Saturday, October 29, 2005


I picked up a book called Meteorology for Glider Pilots. It's old - 1961 - but it looks really good. The author seems to have been a British professional meteorologist and a glider pilot. I'm about halfway through it. The first several chapters are general meteorology, fairly technical. The latter part is how it applies to soaring. Here's the one thing that has piqued my interest so far.

There's a section on katabatic and anabatic flow. Katabatic is downward flow of cool air through a valley... not terribly useful to the glider pilot but something to be aware of. (See a description of katabatic wind in on glaciers in the popular novel Deception Point by Dan Brown.) Anabatic flow is upward flow of heated air along a slope. If a whole slope of a hill or mountain gets heated, the whole lower layer of air along the slope can "slide" up the hill. Not vertically away from the slope as a classic thermal, but along the slope, toward the top. (Maybe there's no "dripping point" to cause the heated air to break loose from the slope.) I don't think I've seen a description of it in any of the other books I've read. They all talk about thermals, ridge lift (orographic), wave, and sometimes shear lines.

Last year when I flew at Tehachapi with three pilots, we flew up the mountains. At the time I was a bit confused as to the sources of lift we were using. The mountains there did not form a distinct linear ridge, as the classic diagrams of orographic lift show. There were thermals that we used, and sometimes we could see the sources of them (rocky areas), but I could not really imagine a line of thermals coming off of all points of a sloping ridge. Sometimes we were flying right up the "spine" of a sloping ridge, and not in a direction that I could say was within 30 degrees of being perpendicular to the wind direction. So now I'm thinking that maybe anabatic lift was happening on the slopes. And if both sides of a ridge got heated, and anabatic flow happened on both sides, the flows could meet at the top (spine), collide, and be forced straight up. That lift could be twice as strong as each slope's anabatic flow. And unless there was a strong wind to one side, it would not have a turbulent area in the lee of the ridge: the lift is going straight up off the ridge, not orographically being forced up and over at an angle. I think this model explains our mysterious ability to fly up the spine of a ridge all the way to the top of the mountain.

I would welcome other pilots (and meteorologists') comments and experiences!

Grounded by a stupid mistake

Today was forecast to be a moderate day, soaring index about 440. Early flights indicated 400-600 was happening. I got set to take off in the PW5 about 1:30. Two guys were up in the Grob, the instructor and a student were up in the Blanik for quite a while... A new student helped me push out and I got set to go. In the ship, on the runway, tow plane parked in front... I went to adjust the rudder pedals and pulled the canopy emergency release instead! Since it was in the open position (the PW5 canopy is hinged at the front), it fell immediately, landing on the runway and putting a nice 1.5" chip in the rear rim (the white part, not the transparent part).

We looked at it for a moment and realized it was not obvious how to put it back on. So we pushed the glider off to the side and looked some more... still not easy. Hmmm... all the experienced club members are in the air... Aha! Look at the manual! No, it talks about lots of things but not how to put the canopy back on its hinge. I know, wait for the instructor to get back! "No, I've never even flown that model..." After messing around for a while, I got it figured out. By then it was 3:00, the weather was so-so, and I was not in a mood to try again.

Other members tell me I'm not the first to do that. One pilot pulled it in flight, but fortunately in the closed position the two rear latches hold it on. Others have done it on the ground but I'm probably the first to have it drop and cause damage.

What contributed to the mistake? (Not making excuses, just examining the situation to see how to improve.)
  • Inexperience: I've only flown the PW5 3 times. But the canopy release is bright red, and the pedal handle is dull red and down low. Should have been obvious.
  • Distractions: Answering a student's questions while preparing for flight. I don't think this was a big part of it.
  • Rushing: The tow pilot had started her engine as soon as the previous glider took off, and I had already given her the "kill" signal once. I knew I had several steps to go to be ready: belts, pedals, positioning my GPS, water tube, radio mic. The belts were all twisted up... I know it's up to me to do all my steps regardless of the tow pilot - no one was behind me waiting - but it still annoys me when they're ready to go and I'm not.
Next time...

Sunday, October 09, 2005

Two passengers

Saturday I took two friends for rides in the Grob 103, M and his son K.

K is a 13-year-old who goes to my church and is somewhat interested in aviation. He'd been waiting all summer for our schedules to coincide. The day was hazy and about 75-80 degrees, a cold front having just gone through. Wind was about 12-14 kts at 45 degrees to the runway, and I decided it was OK. (Later I checked and that works out to a 9-10 kt crosswind component. I was comfortable with the wind, and it did not cause any problems on takeoff or tow.) Lift was forecast at 250, and it that's about all we got. We took a 3800' tow, nearly to the top of the haze layer and a bit below the few clouds that were around. About 5 minutes into the flight, I noticed I had no yaw string! K was OK with the flying and turning, so I went ahead and worked some of the weak lift and zero sink, and we got a 31-minute flight out of it. The crosswind was still present at landing but not a problem - I even got a compliment from someone on the ground about my nice straight landing.

I had tried to take M before in the Blanik L13, but since he's 6' 7" he was too tall. But he fit in the back seat of the Grob just fine. He gets motion sick but has been soaring once before and wanted to go again. I promised to take it easy. The wind was still about the same, brisk but not too strong. (This time I added a yaw string! I think we should put that on the daily inspection checklist.) We again went to 3800' and let off in light lift which promptly disappeared. We flew around a while and found less lift than last time. I think the haze/smog was inhibiting the heating of the ground, and the wind was blowing out the thermals. M had a good time looking at the nearby lakes and finding the route we had driven in on. There wasn't much lift to work with and M started to feel slightly ill after about 20 minutes so we came down, making it a 26-minute flight.

I was high on late downwind and base leg, so I used a turning slip to bring us down, which worked quite well. Landing in the crosswind was again OK - I seem to naturally find the correct slip angle for a straight approach. But I let my speed get low at the very end and probably stalled at about 3" to 6" above the ground - a bump but not too hard. So that's on my things-to-practice list... I have never done that in the Blanik or PW5, so maybe it has something to with the apparent attitude from the cockpit, or the effectiveness of the spoilers... I need to watch the speed more closely after the flare.

Another thing to remember with the Grob: an instructor pointed it out and I have noticed it too. The Grob rolls into a turn rather slowly, so you need to start the turn from base to final just a bit earlier than you might think, or you overshoot the approach and have to make a more-than-90-degree turn to final, which is NOT a good thing.

I'm up to about 39 hours of logged time.