| Peter
Taylor, kite expert, explains how the draco was
made to produce a noise. With Tim and Valerie looking after
the head and tail, my contribution to the project
was to investigate the noise made by the draco.
Unfortunately there is very little direct
evidence for the nature of the noise or how it
was created, so this element of the
reconstruction was very experimental.
Available
evidence
I was hoping that the
Niederbieber draco head would contain some clues
– some internal mounting plates or holes for
example – but that proved not to be the
case. But I’ll come back to this later!
We did extensive Internet
research, stating with the excellent Fectio site
– and I recognise there may be other sources
which this has overlooked, but which were not
open to us in the time available. A rather
enigmatic picture emerges:
- We
found nothing about how the draco sound
was made, apart from a much later mention
of ‘reeds’.
- Descriptions
of the sound varied from whistling
through hissing and ‘eerie’.
- Descriptions
of when the noise was made varied from
‘on parade’ to ‘much
movement’.
Specification
From this we outlined a
specification for what we were trying to achieve
with our draco noise maker:
- The
noise should be loud enough to be heard
above cavalry
- The
noise should project over a reasonable
distance
- It
should be a practical solution – not
too large or heavy
- At
worst it should work at horse gallop
speed – ideally less
- Consistent
with the contemporary technology
- A
good fit for the evidence that does exist
Candidates
We’re looking for
solutions with specific acoustic properties; it
has to produce resonance which can be excited at
low pressure and in a compact structure. A high
pitch noise would be ideal – low pitch would
tend to get lost in the cavalry noise. We
explored a number of different possibilities.
The head
Is it possible that the head itself could be
responsible for the noise? It’s an
attractive theory, but unlikely to work. The
fabrication process produces a structure which
isn’t easy to resonate. You might get a
low-level noise from wind moving over the teeth,
but it would not be nearly loud enough at the
speeds we want. There is no evidence for
resonating structures inside the head – and
none of the reconstructed heads have made a
noise.
The tail
The tail does make a noise – a combination
of fabric rustling and streamers flapping. But it
isn’t especially loud and it doesn’t
project.
Whistles and flutes were
known in Roman times – drill flutes were
used by the army. They can be made to work at low
pressure, they are compact and can produce a
noise that carries well - and is pitched above
cavalry noise.
Is it possible that reeds
were used to create resonance? Maybe, but you
would still need a resonant chamber of some kind
and our target speeds would not create enough
airflow to make this work. Musical instrument
makers said ‘no way’.
We looked at a number of
possibilities for using string. Aeolian (wind)
harps can produce loud noise, but are really too
big to be a practical solution. It’s
possible to make much smaller harps but they are
not loud enough. Moving from a round string to a
flat ribbon gives much more volume for a given
size. Either way, the sound produced is a poor
match for our whistle/hiss/eerie goal.
We did consider the
possibility that string resonators might have
been fixed directly to the draco head –
between the teeth for example. But the surviving
head has no evidence for this idea.
Another wind-powered
noise-maker uses rotating vanes – we
rejected this as anachronistic.
We explored the idea that
wind flowing through the draco head might excite
a column of air in a hollow tube – an organ
pipe or didgeridoo effect. It might work, but
sources indicate that the draco head was mounted
on a spear or spear shaft. From all of this the
flute approach seemed the strongest candidate.
For a given size they will produce by far the
loudest noise and are consistent with the
technology available.
Prototype
A single flute tends to
produce a pure tone – not very eerie –
but two or more flutes can be tuned to give the
right effect. Our friends from Weifang supplied
us with a range of different wind flutes –
these are single note flutes which are used for
whistle kites – not widely know in the West,
but a key part of the Chinese kite tradition.
They are made from traditional materials –
hollowed gourds with a carved wooded top, or
lacquered wood for the smaller ones. We made a
quick test rig by mounting various whistle
combinations on a shaft – these
produced the right sort of noise, much louder
than expected and worked at horse speed. (This
gave the horses some early exposure to the noise
to get them accustomed to it.)
Experiments
In the Time Team
tradition, you really do get just three days to
put it all together. Until the draco head and
tail were finished all I could do was use the
test rig and do some measurements. Using the
crazed side-by-side bicycle with Rick steering, I
could hold the rig and wind meter. We had good
results at about 12 mph – well within our
goal. So far so good…
Mid morning on day 3 we
were able to start experiments with the flutes
mounted inside the draco head. The original plan
was to mount them on a sound board – for
speed we used the trusty BluTack – hardly
authentic, but enough for a test run. First tests
were with the head alone – the tail
wasn’t ready at that stage.
This didn’t work at
all well; it was much quieter and we needed more
speed (20 mph + ) to get the flutes working at
all. The problem was air turbulence –
or sheer lack of air flow. Either way, adding
more flutes would make matters worse, not better.
And of course we needed good airflow through the
head to inflate the tail. The obvious solution
was to mount the flutes externally. But our
assumption had been that the noise maker would be
inside the head - and I wasn’t quite ready
to abandon that approach.
In the end, a fresh look
at the evidence with the Time Team crew swung it.
Assuming the nose maker was organic and inside
the head, it would of course have long-since
decayed. But the decay should have left some form
of residue. The lack of residue suggests that the
noise maker was not inside the head. With no time
left for further experiments, we decided to go
for broke and mount the remaining whistles on
battens that would fix to the spear shaft with
leather thongs. No testing, no fine-tuning. From
here it is straight into filming.
Results
The first couple of runs
were not encouraging; the crew wanted to film
against a backdrop – which meant downwind,
the worst possible direction.
Into the wind, things
start to get better, but for the first few runs
Alan (Larsen) is still trying to find the best
way to control the whole assembly; the draco head
is heavy, the tail pulls in the wind, and the
flutes need to be angled correctly to get the
best sounds. We are getting sound from the large
flutes – but nothing yet from the small
sets.
Finally, good results;
riding into the wind, the small flutes kick in
and sound becomes a wail. Later we find out the
sound was easy to hear over 200 metres away. What
next? There’s obviously potential for more
research. Some representations of dracos show a
much more ‘open mouth’ style –
which might have worked better with the internal
flutes. From our experiments though, I think
there’s a strong case for flutes and for
mounting them externally – even if that was
an ‘in-the-field’ modification.
Click
here for the website of the
original 2005 Time Team episode.
See
also:
Making the Time Team Draco is
Copyright © 2005, Peter Taylor. All rights
reserved. Used with permission.
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