Avoiding getting Blown Back
at the Westlake Cliffs above The
Dumps
The
site is called Mussel Rock, but the slang name is even better
known The Dumps. One of the greatest hazards that 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, I promote
that 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 much 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 Mussel Rock/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:
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 need 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 right away. 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 that you will have
good or better penetration in. 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,
you would 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 serve as beneficial.
You just 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. As a
result 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 wings penetration
is only related to the horizontal component of the wind's speed.
Because the wind in front of the cliffs 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. Wind speed increases because more air is trying to fit
through a smaller area. 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 now 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
More paragliding
articles
Dump
Site Checklist
June 26, 2004
Ann Sasaki
The Dump
is a great coastal soaring site with varied flying conditions
and terrain. Over the years, there have been many serious accidents
and incidents involving visiting and local pilots. Please review
this Checklist and the more comprehensive Coastal Site Advisory
before you fly here. Thanks for your cooperation.
Required
Pilot Skills:
Minimum of a Para2 rating (or foreign equivalent)
Able to ground handle the canopy in high winds
Have a strong reverse launch
Know how to deflate the wing quickly upon landing in high
winds
Know how to increase penetration and decrease altitude
Familiar with Ridge Rules
Conditions
to be aware of:
Large
Wind Gradient: The wind can be MUCH stronger above
than at launch. Stay LOW and well in front of the ridge on strong
days.
Shear Turbulence: There can be strong turbulence
where two air masses going in different directions meet. Shears
are common at the Dump and pilots should not launch into or
fly in strong shears.
Whitecaps: Whitecaps on the ocean indicate
strong winds. Pilots should consider landing when these form.
Fog: Fog can develop quickly and creates
a dangerous lack of visibility. Do NOT fly into the fog.
Rotors: Rotors are found in the lee side of a ridge, spine
or other formation. Rotors CHANGE according to the wind direction.
Do NOT fly into rotors - you will find severe turbulence.
Wind Direction: Wind direction can change.
Check the direction as you fly and before you land. Do not fly
downwind close to the ground or land downwind.
Changing Conditions: Wind direction, wind
speed and gust factor can change quickly. Fog and shears can
develop rapidly. Always check for changes in the flying conditions
and land if prudent.
High tide and no beach: In the winter and
at high tide other times of the year, there is often NO beach
in front of Westlake. Be aware of this and be within glide of
an alternate LZ if there is no beach. Check the beach size before
you launch.
Hazards
to beware of:
Power
lines and houses along the ridge, major roads and highways behind
the ridge.
Bowls and gaps where the wind is stronger because of the venturi
effect.
The ocean is extremely cold and often has large waves. Landing
in the water can be fatal due to hypothermia and getting tangled
in lines and drowning.
Concrete and other debris at this site because it has 20 years
of landfill use.
Heavy traffic in the air - paragliders, hang gliders and RCs.
Clear all your turns and follow Ridge Rules. Be respectful of
other pilots in the air and give them plenty of room.
The high Westlake cliffs have a big wind gradient. Do not
fly Westlake if you are inexperienced.
Equipment
all pilots should have:
Certified
glider in good condition
Harness with quick release buckles
Helmet, proper footwear, gloves
Hook knife or other knife that can cut through risers if you
go in the water
Speed bar to increase penetration in strong conditions
Please note:
It is important to get a site intro from an experienced local
pilot or instructor.
In an emergency:
Daly City
Fire Department - (650) 991-8092
Daly City Police Department (650) 991-8119
Please note that calling 911 from a cell phone often results
in a long wait so it may be faster to call the direct phone
number listed above.
