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Icaro Laminar 13 MRX: Difference between revisions
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→For nerds ... and hang glider pilots who want to survive this sport
(→Basics of pitching moment and longitudinal stability: Total moment) |
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All the points described here can be tested and verified using the FlightGear hang glider ''Laminar 13 MRX''. This should improve the understanding and might help to avoid extrem flight situations or to train safe recoveries from such situations. | All the points described here can be tested and verified using the FlightGear hang glider ''Laminar 13 MRX''. This should improve the understanding and might help to avoid extrem flight situations or to train safe recoveries from such situations. | ||
'''This section is still under construction.''' The current status is June | '''This section is still under construction.''' The current status is June 25, 2025. | ||
As an introduction, reference is made to two threads in the German Hang Gliding Forum, in which the static and dynamic longitudinal stability of weight-shift controlled hang gliders is examined in more detail: | As an introduction, reference is made to two threads in the German Hang Gliding Forum, in which the static and dynamic longitudinal stability of weight-shift controlled hang gliders is examined in more detail: | ||
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# Then, due to the rear center of gravity position (fully stretched arms), an extremely fast rotation begins. Jesper drifts from the sideways deflected position to the center. The right hand no longer rests relaxed on the control bar (Is this an indication that he has pushed-out deliberately?). | # Then, due to the rear center of gravity position (fully stretched arms), an extremely fast rotation begins. Jesper drifts from the sideways deflected position to the center. The right hand no longer rests relaxed on the control bar (Is this an indication that he has pushed-out deliberately?). | ||
# t=5:08s: At this point, the harness/legs fall symmetrically into the rear wires. The negative lift forces are now only transferred to the pilot via the rear lower wires and the hands at the control bar. The nose of the hang glider points vertically downwards. | # t=5:08s: At this point, the harness/legs fall symmetrically into the rear wires. The negative lift forces are now only transferred to the pilot via the rear lower wires and the hands at the control bar. The nose of the hang glider points vertically downwards. | ||
# t=4:18s to 5:18s: Continuous increase of the negative dihedral (increasing negative | # t=4:18s to 5:18s: Continuous increase of the negative dihedral (increasing negative aerodynamic force). | ||
# t=5:16s to 5:18s: The left and right uprights bend symmetrically outwards. The hands are still holding the controlbar and the feet are still resting on the lower rear wires. | # t=5:16s to 5:18s: The left and right uprights bend symmetrically outwards. The hands are still holding the controlbar and the feet are still resting on the lower rear wires. | ||
# t=5:19s: Breakage of the right upright. Right hand loose (?). t=5:20s: Right hand back on the controlbar but further left. t=5:21s: Right hand loose again. Left hand continues to clutch the control bar. The hang glider is approximately inverted (see alignment to the horizon). | # t=5:19s: Breakage of the right upright. Right hand loose (?). t=5:20s: Right hand back on the controlbar but further left. t=5:21s: Right hand loose again. Left hand continues to clutch the control bar. The hang glider is approximately inverted (see alignment to the horizon). | ||
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The orange curve describes the change in angle of attack Δα induced by the gust (left y-axis). | The orange curve describes the change in angle of attack Δα induced by the gust (left y-axis). | ||
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The blue curve shows the influence of the gust on the inflow velocity. This is best represented 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 | The blue curve shows the influence of the gust on the inflow velocity. This is best represented 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 aerodynamic forces and the absolute momentum scale linearly with the dynamic pressure (P<sub>dynamic</sub> = ½*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 aerodynamic 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 aerodynamic force and the moment must be multiplied to obtain the new values with gust. | ||
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The previous diagram shows that the dynamic pressure increases by a factor of approx. 3.5. This does not have any effect on the absolute moment, as 0*3.5 is still 0. However, the | The previous diagram shows that the dynamic pressure increases by a factor of approx. 3.5. This does not have any effect on the absolute moment, as 0*3.5 is still 0. However, the aerodynamic force / lift also increases by this factor. The hang glider is therefore accelerated upwards by the higher lift ( first without changing its attitude). The superposition of this rate of climb with the inflow velocity results in a reduction in the angle of attack. We move on the moment curve (blue curve in the moment diagram) to the left. Although the change in angle of attack and hence the increase in moment is only minimal, the ''absolute'' moment increases by a factor of 3.5, which in the end leads to the significant pitching up. | ||
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