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Icaro Laminar 13 MRX: Difference between revisions
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→Tuck avoidance: Text Falcon and Laminar
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Firstly, the analysis of the | Firstly, the analysis of the Sensor video (''tumbling a hang glider''): | ||
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[[File:MomentDiagram AssignmentSensor en.jpg|left|thumb|800px|Assignment of the flight attitude and pilot deflection in the moment diagram (see Sensor video)]] | [[File:MomentDiagram AssignmentSensor en.jpg|left|thumb|800px|Assignment of the flight attitude and pilot deflection in the moment diagram (see Sensor video)]] | ||
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# The pilot wants to initiate a spin, but does not succeed (Point 1 in the slide). The angle of attack is very high (estimated α>45°). He is probably already in a stall. | # The pilot wants to initiate a spin, but does not succeed (Point 1 in the slide). The angle of attack is very high (estimated α>45°). He is probably already in a stall. | ||
# 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. | ||
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# '''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 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 | # 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 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. | # 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. | ||
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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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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. | ||
In 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 (point 1). | ||
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). | 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). | ||
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[[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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In the Falcon video (''Extreme Hang Glider Whip Stall'') you can see a pilot who is only a passenger of his own hang glider most of the time. Due to the excessively high towing speed, he is hanging paralysed in his harness until he releases the tow rope or the weak link breaks. Due to the overspeed, the hang glider then pitches up to an almost vertical attitude. In terms of flight attitude, this is really the worst position. | |||
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 (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, 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-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. | |||
This '''fully-pushed-out position is very beneficial''', as it reduces the negative moment in phase 1 (less excitation) and significantly increases the positive moment in phase 2 (stronger deceleration). In the diagram, the moment changes from the blue to the yellow curve. | |||
As a result of the increased deceleration of the hang glider, the pilot (due to his inertia) is accelerated backwards much more violently relative to the hang glider (compared to the Sensor). This would have inevitably led to a tuck if there wasn't a '''fundamental difference''' to the Sensor and U2: By clutching the control bar extremely tightly, the pilot does not rotate around the hang point (like the Sensor and U2 pilot) but around the control bar! | |||
The pilot's center of gravity does NOT move further backwards but instead slightly forward again until the pilot is aligned parallel to the control frame! In the diagram, the moment curve in phase 2b is back on the blue curve. | |||
'''A small but essential difference with a big effect!''' | |||
The hang glider does not tuck, although the rotation is only stopped at an angle of attack significantly lower than α<sub>0</sub> (recognizable by the negatively deflecting sail and the tensioned luff lines). | |||
[[File:MomentDiagram Falcon en.jpg|left|thumb|800px|Falcon Video: Defining the individual phases in the moment diagram]] | [[File:MomentDiagram Falcon en.jpg|left|thumb|800px|Falcon Video: Defining the individual phases in the moment diagram]] | ||
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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. | |||
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. | |||
'''Important: in phase 2 and 3 the center of gravity was at no time behind the trim position!''' | |||
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This relationship between the center of gravity and tuck or recovery is illustrated again in the following slide: | |||
[[File:Comparison cg near a0.jpg|left|thumb|800px|The correlation between pilot position and tuck or its avoidance]] | |||
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[[File:Analysis Tuck Jesper Diagram.jpg|left|thumb|800px|Time sequence of Jespers tuck using the moment diagram]] | [[File:Analysis Tuck Jesper Diagram.jpg|left|thumb|800px|Time sequence of Jespers tuck using the moment diagram]] | ||
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