Chapter 1 - Priorities
In preparation for the World Record Encampment at Zapata, I would like
to provide some information to the participants regarding flight
techniques and planning. Hopefully, it will assist in the setting of
several new records. In any event, I hope that the information provided
will allow you to fly much further than would otherwise be possible!
Many factors contribute to long flights. These variables are of
different relative importance, and as one variable changes it may
likewise change the rank or quantitative importance of the others. Here
are some key parameters, particularly for soaring designs of low wing
loading such as Hang Gliders and Very Light Sailplanes:
1) Strength of Soaring Conditions.
2) Reliability of Soaring Conditions.
3) Duration of Soaring Conditions.
4) Organization of Soaring Conditions Along a Flight Path.
5) The Ambient Winds.
There are, of course, other factors. The effects of altitude could be
added as a 6th, but in the whole scheme of things it is generally less
important than many would think. For our specific application, it is not
important enough. We will limit this discussion to these 5 priorities
because they are the major contributing ones. Notice that the first 4
all relate to the vertical character of the soaring conditions while the
last one relates to the horizontal environment. The 4th one is
transitional because it measures the vertical quality's distribution
through a horizontal plane.
It is useful to think about the vertical and horizontal components,
because the vertical character is important qualitatively (will
determine whether we are still flying or on the ground) and
quantitatively (faster and fewer climbs result in more distance
covered). The horizontal character will impact directly the distance we
cover, which is our goal, and is a strong quantifier. Likewise, our
glider performance is easily defined in terms of horizontal and vertical
components. So these become a common denominator for the analysis of a
given glider in a given set of flight conditions.
It is a useful exercise to ponder these 5 factors, and think deeply
about how each relates to the other. One example of that just occurred,
with the discussion of vertical and horizontal components.
Where would you order the 5 in priority?
You may wish to stop right here and do this for the next day or so. More
might be learned in this exercise than anything further which might be
written. The more time you spend with this question, the more other
important questions will spring to mind. As you slog through it all,
there will be a point where the questions start diminishing or at least
becoming fairly insignificant.* When you reach that point, you start to
get a grasp of the real essence of the thing. This sort of exercise
results in an understanding of operational principles, as opposed to
rules. These principles can then be applied in different ways, under
different circumstances.
Different days...different times of the day ...different
sites...different gliders. If the consideration can't be applied in
different circumstances, than this becomes a dividing line which defines
the consideration as a rule, not a principle. We will try to concern
ourselves with principles, and then apply them illustratively to
specific circumstances.
Think about this for awhile, and then I will ramble on a some more.
Footnote: * I suppose it is safe to say that if the questions were ever
to stop, we might lose interest in soaring. However, I suppose it is
even safer to say that the questions will never stop. We are dealing
with such a complex environment, which makes it all so glorious! Aren't
we privileged to enjoy this activity?
Chapter 2- A Long, Long Day
For very light gliders and most circumstances, the duration of the
soaring conditions and the ambient winds will top the list. Hands down.
Let's examine the duration factor first...not because it ranks above the
winds (they probably rank on par most days)...but since it should be a
"no-brainer". If you are flying in conditions that provide for an
average XC speed of 25 mph and you have a 4 hour flight, you've made 100
miles. If you can fly at that speed for 8 hours, 200 miles. Fly for 12
hours and you've put 300 miles behind you. Like I said, a "no brainer".
Even so, the time factor has traditionally not been given as much weight
as the strength of the soaring conditions. Most pilots are dominated by
what their instruments are telling them and the implications of speed-to
fly theory. Its real, it works, but it doesn't claim to take account of
the whole set of circumstances.* Because of this myopic focus, many have
reasoned that the stronger the conditions, the further they will fly.
And that unless they're in really big air with altitude, its pretty much
a waste of time. I doubt they have ever pondered the original question
regarding priorities very deeply.
Actually, for very long distance flights and provided at least a
reasonable level of lift, we will find that strength of conditions or
flying a precise speed to fly ranks very low on our list of priorities.
It starts moving up as wing loadings increase, and for the highest
performance sailplanes it moves up near the top. However, the duration
factor remains high in priority no matter what we are flying or what the
particular conditions because it has an overriding quality to
it...becoming a multiplier for whatever the sum total of everything else
is.
It might be beneficial to analyze a long day in three segments: 1) The
early start; 2) The middle portion; and, 3) The late finish. The middle
portion from a site that generates especially long duration flights
might easily correspond to an entire flight from more typical soaring
locations. Even so, there are some things to especially consider about
it and we will do so shortly after an examination of the other two
portions. For these discussions, we will assume thermal soaring
conditions rather than ridge or orographically generated lift.
Early starts are an interesting animal. In most locations, the start of
reliable cross-country flights is inhibited at least in part by morning
temperature inversions. These will not only limit the height of the
workable lift band, but can also result in very weak thermals which are
not very closely spaced. It is possible to benefit from such conditions,
but generally not unless there are good tailwinds to move you along.
Otherwise, the risk of landing out early weighs against the slow
progress resulting from weak conditions. When the wind is present, the
most successful strategy is to determine a minimum climb height with
which you are comfortable, cautiously leave the site, and hang with the
lift much longer than normal when in doubt. If the winds are moving you
along, you can afford to linger in modest or zero lift...even mild
sink...if you think something worse is just ahead. The conditions for
the day have just begun, and so you have the development curve and time
on your side. Things should improve if you can hang on. Patience is the
key flight quality at this time.
Often at these lower altitudes, thermal development is cumulative in
effect. If you leave a weak thermal and forge ahead over unlikely
terrain you might find nothing but sink. However, if you hang with the
lift you have, you'll often find that when it drifts over the next
beneficial ground feature it will gather steam and either take you to
the next lifted level or connect with other lift that makes faster
forward progress possible. One must be very patient in conditions like
these until the day has truly switched on. The other alternative gives
you an opportunity to study ground features...up close and all too
personal!
When flying the prototype Carbon Dragon, which possesses excellent
soaring capabilities, I will leave whenever conditions result in climbs
to an altitude of 1,000'AGL. I don't recall ever landing out early.
However, there have been a few times when the inversion only lifted
another 1,000' or so in the ensuing 2 hours and the conditions were
quite weak. Gaining 50 or 75 miles on the task during an early start
like this is worth the effort. When the day turns on, then you can roar.
Sprinkled here in there around the world, in far too few locations, are
some very special sites. Early in the day they start working and they
are generally immune to a morning inversion. Zapata is such a site, for
a variety of reasons. Due to various patterns, there is a strong flow of
unstable air which moves into the area during the night and overruns the
previous day's conditions. It sort of channels and then funnels right
into the region we start from and fly through in the beginning portion
of the flight. Convection can start quite early and at times does not
require the sun's heat to trigger the first pulses.
Not too long into our first exploratory excursion there, I photographed
active and fresh fracto cumulus forming just before sunrise at about
1,000'. The mechanical push of the wind, moving unstable air modestly
upslope, was all it took to start things off. Once the sun rose and the
faintest of surface heating began it got much better.
The lack of a distinct low altitude inversion means that as the surface
continues to heat, the top of the climb band just continues to rise in a
nearly linear manner. Barograph traces from the site confirm this, and
the progress is rapid and reliable. Interestingly, the bottom of the
climb band on such traces also rises in a nearly identical manner so
that lines drawn through the top and bottoms of the climbing portions
possess very similar slope. This is an indicator of something quite
remarkable...thermal spacing remains uniformly proportional in relation
to glide capability between thermals. And the spacing is quite favorable
with abundant lift! So as the climb tops rise, pilots can increase their
interthermal speeds and take advantage of the growing climb bands.
Very early starts are possible from Zapata. Last year, during some
uncharacteristically blue morning cycles, starts were generally taken
around mid-morning. This still provided for some very long days.
Hopefully this year they will be even longer.
In the next installment we will examine the late finish and the middle
portion of a long day and the role each plays in this regard.
Footnote- * Keep in mind that our goal is flying far...for distance.
This is a focus which is very different from flying fast, as in a racing
competition. Although flying fast and flying far might cross-over at
times in our set of priorities, they will not always do so. Flying the
correct speed to fly while competing against a field of other pilots who
are all sharing the same conditions and the same goal would moves this
aspect dramatically onto a list of flight priorities. Many of the other
decisions we are considering have already been set...they are not
variables for consideration. So, often the task winner has relied upon
only one or two parameters in his successful
Davis Straub
davis@davisstraub.com
www.davisstraub.com/OZ