Clément Ader's Avion III, the "Bat"
Clément Ader's Avion
III, otherwise known as the "Bat", one of the centrepieces at the
Musée des arts et métiers, was restored in the 1980s by the Musée de
l'air et de l'espace at its workshop in Meudon, near Paris.
Clément Ader's Avion III in 1895
The aircraft, which
has a wingspan of over 15 metres and is equipped with two 20-HP steam
engines and two propellers, was built between 1894 and 1897 in Paris,
in the rue Jasmin workshop. The materials used were basically wood
and, for a small number of parts, steel, brass and aluminium. The web
on the wings was made from silk pongee which, in spite of its tight
weave, is permeable to air.
Experiments on the
prototype, which required a considerable amount of work, began in
October 1897. Interrupted after an accident, the work was not
continued due to a lack of financial resources. However, Ader claimed
that a 300-metre flight had taken place, a fact confirmed by two
Biruta Kresling was
given the opportunity of studying the airplane close at hand when it
was 'dissected' - 'taken to pieces', enabling her to find out all the
details relating to its manufacture and produce a series of drawings.
She was immediately struck by the great intuition shown by Ader in
transposing the mechanical principles of bat flight, particularly
that of the flying fox.
Clément Ader's Avion III in 1908
With the impression of experiencing a remarkable adventure, Biruta
Kresling laid bare the aircraft's design, revealing the astonishingly
bionic (before the term was coined) elements which inspired Clément
Ader, engineer and prodigious inventor, and examining the new ideas
Although the 'Bat'
plane remains virtually unknown outside France, and in spite of the
fact that Ader's copy of the natural model (faithful right down to
the terms he used - 'arm', 'forearm', 'fingers', 'elbow', 'wood')
seems naive and clumsy today, all these technical concepts, for which
Ader had no theoretical bases or experimental means at his disposal
other than those he used himself (large flying models, a glider, the
Eole aircraft and, finally, the life-size plane itself), were
extremely advanced for the time.
between the aircraft and the animal are by no means coincidental.
Ader did in fact recommend building the wings of low-speed planes on
the model of a bat's wing, and those of high-speed planes on the
model of a bird's wing.
Among the many
similarities between 'Avion III' and the flying fox or birds, we will
look at just a few examples.
Doubtless aware that
the pilot would be unable to steer such a complex aircraft without
the assistance of self-stabilizing devices, depending on the shapes
and materials used, Ader invented mechanisms such as propeller blades
inspired by the quills in birds' wings, made of paper and bamboo - a
sort of 'propfan' and blade 'with automatic variable pitch'. The
shaft of the propeller blades consisted in a central strand made of
cork onto which thin sheets of split bamboo were assembled and stuck.
The unit was mounted in such a way as to flatten out at high speeds,
automatically regulating the angle of incidence.
The 'thumb' of the
flying fox combines two functions: firstly, the unfurling and
automatic tensing of a membrane similar to the 'leading edge flap' in
an aircraft, followed by the folding back of the wing, with the thumb
now acting as a hook enabling the bat to grip onto the branch of a
tree. The same coupled mechanism - a safety device for the animal -
gave Ader's flying machine, designed for military aviation, an
essential, dual function: the wing could be tensed and then folded
back, meaning that large wing surface areas could be reduced. A
single mechanism thus facilitated the processes of putting the
aircraft into operation rapidly by unfurling the wings, bringing it
to rest, transporting it from the airfield to the hangar, followed by
fast, easy removal and dissimulation once it had landed.
X-rays of the 'arm'
of Avion III showed its hollow inner space to be criss-crossed with
thin wooden rods driven into the sides of the tube. These make the
arm rigid, similar to the bony trabeculae - the thin rods which
reinforce the humerus in birds.
As Director of the
Musée de l'air et de l'espace, General Pierre Lissarrague supervised
restoration work on the plane. He began by carrying out a critical
study of the countless technical notes in Clément Ader's workshop
notebooks. In order to check that Ader's ribless wing did indeed have
the hollow profile announced in the patent, Lissarrague came up with
the idea of testing an original half-wing from the plane, with its
'arm-bones' and 'fingers', covering it with a new layer of silk
pongee, just like the one on the original wing which was used as a
model, and exposing it to natural wind. The experiment took place
outdoors, on the west coast of the Cottentin peninsula. The
'automatic ' curve of the thin 'fingers' and the membrane of the
aircraft could thus be observed in simulated flight, as could the
profiles along its wingspan. The placing of reflective strips under
the wing enabled the shape of these profiles to be photographed,
while measuring the way in which they are positioned in relation to