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De Havilland DH93 Don
Above: I've painted these Don's as if they
had entered service in their original role - In this case in the
markings of No 1 Air Observers School at Desford around 1939 (they
actually used Avro Ansons).
Designed
to Spec T6/36 the beautiful looking DH93 Don was an all-in-one training
workhorse. Student pilot and instructor sat side-by-side up front, while behind in the cabin was
accommodation for a trainee WT (radio) operator and behind that a hand-cranked turret for a trainee air gunner
with a Lewis gun. In the wing was a Browning machine gun so that the
student pilot could get in some air
gunnery training, and there were racks for 16 practice bombs
(little 2 pounders) it is presumed that there was a hatch in the floor
for a bomb-sight to allow
a trainee bomb-aimer to practice his art. Power was provided by de Havilland's air-cooled Gypsy XII* engine
of 525 hp (air was taken in by two inlets at the root of the wings and
directed over the engine from the
rear) one of the most powerful air-cooled inline piston engines ever
produced. With a retracting undercarriage and variable pitch prop
the Don was very state-of-the-art when the prototype took to the air in 1937. The Don was named after
the title used by British university professors, clearly reflecting its
role as a trainer. Its wooden construction was based on the practices
pioneered in the DH 88 Comet racer and DH 91 Albatross airliner,
construction methods bought to perfection in the DH98 Mosquito. The Air
Ministry ordered 250 examples of the Don, specifying that it also
needed a version capable of being used as a 4-6 seat communications
aircraft.
The Don as originally designed, with turret. Note the small finlets
under the tailplane and the anti-spin strakes ahead of the tailplane.
The finlets were added after initial testing of the prototype (L2387
shown
here).
Only L2387 and L2388 were built with turrets.
The
philosophy behind the design was that just one type of training
aircraft could meet the bulk of the needs of training the whole range
of aircrew - pilots, navigators, WT operators and air gunners. With the
Airspeed Oxford complimenting it in smaller numbers to finish off the
training for multi-engined types. However it quickly became apparent
that large numbers of multi-engined trainers would be needed to train
the pilots of the many multi-engined bombers ordered into production
for the RAF expansion, and that these multi-engined trainers would be
better than the cramped DH93 Don for training navigators, bomb-aimers,
WT operators
and air gunners. It was also evident that a trainer with higher
performance would be required to prepare pilots for the new Hurricane
and Spitfire fighters recently ordered into production. So the Air
Ministry canceled the DH93 and instead ordered the Avro Anson (already
in production as a coastal patrol aircraft) for use as a trainer and
increased orders for the Airspeed Oxford (23/36). Also the Miles
Master* was
ordered as a trainer for fighter pilots (later augmented by the Harvard
from the USA) and the much smaller and lower-performance single-engined
Percival Proctor (20/38) was obtained specifically
for training WT operators. This meant the only role left open to the
Don was that
of communications aircraft, which had been an after-thought to the
original specification.
The production run
for
Dons was cut to 50 aircraft and 48 of these were in the 6 -4 seat passenger configuration
with the rear
turret deleted. Only 30 were built to full flying condition. One
(L2394) was on the strength of 24 Squadron and 10 were alocated to various RAF
stations as communication "hack" aircraft. One (L2412) was allocated to
the Royal Aircraft Establishment, one to A&AEE at Martlesham Heath
(L2391) and another (L2407) went to No 1 Electrical and Wireless School
at Cranwell. Another ten aircraft were allocated to various flying
training establishments around the UK, but some of these may have only
been used for static instruction. The rest were delivered without
engines to be used as instructional airframes at RAF technical schools. In service the Don's Gypsy XII
engine proved to be a bit troublesome, overheating being the main
problem, although only one Don was ever
lost in a crash, (L2391 at A&AEE) and then no-one
was hurt. Only 90 examples of the Gypsy XII were ever built, so it's
not surprising de Havilland never got around to fixing all the bugs.
The DH98 Don as it entered service, as a communication aircraft with
turret deleted.
.Various commentators explain away the
perceived "failure" of the DH 93 by saying the aircraft was rejected
after Air Ministry testing at Martlesham Heath, implying it was
found to be too heavy
for the power of it's engine, but there seems to be no real evidence
for
this explanation. It is true that the performance was slightly
disappointing, not quite reaching the top speed of 200 mph originally
specified in 6/36. But it would seem there was no real failure of the
DH93 itself, just a realisation by the Air Ministry that one type of
aircraft was never going to meet all its training requirements. It may be unwise to attributing this change
of
heart solely to the big-wigs in the Air Ministry. It must be remembered
that a lot of aircrew training was sub-contacted to civilian companies
(such as Reid and Sigrist) with aircraft provided by the RAF
and painted in RAF colours - The opinions of the companies concerned as
to what was the best type of training aircraft obviously
carried a lot of weight.
De
Havilland had largely kept away from tendering for RAF orders since the
late 20's , preferring to build up their position in the civil
aviation marketplace, a policy
that had been a resounding success, by the mid 1930's they were the
most profitable British aviation company. With them setting up a production line for 250 Don aircraft
and then seeing the order reduced to only 50 you can see why de
Havilland shunned doing Government
work! But there was a silver-lining to this cloud; at the start
of
the war de Havilland had to stop production of its DH91 Albatross and DH95 Flamingo airliners, but
what
to build in their place? Biplane Tiger Moth and Dominie trainers
hardly seemed the best use of it's
resources - Enter the Mosquito! The Tiger Moth production line was
moved to the Morris factory at Cowley and Dominie production went to
Loughborough, and by 1941 the Hatfield factory was turning out
Mossies - But if the Don had been kept in production there is every chance that de Havilland would have
felt confident that they were "doing their bit" and never
initiated
the private venture that resulted
in the Mosquito design.
By the
start of the war there were no Dons left flying, they had all been
relegated to instructional airframes. But it was the availability
of the Gypsy XII engines stripped
from them
which allowed the small fleet of DH91 Albatross airliners, to be kept flying until 1943.
I've always found it strange that on the brink of World War II
Britain could afford to junk 50 already-built advanced monoplanes.
Assuming the problem was the unpredictability of the Gypsy XII engine
surely an easy remedy would have been replacement by a more reliable
radial engine? - One could imagine a Don with an imported 550hp Pratt
& Whitney Wasp, or maybe even an 800 hp Bristol Mercury or
Peseus,
which would have given a big boost to performance. - with the air
intakes for the Gypsy XII blanked off the resulting aircraft would have
still had the beauty one associates with de Havilland aircraft. -
All hypothetical.
Performance Statistics
Max Speed - a respectable 189 mph, quite high considering its engine
only produced 525 hp, Speed was virtually identical to the Anson
and 20mph faster than the Oxford
Range - about 900 miles, again quite good for a training aircraft
of this vintage and suprisingly superior to both the Anson and
Oxford.
Ceiling - 23,300 ft - more than enough for its intended
role and considerably higher than either the Anson or Oxford
Notes
* The Gypsy XII was later renamed the Gypsy King I
** It is worth noting that the Miles Master itself started life
as the Miles M9 Kestrel project which was itself tendered to the same
specification as the DH93 (Air Ministry Spec T6/36).
SOURCES
"Out-moded Teacher - De Havilland's Don Crew Trainer" - An article by
Daniel Ford in Air Enthusiast magazine edition 105 May/June 2003
"The British aircraft Specification File" by KJ Meekoms and EB Morgan,
an Air-Britain
publication.
Links
Don
in the "Flightglobal" archive
Wikipedia
Spitfire
| Bf109 | Skua | Roc
| Blackburn B20 | Blackburn B40 | DH Don | BP
P100 | Venom | Hawker Henley | Cunliffe-Owen OA-1