Monday, June 27, 2011

Mountain wave passenger flight

My friend Jim has been wanting to go for a glider flight for a long time, and we finally decided the only way we'd work it into our schedules was to take a day off work and just go. He'd been in a small power plane before, so we figured he'd do fine in a glider. Today the forecast for Crystalaire was for 99F, good thermal lift, winds out of the west-southwest at 10 to 15 knots.

We took off about 1:00 in light south-southwest winds and let off in good lift over the Second Ridge. We very easily gained 2,000 feet, and then another 1,000. Couldn't quite break the 10,000' mark, but it was working well. I kept the banking to about 35 degrees, and Jim handled it just fine. I looked around for more lift, and all I found was light sink and some turbulence upwind of the ridge. It was a little puzzling, because the south side of the ridge wasn't working like ridge lift based on where I thought the wind was coming from. Not finding a second thermal, we dropped off the hills and out to the desert... and found no lift there either. We landed after 38 minutes. I knew the lift must be better than that, because other gliders had been up for an hour or more. Jim was game, so we decided to give it another try.

We let off again in good lift, a little higher this time. I heard two other gliders on the radio trying to make visual contact, and one said he was at "13,400 in wave over the Punchbowl". Hmm... I'm over the Punchbowl too, but about 4 to 5 thousand feet lower. Huh? Wave? Duh! Of course! Wave! That wasn't thermal lift last time, and it wasn't random turbulence south of the ridge, it was rotor! The wind was blowing over the tops of the mountains, bouncing off the floor of the valley south of Second Ridge, and going up. So... I flew parallel to the ridge and immediately contacted smooth wave lift at about 5 knots. Then 6 knots. Occasionally 8 knots. Eventually 10 knots! In no time we were over 11,000 feet. I found where the rotor started south of the wave, and found the apparent east and west limits of the lift. We got as high as 12,200 feet, though much of the time we were down around 10,500. This is more like it!

This was really only my second time flying in serious wave lift, so I spent some time exploring the limits of it and just enjoying the view and giving my friend a nice smooth scenic ride - that wave lift is amazingly smooth! After about an hour and a half we decided to head back out over the desert and shoot for a two-hour total total time. I knew that losing 6,000 feet would take a while. Heading north, I found sequential patches of moderate turbulence and smooth lift. So I think I traversed secondary and tertiary waves. As we were wrapping up our flight, I heard one of those two other gliders going in for a landing, but the other checked in at 16,000'. We ended up just two minutes short of two hours on that second flight.

So my lesson for today: a south or southwest wind across the San Gabriel mountains can set up wave where I have been looking for thermal and ridge lift. What's surprising to me is how short the wavelength is. From the top of the ridge where I think the wind is getting deflected upward, to the upward flow of the primary wave seemed to be about just 3.5 miles. All the soaring educational materials I've seen about wave talk about the wind bouncing off a stable air layer down low, not off the ground, so I have not been thinking about the wave setting up right in the mountains, but that's what it seems to be doing. And the wind was not all that strong: 10 knots on the ground, not sure how strong at altitude. So I need to think about wave forming in a wider variety of conditions than the books talk about.

A great day!