Sunday, April 25, 2010

Winch weekend - Day 2 - Lots of Flights

The weather yesterday included some small cumulus clouds indicating that there's some moisture left over from last week's storm. I'm hoping that will stick around, since today (Saturday) is supposed to be even warmer. It doesn't turn out that way. There are some decent thermals, and a few pilots get away from the airport and get up to about 6,000 MSL or so. But it's all "blue", meaning no clouds to mark the thermals. And they seem to be strong enough to work if you're about 1,000 feet or so AGL. But most of our focus today is on winch training, refining techniques, and a few guest rides. We haven't done any winching for a few months, so even those who have sign-offs like to go up once with an instructor.

We interleave our flights with those of the local club; they're flying a Schweizer 2-22 and a Blanik L13 like ours. We set up on a north-south runway that's about 3000' or so long. In theory you could get to about 1,500', and I think several flights achieved 1,200 to 1,300. It depends on how steeply the pilot climbs, which is somewhat dependent on experience. It also depends on the winch providing the right speed at the right time, which is partly experience on the part of the winch driver, partly the power and smoothness of the engine and transmission, and partly ESP. The winch is so far away, I don't think they can really see how the glider is doing. More modern winches have a "constant tension" mechanism which smooths this out, but our clubs don't have such devices.

I have had a winch signoff for some time, and have flown several flights with instructors since then, but have not had the opportunity to launch either solo or as PIC without a CFI. Another pilot and I take one of the early launches, with me doing the flying from the front seat. The launch goes well, but I'm not very aggressive with my climb angle, so we only get to 700' AGL. That's not really enough altitude to go hunting for a thermal, so I turn back toward the starting point, intending to make an abbreviated pattern unless we stumble into something really good. But we get right into bad sink instead, and really soon we're down to 400' AGL and not in a great position for a standard pattern. I work out kind of a base leg without losing too much altitude, and then as I get lined up for final, we're in some lift. So I find myself at about 400', midfield, and needing to slip off altitude to land in the second half of the runway. The Blanik slips well, so I get it down and stopped but slightly into the dirt overrun at the end of the runway. (One thing none of us realized until later is that the last few hundred feet of the runway is downhill a bit, so that doesn't help with the stopping.)

Now that I have had time to think about it, if a launch is less than "pattern altitude" it might be best to just stay right around the release point of the runway looking for lift. That way if it doesn't pan out you could just turn around into a final approach. The turnaround time for the winch cable is such that no one will be taking off right away to create a conflict.

My next flight is with our CFI. This launch my angle is a bit more aggressive, and we get up to 1000' AGL before it back-releases. We snoop around and find some decent lift (up to 700 feet per minute at times) that takes us up another 1300' or so. We're not really looking to get away, just work on the launch and landing, so when the lift doesn't take us up very high we come back in about 15 minutes.

Late in the day, of the other pilots S is ready to try the PW5. The first launch doesn't go according to plan. Shortly after taking off, before he starts to rotate into his climb, the parachute inflates and is dragging the ground, and the glider passes it, so S releases and lands straight ahead, nearly all the way down the runway. It was a clean aborted launch, but we're trying to figure out why the line and the chute lagged. The way we figure it, the PW5 is 200 pounds lighter than a Blanik, and has only one occupant, and is very slippery. Once it's airborne and loses the rolling friction of the wheels, and is still in ground effect, it has little drag, so if there's the slightest loss of tension in the line, the parachute can inflate and dragging the line down, and the glider can then overrun it. Once the glider rotates, the wing angling through the air presents a much bigger load (and drag). So it would be important to climb, at least a little, shortly after takeoff. We're pretty conservative about not rotating into the steep climb until we're a hundred feet or more off the ground, so there's a fine line between rotating too early and too late. More on this in tomorrow's post. S takes off again later, and all goes well... I think he released at about 1500' the second time.

Despite not getting started until close to noon, and a 40-minute wait when the winch blows a radiator hose clamp, we get in about a dozen launches of our ships and the other club does quite a few as well.

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