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ANNOUNCING THE 30TH ANNIVERSARY DVD
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November 15, 2009
The serenity of the summer sky is an illusion. If suddenly, by magic, we could see the
movements and shapes defined by the temperature and pressure
interfaces of different segments of air, we would find ourselves
in a bizarre theater more alien than any distant planet. And we
would be well on the way to deciphering the enigma of
meteorology. Unfortunately, masked by its own transparency,
the sky gives hints to its nature only by its effects on other
things. We are left to theorize what action of the air caused a
cloud to form, established a lenticular above a mountain range,
carried an eagle to cloudbase, formed a destructive tornado, or
brought a drought to Africa. As soaring pilots, we are constantly challenged
to visualize the most efficient aerial pathway to altitude and
distance. In this quest we employ various tools, most notably:
the variometer. This instrument measures the rate of change in
atmospheric pressure. It's sister instrument the altimeter
measures the change in pressure. Virtually all soaring pilots rely primarily on
pressure-sensitive instruments to aid their understanding of an
energetic and constantly changing atmosphere. This seems
perfectly normal until one considers that the prime mover - the
originator and force behind atmospheric dynamics - is not
pressure. It is temperature. How would a temperature-sensitive instrument be
used in soaring? This question has intrigued several researchers.
The first significant experiments were made in the 1960s with
sailplanes. A new development in solid-state electronics was the
"thermistor," a device that varied electrical
resistance with minute changes in temperature. By mounting a
thermistor on each wingtip, the researchers reasoned, it would be
a simple matter to turn in the direction of the warmer thermistor
to locate a thermal. Unfortunately, in practice this was not
effective. There were several problems. The speed of the
sailplane and the extended response time of the early thermistors
conspired to provide essentially useless data. The distance
between wingtips did not seem to be great enough to generate a
reliable temperature difference. And sinking into warmer air or
rising into cooler air wrought havoc with all attempts of
measurement. But even if these problems had been overcome,
the basic premise dictated that the thermal have a relatively
laminar temperature gradient from periphery to core. If this is
not the case - if, for instance, thermals shed pockets of warm
air which separate beyond wingspan distances as they rise - then
the concept of thermal location using wingtip sensors is flawed. MY QUEST FOR A TEMPERATURE VARIOMETER In 1984 I was fascinated to discover that the
world's most accomplished cross country hang glider pilot, Larry
Tudor, was sensitive to small changes in the temperature of the
air he felt on his face. Sensing small increments in temperature,
he frequently tracked warm bands of lift along the crest of
shears. Could the ability to sense these small changes in
temperature be a factor in Tudor's consistantly stunning
performances? I was determined to find out. My own ability to feel small variations in
temperature is rather limited. I tried flying with thermometers,
but even the most sensitive were too slow in response to allow me
to develop a strategy that offered any indication of positive
results. What I needed was a very fast rate-of-change thermometer
that functioned much like an audio variometer. Unfortunately, such an instrument didn't exist.
And despite my training in Mechanical Engineering, I did not have
the electronic expertise to develop one. In October 1984 I wrote
to a prominent hang gliding instrument designer hoping to
stimulate his interest in a development project: "In my discussions with Tudor and other leading pilots, I have found that significant decisions concerning proximity to thermals and orientation of shear lines are made on the basis of perceived temperature increase. With our slow speed, we can determine the differential with a 180-degree turn, possibly obtaining a superior measurement than possible with a sailplane... "I am greatly interested in doing whatever
I can to help develop such a device by doing flight tests in the
Owens Valley. Contrary to popular belief, thermal conditions
exist year round in the Owens Valley and the nearby launches are
seldom closed by snow." Although the idea was received with inierest, I
was told the costs involved for developing a prototype and the
time constraints of other ongoing projects, not to mention that
such an instrument would probably appeal to a very small market,
would tend to keep any research on the back burner. So for a year
and a half, the idea remained nothing but a remote yet
tantalizing prospect. Then in May 1986 I was utterly astounded to
come across an article in the June issue of "Whole Air
Magazine" titled "The Thermal Snooper" by Alan and
Jeff Fisher! THE THERMAL SNOOPER Alan Fisher lives in Huntsville, Alabama, where
NASA has it's Marshal Space Flight Center. Much of his career was
spent designing special radio equipment for the early scientific
satellites, including those that mapped the Van Allen radiation
belt. Today, as the owner of Digi-log Circuits, he manufactures a
magnetic card reader. And when he can find the time, he pursues
other projects he describes as "interesting and
worthwhile." When his son Jeff began hang gliding, the need for an instrument that indicated lift became apparent to Alan. Not being a pilot himself, he was not inhibited by the conventional logic that would have led to the building of a form of barometric variometer. Instead, he chose a fresh approach. "Air rises primarily because it is warmer
than the surrounding air," he reasoned in the article.
"That is clearly the case for thermals. And even though wind
movement rather than air temperature is the prime cause of ridge
lift, that air is also likely warmer because it has been
deflected from a lower level. Therefore an indicator of subtle
increases in airstream temperature might well alert a pilot to
nearby lift and greatly assist him in finding, and remaining, in
its warmest core." With this simple concept in mind, Alan designed
his first temperature variometer. He knew nothing about previous
attempts along similar lines other than having heard a rumor that
a hang glider pilot somewhere had found his own temperature
sensitive instrument to be useless in flight. Undaunted, Alan
created a prototype unit for Jeff, who eagerly headed off to his
local flying site. Unfortunately, the first Thermal Snooper proved
useless in flight. But Alan was certain his concept was solid. The
glass bead thermistors that nestled under their protective shield
were definitely capable of measuring the small temperature
changes required. The instrument simply needed tuning. Further
adjustments were needed in sensitivity, time lag, lapse rate
dampening, and more esoteric technical aspects of the design. He
doggedly kept at it. And by the third model, Jeff began getting
positive results. In November 1985 Jeff entered a weekend cross
country competition at Walker's Gap, Alabama. He was the only
pilot without a variometer. Yet, with only 50 hours of flying
experience, he placed third. In the article, he expressed his excitement
over the Thermal Snooper's potential: "I was amazed to hear its pitch rise seconds before feeling any indications of a thermal ahead. And once within a thermal, it warned me if I circled too close to the edge. The first thermal indicated took me to 1500 feet above launch. I was able to track its movement all the way up. "Whenever I had to revert to ridgelift to
maintain [altitude], the device then distinguished between gusts
and thermals. I was now no longer wasting turns to work what I
otherwise might have thought to be a thermal." Alan had succeeded in developing an instrument
that promised incredible gains in soaring efficiency. And I was
particularly impressed by the Thermal Snooper having changed
Jeff's concept of a thermal. "I always imagined that the effects of a
thermal stopped at the sink-to-lift boundary," he wrote.
"It surprised me to realize that air significantly outside
the shear action is detectably heated." I had not suspected this, either. I wondered
how many other readers had realized the implications. If true, it
would have a tremendous impact on the future of cross country
soaring because it would expand our ability to sense thermals,
resulting in longer flights. Alan's Thermal Snooper was the
instrument I had been yearning for. I had to get my hands on one.
Like the vario, it promised to serve as another pair of eyes that
would see beyond the limitations of my own. Perhaps by joining
vario, Thermal Snooper, and intellect, the mystery of the sky
would unfold as never before. I drafted a letter to Alan offering to conduct
a flight testing program for the Thermal Snooper in Owens Valley.
I included a copy of my film AOLI COMET CLONES AND POD PEOPLE to
demonstrate the conditons that exist in the Owens and, I assured
him, persist throughout the year on a lesser level. I was
confident there was no better place in the northern hemisphere
for winter testing. Sure enough, the Thermal Snooper arrived in
Owens Valley in late September 1986. It was nothing but a small
circuit board, the components coated with a thick layer of
cream-colored epoxy to protect against the elements. Attached to
the board was a nine-volt battery, a crystal-driven
(piezoelectric) speaker, and a curving shell of copper which
protected the tiny, exposed thermistors from sunlight and abuse.
It looked more like a hunk of candy than a soaring instrument. I snapped the battery into place and the
Snooper immediately started beeping much like a Litek vario I'd
once owned. After a few minutes the circuits normalized and it
quieted down. Alan claimed that it "beeped" once for
each fractional rise in temperature, and "booped" once
for each fractional decrease. I held my finger near the thermistors. The
Snooper began "beeping" happily. A big grin formed on
my face and wouldn't go away. EXPLORATIONS WITH THE THERMAL SNOOPER Fall had come to the Owens Valley, bringing the
smooth north winds and the big, lazy thermals that would quietly
disappear at the level of the highest peaks. It was a time to
relax, a time to come down from the intense highs of the cross
country season and again enjoy flying for flying's sake. The
advanced pilots had gone home, burned out, sated. The
intermediates worked the ridge lift of their local hills and
longed for the next summer to hone their thermalling skills. Some
day they would discover the Owens Valley in the Fall and Spring.
But for now, as always this time of year, I was alone. The peak I favor in Fall is Mazourka. It stands
out from the northern Inyos in the path of the valley winds. In
the summer, long and shallow Santa Rita Canyon gathers the south
wind and guides it to the summit. It was at the head of this
canyon I had located the 1984, and part of the 1985, Owens Valley
XC competitions. But in the Fall and Spring, the north wind
collides with Mazourka, rushing up its steeply cascading flank to
offer thermal-rich ridge lift, while ten miles to the north
Tinnemaha Reservoir indicates the wind strength and direction in
the valley. From the summit at 9140 MSL (Measured from Sea
Level) the view is inspiring - all the more so because Mazourka
is the only mountain launch in Owens Valley to offer an
unobstructed view in all directions. Just east of Mazourka, the
main spine of the 11,000+ MSL Inyo Range marches north to descend
into the rolling hills of Westgard Pass, then rises again as the
great White Mountains. Westward, the raw granite spires of the
Sierra Nevada rear from the valley floor to form an unbroken
wall, reaching over 14,000 feet. Between these awesome ranges the
boulderstrewn alluvium, pockmarked by magenta cinder cones and
scarred with tortured fields of dark lava, is cut by narrow,
brush-choked streams that gurgle from every canyon only to be
seized by the Los Angeles Aqueduct, leaving the meandering Owens
River to struggle pitifully southward alone in a futile attempt
to moisten the red eye of Owens Dry Lake. The day was extraordinary. A broken cloud
street of the classic type with flat-bottomed, underdeveloped
cumulus had established itself along 100 miles of the Inyo-White
range. Cloudbase beckoned a mile above Mazourka. Across the
valley, the crest of the Sierra was laced with a narrow and
continuous band of cloud. Only the tallest snowcapped peaks
pierced the cloudtops. At the north launch point on Mazourka summit
the wind was light to moderate (5 to 15 mph), driven from the
north but veering due to thermal cycles, resulting in a
predominant northeast wind with an occasional west. But every few
minutes the wind would straighten and hold north, the optimum
direction for launch, for 20 seconds or longer. Several gaggles
of ravens and hawks, the lords of Mazourka, drifted on thermals
above me. I decided to set up. The glider I'd chosen for this flight was a
Pacific Wings Express "Racer," a fast European
design that had carried me 178 miles great circle distance from
Horseshoe earlier in the season.* My hook-in weight of 215 pounds
resulted in a wing loading of nearly 2 pounds per square foot,
and therefore demanded an aggressive thermalling technique with
tight turns centering the core for effective altitude gains.
Because of this, I felt the Express would be ideal for testing
the Thermal Snooper. I clamped the Snooper to my instrument mount
and turned it on. It's "beeps" and "boops"
were easily discernible from the "chirps" and
"buzzes" of my variometer. I assumed the Snooper would
quiet down after the circuits normalized - but it didn't. That
was my first surpise. Instead of remaining silent like my vario, the
Snooper was giving me a running commentary about the quality of
thermal cycles rolling through launch. When a freshening breeze
began to tease the first flag 100 feet down the mountainside, it
would begin to "beep" hesitantly. Then as the nearer
flags became agitated, the "beeps" would increase
excitedly. If the thermal was centered and all the flags stood
out from the north, the Snooper would fall silent. But when the
flags skewed off to the east or west as a thermal passed to the
side, the Snooper would immediately follow its "beeps"
with a series of low "boops." Fascinated, I stood at takeoff for 20 minutes.
For each cycle that passed through, the Snooper gave an
indication of it's size by the duration and frequency of it's
"beeping." A few "beeps" meant a small,
short-lived thermal. Many "beeps" told of the arrival
of a large thermal. At some point during each thermal's passing,
the Snooper would begin to "boop" - a few
"boops" for small thermals, many "boops" for
large thermals. It was obvious that these "boops"
warned of the "downside" of the thermal's cycle. Years of observation have led me to attribute
the majority of takeoff accidents in thermal * the ninth-longest hang glider flight ever made. conditions to pilots launching into the tail
end, or down-side, of thermaI cycles. It took a lot of practice
to read thermals accurately, and some pilots just never became
adept at it. Now here I was with a tiny instrument clearly
identifying both the up and down sides of each cycle! I was
impressed. Even if the Thermal Snooper didn't do anything else,
it promised to make mountain flying a lot safer. But surely, if it could read thermals on the
ground, it could read them in the air. I eagerly shouldered the Express.
When the Snooper announced another large cycle, I was airborn by
my fourth step. The air was straight, smooth, and lifting. The
vario began "chirping." The Snooper fell silent. When I am first to launch, I never attempt to
work the occasionally treacherous takeoff thermal. It has never
proved necessary for me in the Owens because there is always
another just as good nearby. So I flew fast and straight away
from launch - and out of the thermal lift. The vario went silent
and the Snooper began to "boop" just like it had on the
ground during a down-cycle. With the gentle ridge lift helping
sustain me, I turned to seek out the resident "thermal
snake" on the knife-edged western shoulder of Mazourka Peak. As usual, it was there. But the Snooper started
beeping just as the glider encountered a bit of sink prior to the
lift. "Odd," I thought, "that the vario would
register sink and the Snooper a thermal, simultaneously..."
Then the vario started screaming. I banked up the Express and
centered in 600 fpm (Foot Per Minute) lift. And the Snooper
quieted down to nothing. I deliberately left the "snake" at
11,000 MSL, knowing I could return at any time. The Snooper
"booped" as I flew out, then became silent as I turned
upwind of the ridge in search of a random thermal. I'd lost 1000
feet when the Snooper began "beeping." The vario,
however, continued to indicate the 150 fpm sink rate the Express
averaged in glide. After ten seconds or so, the Snooper
"booped" a few times and fell silent. The vario
remained unchanged. "I must have passed by a thermal" I
thought. "A thermal far enough away that my vario couldnt
sense it, but close enough that the Snooper could!" Eager to give the theory a try, I sent the Express
into a thermal search pattern. I began with an evenly-banked 270
degree turn. Finding nothing, I rolled out, wings level, and
prepared to cross my previous path to repeat the turn on the
other side. But almost immediately the Snooper began to
"beep." After a few seconds more, the vario
"chirped" and a wingtip lifted. I count to three, then
threw the Express into a climbing turn. The Snooper quieted down
as I centered the core, and the vario sang 600 fpm up. I left the thermal and searched out many
others. Each time, the Snooper would alert me to the presence of
a thermal long before the vario. If the Snooper kept
"beeping," I would run right into the thermal. If the
Snooper stopped "beeping," I would execute a search
pattern. I only guessed the correct direction to turn about half
the time, but a thermal was always waiting somewhere along the
search pattern. I was amazed that every time the Snooper sang out
a series of "beeps," I found a thermal - regardless of
what the variometer indicated. And I was finding thermals that,
without the Snooper, I would simply have passed by, never even
suspecting their existence. The implications were tremendous. "Wow!" I thought. "This thing is
going to boost the average cross country flight by a whole bunch
of miles!" I rode the last thermal in this series to
cloudbase at 14,500 MSL and headed southward in a light mist of
ice particles. The cloud was not generating lift, however, and I
began losing altitude at 100 fpm. The Snooper "beeped"
constantly at a slow, steady rate. It was registering the rate of
change in temperature as I descended into warmer air. This lapse
rate sensitivity hampered its ability to sense thermals, but I
found one with my vario over Mazourka Canyon with 10,000 MSL. This thermal was the roughest I'd encountered.
It kicked me out, sending the vario and Snooper into paroxysms of
"buzzing" and "booping" during the dive. The
dive was so wild that upon recovery, I didn't know which
direction to go. I initiated a wide, sweeping, turn, hoping to
stumble back into it, but the Snooper began "beeping"
so I rolled out and hit the thermal dead-center. It felt broken
up and multi-cored. The vario would'nt give me a steady reading
because pockets of sink were mixed in with 1000 fpm up. The
Snooper, likewise, was constantly "beeping" and
"booping." I kept searching for a core I could work and
was rewarded by the Snooper quieting down a bit. I remained in
this area, for although the air felt almost exactly the same, the
average lift incidated by the altimeter was much improved. My favorite challenge in Fall and Spring north
wind conditions is to try to cross the area of rotorless sink
that exists for a few miles south of Mazourka Peak by riding a
thermal onto the crest of the Inyos. Once there, it is often
possible to make a 20-mile out and return along this steeply
rising range. With this hope in mind, I left the broken thermal
and, encountering only light sink at higher altitude, reached the
crest 11 miles south of Marourka with a healthy 12,000 MSL. At
this point, I discovered another function of the Thermal Snooper. I was hoping to find a "thermal
snake" leaning downwind of a north-facing peak. On a good
day, the ridges that descend from the spine scoop up the north
wind, turn it eastward, and herd the thermals into the mountain
where they blend into continuous ascending streams. Unlike the
Sierra, where these tend to exit high ridge points far out from
the peaks, the terrain of the Inyos leads the streams to the very
crest. So I was envisioning a highway of "thermal
snakes" waving like sea grass in current along the crest -
when the vario chirped. I banked up the Express to enter the thermal
and was rewarded with a physical sensation of vertical
acceleration. But not until I was halfway through the turn did I
notice that the Snooper had remained silent. "What's this?" I wondered. "Has
the Snooper stopped working?" At that moment the glider dropped into strong
sink. I continued the turn, hit lift again, and again passed into
sink. The altimeter told me I had lost 200 feet in each
"360." The Snooper's silence continued. I flew southward and hit more lift. Again, the
Snooper was silent. But this time, instead of turning, I slowed
the glider until the lift diminished, then sped up, anticipating
sink. Sure enough, it was there, stronger than before. "These aren't thermals. They're
eddies!" I realized, remembering how Jeff Fisher had
encountered the same phenomenon at Walker's Gap. Because eddies
are constant in temperature, unlike thermals, the Snooper
remained silent passing through them - while the vario registered
their effect. By its very silence, the Snooper was providing me
with information just as valuable as any gleaned from the sounds
it made. I was gradually becoming more proficient in interpreting
its functions: "Beeps," "boops," rate of
each, and for cores - and now for eddies - silence. I've encountered eddies on virtually every
cross country flight of my 3400 miles of accumulated straight
line distance in and from Owens Valley. But thanks to the Thermal
Snooper, I won't be fooled anymore. I was beginning to get an
idea of what a powerful tool the Snooper could be. All these
inefficiencies it helped to eliminate were quickly adding up to
big gains in cross country performance! The sink was growing worse with every foot I
lost. I began to notice a growing headwind from the east, out of
Saline Valley. I tried to find a thermal rolling up the east face
of the range, but I was running out of altitude fast. When my
flying wires jerked in the growing turbulence, I pulled in the
speed bar and sped westward, away from the Inyos. Although a few
pilots have made a leeside run of these mountains, it is not the
type of flying I enjoy. Thermal turbulence can make me shout with
exhilaration, but lee turbulence is inherently dangerous and I
tend to distance myself from it. The tailwind really allowed me to cover ground
during my "escape." Strangely, the Snooper did not
"boop" very enthusiastically during this descent. I
assumed the easterly wind was flowing over the crest and down the
west face, feeding cooler air to the lower altitudes. After a
four mile glide, I turned north with 2800 AGL (Above Ground
Level) to investigate the southern foothills of Mazourka. This
area often provides thermal lift regardless of wind direction,
but what I found there exceeded my expectations. The wind was out of the north again at 2500
AGL. I was penetrating at five to ten mph ground speed with a 150
fpm sink rate. But as I approached the first foothills, where the
great wedge of Mazourka begins its long climb northward from the
valley floor, my sink rate dropped to zero in glass smooth air.
Something unusual was going on. As I continued north against the
wind for one, two, then three miles, I realized I was in a shear.
I couldn't believe my luck; to have encountered
a shear on my first flight with the Thermal Snooper! I was very
excited. I began a series of long-legged S-turns. The Snooper
never "beeped," but when I headed too far away from
Mazourka or approached too closely to its rising flank, the
Snooper would give out a solitary "boop." Between these
"boop" points, I located the crest of the shear.
Slowing down, I soared against the wind in 50 fpm lift for six
miles. Then, as I rose above the altitude of Mazourka Peak, the
shear disintegrated. I returned along the shear to its southern end,
then ran north again for a few miles. I was astounded to realize
that the Snooper was helping me map the shear - define its
character and determine its orientation. I hadnt really expected
this most esoteric of potential applications for the Snooper to
actually work on the first try. But it did! Wow, was I excited!
I'm still excited! Summertime shears, here I come... By the way the shear set up, I deduced the
descending easterly winds out of the Inyos had pushed underneath
the warmer air flowing southward down the valley, causing it to
well up and over the cooler air along Mazourka's western flank.
This created an invisible ridge standing out in front of Mazourka
that the Snooper magically allowed me to see. With regret, I left the shear to search for
sink. The shadows of the Sierra were halfway across the valley.
Soon the sun would abandon the Inyos and the Autumn cold would
set in. It was time to find my motorcycle and retrieve my van
from the peak. I spiraled down and set up a landing approach. It
was in these final moments that the Snooper surprised me again. It had been "booping" occasionally
during my descent, but at 20 feet it started "beeping"
excitedly. "Oh no! I'm flying into a thermal that's
breaking off!" I thought, sucking in the bar. But it wasn't
a thermal, it was dead air. My 20 mph headwind suddenly vanished.
Severe wind gradient. I hadn't expected it. The presence of the
shear and the lateness of the day had suckered me into thinking
the wind would be blowing all the way to the ground. But the
Snooper had sensed the warm, still air hugging the desert floor
and warned me. My extra speed had prevented a low-altitude stall
and allowed a good landing. I sent Alan Fisher a report of the flight. He,
too, was excited and encouraged by all the additional
applications that were being discovered for rapid descent. Over
the following months Alan sent me several different versions of
the device in attempts to overcome the lapse rate sensitivity
problem without degrading its performance. FURTHER EXPLORATIONS In November I'd been playing around in light
thermal lift over Santa Rita Flats with a friend who was soaring
a 1939 Piper with the engine off. When he headed out, I resumed
the downwind leg to my motorcycle, parked ten miles south of
Mazourka's summit. Halfway there the lift faded. I found myself
at 400 feet AGL searching for lift along the line of abruptly
falling hills on Mazourka's western flank. I'd grown quite used to the Snooper by now. I
no longer regarded it as an instrument separate from my vario.
Instead, the vario was now a complete instrument operating on
principles of temperature and pressure - as seemed perfectly
logical. Indeed, what seemed illogical was the fact that the
soaring community had relied for generations on an incomplete
device! As I ran the ridge southwards, the Snooper
would tend to get excited in the most promising areas. I'd slow
down, then, and hunt around, happy to find zero sink to simply
extend my glide. After a passing above a series of mashed-up,
crosswind hummocks that offered little potential in the way of
lift, I came to a prominent descending ridgeline that formed a
bowl to the north wind. Confident of finding lift there, I cut a
path along its face. The Snooper "beeped" agitatedly
but there was no lift. "Strange;' I thought. 'Why would the
Snooper go off when there's no lift? I became suddenly uncomfortable without knowing
why. I moved away from the ridge and sped up a bit. The Snooper
continued to "beep" quickly. The hairs on the back of
my neck stood up. Then, as I flew past the falling crest of the
ridge, heading west into the valley, the rotor hit me. It threw
the Express into a snap-roll to the left, hurling me
toward the rocks. I stuffed the bar to my knees and countered
with a roll to the right, clearing the ridge with several
wingspans to spare. Later, it bothered me to realize that I would
have passed much closer to the ridge if I'd not had the Snooper,
thinking that the wind had died when in fact it had actually
reversed direction and strengthened while I'd been working
the lee, unsuspecting. What had happened to trigger the Snooper? I
surmised that the new south wind had placed a "cap"
over the leeside pocket. Trapped in the sunlight, it had heated
up with nowhere to go. Then, of course, I flew into it. By March the snooper had evolved into a compact
hunk of epoxy about half the size of a pack of cigarettes,
looking utterly indestructible apart from the fragile, shielded
thermistors. Alan had solved the problem of its beeping when
rapidly descending into warmer air with some circuit design
wizardry that was totally beyond my comphrehension. Now the
choice for this summer's production run had narrowed down to two
nearly identical units, both of which I was flying with. Alan
said they differed only in response time, but one became my
favorite and was chosen for production. One afternoon I left Mazourka with 12,000 MSL
and reached the Inyos only to discover the easterlies flowing
downslope. I flew out into the valley but found no lift. Two
miles from my motorcycle, I was down to 300 feet. Not wishing to
walk, I concentrated on the Snooper's occasional beeping to
circle in warmer areas of ground heat. Although my variometer was
indicating nothing but zero sink, after a series of 360s I would
find myself 30 feet or so higher. Gaining what little I could, I
would head north and repeat the turns the next time the Snooper
"beeped." I lost 200 feet during the first mile and
completed the second with only 100. After landing, I got a funny
feeling that I could have kept going indefinitely at 100 feet! I
have always admired the exceptional hang glider pilots who could
do this kind of thing but I had never been particularly good at
it. Now the Snooper was making it almost easy. April 25 was a day of record high temperatures,
producing surnmer-like flying conditions on the Sierra. I was
chasing two other pilots who had left the Sierra for the Whites.
But I stayed on the Sierra for a few miles farther, hoping for a
big altitude gain on Mt. Tinnemaha that would allow me to cross
the Owens Valley to the Whites at a point north of Black Mountain
and possibly get ahead of them. This strategy got me into trouble. For some
reason the south wind turned easterly at Mt. Tinnemaha just as
bad lee turbulence drove me from the mountains at a low altitude.
I was unable to penetrate this wind. My options were to land in a
rugged area of the alluvial fan or to find a drifting thermal,
ride it across deep and narrow Big Pine Canyon and up to Coyote
Flat. But if I lost the thermal between the canyon and mountain
flat, I knew I could get into a desperate situation, one that
would make landing on the alluvial fan look like a picnic. Down to a few hundred feet over ugly terrain,
no radio, no retrieval, no nothing - and the Snooper
"beeped!" I hunted around for the thermal. It wasn't
much, but at least I'd stopped sinking. I drifted on the weird
wind over nasty Big Pine Canyon, trying to find the core where
the Snooper would quiet down. Finally, I found it. I even started
to get comfortable, climbing now at 50 fpm. Then the Snooper
started "booping" on one side of my circles. I adjusted
my turns, leading them more to the north, until the Snooper went
silent once more. The thermal had changed direction in a wind
shift. Now I was heading north. The Snooper made it a lot easier to stay in the
core as the thermal rose through different bands of wind
direction. Much easier than it had ever been with just a
variometer. "Just wait until the flatland pilots get
their hands on Snoopers!" I thought, drifting for 30 miles
up the center of Owens Valley. "They'll go nuts!" NEW VISIONS Using the large Fall and Spring thermals of
Mazourka as a guide, I estimate that the Snooper senses a thermal
at twice the distance from the core as does the variometer. This
distance decreases as the power of the thermal increases. In the
2000 fpm thermals I encountered on the Sierra in late April 1987,
the Snooper led the vario by only a second. Perhaps the speed of
a rapidly ascending thermal prevents the parcels of heated air
shed by the thermal from spreading outward as easily as seems to
be the case with slower thermals. Of course, in such powerful
conditions the vario and Snooper become much less important to
the pilot than in weak conditions. If we consider a thermal as a sphere for
purposes of calculation, the Thermal Snooper increases the radius
of detectability by a factor of two for encounters along any
horizontal line. In cross section on a horizontal plane, each
thermal offers the Snooper four times the detectable area as it
does the variometer. And in volume each thermal is eight times as
large for the Snooper as it is for the vario. Theoretically, at
the very least, a pilot skilled in the use of a Snooper should be
able to detect twice as many thermals as a pilot with only a
vario, although I suspect that the actual capability is much more
than doubled. Of course, thermals are not spheres.
Contemporary theory envisions a rapidly rising bubble of warm air
pushing its way through the relatively stable air in its path. As
it passes, cooler air rushes around and below to fill in the area
it has vacated. This causes sink around the thermal. This theory was developed by observation from
sailplanes. But a Thermal Snooper mounted on a hang glider
traveling 20 mph suggests a slightly different picture - one that
may revolutionize soaring techniques. Imagine discrete segments of warm air from the
thermal's outer layer being constantly torn away and set spinning
by friction with the cooler air through which the thermal is
rising. The thermal will be completely surrounded by these
swirling segments of warm air and they will continue to move
outward as they cool. These are what the Snooper senses. I have
termed this new vision of a thermal the "sloughing
thermal." I will not be in the least surprised if the
Thermal Snooper becomes a standard feature of every flight deck,
be it on a Dacron or fiberglass soaring machine. What does
surprise me, and continues to surprise me, are the new
applications being found for the Snooper.
FINDING THE SLOUGHING THERMAL When using the Thermal Snooper to locate sloughing thermals, the same techniques are used as when locating thermals with a vario. The Snooper and vario work in unison, enhancing the likelihood of finding lift. Think of them as one instrument. The Snooper is the more sensitive aspect of this device. It tells you a thermal is nearby. The vario tells you when you are actually touching the thermal. It verifies your guess. The Snooper will "beep" when it senses the warm eddies sloughed from the thermal (1). If the "beeps" stop, immediately execute a 270 degree turn that leads back to the central point of the beeping (2). Regardless of which way you choose, you will intersect the thermal. The Snooper will continue to beep as you approach the core, but the vario and tactile feedback must be employed to center it (3).
MASTERING THE SLOUGHING THERMAL The Thermal Snooper allows the pilot to recognize the presence of a thermal from far outside the point where his vario would register anything. First, the warm eddies are sensed (1) and the Thermal Snooper begins to "beep" while the vario remains silent. Next (2) the vario may indicate sink but the Snooper will continue beeping. Entering the ascending outer layer of the thermal (3), the vario will register lift as the Snooper continues to beep. Finally (4) when the thermal is cored, the vario registers lift but the Snooper is silent because the temperature of the core is constant. |
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