Thursday, December 27, 2007

Sleigh Ride

We often call a glider flight a "sled ride" if there's no lift found, because it's a downhill ride all the way from release to touchdown. But since this was the last Saturday before Christmas, let's call it a sleigh ride. And this day of soaring involved some frost and ice!

The forecast was for 450 or so fpm of lift up to 5000 or 6000 feet, but there were hints of an inversion which could defeat the lift. I was determined to fly regardless of lift, because I had not been in the air for about a month. It was very clear due to recent rain, and had been cold overnight. There was frost on the wings of the Grob and the PW5, which I have never seen at Hemet before. T commented on my blog post about the water collecting in the PW5's spoiler boxes and horizontal stabilizer, so we checked the boxes and were surprised to find ice. And not just a little skin of frost - a hard layer of ice a good quarter inch thick and about a foot long! It took quite a bit of work to break it up and pull it out so it would not interfere with the spoiler arms. Then we checked the drain holes in the boxes... one on each side was plugged with dirt, which explains why the water accumulated. Something else to inspect and maintain. There's something to learn every day on every flight!

I planned to take a high tow because I expected there to be no lift. The ground temperature was above the trigger temp, but if the air was too stable that wouldn't matter. On the way up, I decided to use the Outside Air Temperature (OAT) display as I have mentioned before. On the ground, it registered 25C, or 77F, which is way more than the 63F thermometer in the shade on the shed was indicating. So the dark runway must have been heating the air just at ground level. I didn't watch the OAT right after takeoff, but at about 400'-500' AGL it was already down to 16C. It kept going down fairly rapidly as we climbed, and then it stuck at 9C at about 1500'-2000' AGL and stayed there all the way up to 3800' AGL where I released. So there was a definite inversion layer - a big thick layer of 9C air that was not getting any cooler! I knew that I would not find any lift in that zone.

The flight was nice anyway, even if was a sleigh ride. The visibility was incredible! Usually we have some haze or smog, but this day was crystal clear. I could see quite a ways out into the ocean, and the sun was lighting up the water like gold. The mountains and all the lakes were gorgeous. This is why I fly.

I played around a bit with airspeed and sink rate, trying to get the minimum possible sink. Maybe sometime I'll take notes on them and see how they compare with the published polar.

I did find a few bumps at 1200'-1500' AGL, below that inversion layer. I circled a few times and found nothing better than zero sink. All too soon it was time to come in and land. My flight time from 3800' AGL was 26 minutes, or 146 feet per minute - right at the theoretical minimum sink rate for the PW5.

A reminder for the new year: the Air Safety Foundation recommends that your first flight of the year be with an instructor. Not a bad idea!

1 comment:

smiss said...

Well, I'm glad you got a flight in Roger. I'm in a state of suspended aviation myself. Crappy weather since I got back from NZ, then I bumped into my local club members on their summer camp at Cootamundra in western New South Wales when I was visiting my Mum after Christmas (but no chance of a flight - only one two-seater there and it fully committed to cross country flights), an incident with one of the club's other tugs put a stop to flying at Camden, and today (my other chance of a fly), there's no answer on the duty pilot's or the clubhouse phones, so I guess there's still no flying. I'm tearing my hair out here!