Sunday, June 11, 2006

Two so-so flights

The forecast was for 261 to 4650' if it heated up to the trigger temp of 81. Forecast highs ranged from 78 to 80. There was to be an inversion, but weaker than it usually is. See last week's blog... if the temp exceeds the trigger temp even a little, I'm hoping for some thermal activity. As I drove out, weather reports were showing about 81 to 82.

I got to the field later than I had planned, and took off about 2:15 in the PW-5. It was Sunday, and although I didn't expect many club members to be out, I thought some might be since the airport was closed for an air show on Saturday. Nope, no one else there. But the PW5 is light enough to push out by myself. Well, I did get another guy to help since the wind was a little gusty. He reported a little lift but not very long flights in their PW-6.

First flight I found a few bumps, no major sink. Some turbulence - I think the wind was knocking down the thermals. But there were some hints, and the day was so nice I couldn't just settle for a 19-minute sled ride.

So I went right up again. By now it's 3:22. Again I glided around without finding much. I tried over a burned area, thinking the black ground might be working - no luck. But just a few hundred feet from the pattern altitude, I found a weak thermal, averaging maybe 1.5 to 2 knots. It took a while but I got about 900' out of it (max altitude probably 3900'). Not quite as high as the NWS and I forecast, but it was better than nothing! I couldn't find any more, so I finished up with a 38-minute flight.

Sunday, June 04, 2006

Trigger temperature

Yesterday's lift was much better than the NWS forecast and my forecast spreadsheet indicated. Based on a max temp forecast of 100F, my spreadsheet had indicated that the thermal temperature would be very close to the lapse rate temp all the way up, with a soaring index of only -1. The NWS forecast only 126 fpm lift @ 5000' MSL and a trigger temp of 132 F.

But the actual high at Hemet as measured by our thermometer was 106F when I took off and 109F when I landed. So I went back to my spreadsheet and plugged in 106: that changes the thermal index to -4 @ 5000. 109 takes it to -6. Much better! With just a few degrees additional heating, the thermal line pulls away from the ambient line quite a bit. And my trigger temp calculation was 98F, vs. 132 by the NWS. So... I need to look into trigger temp calculations and see how the NWS and I differ. 109-98=11 degrees, clearly over the trigger. And thermals were definitely being triggered... all over the place!

So what did I learn? If my forecast indicates the trigger temp is near the max forecast temp, try a few different temperatures and see how the lift forecast changes. Then I'll be prepared to evaluate the lift possibility as the day's actual temperature progresses.

Saturday, June 03, 2006

Longest flight so far!

Today the soaring forecast was dismal: 150 fpm, due to very warm air aloft and a 5000' thick inversion. But the forecast turned out to be wrong. The ground temperature cranked up to 106 degrees, and apparently that was enough to punch through the inversion, or it lifted, or something. Some of us were able to get up over 6000' MSL. I found 2-4 kt lift all over the Hemet valley!

I was able to complete the "cross-country practice triangle" that I've been working on. It's three legs of about 16-17 mile each, but centered on the HMT gliderport so you're never too far away. I found lift two or three times on each leg, so it pretty well simulated the requirements of a cross-country flight. I did it one and 2/3 times, for a total of about 80 linear miles. Her's the flight trace:

This was one of the few flights I've had where I got high right away and then was able to stay within a lift band, so I was rarely desperate for altitude. Thermals were plentiful enough that I could finally spend some time practicing different centering and searching techniques I've been studying... usually I'm scratching for any lift I can find.

I was almost done at about 1:45... so close to the two hours! But near the airport, with about 200' to go before having to enter the pattern, I found a decent thermal that took me back up to 4500' or so, taking me to the 2-hour mark. I used up all my water and was getting pretty hot and tired, so I brought it down for a 2:17 total. That's one of the two 2-hour flights I need for my Bronze badge!

I intentionally took the Grob so I could get current in it again. I will probably take some passengers up soon, and wanted to be safe in it. No problem - I really enjoy flying it, although it does take a LOT of rudder rolling into turns. I think the long wings make it easier to catch thermals than in the little PW5.