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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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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 July | '''This section is still under construction.''' The current status is July 26, 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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* 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. | ||
<br> | <br> | ||
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# To stop the stall, the pilot pulls in slightly to the trim position (Point 2). The angle of attack is unchanged. The moment is now clearly negative. This leads to the extreme pitch-down. | # To stop the stall, the pilot pulls in slightly to the trim position (Point 2). The angle of attack is unchanged. The moment is now clearly negative. This leads to the extreme pitch-down. | ||
# In exactly this pilot position (relative to the wing), the system - consisting of wing and pilot - continues to rotate. The angle of attack is continuously reduced. In the diagram, the hang glider moves from the right to the left on the blue curve. | # In exactly this pilot position (relative to the wing), the system - consisting of wing and pilot - continues to rotate. The angle of attack is continuously reduced. In the diagram, the hang glider moves from the right to the left on the blue curve. | ||
# At | # At Point 3, the blue curve intersects CM=0 at alpha=25°. The area under the (negative) moment curve (between Point 2 and 3) is a measure of the strength of the rotational excitation. | ||
# For α<25° (to the left of | # For α<25° (to the left of Point 3) the moment is now positive. The deceleration of the rotation has started. | ||
# α<sub>0</sub> is reached at | # α<sub>0</sub> is reached at Point 4. From then on, the lift becomes negative, which results in a reversal of the control effect (see Figure 2). | ||
# '''Up to this point the hangstrap is tight!''' | # '''Up to this point the hangstrap is tight!''' | ||
# If the pilot would remain in this position relative to the wing, it would continue to move to the left on the blue curve. The momentum there is still positive up to α~-15° and the deceleration effect would still be present. However, the pilot now has to grab firmly the basebar because otherwise he would fall into the sail due to the downforce. | # If the pilot would remain in this position relative to the wing, it would continue to move to the left on the blue curve. The momentum there is still positive up to α~-15° and the deceleration effect would still be present. However, the pilot now has to grab firmly the basebar because otherwise he would fall into the sail due to the downforce. | ||
# Due to the braking effect, the rotation of the wing is almost stopped at | # Due to the braking effect, the rotation of the wing is almost stopped at Point 5. However, due to the inertia of the pilot, the pilot continues to rotate (relative to the wing), resulting in a shift of the pilot's center of gravity backwards. This configuration corresponds to the brown curve. | ||
# Since the angle of attack is already less than -2°, the moment becomes negative again, which results in an increase in the (initially stopped) pitch-down rotation. This is the actual tuck. | # Since the angle of attack is already less than -2°, the moment becomes negative again, which results in an increase in the (initially stopped) pitch-down rotation. This is the actual tuck. | ||
# Compare the area under the moment curve from | # Compare the area under the moment curve from Point 3 to 5 (deceleration) with the area from Point 5 to 6 (excitation), which is a lot larger. This is one of the reasons for the high rotational speed that is often observed in tucks. | ||
<br> | <br> | ||
'''The tuck initiation can therefore be separated into four phases.''' The initial phase, in which the pitch-down moment is generated and the excitation phase (CM<0), in which the rotation is excited. This is followed by the deceleration phase (CM>0), in which the rotation is slowed down. In the last phase, it is then decided whether a tuck occurs (CM<0) or not (CM>0). | '''The tuck initiation can therefore be separated into four phases.''' The initial phase, in which the pitch-down moment is generated and the excitation phase (CM<0), in which the rotation is excited. This is followed by the deceleration phase (CM>0), in which the rotation is slowed down. In the last phase, it is then decided whether a tuck occurs (CM<0) or not (CM>0). | ||
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==== Analysis of the U2 video ==== | ==== Analysis of the U2 video ==== | ||
In the U2 video (''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 ( | In the U2 video (''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 more, which results in a very negative moment ( | 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 ( | 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 | 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|U2 Video: Defining the individual phases in the moment diagram]] | [[File:MomentDiagram U2 en.jpg|left|thumb|800px|U2 Video: Defining the individual phases in the moment diagram]] | ||
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It should also be noted that the pilot's legs are temporarily bent up to 90°, which means that the pilot's center of gravity is slightly further forward. | It should also be noted that the pilot's legs are temporarily bent up to 90°, which means that the pilot's center of gravity is slightly further forward. | ||
In the initialization phase ( | In the initialization phase (Point 1), the hang glider nose points vertically upwards and the pilot is approximately in the trim position. At the onset of the stall, the hang glider is likely to slide backwards, which would be equivalent to an angle of attack of 180°. It couldn't be worse! | ||
In the diagram, | In the diagram, Point 1 of the initialization phase is therefore far outside the angle of attack range shown. The pitching moment curve continues to decrease steadily in the area not shown, so that there is an extremely high pitch-down moment at Point 1. Fortunately, the pilot is only slightly in front of the trim position and does not pull-in excessively. This would have resulted in an even worse pitch-down. Even so, the area under the moment curve in phase 1 is huge compared to the Sensor and U2. | ||
In this slightly pulled-in pilot position, he rotates very quickly up to an almost horizontal attitude. From then on, the pilot begins to push | In this slightly pulled-in pilot position, he rotates very quickly up to an almost horizontal attitude. From then on, the pilot begins to push out and his legs additionally move backwards. | ||
The pushing-out should still have taken place within phase 1, so that the control must have been actively executed by the pilot and not by the pitching moment of the wing (moment is still negative here). In this rear center of gravity position, the wing continues rotating until the nose is pointing vertically downwards. | The pushing-out should still have taken place within phase 1, so that the control must have been actively executed by the pilot and not by the pitching moment of the wing (moment is still negative here). In this rear center of gravity position, the wing continues rotating until the nose is pointing vertically downwards. | ||
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The fact that '''nuances can make the difference between tuck and recovery''' can also be seen in the Laminar video (''Whip Stall in Laminar14MRX''). Phase 1 corresponds somewhat to that in the U2 diagram, phase 2 to the Sensor and phase 3 more to the Falcon. For this reason, a separate Laminar diagram has been omitted. | The fact that '''nuances can make the difference between tuck and recovery''' can also be seen in the Laminar video (''Whip Stall in Laminar14MRX''). Phase 1 corresponds somewhat to that in the U2 diagram, phase 2 to the Sensor and phase 3 more to the Falcon. For this reason, a separate Laminar diagram has been omitted. | ||
In the initialization phase, the pilot pulls in a little earlier than the U2 pilot (you have to watch the video very carefully). The stall is therefore not yet fully established. Compared to the U2, | In the initialization phase, the pilot pulls in a little earlier than the U2 pilot (you have to watch the video very carefully). The stall is therefore not yet fully established. Compared to the U2, Point 1 and therefore also Point 2 are at a slightly lower angle of attack. The extent of phase 2a corresponds approximately to that of the Sensor. | ||
The rotation was probably already completely stopped in phase 2b near α<sub>0</sub>, as no unloading of the main suspension can be observed. Only the briefly visible decrease in the dihedral indicates that the angle of attack was minimally below α<sub>0</sub> (downforce). In this case, phase 3, i.e. pitching up, follows to the right of phase 2b. | The rotation was probably already completely stopped in phase 2b near α<sub>0</sub>, as no unloading of the main suspension can be observed. Only the briefly visible decrease in the dihedral indicates that the angle of attack was minimally below α<sub>0</sub> (downforce). In this case, phase 3, i.e. pitching up, follows to the right of phase 2b. | ||
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# 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 controlbar 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. | # 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 controlbar 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 | # 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=4:15s: Jesper is still on the far left. His arms start pushing out. It would be important to know whether he has actively pushed-out or whether the control bar has only moved forward without his intervention and how the bar pressure has changed in direction and strength. In this phase there is no slowing down of the rotation of the wing observable (in contrast to the tuck of the Sensor). It looks rather similar to the tuck of the U2. | # t=4:15s: Jesper is still on the far left. His arms start pushing out. It would be important to know whether he has actively pushed-out or whether the control bar has only moved forward without his intervention and how the bar pressure has changed in direction and strength. In this phase there is no slowing down of the rotation of the wing observable (in contrast to the tuck of the Sensor). It looks rather similar to the tuck of the U2. | ||
# 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?). | ||
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Yes, of course!<br> | Yes, of course!<br> | ||
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 | 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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