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Icaro Laminar 13 MRX: Difference between revisions
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→Impact of gusts on pitch-stability
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===Impact of gusts on pitch-stability=== | ===Impact of gusts on pitch-stability=== | ||
Gusts are brief fluctuations in wind strength and direction. One problem is that gusts can sometimes occur very unexpectedly, even if there was almost no wind a short time before. Moreover, they are typically invisible and therefore difficult to predict. Often it only takes a few seconds before the blast is over again. There are many reasons for this: it can be turbulence, wind shear, vortices, wakes, etc. . The spatial extent of this disturbance can vary by orders of magnitude. | |||
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As hang gliders are slow-flying objects, they are very vulnerable to gusts. Even moderate gusts can have a major impact on the flight behavior, as the angle of attack and the inflow velocity can change dramatically. | |||
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The new inflow speed and direction can be easily determined by vectorial addition of the gust with the undisturbed inflow (speed triangles). Examples of this are illustrated on the following slide. | |||
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[[File:Gust Impact on inflow en.jpg|left|thumb|800px|Impact of Gust on Inflow]] | [[File:Gust Impact on inflow en.jpg|left|thumb|800px|Impact of Gust on Inflow]] | ||
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On the next slide, the influence of the gust on the airflow is shown quantitatively. Two different gust strengths (5m/s and 10m/s) are examined for an airspeed of 40km/h (11m/s, approx. trim speed, left diagram) as well as for a very high airspeed of 100km/h (approx. 28ms, right diagram). The gust direction is plotted on the x-axis. The angle is defined in relation to the undisturbed direction of the airflow. | |||
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The orange curve describes the change in angle of attack Δα induced by the gust (left y-axis). | |||
The blue curve describes the influence of the gust on the inflow velocity. This is best described by the ratio of the dynamic pressure of the disturbed flow velocity to the dynamic pressure of the undisturbed velocity (right y-axis). The idea behind this is that the absolute air forces and the absolute momentum scale linearly with the dynamic pressure (P<sub>dynamic</sub> = 1/2*density*velocity<sup>2</sup>). This means, for example, that a doubling of the free flow velocity due to a gust leads to a 4 times higher air force and moment. Therefore, this representation is more meaningful than the application via the velocity ratio. The value is just the factor by which the undisturbed air force and the moment must be multiplied to obtain the new values with gust. | |||
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When comparing the curves for the two airspeeds, it is clear to see that gusts have a much more dramatic effect at low speeds, both in terms of strength and direction. | |||
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[[File:Gust Influence on A0a and DynamicPressure en.jpg|left|thumb|800px|Influence of Gust Direction and Strength on AoA and Dynamic Pressure]] | [[File:Gust Influence on A0a and DynamicPressure en.jpg|left|thumb|800px|Influence of Gust Direction and Strength on AoA and Dynamic Pressure]] | ||
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[[File:Gust Change in AoA en.jpg|left|thumb|800px|Maximum Change in Angle of Attack due to Gusts]] | [[File:Gust Change in AoA en.jpg|left|thumb|800px|Maximum Change in Angle of Attack due to Gusts]] | ||