snow surface have not been taken into consider-
and ambient temperatures are at their very peak.
ation; a higher density snow will also conduct
Snow and ice, and any foreign matter they con-
more heat to the ice surface than a lower density
tain, act like capacitors and will respond with a
snow. The actual heat budget at the Pegasus site
heating or cooling lag compared with the ambi-
has not been studied in detail, but we feel that
ent conditions.
these guidelines are probably conservative. The
For the most part, the runway will be unable to
Pegasus site was originally chosen because of the
support wheeled aircraft during the period when
relative absence of melt features. As indicated in
the protective snow cover is in place. Processing
the section describing the site selection process,
the protective snow cap to a density and strength
the natural snow cover at the Pegasus site prior to
adequate for some aircraft may be possible, since
construction was approximately 30 cm (12 in.).
it is fairly thin and has a very rigid underlying
Possibly, other materials may suffice to protect
base. For example, at Pegasus in most seasons the
a glacial ice runway from melt problems. We
snow cap could be compacted with heavy pneu-
briefly considered alternatives, including gravel
matic-tire rollers, bringing it to a strength that
and artificial materials (e.g., plastics, metallic foil,
would support the 690-kPa (100-psi) tire pressure
etc.), but these would have required considerable
of the C-130 Hercules. If the protective cap can be
study, environmental assessment, cost, and logis-
made strong enough to support the aircraft type
tical challenges. At sites with an inadequate sup-
that will principally use the airfield, consider-
ply of snow, such alternatives may warrant more
ation should be given to making the snow cap
serious consideration.
permanent. This will avoid the need to annually
Melt features may also form due to introduc-
place and remove the snow cover and thus drasti-
tion of foreign objects. The substances mentioned
cally reduce operating cost and complexity and
above in the section on surface cleanliness will all
the potential for additional problems (e.g., snow
accelerate the process of solar heat-up that can
collection, long-term buildup of snow on the flanks
easily lead to melt problems. In addition to those
of the runway). The topic of compacted snow
mentioned previously, objects such as runway
runways will not be covered here, but can be
markers and flag lines will also act as heat sinks
accessed in Blaisdell et al. (1995), Russell-Head
and can initiate a melt site. Once melting has been
and Budd (1989), and other publications.
started, if there is no significant drop in the ambi-
Ski-equipped aircraft, such as the LC-130, can,
ent temperature or solar intensity, the site will
of course, use the runway throughout the period
become unstable and melting will accelerate. We
when it is covered. This may be somewhat ad-
advocate using only the absolute minimum of
vantageous, but obviously does not make use of
markers on or near the runway. Markers should
the high bearing strength of the underlying ice
be of as little mass, and made of materials that are
and negates the reason for constructing the run-
as nonconductive, as possible. It is also very help-
way in the first place. By using ski-equipped air-
ful to have the markers located at least 18 m off
craft during the period when the snow cover is in
the edge of the runway and surrounded by snow
place, valuable flight days in a short operational
with a smooth surface.
season are not completely lost.
If air operations (skis or wheels) do occur on
the runway while the protective snow cover is in
Requirements for
place the surface must be smooth and free from
protective snow cover
For some runway sites, temperatures and solar
long-wavelength bumps. This may be challeng-
radiation intensity will not be at a level where
ing to accomplish, since the grader may not have
melt features are possible. Obviously, no protec-
adequate flotation to operate on the snow sur-
tion is required at such locations and mainte-
face. A device like our 12-m (40-ft) snow plane
nance will be far simpler.
(Fig. 71), but equipped with a laser-level system,
The intent of placing a snow cover on the
would allow adequate smoothing.
glacial ice runway surface is to protect it against
As mentioned above, we determined at Pe-
excessive radiational heating that could cause
gasus that 2030 cm (812 in.) of compacted snow
melting. In most cases, the protective cover will
was necessary on the ice surface each year from
be temporary, being in place only for a single
about 10 November to about 7 January in order to
critical period in the season. This period of time
completely avoid melt problems. Using this sys-
tem, maximum ice temperatures of about 5C
will be governed by the individual site, and
includes more than just the time when the sun
were reached at a depth of 510 cm (24 in.) in the
75
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