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Icaro Laminar 13 MRX: Difference between revisions
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→Basics of pitching moment and longitudinal stability: Total moment
(→Basics of pitching moment and longitudinal stability: Total moment) |
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''Comment: For this configuration only, it can be shown (e.g. | ''Comment: For this configuration only, it can be shown (e.g. Michael Schönherr, 1977-1979; Horst Altmann dissertation, 1997) that the (mathematically difficult to describe) 2-body hang glider-pilot system can be regarded as a 1-body system (simple mathematical description).'' | ||
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In the prevailing discussions on longitudinal stability, these four moment reference points are often mistaken and mixed up in the argumentation. | In the prevailing discussions on longitudinal stability, these four moment reference points are often mistaken and mixed up in the argumentation. | ||
==== Composition of the total moment ==== | |||
The total moment is made up of two parts. The first part is the moment of the wing, which is determined by the lift distribution and is usually given for a fixed reference point (on the following slide, for example, at the suspension point HP). This moment is mainly dependent on the angle of attack. It is a particular characteristic of the hang glider design and cannot be used for steering.<br> | |||
The second part of the total moment is generated by the aerodynamic force (lift and drag). It is caused by the moment arm (vertical distance from the direction of the aerodynamic force vector to the overall center of gravity). If the overall center of gravity is located behind the force vector, a positive moment (pitch-up) is generated; if the overall center of gravity is located in front of it, a negative moment (pitch-down) is the result. This is shown in the left-hand configuration. For the sake of clarity, however, only the contribution of lift to the total moment is shown here. The drag component has been omitted in the diagram.<br> | |||
This moment is not only dependent on the angle of attack (both lift and drag are growing with increasing AoA) but also to a significant extent on the length of the moment arm (brown dashed line in the diagram), i.e. the pilot's position/control deflection. This moment is therefore relevant for controlling the hang glider. | |||
Consequently, a non-zero aerodynamic force must be present to achieve a control effect. This is practically always the case. Only for the angle of attack at which the lift is zero no controlling is possible. This angle of attack is named α<sub>0</sub>. | |||
For α>α<sub>0</sub>, the lift is always positive. The force points upwards and the steering effect is as described: the further the center of gravity moves backwards, the stronger the pitching-up moment, the further the CoG moves forwards, the stronger the pitching-down moment. | |||
The opposite applies for α<α<sub>0</sub>! Here there is downforce on the wing and the control effect is reversed (right-hand configuration in the slide). Now pushing out results in a pitch-down moment and pulling in causes a pitch-up moment. | |||
The '''reversal of control effect at α<sub>0</sub>''' is an inherent property of weight-shift controlled hang gliders. Understanding this principle is essential for safe flying. It must therefore be an integral part of hang glider instruction!<br> | |||
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