Icaro Laminar 13 MRX: Difference between revisions

'''This section is still under construction.''' The current status is July 26, 2025.

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.   

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).

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.

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'''a''' (stronger deceleration). In the diagram, the moment changes from the blue to the yellow curve.

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.  

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 α₀, 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 α₀ (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!'''

The fifth video (Hang glider Tuck and in air collapse Tolmin Slovenia) is a very rare documentation of a tuck out of the blue. In contrast to the previous videos, in which the tuck initiation is predictable (either due to the high angle of attack and/or the pilot's deliberate control input in phase 0), here the hang glider tucks suddenly out of a normal gliding attitude.

This tuck initiation can also be broken down into the four phases described above. The only difference is in phase 0, where the high angle of attack is generated by a '''strong gust''' that must have come '''from behind below''' (The influence of gusts on longitudinal stability is described in detail later in a separate chapter). Phases 1-3 then proceed in the same way as in the previous videos.

# 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 feeling 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).

# 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?).

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[[File:Gust Impact on inflow en.jpg|left|thumb|800px|Figure 12: Impact of Gust on Inflow]]

[[File:Gust Influence on A0a and DynamicPressure en.jpg|left|thumb|800px|Figure 13: Influence of Gust Direction and Strength on AoA and Dynamic Pressure]]

For α<α₀ downforce (negative lift) occurs, which leads to a ‚wire-slap‘ or slack hang strap. A 5m/s gust can be sufficient for this regardless of the flight speed.

[[File:Gust Change in AoA en.jpg|left|thumb|800px|Figure 14: Maximum Change in Angle of Attack due to Gusts]]

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.

The negative angle of attack due to the gust initially only leads to a harmless `wire slap`. The hang glider is pitching up slightly. However, the sink rate increases (see vario) as there is no lift for a while. Up to this point, everything is pretty safe.  

It can also be seen in a positive light: The '''`wire slap` is the alarm for pulling in'''! Depending on the duration of the gust, the pitching down may not be so strong, however it could occur. You are therefore on the safe side by pulling in.

If a gust comes from behind, the wind noise must decrease.  This can be `heard` in the next video example (turn the volume up!). At first, the wind noise decreases to almost nil. Only then the hang glider starts to pitch down.