Well, this KAP session didn’t go as planned. Here is how it ended, with me fishing the kite and KAP rig out of the water:
How that happened is a little longer story…
The pictures above show Breton Bay, one of the many small bays and inlets in Southern Maryland. Leonardtown, Maryland sits next to the bay, and there is a small park there where I was flying my kite. This was actually my second attempt at flying here; the previous weekend had nice weather, but the wind died right around the time I was trying to get the kite in the air. This weekend marked the second attempt, and everything seemed good. It was a sunny day, with a north wind blowing out towards the bay. A north wind is needed to fly safely here, since there are apartments and power lines on the inland side.
The wind seemed just about perfect. It seemed to be about 8-10 mph most of the time, with gusts sometimes a few mph higher. Since there wasn’t room for a running launch, I decided on the Barn Door kite, which would have no problem getting in the air in this breeze. Soon after getting the kite set up, it was in the air. I flew it for a few minutes before bringing it down to adjust the bridle by a few centimeters. Then I let it up again, let out 150 feet of line, secured it to a stake in the ground, and observed flying by itself for a few minutes.
Being a nice, albeit somewhat chilly day, there were a few other people at the park. A few older teens were training, doing sprints and jogs. As a side note, one of the things I overheard them say was this, which was presumably supposed to be motivating, but I just found it kind of silly:
The Devil said to the warrior, Are you ready for the storm? The warrior replied, I am the storm!
I’m not sure who this warrior is supposed to be, or why he was talking to the Devil, but in any case, that little saying seemed to get them quite amped up. Other than those kids, there were several other people walking around, a couple of which were interested in the kite. They asked me why I had a remote control, so I gave a short explanation. They seemed quite impressed, and proceeded to snap some pictures of the kite and watch for a while.
The wind featured some small lulls and big thermals, but it didn’t seem like anything that the kite couldn’t handle, so I attached my radio-controlled KAP rig. This is where things started to go wrong. First, I forgot to turn on the PowerShot S100, which I didn’t realize until later. Next, once the rig was up a couple hundred feet in the air, I turned on the transmitter and monitor with the intention of taking a look at the video feed. The video transmitter (VTx) on the rig was off, but I could already see a picture in the monitor as soon as I turned it on. The only problem was, this wasn’t the video feed from the rig. It was kind of dark and distorted, but it seemed to be a picture or maybe a video feed showing a playground. I tried switching the VTx on, but there was no change in the picture. I then turned the monitor off and back on, and it showed something different, but still not the video from the kite. The VTx operates at 5.8 GHz, so there must have been something else nearby also broadcasting on the same frequency and causing interference. My VTx is only set to 25 mW, so it’s not too surprising if the signal was getting washed out by the other user of the frequency.
At this point, I figured all was not lost, since I could still control the rig itself, even though I couldn’t see which direction it was pointing. The rig was low enough that I could still verify that it rotated when I pushed the stick on the transmitter, so it looked like I would just be shooting blind today. I rotated the rig in the direction I thought was towards the town center and flipped the switch to take some pictures (still not realizing that the camera was off). However, right then the kite got caught in a powerful thermal, and I had to focus on flying it, as it was going straight overhead. It eventually overflew and then entered a shallow dive. Letting out some line leveled it out again, so that was no problem. With the variable wind conditions, though, this was clearly going to be a bit of an adventure.
Then the real trouble started. The wind strength picked up, which, as I’ve already noticed on several occasions, tends to pull this kite down. In the past, the kite has always recovered once the wind let up again. Typically, the wind is not as strong down low, so the kite may stay low for awhile in such conditions but eventually go back up. This time, I would have no such luck. I watched as it went down, down, down, not slowing much and eventually running out of space. Letting out line can help in this situation, but only if you can let it out very fast, and only if the wind eases up eventually. The kite and rig both went down hundreds of feet offshore. It was a major bummer, and also pretty embarrassing since people were watching.
Recovering the Kite and Rig
The worst part about it was that I didn’t know if I would get the kite back. My other KAP kite, the Mini Dopero, has also crashed in the water once. That occurred when I had it tied off on a short line without a rig attached, attempting to take pictures of it flying. In that instance, it was tough to wind it back, because the water was shallow and it got stuck. This time, there was an immediate positive sign, in that the kite was clearly floating, as can be seen in the first picture at the top. The second positive sign was that I was able to wind in the line without encountering any significant resistance, so apparently nothing was stuck.
After winding for five minutes or so, the rig emerged from the water. I pulled it out and realized my original mistake: the S100 was off. That could turn out to be serendipitous, since the chances of electronics surviving a water submergence are significantly higher if they are powered off. Several minutes of winding later, the kite emerged. I pulled it out of the water, packed it up, and decided I’d had enough punishment for one day.
So why did this happen? As I mentioned, I’ve previously noticed the problem that stronger gusts tend to pull this kite down. Now, it’s probably true that any kite will get pulled down to the ground at some wind speed, but this one seems particularly susceptible to it. I also have a smaller version of this kite made with wooden dowels and plastic painter’s cloth, and it does the same thing. Here’s what I think is happening.
- When the wind speed picks up, the spars and sail deform. Since the spars are so long (97.5 inches each), they bend quite a lot under enough force.
- The worst of the bending and billowing happens on the bottom half of the kite, since there is no horizontal spar there to help maintain the shape. When the wind is strong enough to pull the kite down, the sail appears very narrow on the lower part of the kite as a result, reducing the effective area of that half of the sail. The picture on the right gives an idea of this effect, although the wind was not strong enough for the kite to be pulled down when that picture was taken. It looks more extreme when the problem starts to occur, which I estimate is when the wind speed reaches Bft 4.
- The reduced effective area on the lower part of the sail moves the center of pressure upwards towards the top of the kite, causing it to pitch up and increase the angle of attack. The increased angle of attack in turn further increases the aerodynamic force, exacerbating the problem. In the end, there is not much you can do once it reaches this state except hold on and hope the wind lets up. Again, letting out line can help somewhat, but only if you can do it fast enough and long enough for the wind strength to lessen.
So What’s Next?
First things first, I have to see if any components on the rig are salvageable. My greatest hope is for the S100, which was powered off for the entire flight. As I write this, it is sitting under a pile of rice along with the electronics from the rig. I will let it sit for several days before attempting to turn it on. If it works, I will still be able to use it with my fixed-angle AutoKAP rig. I don’t have much hope for the electronics from the rig, which were powered on when it hit the water.
Regarding the kite, though I’m glad to have gotten it back, I’ve decided not to use it for KAP anymore. To be honest, I have noticed the problem in enough of my flights that I was starting to get uneasy using it for KAP anyway. Its usable wind range ends up being quite narrow if you want to avoid the situation altogether. And unless there is a steady sea breeze, it is hard to fly in such a narrow wind range, because during the course of a flight there will either be lulls during which the lift is not enough to keep the rig in the air, or there will be stronger gusts that threaten to pull it down to the ground.
Having heard a lot of positive stories about Rokkakus, I think I will replace the Barn Door with one of those, or a derivative. Sandro Macchi, who goes by the handle smac on the KAP forum, has been testing vented Rokkakus and reports that the usable wind range is excellent. Rokkakus are legendary for their stability and high line angle, which are also great features for KAP. My current plan is to build one 7 feet tall, which would be in between the size of the Mini Dopero and Barn Door. I may also “splurge” on some very lightweight ripstop polyester sailcloth this time instead of the 0.75 oz ripstop nylon I used for the others, which should bring down the minimum usable wind speed close to the Barn Door’s. The shorter spar length should reduce bending, which, combined with the vents and just due to being a Rokkaku, should give a significantly higher upper wind range than the Barn Door. It will also be much easier to set up at the field, since I’ll be able to transport it with the horizontal spreaders in place. (The Barn Door needs to be fully set up each time, which takes me 10-20 minutes.) Here is a picture comparing the three kites.
I am disappointed that the KAP session didn’t go as planned, and I’m definitely not looking forward to spending more money to replace whichever components got killed by being submerged in water. On the other hand, I’m excited to build and fly a new kite! And yes, I do plan to return and finally conquer this location! Mishaps happen; the important thing is to learn from them. Stay tuned for more information about the new kite as I start building it!