Jetrader - November/December 2008 - 28

when cleaned up in ﬂight. Only seven were
built, and wood was the principal material
in its construction. It had four DH 525hp
inverted V-12 engines, constant speed
propellers, slotted ﬂ aps and retractable
landing gear. The major innovation was
the molded-composite fuselage shell with
an end-grain balsa-wood core and birch
plywood outer skins. The wing was made
in one piece with a laminated spruce-spar
and birch skin. Other than the engine
installation there were few fasteners, it
was mainly glued together. Designed by
A.E. Hagg as a long-range mail plane,
the two prototypes were damaged-one
in March 1938 with a forced wheels-up
landing and the second with a broken
back during overload landing trials. Both
were repaired.
Imperial Airways, the forerunner of
B.O.A.C., took ﬁve with a 22-seat layout
between October 1938 and June 1939
for the European routes. Meanwhile the
two prototypes were used from 1940 by
the RAF as a shuttle service to Iceland
after the army occupied it to forestall a
rumored plan of a German invasion. By
1943 there were only two survivors, the
others being lost in landing accidents and
enemy action, notably the blitz on Bristol
in September 1940. The remaining two
were scrapped in September 1943. The
two major problems were the excessive
ﬂexing of the airframe in ﬂight and the
deterioration of the structure from rot.
Although it was not a commercial
success, its elegant method of construction
was to be the basis for the de Havilland
submission of a design for a twin-engined
ﬁghter bomber in response to the Air
Ministry's P.13/36 speciﬁcation. The result
was the Avro Lancaster and Handley Page
Halifax four-engine heavy bombers and
the two-man crew DH Mosquito. It was
one of the fastest aircraft in WWII before
the advent of jet ﬁghters. The bomber
version had a top speed of 419 mph at
28,500 feet and a still air range of 1,470
miles, more than enough for its regular
night sorties to Berlin carrying a 4,000 lb
"cookie" blockbuster, shaped like a large
propane tank. It carried no armament but
was equipped with the extremely accurate
H2S radar bombing aid.
Although designed as an unarmed
bomber, the Air Ministry initially ordered
only a photo reconnaissance version with

The de Havilland Mosquito

Merlin 21s, which had a single-stage
supercharger. Later PR models had the
Merlin 114 engine with a two-speed, twostage supercharger, a pressurized cockpit
and an operating altitude of 40,000 feet.
It was capable of 425 mph.

Rough Materials
So why was wood the principal material
used in its construction? Aluminum alloys
were in huge demand for the production
of ﬁghters and bombers in wartime
Britain, whereas spruce and birch plywood
were relatively plentiful. Further, trained
metal workers were likewise engaged
in the assembly of metal aircraft, but
woodworkers were readily available, and
de Havilland had developed the use of
plywood to generate a smooth, rigid-butlight structure in its DH 88 Comet racer,
which won the England to Melbourne,
Australia, race in 1934, (see: Jetrader,
November 2005). For the Albatross, the
10 mm thick end-grain balsa core was
sandwiched between 2 mm birch skins and
proved that a low-drag, smooth airframe
could be produced.
The Mosquito fuselage was split
longitudinally and the internal frames, 2 mm
inner skin, balsa core and outer skin were laid
up, glued and formed on wood male plugs.
Each half then had all ﬁttings, control runs,
electrics and hydraulic plumbing installed
before gluing them together. Prior to this,
a bottom section was cut away from each

28 The ofﬁcial publication of the International Society of Transport Aircraft Trading

half and used as the bomb bay doors. The
two, one-piece laminated spruce spars were
covered with stressed birch ply; two layers
on the top surface and one on the bottom,
with each engine radiator inside the wing
leading edge between the fuselage and
engine nacelle. The result was a light, rigid,
smooth-surface airframe of extremely low
drag and high-speed capability. Production
was at a high rate and distributed among
the furniture industries, car manufacturers,
aircraft manufactures Airspeed and Percival
and de Havilland's own shadow factory tucked
well away from likely bombing targets.
The bomber version initially carried
a 2,000 lb bomb in the bay and a 250 lb
one on a hard point under each wing. The
precision of its bombing capability was
legendary. Outrunning the Messerschmitt
ﬁghters, the unarmed Mosquitos destroyed
Gestapo barracks, records and interrogation
buildings in a number of cities in occupied
Europe. This included their HQ in Oslo and
the Schott optical works at Jena.
The bay was capable of carrying a 3,000
lb bomb plus two 500 lb bombs under
wing, or the 4,000 lb "cookie" after the
doors were modiﬁed, which then became
the standard version. With the advent
of the Foke-Wulf Fw 190 ﬁghter and its
slightly superior speed over the thenversion of the Mosquito, it was switched
from day to night bombing and navigated
to its target by the intersection of two
converging radio beams from stations in
Jetrader - November/December 2008

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