We knew that there was possibly a problem with our cable, because we'd had several breaks last time we used the winch. Although the Spectra cable is very strong, it can get worn and damaged. We can see some worn spots in the cable, and we have a couple of theories about what caused it:
- One time a fairly large loop of cable developed along one side of the spool, i.e. the cable had a bit of slack when the spool went around. The cable that was then laid down alongside that loop could have rubbed against it and worn it down in the area of that loop. The loop was temporary, and removed itself the next time the cable was pulled out, and as far as I know it has not happened again.
- The cable was worn by dragging over a peak in the middle of the runway where we operated for a few weeks. Usually a cable does not get a lot of wear, because it's pulled out slowly, and when it's pulled in quickly for launching, it's not on the ground very long - the rising glider lifts it up. But this particular runway has a noticeable hump in the middle. For the first few seconds of the pull, one section of the cable is subjected to quite a bit of friction. On a flat runway, the ground friction would be fairly evenly distributed along the length of the cable. With a hump, it's like dragging the cable over a corner.
We'll probably never know exactly what caused the wear, but we are expecting more breaks until all the weak areas are spliced. We may reverse the cable on the spool, if the worn area is toward one end. If the runway is not too long, the worn section may remain on the spool.
One of the nice things about the FAA's ruling in our complaint against the County is that it explicitly provides for winch operations. As long as we are following standard radio procedures and the operating manual that we and the County developed, winch launching from the glider runway (4/22) can coexist with power traffic. We can even announce a two-minute pause in power traffic if necessary.
But before we could safely launch, we needed to work on the field. The County has allowed a lot of weeds, mostly tumbleweeds, to grow on the north side of the airport. Many of them are close enough to the runway to be a hazard - last weekend one pilot had a wingtip go through a tw as he was slowing down after landing - it was enough to divert him off the runway a bit, but fortunately he was not going very fast and got it back under control. One of our club members provided a "drag", essentially a length of heavy railroad rail on chains, pulled behind his vehicle. This did a great job of cutting off the tumbleweeds (which are designed to break off at ground level), and did a partial job of clearing them out of the way. I raked many of them out of the way, and we then had enough clear areas for takeoff and landing. If we get a good west wind, it might clear them all completely out of the way. But if we get a north or south wind, we'll need to rake them out of the way again. The County needs to take care of this!
Eventually we were all set up and one of our instructors took the Grob up for the first winch launch, taking off on runway 22 to the west, and landing on 4 to the east. He got up to about 1,000' AGL before the line back-released. There was essentially no wind, so that was a pretty good altitude. A headwind helps the glider climb faster, getting to a higher altitude before topping out over the winch.
He and I went up next, me flying as PIC from the back seat. One disadvantage to the back seat is that you can't see the rope at all - not that you can very well from the front either. The launch and climb were normal, if maybe a bit slower than we might like. We were up at about 800' AGL when I sensed that we lost the rope. He said it hadn't back-released, so we concluded it was a rope break. But we were in lift! We climbed 200' right away without doing anything. In the slippery Grob, 800' is a decent pattern entry altitude, and we were just over the end of the runway, so we actually had a about 300' or more of altitude to use to explore just a little. There was a bit of lift in the area, just enough to take us up to 1,100' AGL and keep us aloft for a few minutes. The thermal was hard to center - I got lift on one side of the circle and zero sink on the other side.
Soon we came back to land on 4. Other than slightly overshooting my final turn, my landing and rollout were great. Since we had the whole length of the runway, I did a smooth "wheel" landing, closed up the spoilers, and rolled all the way back to the starting point.
Unfortunately, that was the last flight of the day. Finding and untangling the cable, and repairing the break, would consume the rest of the time we had available (remember some guys needed to make it a short day). For the next winch launch day, we plan to reverse the line on the spool.