Thursday, May 23, 2013

Lock out on tow

A couple of weeks ago I had an experience I'd rather not repeat. I think there are some lessons that can be learned, so I'll share. In short it was a hang gliding launch that went wrong. I got away with it but just barely, I was exposed to far more risk than I was comfortable with...

The day seemed fairly harmless, wind was SE on the ground at 5-15mph a little gusty - but that's Texas. Above 200ft it was probably S @ 20mph. Air was unusually cold for the wind direction. I had already taken one flight.

I came out of the cart very smoothly, level and perfect airspeed. Just as I was starting to relax into the tow, I got whacked on the right wing. That made me climb and yaw significantly left. With full right weight-shift I came back into line (though I was still high). Just then the second surge hit, this lift was a lot more turbulent.
I went to pin of with my right hand, I was already too high, and surging upward, right after taking my hand off the bar the right wing rapidly lifted.
I was happy that Joel beat me too it and gave me the rope. As you can see from the sequence below, I had quite a bit of energy from the sling shot effect, but also with the air being pretty radical. Even off line I continued to be pitched up despite pulling in. All to soon I was without airspeed in a bad sideslip, I think the images are 2 seconds apart.So the sideslip was about 4 seconds (that's a lot - I was begining to think I would side slip to the ground).

The nose did come around as I dumped the VG, and I was flying low right back into the air that had caused all this, downwind and I was dragging the the 180ft tow line. I was a pretty unhappy chap!
I think some of the nasty air actually helped get my glider back into the wind for a no step (check your underware) landing. I'm not for a moment going to claim full authority over the glider. From roll out  to kissing the ground was less than a minute.

So what can be learned from all this ? We certainly are exposed to a higher level of risk from 20-80ft on tow. Are there things that increased my exposure? After having mulled over this a while I'd say there were three different possibly companding factors.

1. I think I was flying with too much VG (4/5) This compromised my roll control.

2. I had a camera on my sprog, and I've noticed before at high airspeed, the handling does weird stuff (probably on acount of the zipper being open and air pressure changing the camber).

3. In Luling we tow at higher airpseeds, this narrows the envelope that a glider should be in behind the tug. Which in turn will reduce the amount of turbulence that can be handled.

I think each of these factors on there own are innocuous, but combined had a dramatic result. I'd rather not do that again.


Tom Lanning said...

Thanks for sharing such an intense and eye-opening experience. Glad it worked out ok and that you learned something without much cost.

Ben Dunn said...

Right-on Tom. I hope others can learn something too. being leery of open zippers for one. Its like flying with a swimming pool of air in your sail! I've had it three times now. Not good speed gliding near terrain or on a fast tow. Probably good for a mag article ?

Glen Volk said...

Holy Smokes Lad. I almost puked.

See you at SCFR?

Chas S. said...

Would the ability to release without having to let go of the control bar made much difference?

Anonymous said...

"right after taking my hand off the bar the right wing rapidly lifted"

you would have been probably more confortable with a mouth release or a 2 points with a lanyard already in your hand..
We all should.

Mark Frasca said...

Damn Ben, glad it worked out in the end. How much zipper did you have open?

Ome Ga said...

Another big risk that you didn't mention is if the tow rope caught on something on the ground while you were still attached to it. I don't even want to think about what would have happened in that case.

On his surface tow rig, Pat Deneven has us rig an automatic release. If you go too far out of line with the tow rope it releases automatically. Would this work for aero-tow?

Ben Dunn said...

Some good questions and comments here.

1. 2 point release (or actually 3). Every system has it's pitfalls.
A 3 point release has partial tow from the keel, if you hit a gust, the yank force is distributed better. The pro-tow (I was using) generates a nose up rotational inertia (bad). A 3 point tow would have helped in this situation.

2. A brake handle release may have gained me 1/4 of a second, which this close to a tumble could make a big difference. Mouth release - I've seen a tooth lost that way, the day before his daughters wedding... better than a tumble though...

3. I had about 1/3 to a half of the outer zipper open. I'm sure different glider are effected differently. Something to be leery of especially at high speeds. I don't think I'll do this on a fast tow again.

4. the auto release - not really designed with aerotow in mind. I think it could release at in opportune times, but also not during a lockout.

5. Dragging a rope is always bad. I would have released it had I not been flying 60mph downwind through a dustdevil, at trees. I chose instead to fly the glider, since I could not do both.

Stephan said...

Hey brother, that looked scary. I am thinking the sprog zipper was the biggest culprit inducing the roll over / pitch down. I think it was Eric Williams at the Rob Kells last year who saw that my sprog zipper was open while getting hooked up to tow. He closed it and pointed out that it affects pitch stability and was aware of a pilot that nosed in because of that mistake. You might want to check with him to get the facts.

gordon rigg said...

Glad you are ok.
If yoy want to hang stuff out of the sprog zips fit two zippers so you can keep the zip snug round the camera bracket

Anonymous said...

Hi Ben,
I read about zip and VG but I would insist on the bad "Standard" equipment. For me it is clearly unsuitable to face critical events as yours.

A brake handle release may have gained me 1/4 of a second
If the tug released first, you probably lost more than 0.25sec by
1-waiting before to decide to take your hand off the bar despite the necessity to pull it fully.
2-reaching a release not already in your hand (I rather thought a lanyard already in your hand than a brake lever) or in your mouth.

You lost time AND you made the event worse cause if you're just approaching a lockout, taking a hand off the bar could be the very thing that puts you into a lockout.

Mouth release - I've seen a tooth lost that way
No way to loose any of your teeth here :

Ben Dunn said...
This comment has been removed by the author.
Ben Dunn said...

A second zipper is a good idea, I've flown with it half open (for the camera) probably 50 times, its seems only an issue at high speed. But You never know when you might have to go high speed, so yeah a second Zipper is a good idea. I was cutting a corner there.

Someone also pointed out more tell tales might have shown the approaching dust devil, it might not, but certainly not a bad idea.

That mouth release looks interesting, I'm leery of complexity. Having been involved in towing Hang gliders for 23 years I seen some odd things you'd never imagine happening. But this looks like something worth trying.

Of course preventing a lockout is always better than treating the symptom.

skypuppy said...

Soooo glad you pulled it out of the pooper and lived to tell the tale!

I'm convinced that the brake handle release is the quickest and most reliable way to go. I can slap the handle without even looking and have my hand back on the base bar in the blink of an eye. The small amount of drag is well worth the benefits, IMHO.

Stay well, hope to see you around some day! :-)

Kingstilts said...

Golly! Most fortunate that you had a little altitude and an attentive tug pilot.

Clearly, an experienced pilot's first instincts, in a tight spot, are to "fly the glider" (with both hands. An emergency proceedure that requires a release of grip will cause both delay and compromize of control.

An inflated sail causes pitch instability. The nose cone of my LiteSpeed came free during a flight a few years back and the glider was almost unflyable.
I mount a camera at the sprog junction with the leading edge. I simply reversed the Zipper joiner and it closes pretty snug.

- said...

It all happens so fast. That's why I created the GETOFF release. Keep it in your hand for instant action.

Anonymous said...

Shadetree Scholar said...

Ben - Thanks for posting this. I was a witness to the event, but being a novice pilot, did not understand everything that was going on. I just knew I was witnessing 1) a very serious event, and 2) some amazing heads-up flying. Now, thanks to the information you (and others)have shared, I have a better understanding of the event, which hopefully will keep me from getting into a similar situation down the line. Thanks again!

Verla said...

This is cool!

bluemax77 said...

Past 90 degree turn, close to the ground, semi out of prone - asking for trouble...

Augusto Furtado said...


Augusto Furtado said...