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The Historic Aircraft Collection Ltd. (HAC) has a number of
single and two-seater Hawker Biplanes under restoration. The
restorations are being carried out by HAC's sister company,
Retrotec Ltd. HAC completed and flew their first
restoration, a Hawker Nimrod I, S1581 (G-BWWK), in 2000,
with the second, the more sophisticated Nimrod II, K3661 (G-BURZ)
on the 16th November 2006.
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Nimrod I S1581, Henlow |
Nimrod II K3661, Duxford |
| © Guy
Black |
© Col
Pope |
The Hawker series of biplane fighters and military
two-seaters developed from the Sopwith aircraft of the First
World War. The availability of the Rolls Royce water-cooled
V12 "F" engine - later to become into the famous Kestrel
series of engines, and the rapid development of metal
airframe structures, resulted in the sleek and beautiful
silver-painted Fury fighters and Hart two-seater light
bomber and training aircraft in the late '20's. Of course,
the Fury directly lead to the famous Hurricane fighter,
whilst the Hart developed into many sub-variants, ending in
the Hind, some still in use during the outbreak of the
Second World War.
 Aircraft
from the First World War period were usually wooden framed,
wire braced and covered in linen fabric. Aircraft produced
in the 1930’s were of transitional construction. This next
phase of development was substituting the wooden frame for
one of tubular steel or as was to become more common,
sections made from formed rolled steel strip. Steel in this
case being of a high tensile nature and therefore very light
and rigid structures could be made. The problem that
restorers of aircraft of this period face, is that the steel
corrodes and being so thin is almost always unusable a
second time around. Fortunately the fitch plates at all the
junctions were made of stainless steel and these mostly
survive in good order. The aircraft from Afghanistan
however, were located in an arid desert area, and most of the
tubular structure is re-useable.
In the case of the Hawker biplanes, the tubular structure
used squared ends so that a joint could be made with the
stainless steel plates. It was a requirement of the Air
Ministry at the time that these aircraft should be easily
maintained in outlying empire countries, where welding
facilities may not be available. The structure was therefore
held together with close fitting ferrules held together
between the plates with flared mild steel tubular rivets.
 Nowadays,
tubular rivets are not available nor are the high tensile
strip steel and tubes utilised, so this has resulted in a
major development programme at Retrotec to re-manufacture
the material and re-create machines to produce the tubular
rivets and these sections exactly as they were by Hawkers.
 The
wing design incorporated a faceted wing spar made of a rolled
steel strip, closed and riveted
together with a high tensile steel web separating the top
boom from the lower boom; this produced a very strong
structure. The machine used for this process is called a
roll-forming mill and at the time the spars were
re-manufactured for us by one of the few companies
left in the UK that had a machine sufficiently large to do
this work. this company has now closed down, but we saved
the special machine from the scrapping, and is now in
storage. The special
steel used had to be made for us by a Swiss steel company
who arranged a unique smelt. Having solved both these
problems, we were able to go ahead and undertake the
extensive engineering work required to rebuild the aircraft.
 One
special feature on the Hawker biplanes is the squaring of
round tubes where they meet at the fitch plate. This was
done at the time by a tube-squaring machine and
unfortunately when the project was initiated, none were
known to exist. A chance discovery of a set of rolls in a
South African scrap yard, combined with photographs of the
original machine, enabled Aero Vintage to remanufacture the
machine. Other machines have also been installed to
remanufacture the special streamline tubing used on the wing
struts, and to produce the tubular rivets, from
newly-manufactured low tensile steel tubing. |
