MOUNTAINTHERMALS

PART 1

by Gavin Wills

Cloud Huggers &Rock Hopperstain minimum experience. The mountainpilot must be able to handle his glideraccurately without conscious input, landanywhere, and have confidence in hisatmospheric model of how, why and wherethe mountain thermals work. A steelynerve and a sense of wonder also help, asgorgeous panoramas, soaring eagles andspectacular views unfold and distract. Agood memory for terrain and landoutoptions is desirable so the map stays nearlyfolded when the GPS points at a nearbylandout which happens to be located onthe other side of an insurmountablemountain ridge!

"Never turn towards the hill or thermalbelow the ridge crest" Roger my earlyinstructor told me. I often think of himand his words when, locked in a canyon of

on the right.

Hot air rises up themountain slopes ascurtaim and streamsoffthe peaks as.fromchimneys. Glider A is

red rock, I turn towards the mountain wallfighting a rough, narrow thermal. What hereally meant was "Don't hit the hill, buddy!"So I add a few knots for mother and try tomaintain a medium angle of bank that ifsteepened can steer me out of trouble.

If trouble does loom and the hill gets tooclose for comfort on the inside of a turn, Imaintain the same angle of bank as themountainside and drop the nose a litrle toexit along my escape route. Remember thefuselage can be a few feet off the hill if thewings are parallel to the slope. It's not anice place to be but, along with yourescape route, it's wow remembering!

Surprise, surprise! On mountain thermaldays puffy cumulus form up in lines. No,they are not cloud streets. They mark thebest thermals and follow the lines of the

o ~_. . ..... __ _------_ ..

"I think I just got my money'sworth!" exclaimed Harmanfrom the back seat. With aturbulent shot of sweet air

Hawkwing (my Duo Discus) surged offthe razorback ridge and wrapped into asteep spiral climb. Jagged spires of rockdropped away as Harman exclaimedagain, "I would never have looked inhere for lifd"

Still low and locked between walls ofrock above sapphire-blue waters, the gliderlifted clear of the razorback and pointed upthe ridge to the black peak a thousand feetabove. "Shouldn't we circle to climb somemore?" But even as Harman spokeHawkwing swept up the precipitous ridgeuntil the black peak scraped below the noseand the glaciated mountains of NewZealand's Mount Aspiring National Parksprang into view.

For my money, soaring amongst themountains is the most exhilarating andchallenging way to fly gliders. Rocks, cliffsand trees flash past the canopy as onesweeps skyward in powerful narrow-guttedthermals. Mountain thermals are myfavorite soaring engine.

On a good day, when the winds are light,mountain thermals originate from hot spotsin the valley floors. They rise up the sun­baked mountain flanks to crest the ridge asnarrow curtains of hot air. Mountain peaksact as chimneys drawing these multiplesource curtains together into single thermalsof exceptional strength. The strongest Amountain thermals are usually found above » .••••...•••••.•.••.....••_

the highest peaks (see the diagram).Mountain thermal soaring requires a cer-

38 Soaring Magazine

About the author:Gavin Wills co­produced anddirected theaward-winningsoaring films"Windborn, aJourney intoFlight", and

"Champions of the Wave." He oper­ates a Mountain Soaring School atOmarama, New Zealand fromOctober through March and fromTelluride, Colorado during theNorthern Summer. Details may befound at www.GlideOmarama.com

each 180-degree turn is in a bubble of lifthe gently climbs to the saddle, gets a wingover the ridge and begins to circle. A fewhundred feet above the ridge he points atthe nearest mountain "chimney" and rid­ing the curtain of air rising off the ridgehe is lifted upwards to the peak. Here hedecides to rock hop rather than take theclimb, so he accelerates in the strong liftand barrels on down the ridge.

On the good days mountain thermalflying is the soaring pilot's delight but onthe difficult days it can become a rock­scraping, gorge-following nightmare. Parttwo of Mountain Thermals will discusrecognition of the tricky situations andhow to deal with them.

In the meantime enjoy a mountainthermal or two. Or, if you are not in sucha lucky place as I am, then, at the least,dream about them!carefully figure eights up the sunny face of

the very low peak until he can "point hiswing" at the peak and fly around it. Thenwith his wing pointed steeply down at thepeak he thermals upwards and notices thathis drift is leading him up the ridgetowards the high peak. Drifting onto thehigh peak, he gets too close to thermal. Sohe climbs the last few hundred feet byagain circling the peak. Then, steepeninghis bank to point his wing at the summit,he climbs rapidly and happily towardscloud base. He has been lifted by thestrong thermal gusting from the moun­tain's "chimney".

Glidet B is a little higher and elects totry and get a wing over the main ridge. Heflies to the lowest point, a sunny saddle,and begins to figure eight. By ensuring

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main ranges. As you climb to cloud baseand rhank your thermal source (an impor­tant mountain flying technique!) you willnotice the cloud is often over a beautifullyshaped mountain. Dolphin happily alongyour "cloud street" and notice which peaksare producing clouds and wonder why.The "why" may help when the clouds dis­appear and/or you change from a cloudhugger into a rock hopper.

When cloud base is lowish - within afew thousand feet of the ridge tops ­then rock hopping along the ridge cresr isoften faster then cloud hugging. At ridgecrest you track along nearly continuouscurtains of rising air and accelerate in thestrong surges over the mountain peaks.However, when cloud hase is 10,000 feetabove ridge top, as in Colorado's RockyMountains, cloud hugging is a comfort­able way to go!

Horror of horrors, sooner or later youwill find yourself below ridge top andscrabbling to climb back up. Firstly, relax!- the valley floor is probably far belowyou. Secondly, if it is a good mountainthermal day the thermals are likely to orig­inate from the valley floor and will helpyou back up. But you have to quicklychange down a gear or two to cope withthe much weaker conditions below theridges and their thermal-focusing effects.

As soon as possible, identifY the steppingstones that will lift you back to the mainridge crest. Then, in the absence of obvious,well-defined thermals rising from the valleyfloor, work "curtains" and "chimneys" toger your wing over almost any low ridge.

In the diagram, Glider A slowly and

June 2002 39

by Gavin Wills

MOUNTAINTHERMALS

PART 2

Outslllartingthe Sirens

Understanding the terrain and the wind may get you home when nothing else will

Approaching the summit ofa mountain ridge. There is little clearance between ridge top andcloudbase here.

Two and I had to do. And this is how wedid it. First we took stock and updatedthe day's "atmospheric model." Then weidentified lift sources and energy lines,planned a route, crossed our fingers andset off without looking down.

We started our stock take with theobvious, and kept it simple, rememberingwe had to fly and think clearly at thesame time. (Something that soaring menare not famous for!)

1. Air stability.Broken thermals rising 4,000 to 5,000'above the desert floor have been our soar­ing engines all day. They will weaken anddie with the setting sun. The sun is 30degrees above the horizon. Maybe twohours of heating is all that is left of theday at this latitude. With two hundredkilometres remaining at an average speedof 100 kph there is no time to recoverfrom mistakes. Good decisions and effi­cient flying will be essential.

The remote salt pans glisten in thelate afternoon sun. In the HighMountain deserts of Nevadathey are desperate outposts for

soaring adventurers that beckon weary fliersdown to land, then drown them in heat,loneliness and wind-blown salt.

With nearly two hundred kilometers torun across half a dozen salt pans and fourmountain ranges, we knew we would haveto pay careful attention to what was left ofthis mountain thermal day. One mistakecould become a night in the desert siren's

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arms followed by a multi-day retrieve overuncharted dirt roads. Crew costs alonecould amount to a ton of ghastlyBudweiser!

So pay attention, reader! One day youcould be faced with a similar soaring chal­lenge! One in which your skill, your expe­riences and your good understanding ofmountain thermals might get you homeagainst the odds.

Still airborne, but now alone and con­fronted with a potential mountain ofBudweiser, this is exactly what Uniform

2. Moisture content.The air is dry and the thermals blue.There will be no clouds to follow. To findthermals we will have to recognize theirsources. But at least overdevelopedcumuli will not obscure the sun! (Lookon the bright side!)

3. Terrain.Four north-south mountain ranges liedirectly across our track (see Fig 1.) Thehighest, called Mount Wheeler, rears7,000' above the desert. Silhouetted 140

Soaring Magazine

Figure 1. Picking the right route home!Consider the terrain, sun angles, the valleywinds and the upper winds.

kms to the west we notice that its south­ern end is close to our direct track home.

The remaining ranges, broken by occa­sionallow passes, rise only 1,500 to3,000' above the sand. The late sun willheat their western flanks while their east­ern slopes cool in deepening shadow. Wenotice that most of these low ranges haveeven lower hills scattered a few kilometersto their east.

4. Wind.In the mountains, wind is everything. Weneed to know the wind All Ways at EveryLevel and All the Time. Today we reckonthe upper wind at thermal top height issouthwest at about 25 knots - that's whythe thermals have been so broken andsheared all day. The morning forecast sug­gested that this wind would continue intothe night without abatement. Wind,therefore, will be an important tactor forthe journey home.

What about the wind on the valleyfloor? Our buddy Jeff landed a couple ofvalleys east and reported southerly windson the ground gusting to 30 knots. It islikely that, encouraged by the upper flowand drawn in by the day's heating, strongsoutherly winds will continue up all thevalleys at least until sunset. Thermalstherefore will originate only in areas shel­tered by the hills and mountains.

Will the wind at ridge top height runalong or across the ranges? A sixty-fourthousand-dollar question! For the lowranges we assume the worse case - thatthe valleys' southerly winds will also blowalong the ridges. However on the highslopes of Mount Wheeler we hope theupper level southwest winds will blowobliquely across the ridge. We count onthat for the final glide home.

5. Thermal Triggers.Thermal heating will occur only amongstthe mountain ranges. Therefore thermaltriggers will probably be three-fold;mountain peaks chimney-ing thermalsfrom sheltered valleys, mountain ridgesfocusing curtains of rising air and the coolwind itself, chiselling off bubbles ofground heated air as it swirls into shel­tered corners

So what has all this brain work doneexcept sink us inexorably towards the saltpan sirens? Hopefully this combinationof observations, assumptions and deduc­tions will have helped us create a useful

August 2002

current model of theatmosphere. Hopefullythis model will pointus to those essentialstepping-stones andenergy lines that willenable us to soar overthe seductive sirens andget us home in time forwhisky and bed.

So now the plan (Fig1 again). We will try todolphin-soar south­wards, into wind alongthe first mountainrange. We will cross thenext two valleys at theirnarrow points and bewell upwind of MountWheeler - just like insailing, being upwind ismoney in the bank. Then we will back­track north along the third range, floatingdownwind until we can reach the south­western flanks of Mt. Wheeler. There theslopes have sheltered aspects, and sun andwind should work from low down to helpus climb to Mount Wheeler's summitridge. From there, high above the soddingsirens, we will (hopefully) start the fin~

glide home.We will search for climbs in only two

kinds of places; southwest-facing bowlswhere heated air may be swept skywards,and around sunny hills that are shelteredfrom the prevailing valley wind. Oncebeyond the upwind plug, and if theclimbs become weak or broken, we willdump our water ballast to maximizeclimbs from the dying thermals. Anythingto avoid the salt pan sirens!

Each of these considerations - air sta­bility, water content (clouds), terrainaspect, thermal triggers and the wind ­are important. The most important areterrain aspect and the wind because theycontrol the air's heating by the sun. Whenthe sun and the wind work together thesoaring is much easier than when the sunworks against the wind.

The source and strength of the valleywind is important. For example, valleywinds that blow off bodies of water orare simply very strong can shut downthermal activity in exposed places. Thesmart pilot can almost always find thosesecret spots that are sheltered fromunkind valley winds.

Did the little LS-3 called U2 make it

home across the desert that night? Ofcourse!

We followed the plan to the letter; dol­phin-soared the ridges, dumped ourwater, climbed gently over mountainchimneys and Boated onto the base ofMount Wheeler. Here a dying thermaland the prevailing southwest wind sweptus aloft for a long fast final glide into thesetting desert sun.

Last home, but safely back at Ely,Nevada our relieved crew rewarded uswith nearly a ton of Budweiser! We toast­ed our thermal sources - for once againwe had outsmarted the desert sirens!

About the author:Gavin Wills co­produced anddirected theaward-winningsoaring films"Windborn, aJourney intoFlight," and

"Champions of the Wave." He oper­ates a Mountain Soaring School atOmarama, New Zealand fromOctober through March and fromTelluride, Colorado during theNorthern Summer. Details may befound at www.GlideOmarama.com

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