Sunday, January 22, 2006

Funky Day at Kahana

Prior to hiking up, the air on the beach was straight in and steady. The sky was mixed clouds and sunshine with clouds blowing into the valley. The forecast and known weather systems and earlier sensor readings indicated trades, tending toward easterlies.

Up on low launch the wind was fairly cross from the NNE, with some gusts. Alex took Fireman tandem finding lift immediately. I chose what I thought was a nice lull to launch, then found myself elevatoring straight up on only the second flight of my new small Sport 3. There was plenty of lift. Bob and Ray soon followed into the air. I saw what I thought was Ray performing little wingovers just off launch. I thought "He must be bored with normal conservative flight." He later reported that it was some funky air just off launch that made him do it. Alex reported he found similar conditions in trying to topland there (a flightplan he abandoned because of it).

Alex, Bob, Ray, and Fireman all reported experiencing funky air on approach to the LZ just before me. The streamers on the beach were occasionally flying from the direction of the rhino horn near launch, other times going limp. Despite the suggestion being made that I might land at Punulu'u, I braced myself to instead explore the funky air.

I took an approach near to my normal pattern, heading toward the corner of the bay next to the boat ramp, but definitely staying over water. At one point while facing the trees but slightly toward the LZ, I starting elevatoring down fast. Alex offered that I could just ride the sink all the way down! No thank you sir!! After waiting to see if the sink might be short-lived, I let up on my brakes and turned a little more downwind to speed up and hopefully escape the sink that seemed might just take me all the way down to the water. Free from the sink and approaching the beach's edge, I initiated a gentle turn to the left to try to get faced back toward the wind. I am not sure how much brake I used for this, but my best guess is that I had very little right brake on. Perhaps that is what allowed the right side of the glider to collapse. Or I might have been weight-shifting left with right brake (for a flat turn). Either way, the right side was less loaded and collapsed when it found funky air. I felt it happen, but perhaps didn't respond quickly enough to prevent or dampen it. Quick assessment: am I falling? No. Am I spinning? No. Good! Let's go land! I felt what I believe was its attempt to reinflate (hey, it's a DHV1-2, no worries, right?), but when I could feel that it was still limp, I looked up to see a cravat (the wing tip mercilessly tied up by its own lines). I kept my light left weight-shift to keep the left turn going as I tried fruitlessly to get the 25% cravat out. Fortunately, I could feel that it was still flying reasonably well (thought I preferred to have the whole wing) and so in agreement with the insistence of my esteemed colleagues, I proceeded toward the gap in the trees. On the way, floop! the wingtip came out (just to make things more interesting). In retrospect, I think it finally reinflated because I weight-shifted right a bit to turn back toward the beach. From then on the air was smooth (the streamers were flaccid) and I was able to negotiate a U-turn in the keyhole to land safely, much to the relief of my generous (in their landing advice, as well as post-flight refreshments) and joyous (perhaps also attributable to the post-flight refreshments) colleagues.

Final analysis and questions:
The Sport 3 collapse on approach: I think the collapse was most allowed to occur because of very light loading on the right as I was turning to the left. It may be that the sink I had just run from caught up with me on that right side. I do believe I reacted with increased brake on the right side as I felt it going slack, but perhaps not quick enough. I'm not really sure. I certainly am looking forward to more time with this wing, and this day provided some interesting (albeit high risk :-0) experiences with it. Fortunately, as I had just done a few practice asymmetrics, I had an idea of what to expect flying it with the collapse/cravat. In my practice runs, the wing tip opening was delayed and seemed to require a bit of brake action to promote opening. This action did not, of course, work on my landing approach as the tip of the wing was caught pretty tightly in some lines 1/3 of the way in from the end. Weight-shift to the collapsed side (which is counterintuitive from our earlier training) seemed to be the answer - more research to come on this.

Wind direction and rotor:
If it was so east, then why were there so many indications of north? Cross from north on launch. Folks in the air talking about it being more north (or at least NE instead of E or ENE). I know for sure as I was trying to cross the bay, hanging under some clouds, using their suck to help me keep me afloat so I could make the other side, that those clouds were moving perpendicular across my path (NE or NNE) toward the valley. The streamers on the beach pointing from the N - wow, if that's from the E rotor, that really is scary.
Kahana gurus: can E really seem so N? How can newbies and old bags like me recognize the signals of extreme E? Do you think the weather simply switched on us? (The weatherflow sensors don't show this.) Did I misinterpret some of the signs that were there?

p.s. Sorry, my editor passed out in a drunken stupor last night, so you get the long version. She's such a lightweight!


Anonymous said...

Well done, June. I had a similar experience coming in to the LZ at Kahana when I first got my Sport II, but other than slight directional input on my part to stay on course the glider pretty much sorted itself out. DHV1-2s are good that way. Anyway, I'm glad you had a safe and interesting flight with your new glider.

firedave said...

Sandy it was good flying all the way on your part, "yer all grow'd up now". The collapse probably occured as you turned to your left and released the right brake into turbulent air and your lines snatched up your wingtip. The wing was still flying fine so there wasn't any real worry there. You were low in rough air so the best thing to do was to continue flying it in as you did. Two ways to fix a cravat: Reach up and pull on the stabilized line or outside A line. Or steer toward the cravat to take the pressure off it and steer back away to put pressure back into the wingtip. This is what you did and it opened up. It is better to use more weight shift and less brake pressure during large cravats to avoid spinning the glider.
Weatherwise, the wind was strong from the East, you could see it bending around Crouching Lion. This causes it to rotor around and blow from the North on launch and at the LZ as it bends around to fill up the bay. The problem is the air doesn't move uniformly as it bends around and hence the bumpy air especially at the LZ.
Makes flying there more fun though.

Alex said...

Great write-up Sandy! I'd also like to hear from Nightshift about the Sasquatch that cracked his ankle-bone yesterday, but somehow I don't think we're going to see that tale in print anytime soon.

By the way, the picture of you over the jet ski was taken by Dave as my tandem passenger. Dave also took a couple of pictures of our heads in tandem flight together, but they're too scary to publish on a family site like this one.

Here are some of my thoughts about wind direction at Kahana.

The NWS 7-day forecast was calling for E 10-20. But that doesn't really give you any hint that it's going to be too east. When they say E it could be anywhere between ENE and ESE. Also please note that we recently corrected the iWindSurf sensor at Punaluu but we went too far the other way - right now if it says E it's probably more like ESE. We need to tweak it back slightly to get it just right. In the meantime I would rely on Kailua or Kaneohe for direction at Kahana.

A great test I learned in the old days of flying Kahana was to check the cloud drift from the boat ramp before flying - if the clouds are coming from the crouching lion formation across the bay, or more from the left, no worries. If they are coming from the right of the lion, you could be in for some rotor on the beach. I still use this test and it's a good rule of thumb. Yesterday it was a touch to the right when I hiked up. I knew it was marginal but sometimes it seems worth taking the chance. You can always go land at Punaluu if it seems really ugly down there. It's especially useful to have someone like Suicide Pete who's not afraid to try it first so you know how bad it really is.

Unfortunately, you can't really tell the overall wind direction by watching the streamers on the beach. All they can tell you is what the local wind parcel on the beach is doing - which is most important when you're actually landing. It's also a good way to check the consistency of the beach wind before you hike up. And like Dave says, we've seen the streamers on the beach do all kinds of things on days when the wind is too east and can't make it into the bay cleanly. They will often show gusts bouncing off the the north side (like yesterday) and sometimes they'll blow straight out of the valley (yuck).

Also, you can't tell what the ambient wind is doing by checking the direction from low launch. It always comes in there from the valley to the north. That's just how it flows there, and we've learned to ignore it as an indicator of overall direction. It just means it's a crosswind launch every time.

To check if the wind might be too east to land Kahana safely, I suggest that pilots first stop at the boat ramp and use the lion test before they hike up. Combine that with a check of the streamers on the beach, and make sure they blow smoothly in a consistent direction for long periods of time. Once you've hiked up, you can see the wind lines on the water from launch very clearly, and you can judge how east is it by how much the lines have to bend to get around into the bay from Kaaawa. Also, once you've launched, you can definitely tell what the wind is doing in the air by which way your glider goes straight without applying brakes or weight shift. Although we need to keep in mind that sometimes the direction of the wind above launch is not quite the same as it is below launch. Also the wind direction can change just a slight amount and have a huge effect on what happens over the bay.

We have found that a strong day that goes too east will throw ugly rotor waves across the bay, which are visible as lines of dark crossing an otherwise shiny surface from the beach. Often they'll bounch off the north side, like yesterday. On light days that go too east we'll more likely see offshore pulses of wind from out of the valley.

I know that many people have doubted that an easy and benign place like Kahana can have such a dark side. If you fly there only on days when it's definitely east or somewhere north of there, you'd never believe it. But for most people it only takes one good whack to get their attention. That's the boogie man of Kahana.

For some reason, we've never experienced rotor on the beach on a day when the wind was blowing from a more northerly direction. Even when we've launched from the other side of the bay, over the lion, we've had clean air at the LZ. There's just something about the flow from the E (or ESE) that complicates our landings in such a special way. Not that you didn't handle the turbulence with your usual aplomb -- great job. I've seen some dramatic collapses and parachutal stalls in that kind of stuff, and I once saw someone spun 180 degrees in an instant, I forget who. One time I was slammed out of the sky straight down into the surf on a day like that. These days I'm much more likely to go for Punaluu if there's any doubt, since the beach there can handle a breeze from the ESE without any complications.