Boulton Paul Defiant

[TheGreenAnger]

In my ignorance I had always thought this fighter had been a total dud, but an article in this month's Fly Past Battle of Britain edition has disabused me of this total prejudice, although the lack of forward firing armament was a huge disadvantage against the advanced German fighters and the rear turret slowed the aircraft due to its weight and drag. It did better as a radar equipped night fighter.

https://www.dailymail.co.uk/news/articl ... craft.html

[TheGreenAnger]

I am interested to read that not only did the Defiant's turret hobble the aircraft's performance, but it made for a death trap for the poor gunner who had real difficulty egressing the aircraft in extremis.

The turret concept was also considered for both the Mosquito (and the Lysander as well)

The Mosquito Turret...!

At the de Havilland Aircraft Museum, at the birthplace of the Mosquito near London Colney, Hertfordshire, towards the after point of the canopy transparency on the surviving prototype is a faint line running transversely up its left-hand side. This was a rub mark indicating the forward edge of a fairing which was to be added in order to streamline a power-operated turret, fitted to the aeroplane during aerodynamic trials for such a set-up on a specialised night fighter. In contemporary retellings of the Mosquito story, there is little mention of a turret-armed version, given the designation DH98B Turret Fighter in at least one piece of surviving documentation. Even specialised references provide scant detail of the installation and why it was considered in the first place.

The first sources date to the type’s conception, when senior figures in the Air Ministry were opposed to the idea of a bomber with no armament. However, it is seldom realised that the concept of an unarmed ‘Speed Bomber’, as coined by the commander-in-chief of Bomber Command, Sir Edgar Ludlow Hewitt, was not rejected out of hand. Rather, it was believed that Geoffrey de Havilland was exaggerating the proposed performance of his prototype.

During aerodynamic calculations made on 9 October 1939, de Havilland staff under R. E. Bishop studied the effects of defensive armament on the Rolls-Royce Merlin-engined proposal. de
Havilland had investigated powering his bomber with either two Merlins or Griffons pending availability of the latter; early concepts had it using a single Napier Sabre or two enlarged Napier Daggers. A simple two-gun tail turret would cost 500lb in weight and lose 20-30mph in speed, it was discovered. Assessments were then made of the impact of a two-gun turret with a single underside traversing gun on the proposed machine’s performance against the larger Griffon-engined design. Its take-off weight would climb from 15,600lb to 18,000lb. On the 17th, weight and speed estimates were calculated following a proposal that the larger machine be fitted with a standard four-gun tail turret. It added 2,400lb in weight and made the design more difficult to manufacture.

Naturally, performance decreased considerably. Maximum speed at 19,000ft fell from 409mph for the smaller unarmed prototype to 355mph, and cruise speed at 15,000ft was 279mph compared to 325mph for the Merlin machine.

Mossie Mock Up.JPG (33.06 KiB) Viewed 258 times

AVM Arthur Tedder, director general for research and development, and Assistant Chief of the Air Sta AVM William Sholto Douglas both agreed on 1 November that the bomber would be of value if it were given adequate defensive provision in the form of a tail turret. Sholto Douglas stated, “if designed without effective rear defence, it could only be considered as a development aircraft for possible use on fast reconnaissance duties”. Despite this, his rejection of the aeroplane was due to the belief that the supply of turrets would tax existing resources. Seven days later — contrary to previous estimates — de Havilland’s chief engineer C. C. Walker advised that with a Nash and Thompson FN4A four-gun rear turret, a 1,000lb bomb load and a crew of three, the Griffon-engined aeroplane could reach speeds of 390-400mph at 20,000ft. He added that, owing to the type’s relative simplicity, it could go into production quickly.

Tedder now told de Havilland that two prototypes of the four-gun turret-armed aeroplane were required from the rm and that it should proceed with constructing a mock-up straight away. Drag estimates were based on data obtained from tests with Airspeed Oxfords and de Havilland Dons, fitted with (unpowered) dorsal turrets. These were forwarded to the Royal Aircraft Establishment at Farnborough for consideration, along with wind-tunnel models for additional testing. Naturally, de Havilland was reluctant to abandon the unarmed prototype of what was now designated the DH98. It said it would be awkward to proceed with two different prototypes within the specified time of nine months.

Air Marshal Wilfrid Freeman, that early champion of the Mosquito, agreed. At this stage still the Air Member for Research and Development, he was wholly opposed to the turret-armed design. Freeman proposed the unarmed example should take priority, gambling on its promised extraordinary performance and that the firm would build the Griffon engined prototype after the unarmed machine had proven itself, within nine months of its completion. Obviously, with the success of the firrst prototype DH98, the tail turret-armed, Griffon engined variant was not built. This was probably a good thing, as it would have used up scarce resources, just as Sholto Douglas predicted. That wasn’t the end of the turret-equipped Mosquito, however.

In mid-1940, discussions about the requirements of future service night fighters were held within the Air Ministry, including tactics that Boulton Paul Defiant gunners in their trainable turrets were to exploit. The ability to train the guns upward to direct concentrated fire into the unprotected bellies of enemy bombers were a necessity, as mooted by Air Marshal Philip Joubert de la Ferté, air advisor on combined operations. With increased nigh bombing against British cities by the Luftwaffe in the autumn of 1940, specification F18/40 was released on 11 October. It called for a fixed-gun, two-seat night fighter equipped with six 20mm Hispano cannon to be put into production and service relatively rapidly e (edited) descriptive text from the specification read, “To meet Operational Requirement OR.95, the primary role will be the interception and destruction of enemy aircraft at night. In the interests of quick production, wood or composite construction will be accepted. This aeroplane must have high performance and a powerful armament. Free and unobstructed vision for search for both the pilot and the AI [airborne interception radar] operator is particularly important. The aeroplane will have fixed guns, good handling qualities [are] also an essential requirement and in particular the aeroplane must be easy to land at night. The aeroplane may be single engined, twin engined, a tractor or a pusher, as may best meet the requirements. a single engined tractor is preferred. "Following discussion around the advantages of a trainable turret, on 9 December an addition was made to the text: “Armament changed to include dorsal power operated turret. Endurance increased by one hour”. the successful design to this specification was intended to repla ce the Defiant, which, despite its unremarkable performance in the first half of 1940, eventually found success at night, remaining in service as a dedicated night-fighter until mid-1942. - Grant Newman