De Havilland DH93 Don
The De Havilland Don prototype as originally built, complete with turret. At this stage it has not yet aquired the finlets under the the tailplane. An extremely "clean" aircraft, the air-cooled Gypsy XII did not need a radiator . The wheels protruded a little when retracted, which would have helped reduced damage in the event of a wheels-up crash-landing.
Designed to Air Ministry specification 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). 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 Don Turret in close up. The purpose of the "box" to the rear of the turret is unknown. Note that a direction-finding (DF) radio loop is mounted on the top of the cabin.
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, observers (navigator/bomb aimers), radio 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 "flying classrooms" than the cramped DH93. 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 more examples of the Avro Anson (which had started as a small airliner adapted for 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. A full list of Don production number, serial numbers and brief notes on their use can be found in a table published in the Summer (June) 2013 edition of Air Britain Aeromilitaria magazine at the end of a short article by Phil Butler.
Some sources say the Don's Gypsy XII engine proved to be a bit troublesome, overheating being the main problem reported, 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 perhaps 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 would seem that the performance was slightly disappointing, not quite reaching the top speed of 200 mph originally specified in 6/36. But there was no huge 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. In the late 30's the priorities for aircrew training changed considerably. The need for longer and better training in the skills of navigation becoming particularly evident (read C.G. Jeffords book "Observers and Navigators" for details of the big changes in the roles and training of navigators in this period), and the extra room in twin-engined designed such as the Anson and Oxford had many advantages for such training.
Another view of a Don in Commications form. The RAF, Royal Navy and Air Transport Auxiliary had a desperate need for aircraft in this class for ferrying staff and equipment around. Various civil types were impressed for service to fill this gap. Just why the Don was not retained in this role is a mystery.
De Havilland was not as dependent on RAF orders as other British aircraft companies, 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 one drawback of doing Government work! However de Havilland was rewarded with extra orders for Tiger Moth trainers and was even asked to build some of the Oxford trainers to be used in place of the Dons. Oxfords were produced at the de Havilland factory at Hatfield alongside Dominies and Queen Bee target drones, until the Mosquito was ordered when the Dominie line went to Loughborough, the Oxford line was closed down.***
By the start of the war all the published sources I can find indicate there were no Dons left flying, they had all been relegated to instructional airframes (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). However Janic Geelen, the author of "Magnificent Enterprise - Moths Majors and Minors" suggest that deHavilland may have retained one Don for their own use for communications duties into the early war years.
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 a hypothetical flight-of-fancy of course.
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 twin-engined Anson and Oxford.
Ceiling - 23,300 ft. More than enough for its intended role and considerably higher than either the Anson or Oxford.
DH 93 Don, Note how similar the tailplane is to the famous DH88 Comet racer.
What If ?
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). If the Don had entered large-scale production maybe DeHavilland would have been satisfied they were "doing their bit" - and never gone on to develop the outstanding DH 98 Mosquito?
* 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).
*** Thanks to Janic Geelan for putting me right on the way deHavilland moved production around to cope with the demands of the war - see his book "Magnificent Enterprise -Moths Majors and Minors"
"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.
"The De Havilland Don" a 3 page article by Phil Butler in the Summer (June) 2013 edition of Air Britain "Aeromilitaria" magazine.