Friday, July 03, 2009

Tehachapi Valley

Our club is flying at Tehachapi (Mountain Valley Airport) this weekend. We have the PW5 and the Grob 103. There are only a few club members here, so long flights are possible. For several reasons, I did not plan to do any true cross-country soaring, so I juat flew over the valley and the immediately surrounding mountains.

It turned out to be a great day for thermal soaring! Lots of cumulus clouds to mark lift, but not enough to block the sun; no overdevelopment, and not much wind. I let off at 3000' AGL (7200' MSL) and hooked a good thermal right away. Although there was plenty of lift to be had, there were still several challenges. Some CU that looked to be developing (e.g. concave bottoms) never panned out. Some were ragged and I think indicated rotor rather than lift, though the wind was only about 15 knots. There were some VERY rough areas near the Tehachapi Mtns. I found quite a number of thermals both under CU and in the blue, commonly getting up to 12,500' MSL or so. The highest was 13,300', for a maximum gain of 6,100'. I found lift of up to 700 ft/min sustained, and it got really strong just under the cloud bases. I also found some serious sink (900 ft/minute for 2-3 minutes). And sometimes entering thermals I hit the biggest bumps I've ever encountered - knocking me way up out of my seat although my belts were as tight as possible.

I went as far west as the Tehachapi Loop (a somewhat famous railroad circle), as far east as the end of the valley, and as far south as the top of the Tehachapi Mts. Since I wasn't planning to go anywhere far, I used the opportunity to explore and compare SeeYou Mobile with the Borgelt B50 Super Vario that's installed in the ship. For the first half of the flight, the audio Speed To Fly correlated very well with the STF on SeeYou: when I sped up to the SeeYou STF, the Borgelt "faster" tone shut up. (That is, after I set he correct polar: SeeYou was still set to a Grob 130. Oops.) But after an hour or so, the B50 was always saying "faster" no matter what the lift was doing. This was really annoying, so eventually I quit using "cruise" mode and stayed in "climb" mode while flying straight. This made the display a simple vario, which was fine, but gave no STF audio. I've looked at the B50 manual to see if I was doing something wrong, and I can't find anything. I can only conclude that it was a malfunction, and will watch for it to happen again. I have suspected for some time that the vertical gauge that is supposed to show STF was not working, but assumed it was just the meter. Now I'm thinking that maybe it's the computer. If it happens again I'll power-cycle it to see if it resets.

I also used another feature of SeeYou Mobile. The Thermal Assistant gives a visual indication of where in your circle the best lift was found. It also gives an audible tone a couple of seconds BEFORE you get back to a good spot, and it seemed to be really accurate. This is another great feature for helping you keep your eyes outside the cockpit instead of looking down at the display. I wasn't aware of it until I prepared for the class I recently taught... I found it to be helpful.

I thermalled for a while with a 1-26, which was a little tricky because our speeds and glide ratios were different. We "poached" off of each other for quite a while.

The lift today was so strong I had to use spoilers to force the glider down to pattern altitude. I could have stayed up for a lot longer but decided to come down after 2 hours and 40 minutes. It would have been a great day to try for my 5-hour Silver Duration flight, but alas the Volkslogger did not come along on this trip... and it's a real pain to document a duration flight without it.

Tomorrow is not forecast to be as strong, but still probably a good soaring day. I'm trying out a new online soaring forecast site called XC Skies. So far I like it a lot! It pretty well nailed today's weather at this location. I'll have to see how well tomorrow matches its predicton, and try it out for my home field at Hemet.

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