With Historic Aircraft Collection (HAC) founder Guy Black's
permission, the following piece is based on an article on the HAC
The Historic Aircraft Collection was
formed by Guy Black and Angus Spencer-Nairn to restore and operate a
collection of piston engined military aircraft.
Currently their fleet comprises Hurricane Mk XIIa
(G-HURI), Spitfire Mk Vb (G-MKVB), a Feisler Storch, a Chipmunk and an
Behind the scenes a lot of restoration work is
taking place including a number of single and two-seater Hawker
biplanes. HAC's sister company, Retrotec Ltd (formerly Aero Vintage
Ltd), responsible for restoration work, completed their first
restoration, Hawker Nimrod I (S1581) in 2000, and a Nimrod II
(G-BURZ/K3661, see above) in 2006. A Fury I (G-CBZP/K5674), a Hind
(L7181) and an Audax (K5600) are currently in work..
Aircraft from the first world war period were usually wooden framed,
wire braced and covered in linen fabric. Aircraft produced in the 1930s
were of transitional construction where the wooden frame was replaced
by one of tubular steel or, as was to become more common, sections made
from formed rolled steel strip. High tensile steel was used so very
light, rigid structures could be made.
The problem that restorers of aircraft
of this period face is that steel corrodes and being so thin is almost
always unusable a second time around. Fortunately the plates at all the
junctions were made of stainless steel and these mostly survive in good
order, but the tubes and spars usually need to be replaced.
The Hawker biplanes had faceted wing
spars of polygonal cross section made of rolled steel strip, closed and
riveted together, with a high tensile steel web separating upper and
lower booms. The machine used for making the booms is called a roll
forming mill. Original specification steel for the spars was made for
us by a Swiss company who arranged a unique smelt for Aero Vintage. The
tubes of the fuselage structure had squared ends where the joint was
made with stainless steel plates.
It was an Air Ministry requirement that
these aircraft should be easily maintainable in the outlying reaches of
the Empire where welding facilities might not be available. The
structure was therefore assembled with close fitting ferrules held
together between the plates with flared mild steel tubular rivets.
Nowadays neither the tubular rivets nor the high tensile steel strips
or tubes are available from stock leading to a major development
programme at Aero Vintage Ltd to manufacture the material and recreate
machines to produce the sections exactly as were used by Hawkers.
The squaring of the tube ends was done
using a special machine. Using photographs of Hawkers' original machine
Aero Vintage designed and built one, and the chance discovery of a set
of squaring tools in a South African scrap yard allowed squared tube
manufacture to be carried out. Other machines have been installed to
manufacture the streamlined tubing used on the wing struts and to make
the special tubular rivets.
Editor's note. Anyone who visits
Retrotec/Aero Vintage cannot be but impressed by the high quality of
the work carried and the attention to detail in every aspect of design
and manufacture. Also noticeable is the quiet working environment; no
whining 'windy' drills or chattering rivet guns. To those used only to
stressed skin aircraft, the beauty of the tube and wood structures,
recreated by their craftsmen exactly as was done at Hawkers between the
wars, is most affecting. Just think what it must have been like in a
factory filled with lines of these exquisite aeroplanes in peaceful