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
http://ozreport.com