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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
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This section will take a closer look at the special flight dynamics of hang gliders due to their weight-shift control and flexibility. | This section will take a closer look at the special flight dynamics of hang gliders due to their weight-shift control and flexibility. | ||
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 | 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 extreme flight situations or to train safe recoveries from such situations. | ||
<!-- '''This section is still under construction.''' The current status is August 10, 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: | ||
[https://www.gleitschirmdrachenforum.de/forum/gleitschirm-und-drachen-forum/ger-te-hg/935503-das-momenten-quiz Das Momenten-Quiz] | [https://www.gleitschirmdrachenforum.de/forum/gleitschirm-und-drachen-forum/ger-te-hg/935503-das-momenten-quiz Das Momenten-Quiz] | ||
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Further discussions, comments, enhancements or amendments to the following can be made in the German Hang Glider Forum. | Further discussions, comments, enhancements or amendments to the following can be made in the German Hang Glider Forum. | ||
All contributions are more than welcome - also in English if you want. | All contributions are more than welcome - also in English if you want. | ||
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=== Basics of pitching moment and longitudinal stability === | === Basics of pitching moment and longitudinal stability === | ||
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* the only connection from the pilot to the glider is via the main suspension to the hang point (HP) | * the only connection from the pilot to the glider is via the main suspension to the hang point (HP) | ||
* tight (!) main suspension | * tight (!) main suspension | ||
For this configuration, the moment reference point is in the ''' | For this configuration, the moment reference point is in the ''' "common center of gravity of glider and pilot, whereby the entire pilot mass is to be assumed at the hang point"''' (green gradient symbol <big>▼</big>). This point is much closer to the wing. | ||
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* the main suspension is loose and there is | * the main suspension is loose and there is | ||
* no contact between the pilot and the hang glider (pilot is falling aside the hang glider). | * no contact between the pilot and the hang glider (pilot is falling aside the hang glider). | ||
Consequently, the '''center of gravity of the hang glider''' (🟦) must be selected as the moment reference point. During this phase of flight, the hang glider does not even 'know' that there is a pilot next to it. The hang glider must recover on its own. However, this flight condition usually only occurs for an extremely short time. The practical relevance is therefore low. | Consequently, the '''center of gravity of the hang glider''' (🟦) must be selected as the moment reference point. During this phase of flight, the hang glider does not even ''know'' that there is a pilot next to it. The hang glider must recover on its own. However, this flight condition usually only occurs for an extremely short time. The practical relevance is therefore low. | ||
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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. | ||
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==== Composition of the total moment ==== | ==== Composition of the total moment ==== | ||
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''Comment: Due to the dependence of the moment on the load factor, the moment is measured at different speeds for the certification of hang gliders. Different certification limits are defined for each speed.'' | ''Comment: Due to the dependence of the moment on the load factor, the moment is measured at different speeds for the certification of hang gliders. Different certification limits are defined for each speed.'' | ||
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One more interesting point: Every hang glider pilot knows that the glider flies much less stable when flying hands-free compared to holding the base bar. This behavior is easy to interpret using the moment diagram. Longitudinal (pitch) stability is characterized by the slope of the pitching moment coefficient curve at CM = 0. The steeper (more negative) the slope, the greater the stability. When the control bar is held, the blue moment curve applies. For hands-free flight, the orange dashed curve applies, which has a significantly flatter negative slope than the blue one. So, in trimmed flight (and unfortunately ''only'' there), the pilot holds the power to choose the level of stability by either gripping the bar or not. Cool, isn't it? | One more interesting point: Every hang glider pilot knows that the glider flies much less stable when flying hands-free compared to holding the base bar. This behavior is easy to interpret using the moment diagram. Longitudinal (pitch) stability is characterized by the slope of the pitching moment coefficient curve at CM = 0. The steeper (more negative) the slope, the greater the stability. When the control bar is held, the blue moment curve applies. For hands-free flight, the orange dashed curve applies, which has a significantly flatter negative slope than the blue one. So, in trimmed flight (and unfortunately ''only'' there), the pilot holds the power to choose the level of stability by either gripping the bar or not. Cool, isn't it? | ||
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=== Tuck avoidance === | === Tuck avoidance === | ||
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The initiation of the tucks or near-tucks in the other videos can also be subdivided into the 4 phases. The individual phases are just more or less pronounced. | The initiation of the tucks or near-tucks in the other videos can also be subdivided into the 4 phases. The individual phases are just more or less pronounced. | ||
<br><br> | <br> | ||
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==== Analysis of the U2 video ==== | ==== Analysis of the U2 video ==== | ||
In the U2 video ([https://www.youtube.com/watch?v=_nkEQtj08us ''Hang Glide Reserve Deployment'']), the initial state of the tuck initiation is at a significantly higher angle of attack compared to the Sensor due to its flight attitude (nose high) at the onset of the stall (Point 1). | In the U2 video ([https://www.youtube.com/watch?v=_nkEQtj08us ''Hang Glide Reserve Deployment'']), the initial state of the tuck initiation is at a significantly higher angle of attack compared to the Sensor due to its flight attitude (nose high) at the onset of the stall (Point 1). | ||
In addition, the pilot pulls | In addition, the pilot pulls in more, which results in a very negative moment (Point 2). The diagram of the U2 clearly shows that Phase 1 is much more dominant compared to the Sensor. The area under the moment curve is huge due to both the range of the angle of attack and the more negative moment (max. pulled-in). | ||
The opposite is true for Phase 2. As the pilot remains in a fully pulled-in position (green curve), the zero-crossing of the moment curve (Point 3) shifts to the left to a smaller angle of attack. The area under the (positive) moment curve is therefore noticeably smaller compared to the Sensor and the decelerating effect is thus significantly reduced. No substantial reduction in the rotational speed (as with the Sensor) can be observed in the video. | The opposite is true for Phase 2. As the pilot remains in a fully pulled-in position (green curve), the zero-crossing of the moment curve (Point 3) shifts to the left to a smaller angle of attack. The area under the (positive) moment curve is therefore noticeably smaller compared to the Sensor and the decelerating effect is thus significantly reduced. No substantial reduction in the rotational speed (as with the Sensor) can be observed in the video. | ||
But even then, the U2 would not have tucked if the pilot had stayed in front. Either he pushed out reflexively after Point 4 or, like the Sensor pilot, he was | But even then, the U2 would not have tucked if the pilot had stayed in front. Either he pushed out reflexively after Point 4 or, like the Sensor pilot, he was "pushed backwards" by the glider due to his inertia (despite the reduced rotational deceleration compared to the Sensor). | ||
[[File:MomentDiagram U2 en.jpg|left|thumb|800px|Figure 7: U2 Video - Defining the individual phases in the moment diagram]] | [[File:MomentDiagram U2 en.jpg|left|thumb|800px|Figure 7: U2 Video - Defining the individual phases in the moment diagram]] | ||
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'''Important: in Phase 2 and 3 the center of gravity was at no time behind the trim position!''' | '''Important: in Phase 2 and 3 the center of gravity was at no time behind the trim position!''' | ||
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# t=2:20-3:00s: The hang glider begins to yaw to the right (see VG rope deflection to the right). The wing is banked slightly to the right. However, there is no rotation around the longitudinal axis. | # t=2:20-3:00s: The hang glider begins to yaw to the right (see VG rope deflection to the right). The wing is banked slightly to the right. However, there is no rotation around the longitudinal axis. | ||
# Jesper corrects a left-side lift (?) several times and with increasing intensity: first with half, then with full weight shift to the left and finally he shifts his legs as far as possible to the left (more is not feasible, as the space is limited by the left rear wire). By the way: a perfect control technique! The left-side lift must have been caused by a gust/turbulence. The gust can also be recognized by the change in wind noise. However, I myself cannot judge with 100% accuracy whether the wind speed is decreasing (which would be the case with a gust directly from behind) or increasing. But I have the impression that the wind noise tends to increase. The replay didn't show any significant change in speed immediately before the tuck. However, this may be due to the measurement method and evaluation (time-averaged speed). The right hand rests rather relaxed on the control bar the whole time. For me, this is a sign that he is close to the trim position (neither pulled-in nor pushed-out). | # Jesper corrects a left-side lift (?) several times and with increasing intensity: first with half, then with full weight shift to the left and finally he shifts his legs as far as possible to the left (more is not feasible, as the space is limited by the left rear wire). By the way: a perfect control technique! The left-side lift must have been caused by a gust/turbulence. The gust can also be recognized by the change in wind noise. However, I myself cannot judge with 100% accuracy whether the wind speed is decreasing (which would be the case with a gust directly from behind) or increasing. But I have the impression that the wind noise tends to increase. The replay didn't show any significant change in speed immediately before the tuck. However, this may be due to the measurement method and evaluation (time-averaged speed). The right hand rests rather relaxed on the control bar the whole time. For me, this is a sign that he is close to the trim position (neither pulled-in nor pushed-out). | ||
# With the pilot in this sideways deflected position and in this yaw attitude, the hang glider begins to pitch down. The pitching and the rotational speed can be well recognized by the relative movement of the right corner of the | # With the pilot in this sideways deflected position and in this yaw attitude, the hang glider begins to pitch down. The pitching and the rotational speed can be well recognized by the relative movement of the right corner of the control bar to the trees in the background. Tests with ''FlightGear'' show that a '''gust from behind and below''' at a speed of approx. 15-20m/s is sufficient to trigger a tuck. | ||
# At t=3:24s the downward rotation comes to a brief stoppage (see right speed bar in front of the background; you have to look very closely; frame by frame analysis!) I do not yet have an explanation for this behavior. Immediately afterward, however, a much more pronounced pitch-down occurs (pilot is still on the very left; VG rope is still blown out to the right). | # At t=3:24s the downward rotation comes to a brief stoppage (see right speed bar in front of the background; you have to look very closely; frame by frame analysis!) I do not yet have an explanation for this behavior. Immediately afterward, however, a much more pronounced pitch-down occurs (pilot is still on the very left; VG rope is still blown out to the right). | ||
# t=4:12s: The yawing has stopped (VG rope is centered again). The main suspension begins to become slack (first visible at the top of the hang strap). The arms are already slightly pushed-out. The lateral pilot deflection remains unchanged to the left. This situation corresponds to Point 4 in the diagram. The nose of the hang glider is not yet pointing exactly vertically downwards. | # t=4:12s: The yawing has stopped (VG rope is centered again). The main suspension begins to become slack (first visible at the top of the hang strap). The arms are already slightly pushed-out. The lateral pilot deflection remains unchanged to the left. This situation corresponds to Point 4 in the diagram. The nose of the hang glider is not yet pointing exactly vertically downwards. | ||
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# 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 aerodynamic force). | # 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 | # t=5:16s to 5:18s: The left and right uprights bend symmetrically outwards. The hands are still holding the control bar 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 | # t=5:19s: Breakage of the right upright. Right hand loose (?). t=5:20s: Right hand back on the control bar 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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[[File:Analysis Tuck Jesper Diagram.jpg|left|thumb|800px|Figure 10: Time sequence of Jespers tuck using the moment diagram]] | [[File:Analysis Tuck Jesper Diagram.jpg|left|thumb|800px|Figure 10: Time sequence of Jespers tuck using the moment diagram]] | ||
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Either he could have flown a little faster (pulled-in slightly). This would have made him less susceptible to gusts or, ideally, he should have been in the maximum possible forward pilot position at Point 5 in the diagram (at the very latest at α=-4°; CM=0). Admittedly, the time window for pulling-in is very short (approx. 1s). It is therefore important to be mentally prepared in advance and to have automated control reflexes. You can practise this with ''FlightGear'', for example. <big>😉</big> | Either he could have flown a little faster (pulled-in slightly). This would have made him less susceptible to gusts or, ideally, he should have been in the maximum possible forward pilot position at Point 5 in the diagram (at the very latest at α=-4°; CM=0). Admittedly, the time window for pulling-in is very short (approx. 1s). It is therefore important to be mentally prepared in advance and to have automated control reflexes. You can practise this with ''FlightGear'', for example. <big>😉</big> | ||
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==== Impact of VG setting on tuck susceptibility ==== | ==== Impact of VG setting on tuck susceptibility ==== | ||
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<div style="clear:both"></div> | <div style="clear:both"></div> | ||
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There is a (short) '''prewarning''' time for '''gusts from above''' and '''from behind'''. Unfortunately, this is '''not the case with gusts from below'''. | There is a (short) '''prewarning''' time for '''gusts from above''' and '''from behind'''. Unfortunately, this is '''not the case with gusts from below'''. | ||
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Scary but not dangerous at all! At least as far as pitch stability is concerned. Structural integrity is a different story. | Scary but not dangerous at all! At least as far as pitch stability is concerned. Structural integrity is a different story. | ||
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=== Why all this theoretical crap? So how can I avoid a tuck in practice? === | |||
Well, if things are completely out of control (i.e. a situation arises that you didn't expect and/or scares you to death), simply apply the golden rule of hang gliding:<br> | |||
'''Shift the center of gravity as far forward as possible.''' | |||
In most cases, the problem will have solved itself by then. | |||
This requires the following actions: | |||
#'''Pull in''' as fast and as much as you can (without thinking too much - you don't have that time). | |||
#Be prepared to pull in hard to '''counteract the force of the control bar'''. | |||
#'''Prevent''' the '''control bar''' from '''moving forward''' by itself under all circumstances. This is extremely important! | |||
#As soon as the hang glider is flying stabilized again, '''wait a short time''' just to be on the safe side. | |||
#Then '''gently recover''' from the dive by letting the control bar move forward slowly. | |||
#Don't forget to start thinking again. | |||
That's all! | |||
The above applies to unpredictable and sudden events. For planned actions such as the intended flying of whip stalls, acro, etc., however, a lot of thought should be given beforehand. Therefore, a little '''theoretical knowledge can't hurt'''.<br> | |||
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