Educational by Chapter of the Powered Paragliding Bible

I: First Flight

01 Training Process

02 Gearing Up

03 Handling the Wing

04 Prep For 1st Flight

05 The Flight

06 Flying With Wheels 

II: Spreading Wings

07 Weather Basics

08 The Law

09 Airspace   

10 Flying Anywhere

11 Controlled Airports

12 Setup & Mx

13 Flying Cross Country

14 Flying With Others

III: Mastery

15 Adv Ground Handling

16 Precision Flying

17 Challenging Sites

18 Advanced Maneuvers

19 Risk Management

20 Competition

21 Free Flight Transition

IV: Theory

22 Aerodynamics

23 Motor & Propeller

24 Weather & Wind

25 Roots: Our History

V: Choosing Gear

26 The Wing

27 The Motor Unit

28 Accessories

29 Home Building

VI: Getting the Most

30 Other Uses

31 Traveling With Gear

32 Photography


--- Not in book ---

33 Organizing Fly-Ins

34 Places To Fly

35 Preserving the Sport

36 Tandem

Mid-Day Mishap

Thermally conditions dump experienced PPG pilot

See also Chapter 19, Emergencies: Handling Wing Collapses

A mid-day sojourn in moderate winds went sour for one high-time paramotorist resulting in a nearly disastrous impact. Surprisingly, the pilot walked (probably limped) away.

At 20 feet or so while landing, a quick downward gust started folding down the right half of his wing. Momentum and relative wind did the rest, quickly collapsing 70% of his paraglider. All that fabric, now presenting a vertical wall of drag, caused an immediate turn that was aggravated by lift from the open left side. The highly experienced pilot didn't know what happened until a turn began. Then it was way too late.

It took less than one second from the pilots first feel of trouble to be in an unrecoverable situation. Lest anyone think otherwise, realize that it takes the human brain at least one second just to register a strange sensation. The only way out of this was prevention.

Another 20 feet higher and it would have been much worse. Another 100 feet higher and it would have been recoverable.

It appears he felt something because, although on landing approach, he lifted his legs just before the collapse started. Also, it looks like the wing surged forward somewhat. The most likely scenario is that he flew from the rising air of a thermal into a downward swirl on the other side. That jibes with reports from the pilot and witnesses. See sidebar on the thermal theory. One witness said the pilot reported a blast of warm air just before it happened. Wake turbulence (see sidebar) is a possibility that appears far less likely.

Keep in mind, we're analyzing what took 3 seconds to finish.

It seems the wing surged forward, making it more susceptible to collapse and this hit a bit of downward gust. Dampening that surge could have certainly helped but it may not have been enough. When off power and in turbulence, it's a good idea to try keeping brake pressure 2 or so (about 1/4 brakes). I suspect this pilot, with his experience did damp it slightly.

Thanks to Steve for sharing the video, James for helping with information and Brent for his perspective.


Frame A through C show a normal, power off approach. Frame D shows him bring his legs up but the wing hasn't felt anything yet. Frame E reveals the leading edge just starting to be blown down slightly right of center. In Frame F the slipstream is now pushing the wing downward and causing a significant collapse. Notice the pilot is still essentially level and in the same position he has been throughout.  His fate is sealed yet he is only aware that something is amiss. From frame E to F is about a half-second. He has just started to turn right in frame G and, at this point, is essentially a passenger. The only out was preventing entry.

An experienced paramotor pilot who saw it happen offered his thoughts:

It was around noon. And he was flying over the field trying to get down a couple times before. He said he could feel heat rising off the ground. Just before he crashed he was over the black top taxi way.

So the hot sun could have contributed to it for sure. I had just arrived at the field when it happened and I was just off to the right of the camera. Paul's brother Steve shot the video of the crash. I shot Ivan later and made the video.

Another flyer and eyewitness offers:

It was around 11:00 or so...He was flying on the downwind side of the runway. After talking to him, he said that just before the wing gave way he had a blast of warm air hit is face.

If you look at the airport diagram below he was east of runway 12/30. Also there are trees to the west and south at 30' to 60' feet. With the wind coming over these trees, the heat of the runway, the building to the east of that, (Look at the top picture of the website), something could happen. He was the only one flying at the time, too.


Prevention

Flying within three hours of sunrise and sunset, and only during forecast mellow conditions is the best prevention. Some pilots, especially free flyers who are used to stronger conditions, will take on the mid-day risk knowingly. Sometimes they get burned.

Winds appear to have been fairly light. If you walked outside and checked, you have considered it nice. Wunderground historical data showed it to be light that Sept 22 noontime. See the charts at right for a temperature graph. Thanks to Terry Lutke for the weather information.

Skill and choice of equipment also has an effect on susceptibility. For example, being heavy on a wing reduces the likelihood of a collapse at some increase in severity. Your choice of a wing affects it, too. A fast, high performance wing is more susceptible than a beginner wing although it can happen to anything—if the air is going down faster than the wing can handle, the leading edge will react this way. A reflex wing, flown in its most resistant configuration, may handle it better, too. Reflex wings don't fold under as easily although they certainly can and you better know what configurations are susceptible.

Once aloft, a pilot can reduce his chances of this fate by those suggestions covered under Handling Wing Collapses. Essentially keep brake pressure 2 applied, especially with the power off. Fly actively if you've already developed that skill, otherwise, now is not the time to learn it. Using just the right brake inputs to keep the wing overhead (active flying) is a skill that takes many hours to master and pilots who don't fly regularly in moderately bumpy air never acquire it. Strong turbulence is not the place to learn since inappropriate inputs are worse than just holding pressure 2 and letting your hands float with that pressure.

Video of Collapse and Crash

Some interesting points. Notice the video's time counter. It's basically over in two seconds. Ivan is one tough bird! The windsock and other pilot input suggests that winds at the time were relatively light (see sidebar on Weather at the Time).

 

 

The accident happened at this airport although not to this pilot. Photo taken by Phil Adkison of his wife Cynthia. Provided by James Zeman.

Downdraft Collapse

If you fly into a sharp, powerful downdraft it can fold the leading edge down and cause a collapse.

The diagram below shows how a small, powerful thermal could cause it. The exact same thing could happen when flying into the downward swirl of rotor turbulence or a wake from another aircraft.

A paraglider can only fold downward so, as you hit the updraft portion, you're lifted. It feels like when an elevator starts but lasts longer.

Sometimes the wing goes back, sometimes it moves forward depending on airflow in the thermal. The base action is for the wing to go forward slightly because of the momentary apparent weight increase while you accelerate briefly upwards.

But when you fly out of the rising air and into the static or descending air at the thermal's edge, the wing folds downward.

 

 

 

 

 

Weather at the Time

Below is a graph showing the winds recorded nearby from Wunderground. As you can see, base line conditions were mellow.

 

Was it Wake?

I've flown through my own wake many times in spirals and other times and have never had it do anything even close to this.

Of course it could have been wake turbulence. He's shown turning back towards his flight path of 20 seconds prior. That would have been close, but it should have been noticeably dissipated by the time he got there. I could see it if he were on speedbar but that doesn't look to be the case.

So, although wake is a possibility, it seems far more likely that this was caused by thermal induced turbulence.


© 2016 Jeff Goin & Tim Kaiser   Remember: If there's air there, it should be flown in!