Author: Jerome Daoust
Homepage: www.expandingknowledge.com (includes pics and movies)
Accelerator (Usage). You are using your accelerator (speed bar). Do you really need to ? Your wing is less stable under these conditions. Use of the accelerator near the ground, should be for emergencies only.
Do not use the brakes at the same time for these reasons: - It increases your risk of collapses. See Accelerator (Turbulence).
- Small amounts of brake pull will significantly reduce your speed and L/D.
- Resuming max speed after a temporary brake use, takes a long time.
A Collapse (Asymmetric, Recovery) with the accelerator fully extended will induce more violent reactions than at normal flight speed. Look at your wing's DHV test report (see Wing Certification) to find out more.
Stomping on the accelerator will make your wing more likely to Collapse. I have seen this happen. Activate your accelerator in a gradual manner. If you want to use Big Ears simultaneously whilst using the accelerator, perform Big Ears before using your accelerator. Otherwise you risk a Frontal Collapse as you perform Big Ears
See also : Accelerator Adjustment.
Try to fly in front of the slope most perpendicular to the wind direction, such that there will be the least amount of sideways deviation of the wind (useless wind direction component).
Venturi Effect.
A typical Venturi effect : On the mountainside that faces the wind, a dip in the profile will accelerate the wind over it. This typically happens in between two peaks. The horizontal component (windspeed) will increase and the lift will diminish. To cross this area, one should move forward (away) from it, and then get back closer to the mountain after having crossed. Think of it as an aspiration zone.
Blown Back. The wind has increased and you are now going backwards towards a ridge line. Face the wind. If there is no turbulence, use your Accelerator . Hope that the wind will reduce again, but look for potential landing zones behind you (beware of areas in wind shadow). If you have managed to get back in front of the mountain, don't give the wind a second chance, go land. If the problem persists, your options are: - Find lower wind at lower altitude. If you are far in front of the ridge, do Big Ears plus Accelerator to get lower without going back too much.
- Gain enough airspeed to move forward (improving pilot aerodynamics has little influence on airspeed).
Options for gaining a few km/h over max speedbar (watch your GPS ground speed): - Pull down the A risers a few cm. Grabbing the A risers with a thumb-down fist and start twisting by bringing your elbows down (7-8 cm contraction potential). You will become more vulnerable to a Frontal Collapse. Don't shorten so much as to significantly reduce tension in the A risers. Compared to a straight pull on the risers, this method is both less tiring and provides better shortening control.
Adrian Thomas, 2005/10/20: Reach up to the outer A lines, and pull gently down on them (a few cm). It only works on wings which are designed with wash-in (angle of attack higher at the tips) at speed, and because the purpose of such a design is to give you greater leading edge tension (and therefore tuck-resistance) your chance of a Frontal Collapse (Recovery) is higher.
Adrian Thomas, 2005/10/20: Grab the stabilo lines and pull these in. You can pull more than a few cm. This will reduce span, increasing loading, and increasing leading edge tension. Your glide will go down a tiny bit. It is hard to hold the stabilo lines for long. The effect per cm of line pull is smaller than the effect of the "outer A lines" option.
- Go around the shoulder of the ridge. If you are close to the shoulder of the mountain and you can avoid it altogether by letting yourself slip to the side to a safer area, do it.
- Accept that you will go over the top. Remember that "air is harmless, rocks hurt". The idea is to maximize height before flying downwind over the back of the mountain. Try to get into a more aerodynamic position (may not improve airspeed, but will improve L/D). Get as much height as you can by positioning yourself for max ridge lift from the ridge. As you are getting close to the ridge line, perform Crabbing to aim for a gap in the ridge where the Venturi Effect will exit (windier but more laminar). When at the ridge line, turn and "run" with the wind. After the ridge, maximize ground height to try to remain on top of the rotor. In the event that you can't avoid the rotor,
see Dealing with Turbulence.
To reduce your altitude without sacrificing too much of your horizontal speed, use the Big Ears technique or do some Wing-Overs — Note that Big Ears offers more stability.
If you fly very close to the mountainside (15 m / 50 ft or less) beware of turbulence induced by a lower irregular slope. Always have a light tension in the brake that would make you turn away from the mountain and keep some speed (above minimum sink) to be able to maneuver away.
How to Gauge Wind Speed from Visual Clues. See also : Water Surface - Gusts.
| On Land | Water Conditions | km/h | mph | | Still Air, Smoke rises vertically | Mirror-like water surface | - | - | | Rising Smoke drifts, Weather vane still inactive | Small ripples on surface | 2 - 6 | 1 - 3 | | Leaves Rustle, You can feel the wind on your face, Weather vane is still inactive | Small glassy wavelets. | 6 - 11 | 4 - 7 | | Leaves and Twigs move around. Light weight flags extend. | Large wavelets.
Some white caps. | 12 - 19 | 8 - 11 | Thin branches move.
Wind may raise dust and paper. | Small waves.
Frequent white caps. | 20 - 30 | 12 - 18 | Small trees sway.
| M5oderate waves.Many white caps.Some spray possible. | 31 - 39 | 19 - 24 | Large tree branches move.
Exposed wire may whistle. | Large waves.All white caps.Some spray. | 40 - 50 | 25 - 31 | Large trees sway.
Resistance felt when walking. | Seas heap up the waves.
Some foam streaks off waves. | 51 - 61 | 32 - 38 |
The depth of the usable lift band increases with the wind speed. In a light wind, you must remain close to the mountain to get sufficient lift. When the wind is stronger, you can move away from the mountain and still get enough lift.
- At the end (shoulder) of the windward face, the wind will slip sideways instead of going over and producing lift. Avoid these low lift areas.
- You have been flying in lift caused by dynamic conditions, but your ground speed is not the same when flying along the mountain in one direction, compared to the other. This indicates that the wind has a sideways component. To now get over the landing zone with as much altitude as possible : Leave the lift when you have completed the leg that offered the least ground speed. That last effort of going back against the sideways component of the wind will now allow you to leave the mountain and have less to fight against the sideways component.
- You have been soaring for a while but you now realize that you are making less and less turns and facing the wind in a more constant fashion. This indicates that the wind speed has increased while you were flying. Don't look at the others to see if they are still flying, decide on your own to go land.
- The wind has been blowing 20+ km/h (12+ mph) all day, and the sun was out all afternoon. The wind will typically reduce its speed about 2 hours before sunset, and it is possible that the accumulated heat in the ground keeps giving off sufficient lift well in front of the mountainside. Welcome to "magic air" conditions, also known as "valley release".
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