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Avoiding getting Blown Back
at the Westlake Cliffs above Mussel Rock

The site is called Mussel Rock, but the slang name is better known: “The Dumps”. One of the greatest hazards Paraglider pilots face is getting blown behind a ridge or mountain. This site is different from most ridge soaring sites because the launches are well below larger cliffs. Both visiting pilots and local pilots have been blown over the back at the Westlake Cliffs. Prevention is the best way to avoid such a scenario. This article is intended to provide techniques for managing wind increases and what you can do to prevent a Blow-Back when you notice that winds are reaching higher levels.

The launches – Tomcat, Lemmings, Walker, and The Jungle are all at the lower levels of the Westlake Cliffs. There are ridges in front of and to the side of these launches that can be flown without going to the higher cliffs. On windier days, this is the place to stay. Next to Walker launch, there is an intermediate ridge which transitions to the high cliffs. Behind all of the launches are the cliffs of Westlake that are about 600 ft high. The winds can differ greatly between the lower, intermediate and high cliffs.

As a means of preventing Blow-Back, never fly when the wind is stronger than you are comfortable to launch in. On some days, the winds are light at the lower levels, but stronger at the upper cliffs. The key to all flying at these cliffs is to use your senses and observations to continuously observe the wind-speed. On the days when it is stronger at the lower launches, “if launching will take the top of your ability”, you should consider staying on the ground. Flying in very strong winds is just not worth the effort and risk. It should go without saying that if your glider has a speed system, always fly with it ready for use.

Any time you launch at The Dumps, a system of wind-speed awareness should be second nature to you. On lighter days, your crab angle will be less than on a day with higher winds. As the wind speed increases, two things will happen:


• Your Crab Angle will need to be increased.

• Your speed parallel to the ridge will start to decrease.

Keeping tuned in to these two factors at all times will help you manage wind increases. It is even more important when you fly at a site like Mussel Rock. At the launches, Tomcat, Lemmings, Walker and The Jungle, the wind might be 12 – 13 MPH, but at the top of the 600 ft cliffs the wind may be 20+ MPH.

When ascending from the lower cliffs of Westlake to the upper cliffs, you must continually monitor the wind speeds and your ability to penetrate. It is best to stay further in front of the cliffs when it is moderately windy or above. The higher you go on the cliffs, the more clearance you should give yourself in front of the cliffs. If the wind increases suddenly at a higher level, this extra distance will aid you in getting back below the stronger winds and keep you in front of the increased winds that are at the top of the cliff. Never fly above and behind the high cliffs, it just is not a good place to be.

If You Fly On A Windy Day

Notice that the gliders in the below photo
are pretty much following the recommendation
of staying further out as they go higher up.

Photo Provided by Andy Stocker

When your crab angle is increasing and you are forced to point more into the wind, you are being warned that the winds are getting stronger. If you notice that it is getting strong and your ability to penetrate is being compromised, take action immediately. As you rise higher, there is normally more wind. It is the awareness of these wind signs that will keep you out of trouble with blow backs. When the wind is blowing stronger, fly immediately upwind away from the cliff and descend to winds in which you will have good or better penetration. Point straight away from the cliff and combine the use of your speed bar and Big Ears to achieve the combination of descent and high end speed. If the wind is not straight in, there is not much difference. For example, on a day when the wind is blowing from the Northwest, it would be best get away from the cliff by pointing between straight away from the cliff or slightly toward the Southwest. If there are smaller cliffs to the south, this will be beneficial. You need to adjust the angle to find the one that gets you away from the cliff the best.

When you learn to gauge the wind-speed better using these techniques, you will be able to make adjustments when getting higher and before it becomes critical. Using the speed bar alone will help you penetrate the wind, but a better approach is to try to fly below winds where you would ever need to use it. Once you decide you need to get on your speed bar, if you can penetrate without climbing, you may be able to take care of the situation without using Big Ears. But, there are times where you are penetrating with the speed bar, but still climbing. Remember, the higher you go, the stronger the winds will be. Whenever the situation is getting critical, the combination will work best.

Another reason for staying further upwind of the cliff as you go higher is to stay well clear of the wind just above the cliff. Because of a couple of factors, the wind just above and behind the cliff edge will be about 5 – 7 MPH stronger on a windy day.

Virtual Venturi and Horizontal Winds = Higher Perceived Winds

There are two causes for this 5 – 7 MPH wind increase. One is that the air changes above the cliff from angling upwards to moving horizontally at the top of the cliff. The second is that there is compression of the air mass just above the cliff causing a virtual venturi, so there is actually higher wind velocity compared to the wind in front of the cliff.

In front of a cliff, the air is rising as a result of being deflected upwards by the cliff. When you fly in front of the cliff, your wing will not see the full force of the wind. Your wing’s penetration is only related to the horizontal component of the wind's speed. Because the wind in front of the cliffs is deflected up, wings are better able to penetrate there. Once the wind rounds out and moves horizontally above the cliff, you lose the extra bit of penetration that the vertical vector of the airflow helped you with. No matter what speed the wind is blowing, you will have a slower ground speed (lower penetration) behind the cliff than in front.

In addition, there is a virtual horizontal venturi that is created at the top of a cliff. The rising air in front of the cliffs is compressed as it merges with the horizontal air above the cliff. This is also called the "compression zone" because the rising air that is pushing up under the upper air and gets compressed. The rising air squeezes above the cliff and under the upper air. As a result of this virtual venturi, the air must move faster. Notice in the above drawing how the lines representing the wind become more compressed above and behind the cliff.

On a strong day, if you were to reach a point of not penetrating right in front of this area, you would be a prime candidate for getting blown back. If you somehow got into this situation without being on your speed bar, it may not help then because of the increased winds that you could be backing into. If you were going backward into this area with no speed bar and push it just after you realize, it may not be enough. The key point here is that drifting back into this area on a strong wind day is risking your life!

To summarize:

• Check the Wind Speeds before you fly.
  
  
• If you are new to the site, get a full introduction. Read the below Checklist before flying the site.
  
  
• Have a speed system ready on your glider. This means connected, adjusted, and ready for use.
  
  
• Know that the winds can be dramatically stronger and dangerous at the top of the Westlake cliffs.
  
  
• Continuously monitor the wind speeds as you fly.  (Do this via your crab angle and lateral groundspeed along the ridge).
  
  
• Avoid flying higher on windy days.
  
  
• If you do fly higher in stronger winds, fly well upwind of the cliffs as you ascend and traverse the cliff.
  
  
• Know how and when to penetrate out in front and how to descend to lower winds.
  
  
• Penetrate and get down as soon as you notice that the wind is getting strong. When you get on your speed bar, your purpose should be getting down, not staying up in the strong winds.
  
  
• Avoid the area above and behind the top of the cliff at all times.
  
  
• Below is a Checklist for other safety issues related to flying at Mussel Rocks / The Dumps.

Jeff Greenbaum
6-30-04

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