Monday, April 26, 2010
And then there's this interesting comment: "During the steep climb the stick forces are of small value." Some winching experts have pointed out that stable gliders tend to climb at the angle that is the most efficient, i.e. the horizontal stabilizer will tend to orient the wings directly into the relative wind to achieve stability, and so the angle of attack and speed will tend to become optimized. They claim you can unhand the stick and a stable glider will climb well on its own. (I won't try that for quite a while!) The PW5's elevator is really small compared to the wings and the horizontal stabilizer, so it can't override the orienting effect. More on that later.
We set up today on the main runway, launching to the west due to the wind direction. We get an earlier start, which is good for practicing, but it also means the lift isn't working for the first few flights. A visiting glider pilot (not a member) wants to go for a ride, so I go up with him in the Blanik (me in front, him in back). He's been a winch launch passenger once before, so it's not all new to him. We get a good launch, but with no headwind and since I'm not terribly aggressive in the climb yet, we only get up to 900' AGL. We turn left to look for lift, but we get into 5 knot sink right away, so essentially we have to turn back and never get out of the pattern. We come in for a good landing and roll right up to the launching point. Fun, but short. No one else was finding more than 1-2 knots of lift this early in the day, so I don't think we had much of a chance for a longer flight anyway.
Later in the day I set up for a flight in the PW5. As expected, the tail boom comes down, but not very hard. If this winch was as aggressive in the first two seconds as the OCSA winch is, this rotation could be an issue. Once I get off the ground, I get into a slight PIO (which means "pilot-induced oscillation", pitching up and down due to not controlling perfectly). It's not much as PIO's go, and only lasts for about two cycles. But as I mentioned yesterday, if you don't pitch up at least a little bit right away to present a load on the cable, you can overrun it. My two seconds of horizontal flight getting out of the PIO is too long, and I see the parachute slip below me to the left, so I release just before someone on the radio calls "abort, abort". I make a safe and smooth landing on the right side of the runway (to avoid the cable), and roll out about two thirds of the way down toward the winch. This is what we call a "PTT" or "Premature Termination of Tow". It's a long walk back with the glider behind the truck.
After a few Blanik launches and our club pres in his PIK, I'm up again in the PW5. This time my takeoff is smooth and I rotate up and start a pretty good climb. Someone on the radio calls to the winch driver "more power, more power". Before long my airspeed is 67 and flirting with 70 knots. The maximum allowed according to the manual is 65, so I start pulling back to try to adjust the speed (forgetting for a moment the statement "During the steep climb the stick forces are of small value."). Probably my next move would be to call for less speed, but suddenly the speed drops off and I hear/feel the cable release. Bummer - PTT #2. Hmmm... I can't see the chute or the line by this time, but I can't imagine that I overran it at this angle. But there's no time to analyze it: I'm at 400' AGL. That's high enough to turn around for a downwind landing, so that's what I plan to do. I have had a rope break at 300' during auto-towing solo in a Blanik, so I've done this before.
I nose over and ensure I have flying speed. There was very little crosswind when I took off, so it doesn't matter much which way I go. Since the normal pattern is left-hand, I turn left and do a 270-degree turn and get lined up on the runway. Hmmm... The next Blanik is already lined up at the launching point. I know that when you have a PTT from an auto-tow or winch launch, where you go up steeply, you can't really land in the distance available back to the starting point. You would have to descend at the same 40+ degree angle you went up at, and that's not likely in a slippery glass ship. Maybe in a Blanik with flaps and a big slip, but not in this glider. Hmmm... passing over the launching point to the other end of the runway is not an option either, because our pres is landing his PIK there. There's a nice wide taxiway, just as long as the runway, so that's the obvious choice. Since I'm already lined up on the runway, I S-turn to the left and line up again. There's nothing in the way, and I make a nice smooth landing and roll to a stop about 100 feet beyond the launching point. No problem. But there's no way I could have landed back on the runway without overrunning the launch point. It's nice to have options!
So far today I have employed two of the three PTT landing procedures.
I discuss the flight with S, and can't quite figure out why it released. People on the ground thought my climb angle looked good. My slight pulling up and backing off on the stick to adjust the speed shouldn't have dropped the line very much. I'd be ready to go again after a waiting for Blanik or two to launch. But then the winch guys call in on the radio: we're done for the day due to a failed universal joint. Later on I see the U-joint pieces in the hangar - an old repair failed and it spun itself apart. That occurred during my launch, so now at least I know the cause of the sudden power loss and back-release.
By now it's 2:00 in the afternoon, so we break for lunch and tear down the gliders... and change a flat tire on one of the trailers. It was fun while it lasted, but the lift was weaker than expected so no one really "got away" today. The last of us leave the airport about 6:00. Hot and dusty, and grateful to the host club, we drive off into the sunset.
Sunday, April 25, 2010
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.
The club is going out to a sleepy desert airport for a weekend of winch launching. We will take our own winch and also link up with the local club that flies there. We're taking one Blanik L13, our PW5, and one private ship.
We start arriving about midday. When 5 or 6 guys have arrived, we assemble the Blanik. There's always one or two pins that seem to be hard to get in... This time it's a drag pin and the pin that holds the stabilizers down. But we get it done, and one of the newer club members gets to learn how it goes together.
By "sleepy" I don't mean run down... Quite the contrary. This county airport is well laid out and marked, with two runways and taxiways. But there's not much traffic. All day Friday I think there are 2 or 3 airplane takeoffs, and a helicopter drops in for 5 minutes. That suits us fine, and we lay out our winch line on 3000 feet of the longest taxiway. We fuss with the radios and line up the Blanik.
But things never really get off the ground. The winch doesn't have power at the right speeds. The glider starts off briskly but the overruns the line and has to abort. Two out of three times, the steel bridle gets tangled up in the main wheel. Not good! Eventually we scrub the operation for the day and discuss the problem over dinner. (This all sounds so simple... Actually it's about four hours of driving back and forth, talking on radios and cell phones, and moving equipment around.)
Turns out that a recent modification to the winch transmission is not working properly. Under load, it always wants to shift to second gear, and we need third gear for the climb. It's not the kind of thing that can be fixed here, and the member who works on it has somewhere to be tomorrow, so he takes the winch home.
Tomorrow the local club will be here with their winch, so at least we're not grounded for the weekend.
Saturday, April 03, 2010
- I bought a new battery for my handheld radio a few weeks ago, because it seemed that the battery was not holding a charge very long. I usually put it on the charger about 24 hours before I'm going to fly, and I check the battery voltage with a voltmeter on the morning of the flying day, so if it didn't get a full charge for some reason at least I know and I can use alkalines instead. This morning the new battery was dead as a doornail. Zero volts. The charger is putting out, so I'm not sure what happened, and will have to test it this week. At our old field the radio was mostly a convenience but at Elsinore it's a necessity. I'm going to change my routine and charge the radio as soon as I get home, and check it promptly, so I'll have time to charge again if necessary. And now that I think of it, the new battery is significantly bigger than the old one, so it probably needs more than 24 hours to charge anyway. Gremlin #1.
- This morning the club was breaking in a New Tow Pilot. That's a good thing - they need more of them. I think he was already qualified as a glider tow pilot, but was just new to this type of airplane and new to this club's location and operating procedures. Along about 10:00 they started preflighting the tow plane, and it seems that NTP needed to do 10 (count 'em - 10) takeoffs and landings to be qualified in this type. So glider pilot #1 sat for about an hour while NTP did about 7 cycles. Another tow pilot eventually jumped in and launched a few gliders. Later NTP did about 3 more cycles and then started towing gliders. It was interesting listening to the lead tow pilot coaching NTP over the radio. Apparently only one towplane was available for use today, so this caused a big delay in glider ops. I don't think the first glider took off until about noon. Gotcha #1.
- I recently got a new SUV which I can use to tow glider trailers. I have not towed anything with it yet, so I planned to hook it up to our PW5 trailer and see how level it sits, and tow it around a bit to see how it handles. The hooking-up part was fine - the weight of the trailer caused the vehicle hitch to drop less spend a quarter inch. But the trailer had a completely flat tire, so no opportunity to actually tow it around. Gremlin #2.
- Since our club instructor had about three people to fly with, I decided to fly the PW5 instead of a Blanik. We recently relocated it here to Lake Elsinore, and I have not flown it yet. The day was shaping up to have some OK lift, with some CU clearly marking it. So after a quick lunch I started prepping the PW5. The battery was not on a charger as I had thought it might be (the PW5 had been flown once since moving here). So I checked the battery with my voltmeter and it looked good. All went fine with the preflight except that the nosewheel tire was low - VERY low. Gremlin #3. No problem, I now bring a compressor to the field. Except... the little hub crowds the valve stem. There's NO way to get a connector onto it without a valve stem extension. At Hemet, we kept some of them in the flight shack. At Elsinore... well, most of our gear is currently elsewhere. I asked one of the LESC leaders - nope, they don't have any. Ask the guy with the repair shop. Hello? Hello? No one there. I'm not going to poke around in his shop. Any auto parts store nearby? Yep, right after you get into town there are two or three of them. OK, hop into said new SUV and head to town. Don't see any auto parts shops... all the way thru town... finally spot one on the way back, run in, buy a pack of 4 extensions, scoot back to the field. Lift is still working, four gliders clearly having fun under a CU. Let's go for it! With the extension in place, pumping up the tire is easy. Takes about 7 seconds - it's a REALLY small tire!
- While driving back, I get a call from a CFI on my cell. What the heck? Bluetooth system in said new SUV doesn't pick up, and I have to hold the phone to my ear - not kosher in California. Huh. It's always worked before. Gremlin #4.
- Now it's after 3:00. Push out to the line, I'm #4 for takeoff. This will take a while. Gotcha #2. Glass ship #1 takes off. Glass ship #2 takes off. NTP is getting into a groove, and the tow-and-landing cycle is getting shorter. Schweitzer 2-33 backs out of line, I'm next! Lift is still working - there's a line of clouds marking the top of a shear line.
- But the tow plane needs fuel, and that takes a while since NTP is new to the operation here. The clouds are starting to move farther away and get farther between. Gliders are no longer hugging the bottom of the clouds... they're lower and closer to the IP. Gotcha #3.
- Tow plane is back, I'm ready to go. It's now 3:50 and the clouds are gone. Gotcha #4.
- The variometer needle is going nuts! Swinging widely from 10K of lift to 8K of sink - still on tow! I've seen this before, when the battery died on me out of Tehachapi (see my Dust Devil Dash post from September 2007.) Check the voltage: 12.4. That should be fine. Huh. Faulty vario? Water or dirt or bugs in the static lines? I do remember I thought I might have gotten a drop or two in the TE probe socket when washing the plane - could that cause this behavior? Gremlin #5.
- NTP has taken me up to 3000' AGL, and instead of turning to head parallel to the ridge, he keeps heading deeper into the mountains. Gotcha #5: we're at cloudbase and he's still heading away from the field, beyond my comfort zone. I move out to the side to ask him to turn - no result. I remember that the practice here is that tow pilots don't respond to that signal, but they're on the radio and I could ask him to turn. But what the heck, we're high enough and not too far into the mountains, and there's a cloud to my right, so I just release.
- At the Initial Point I make the usual call on the radio. Abeam the end of the runway, I can see a towplane getting into position with a glider. Since we take off and land in opposite directions on the same runway, the procedure is for the wing runner and tow pilot to keep an eye on the pattern, and hold the takeoff if they judge that there is not time before the incoming glider would be in the way. (Even if they did take off, the glider could always turn final early, parallel to the runway, and land in the green area to the side.) So I fly a normal approach and keep an eye on the tow plane.
Coach to NTP: "Hold on, there's a glider in the pattern. The guy didn't make a call."
Me to the world: "The guy did call at the IP."
NTP to Coach: "I heard his call."
Gotcha #6: Due to an odd airfield sharing arrangement, glider pilots are discouraged from making any calls other than the first one at the IP. At other fields we call the IP, downwind leg, base leg, and final leg. That way is safer - Coach would have had four chances to hear my position. I don't like this procedure, but that's the way the owner prefers it.
But at least we got to fly, right?