It built on a proof of concept trial of
the propulsion method carried out by
Athene Works. But unlike the name might
suggest, the previous trial was a success,
although of a simpli ed version at a
smaller scale, and was own by remote
control. All of this was built by a £3.3
million consortium: half from Innovate UK,
the UK’s innovation agency, through the
Aerospace Technology Institute; half from
12 partners, including ve universities,
three high-value manufacturing catapults
and four industrial partners, and led by the
CPI, Centre for Process Innovation (see
box).
What both designs had in common
were their lungs – or, technically speaking,
a 7m ballonet in ated by a bi-directional
electric compressor – to make them go.
As helium is nearly seven times lighter
than the same amount of air, its supply
of the noble gas provides lift. Payload
and the weight of the fabric skin, plus
ight systems, offset this. The team
HOW TO CREATE FORWARD MOTION IN A BOBBING FLIGHT PATH
Generate
mass
Ascent
Lighter-than-air
further decreased the margin between
lift and weight, to a few kilogrammes, by
pumping air into the ballonet: in this case,
a polyurethane bag, reinforced with woven
polymer.
Here is how it works. If the aircraft’s
ight path is tilted slightly down as it takes
on air, the force of the increased mass
pulling it down toward the earth also pulls
it forward. Conversely, the ship rises by
expelling that same air, and provided
the ight path points upward, that again
pushes it forward by the same mechanism
(ignoring the thrust caused by the expelled
AEROSPACE – SATELLITES
COOL TECH
Two technologies developed for Phoenix
UAS, but not ultimately used on the
trial vessel, show potential for later
development.
First, IQE collaborated with CPI on
developing an extremely lightweight solar
photovoltaic cell speci cally intended for
ight applications. Their so-called type
iii/v semiconductor-based cell has a
power production capacity of 1000W/kg,
compared to a gure of ve times less for
silicon-based PV cells. Light in weight they
were; low in price they were not; the cells
proved too expensive to t on the project.
Second, a team at Newcastle University
designed a reversible hydrogen fuel cell
that could either generate hydrogen to
be used for lift or to fuel a combustion
engine, using electricity, or run the
opposite way to burn excess hydrogen
to make electricity. The design was not
suf ciently advanced to be included in
the trial, but the work did provide data to
incorporate in future design work.
Descent
Heavier-than-air
Jettison
mass
air, which is another signi cant source of
propulsion, but which wasn’t measured
in the trial). Some seven square metres
of solar panels mounted on a stubby
horizontal wing, and on rear-mounted
ailerons, power batteries that drive the
compressor. The ship is designed to y
overnight, and then be recharged during
the day from solar cells producing about
500W (according to a sunny November
trial), so it is completely self-suf cient in
energy.
So the ship bobs up and down as it
pootles along, like a cautious swimmer
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