievement given the fact that precision and trick flying have very different requirements and make wildly different demands on the kite and bridle.

Dynamic bridles have previously had some considerable degree of success in improving the freestyle performance of kites, but usually at the cost of precision. Careful analysis of the dynamics of a kite during different kinds of flight (tracking straight, turning, stalls, Axels and Flat Spins, Flic-Flacs and Fade, etc) has identified the desired movement of the bridle in each of these conditions. The Active Bridle configuration is designed such that the bridle not only moves, but moves in the right direction, when required to do so. Whilst it is possible to break down the movement into horizontal and vertical components, as described in the previous section, it is important to realise that the combined effect is a synergy of movement in all 3 dimensions that, when carefully tuned to the size, shape, and aerodynamic qualities of a given kite, can afford a remarkable diversity of control and flexibility to the flier.

The specifics of the movement of the Active Bridle and the effects noted are discussed here in further details:

Stalls and Slides

The Active Bridle makes it easier to control the kite in a stalled position. Kites that are traditionally more precision-orientated are often solid and steady in a stall. Kites that are aimed more towards freestyle flying tend to have greater responsiveness to turning. This sensitivity makes stalls hard to perfect. The kite will typically roll one way or the other, rather than sitting steady with the nose pointing straight up.

A kite with a static bridle will normally stall best when adjusted with the tow point slightly low. This pushes the nose of the kite away from the flier and reduces its forward drive. The relative pressure is increased at the top of the kite as more air bleeds over the nose and leading edges. This force, being applied above the centre of gravity of the kite, further increases its tendency to roll sideways.

The stalled position with the Active Bridle has the nose of the kite being pulled in towards the flier. More air bleeds over the trailing edge and the relative pressure increase is concentrated below the centre of gravity of the kite. This creates a much more stable stall with significantly less rolling of the kite.

The nose is pulled in by the action of the Active Bridle responding to a drop in overall pressure on the kite. When the flier adds slack to the lines, as is typical when executing a stall, this sudden lack of pressure causes the tow point to shift far up, pulling the nose right in. The angle of the kite reaches a point where it will no longer fly forwards and it effectively remains "parked" it in mid-air. While the lines remain slack, the kite will remain stalled.

Taking up the slack on the lines increases the overall pressure on the kite and the Active Bridle shifts the tow point down to allow the nose to drop back again. This permits the kite to power up and fly off. The transition between stall and flight is fast, positive and crisp. There is no "nodding" of the nose of the kite as can be experienced with other dynamic bridle configurations.

Diagram 6 Stalled Position Diagram 6 Stalled Position

The Active Bridle's pitch control not only allows the flier to adjust or correct the orientation of the kite in a stall, but also helps to keep the kite level when executing side slides. To correct an imperfect stall, or to introduce a side slide from a stall, slight pressure is applied to one or other line. In normal flight, pulling one wing towards the flier would cause the kite to rotate in that direction. In the stalled position, pulling gently on one line causes the tow point on that side of the kite to be pulled outwards towards the leading edge as the Stabiliser shifts. The tow point remains high due to the relatively light pressure on the lines and is now in a position above and outside the centre of gravity of the kite. This has the effect of keeping the wing lifted upwards to counteract the natural turning moment induced by pulling the it in towards the flier. This is shown in Diagram 6.

Diagram 7 Tip Stand/Drag Diagram 7 Tip Stand/Drag

When holding the kite in a Tip Stand, or when executing a Tip Drag or Leading Edge drag, the same action of the Active Bridle moves the upper tow point out towards the leading edge when pressure is applied to that line. This helps to keep the kite stable and lifts the nose up enough to counter the tendency for it to roll downwards and snag on the ground. This is shown in Diagram 7.

Axels and Flat Spins

The range of tricks based around the Axel and Flat Spin share the common characteristic that the kite rotates in a flattened orientation with the face of the kite pointing towards the ground. The Active Bridle makes this kind of maneuver easier and cleaner by smoothing the transition into the trick. An Axel is executed by pushing on one line and then giving a sharp pop on with the same hand. The initial push is the setup required to cause the nose to dip, bringing the kite into the flattened position.

The action of the Active Bridle, when slack is applied to the lines, is to raise the position of the tow point, effectively pulling the nose in towards the flier. The push given as a pre-cursor to the Axel "pop" causes the Active Bridle to act in the same way, quickly lowering the nose ready for the transition into the trick.

The movement created by Active Bridle allows the flier to take up the slack and apply further controlled input during the execution of Axel-like tricks. Multiple Axels and Multiple Flat Spins become easier to achieve by the fact that the bridle compensates for incorrect or badly timed input. The required "point" at which a trick requires further input to continue, becomes a wider "zone", making such tricks easier to get right and smoother in execution.

Fades, Flic-Flacs and Fountains

The pitch control provided by the Active Bridle allows some movement of the nose, forward and backward, to regulate the kite's handling of different wind conditions. This movement also proves to be of some considerable benefit when executing tricks such as the Fade, Flic-Flac, etc., where the nose is deliberately pulled far forward or thrown right back.

The Active Bridle makes this transition between states smooth yet positive. It produces a cleaner, more controlled performance that looses little or no height. An Activated kite tends to lock into a Fade and hold it far better than normal. This behavior often implies a limited ability to Flic-Flac in a kite, but the Active Bridle does not appear to have any such limitation. It is possible to hold Rising Fades (Elevators) and also to execute Rising Flic-Flacs with the same kite without requiring any manual bridle adjustment.

The Active Bridle can also significantly improve the performance of Cascades and Fountains. The 3-step "Pop, Pause and Pull" approach to these maneuvers - "pop" the Axel, pause while the kite rotates half a turn or so, then pull the other line to lift the wing up - makes precise control of a Cascade much easier to achieve and also helps to reduce the amount of height lost in each iteration. This allows the flier to perform longer Cascades and eventually progress to the point where the kite gains height rather than loses it: The Fountain. This becomes significantly easier with an Active Bridle.

There are a number of clearly distinct benefits that the Active Bridle gives, such as those discussed already. Going beyond the specifics of certain tricks, the Active Bridle has a feeling and a forgiveness that seems to enhance the flying characteristics of a kite in almost any situation or position. This opens up new windows of possibility and allows the flier to discover so much more about what the kite can really do.

With an Active Bridle, the kite will accept input from almost any position in the sky (and in many cases, on the ground), and behave in a controlled and predictable fashion. This allows many existing tricks to be executed in new orientations and in different ways.

Drawbacks

The Active Bridle improves many characteristics of a kite's flight. To the best of my knowledge, this benefit is granted without any compromise. There is nothing about the way a kite flies that the Active Bridle makes worse.

There are drawbacks, however, but these manifest themselves in the design, construction and understanding of the bridle configuration.

The fact that the bridle is more complex than a static, or other dynamic, bridle makes it harder to design for a specific kite. There are more sections to adjust, more parameters to change and more for the designer to understand about the perceived effects of changing these elements.

To compound the problem, the Active Bridle is more sensitive to tuning than most other bridles. Whilst it is a fairly easy matter to simply get the kite flying, the hard part is the fine tuning required to balance all of the bridle's features against each other. Getting the kite to Fade and Flic-Flac, providing both precision and extreme trick-ability, and have the kite stall well without losing firm, positive drive, are all examples of the contrasting characteristics that can be achieved without compromise, with the sufficient amount of time, patience and understanding.

Constructing an Active Bridle

Lower Leg Loop (x1)

The Active Bridle uses a single lower leg piece running all the way across the bottom section of the bridle on both sides. This section is created by tying a loop (see above) and measuring down the required length (typically around 1.50m) and cutting both ends with enough excess to make flanges. The distance down the line is measured from the back of the loop rather than the knot. When using a bridle stick, the loop can simply be hooked over the nail at the 0-Line to achieve the correct starting point for the measurement.

Diagram 8 Lower Leg Diagram 8 Lower Leg

Two marks are required on the bridle to indicate the connection points for the Activator and Stabiliser section. These are known as the Activator Mark and Stabiliser Mark and are both measured down from the end of the loop. The lengths from the loop to these marks are known as the Lower Activator Mark (LAM) and Lower Stabiliser Mark (LSM) lengths. The overall length of the legs from loop to end is known as the Lower Leg Length (LLL).

The lower leg section is attached to the kite by passing the loop over the lower end of the spine and pulling it up to the T-Piece. The loose end are then fed through the T-Piece cutout from the back. The loose ends are tied, one to each lower leading edge spar, directly below the connector and above the C-clip, using the Frame Knot technique desribed earlier.

Upper Legs (x2)

One upper leg section is required for each side of the bridle, making two in total. These sections are of a fixed length and require flanges at each end. Remember to cut a little surplus length in the line and then melt the flange down until the line is of the correct length.

Diagram 9 Upper Leg Diagram 9 Upper Leg

Two marks are made on the upper leg sections, both measured down from one end (the upper end). These marks are known as the Activator Mark and the Tow Point. The Activator mark will be roughly half way down the line. The Tow Point will be close to the lower end of the line. These lengths from top end to mark are known as the Upper Activator Mark (UAM) and the Upper Tow Point (UPT) lengths.

Attach the upper end of the line (furthest from the Tow Point) to the upper leading edge spar of the kite, directly below the connector and above the C-clip, using a Frame Knot.

Attach the lower end of the upper line to the lower bridle leg at the Stabiliser Point using a Sheet Bend.

Activator Legs (x2)

Two Activator legs are required, one for each side of the kite. These are short lengths (about 15cm) that require flanges in both ends. No markings are required on the lines. The length of the line is the Activator Leg Length (ALL).

Diagram 10 Activator Leg Diagram 10 Activator Leg

Attach one end of the Activator to the lower leg on the Activator mark using a Sheet Bend. Attach the other end to the upper leg on its Activator mark, also using a Sheet Bend. The Activator leg should now connect the upper and lower legs, pulling them slightly in towards each other.

Tracers (x2)

Two tracers are required, one for each side of the kite, made as described in the earlier section. The tracers are attached to the upper legs using a Prussik. The knot should be moved onto the Tow Point mark and then rolled over to lock it tightly in place.

The section of the upper leg below the Tow Point has now become the Stabiliser leg.

Congratulations, your kite has been Activated!


© Copyright 1995-2007 Andy Wardley. All Rights Reserved.