It was early spring, well into thermal season, and perhaps the last day of winter-like weather. Most thermals were being blown apart by a strong north-northwest wind, and any that did rise only added to the roughness of erratic rotor. No clouds other than cirrus, so if there was good stuff above this disorganized junk we’d have to find it by braille. The wind aloft was steadily increasing as we climbed, yet when it finally began to smooth out up near 10,000 MSL, the ‘wave’ yielded scarcely more than zero sink. With no visible markers, all we could do was gently feel around for more, the way you noodle for catfish, careful not to get bit.
Once established in fully uniform flow, we did the old thing where you hover at zero ground speed precisely as possible and note what the ASI says. That number plus two percent for every thousand feet MSL yielded an ambient wind of sixty knots, triple the theoretical minimum for wave. So why so flat? My guess, this oblique wind direction and that non-linear topography upwind of us would generate no wave at all if the wind were any less. Big energy, weak lift. Like sipping from a firehose.
To go anywhere but backwards we’d have to fly faster, but even a small increase in sink rate risked losing altitude and falling out of what little lift we had. Too slow put us in reverse and too fast meant going down. Call it the ‘coughing corner’. Fair enough. So play the cards you’re dealt, invent some way to make use of this particular set of problems, and you might learn more in half a day than whole weekends of booming thermals.
We were situated a mile off the flank of Bear Mountain, west of Tehachapi, and this wave’s axis ran north to our one o’clock as we faced the wind. We nibbled side to side in our crab, experimenting with minuscule changes in pitch, and even goofed at leaning forward or pulling our feet back in unison to effect CG and find some kind of sweet spot. Little in the way of repeatable results of course, but every effort contributed to improved results, and glacial gain into the wind was our meager reward. (One of the few times I’ve found staring at the vario more useful than staring at my belly button!)
It took almost two hours to creep fifteen miles upwind, finally nearing 11,000 MSL above the hills south of Lake Isabella. Peeking across it into the mouth of notorious Kern Canyon is where the lift finally began to improve — from almost one knot, that is, to almost two…
This was starting to look like a rare opportunity we might never have again. Imagine: not running along the east-facing crest that’s a world renowned drag strip for gliders, but straight up-river into the Sierra high country’s very gut! Problem was, it took us so long to get just this far, and there weren’t many hours of daylight left. Beyond Kern Valley airport in the mouth of the canyon, there’d be nothing even remotely landable across countless square miles of steep mountain wilderness, higher and higher the further you go.
So no, it felt like a gorgeous trap, too easy and too tempting. Unique and spectacular as such an adventure would be, we could think of many better ways to die. Especially so early in the season. It may have been mere cowardice, but we’d pushed our luck enough for this sortie and it was time to turn back.
Whereupon we instantly acquired every advantage. The comparative quickness of our retreat should be no surprise, but was nonetheless a marvel to behold. We now had a ripping tailwind, and still that same weak but consistent lift. Because we were returning to land anyway, most of our height was energy we could afford to splurge. Plus our destination, Mountain Valley Airport, now lay almost directly downwind, which meant no more crabbing as we slid diagonally over the wave’s broad crest into inevitable sink, which in this case also served our interest. Even capping our speed at ninety indicated out of respect for turbulence on the way down, our achieved ground speed was, honest injun, 200 MPH, and four minutes later we were ready to enter the pattern!
That’s why some of us find winter soaring in southern California even more fun than summer, and you don’t need oxygen or a heavy coat.
At the risk of insulting your intelligence, however, here’s some sage advice. Best be cautious about quicking the downwind leg first in such a gale, especially on days that end early! We’ll discuss that temptation of fate next week, reprising another true tale from several years ago.
Congratulations this week go to Frankie Freemont. Last Thursday, on his sixteenth birthday, he flew his first solos in both helicopter and airplane. That was over in Las Vegas. Then the next day he passed his private glider checkride here at Crystal. The FAA says Frankie’s the first ever to claim such an accomplishment in 24 hours!
It’s still winter, but we can expect temps in the sixties and mostly light northerlies until the wind picks up on Sunday. According to tradition, our first thermalish conditions may begin sometime in the next couple of weeks… I can almost hold my breath that long!
We all hear lots of talk about wave lift in praise of climb rates, preposterous smoothness and all the rest, yet seldom much mention of wave sink. That’s understandable, but sink is always half of any big picture. Open and endless as wave lift may feel, it’s normally sandwiched between sink of similar volume and strength, upwind beyond the trough and probably downwind behind the crest. And once you’re in it, wave sink feels plenty open and endless too.
In wave sink, whatever your achieved climb rate has been, the corresponding descent will feature an equivalent vertical speed downward plus the 100+ fpm aerodynamic sink rate you had while climbing — think carefully about this, or you won’t believe it. That’s if you remain at the low-end speed you maintained while climbing, and almost anything you might want to do in sink necessitates higher airspeeds.
Theoretically, wave requires at least twenty knots of wind across the hilltop that generates it (and on wave days, 60-knot winds aloft are not rare). For this discussion, let’s stipulate an achieved climb of 5 knots in ambient wind of 30 knots. Response to the equivalent sink, by itself, will roughly double speed-to-fly, and penetrating to the next lift upwind will demand also adding half the headwind. This puts you up around maneuvering speed in any glider, and quickly compounds to 15 knots DOWN, maybe more…
To estimate achieved glide during a wave penetration, subtract the approximate headwind from your airspeed and divide that by the total rate of descent. Example: 75 kts airspeed minus 30 kts headwind equals 45 kts ground speed — and if you’re coming down at 15 knots, you get an achieved glide of 3/1. This is not an exceptional situation; it’s ordinary in wave soaring. For stronger conditions or low performance gliders, the numbers will be MUCH WORSE!
Having fun yet?
Gliding downwind in wave sink is a very different story. Moderate sink in a tailwind of thirty or less requires only moderate increase in speed, which an old-fashioned MacCready ring will give you. For stronger tailwinds and the heaviest sink it gets numerically complicated, but going downwind in wave usually doesn’t take long, whatever the situation, and by the time you calculate exact speed-to-fly, that question may be moot.
Gliding crosswind in wave sink is just a bad idea for almost any purpose, unless you’re intentionally letting it cast carry you down to wherever you wish to go. But this brings us to using wave sink for descent, which can be an efficient, entertaining, and educational way to finish a flight. There are many ways to do this, some not at all recommended, while some are lots of fun. Here’s just one.
Imagine a free standing lenticular, say four thousand feet deep. Climb by its windward face to just a few hundred feet higher than the top, then turn and glide downwind toward it, still slowly rising as you approach the crest. From horizontal flow there, you drift into the reciprocal of all that lift, so softly you may never feel the vertical transition from huge up to huge down. Proceed a few moments further as the cloud below drops away, and once your vario’s pegged on down, turn back into the wind again to face the falling cloud like a helicopter autorotating before a waterfall! Cool stuff, so long as there’s some clear route to safety — or a convenient harmonic waiting a few seconds further downwind…
Now you want a real challenge? Rassle rotor beneath that cloud (bladder permitting), all the way upstream to the windward side again, and climb from there back up into the wave you started from. For that achievement I always award myself an imaginary lennie pin. An inverted one of course, pewter, not brass!
We have multiple accomplishments to celebrate this time around. Kudos to Walt Sweet and Sean Murphy, who both flew their first glider solos last week (Sean’s only fifteen, and Walt… well, he was fifteen once). Further congratulations go to one of our own, crew member Cameron Evans, who completed his Advanced Ground Instructor rating. So from now on, if you have any questions about flying stuff, just ask Cam!