From Wiki, for what it is worth: " In April 1938, performance estimates were produced of a twin Rolls-Royce Merlin powered DH.91, with the Bristol Hercules and Napier Sabre as alternatives."
"Shorts built a half scale version as the S.31 (also known internally as the M4 - the title on the tailfin), powered by four Pobjoy Niagara engines, which first flew on 19 September 1938, piloted by Shorts' Chief Test Pilot J. Lankester Parker."
1/2 scale model flies 5 months after De Havilland proposal is presented. When was work started on both full size and 1/2 scale aircraft?
"On 4 October 1938, for example, De Havilland projected the performance of another design based on the D.H 91 Albatross, powered by two Merlin Xs, with a three-man crew and armed with six or eight forward firing guns, plus one or two manually operated guns and a tail turret."
About the same time (Oct 1938 ) De Havilland did propose an unarmed bomber. It is not until Sept/Oct of 1939 that work begins on the actual DH 98 design.
I guess it depends on what you mean by concept and how close the concept was to the final design.
This has nothing to do with the technology. Mostly, it relates to the timing that specifications are issued.
On 8 September 1936, the British Air Ministry issued Specification P.13/36, which called for a twin-engined medium bomber capable of carrying a bomb load of 3,000 pounds (1,400 kg) for 3,000 miles (4,800 km) with a maximum speed of 275 miles per hour (443 km/h) at 15,000 feet (4,600 m); a maximum bomb load of 8,000 pounds (3,600 kg) which could be carried over shorter ranges was also specified. Major aviation firms entered heavy designs with new high-powered engines and multiple defensive turrets, leading to the production of the Avro Manchester and Handley Page Halifax.
In May 1937, as a comparison to P.13/36, George Volkert, who was the chief designer of Handley Page, put forward to the Air Ministry the concept of a fast unarmed bomber. In his 20-page document, Volkert laid out plans for an aerodynamically clean medium bomber that would carry 3,000 pounds (1,400 kg) of bombs at a cruising speed of 300 miles per hour (480 km/h). There was some support for the idea in the RAF and Air Ministry, but they were muzzled ; for example a Captain Liptrot, who was then Research Director Aircraft 3 , appraised Volkert's design, calculating that its top speed would exceed that of the brand new Supermarine Spitfire. There were, however, counter-arguments that, although such a design had merit, it would not necessarily maintain a speed advantage over enemy fighters for long. The Ministry was also considering the use of non-strategic materials for aircraft production, which, in 1938, led to specification B.9/38 and the development of the Albemarle medium bomber, which was largely constructed from spruce and plywood attached to a steel-tube frame. Thus it can be seen that the idea of a small, fast bomber, possibly made out of non-strategic materials, was gaining support but the specifications for its development were at least two years later than those relating to the heavy bombers that Britiain would eventually use in the war. The Mossie even from before its inception was playing catchup, but this had nothing to do with the technology. De Havilland, for example, was years ahead of everyone else in laminar design, dating back to at least his 1931 comet design, The problem was not the technology, it was convincing the decision makers that it could be done.
That is a fact but when did the first raid occur with the 4000lb bomb?
I believe it was May 1944.
Mosquito (DH 98 )was first planned with 1,280 hp (950 kW) Rolls-Royce RM3SM (experimental designation for what became known as the Merlin 21) engines,. Please note that at this time 100 octane fuel was the best that could be expected in the near future. There was NO MEASUREMENT SYSTEM for ratings or performance over 100 octane at this time. Boost was going to be 12bs at best for while. The discovery that British 100 octane was actually 100/115-120 was still in the future let alone actual 100/130 fuel.
If the mosquito had begun development in say 1938, with squadron delivery in 1939, I dont think there is any argument that these hypothetical Mosquitoes would have been a lot less of a performer compared to the later real world marks. The first real world Mosquitoes with merlin 21s had a top speed of 365 mph, which was still fast enough to virtually gurantee immunity from intercetion. This was because even the earlier marks still had an impressive sustained max cruise speed, and a respecable (ie superior to any other bomber) sustained cruise speed.
If Mosquitoes began entering service in 1939, they may have had a max speed of around 340 mph Im just guessing that number, but if Im even close , thats still more than enough to walk away from any fighter then in existence.
The evolution off the Mosquito design is interesting. i note that this 9and some of the preceding text is in wiki, however wiki has in fact pinched its narrative from a good source, the Point Cook museum.
"After further consideration, in a follow-up letter sent to Freeman on 27 July, de Havilland stated that the P.13/36 specification could not be met by a twin Merlin powered aircraft and that either the top speed or load carrying capacity would be compromised, depending on which was paramount. For example, a larger, slower, turret armed aircraft would have a range of 1,500 miles (2,400 km) carrying a 4,000 lb (1,800 kg) bomb load, with a maximum speed of 260 miles per hour (420 km/h) at 19,000 feet (5,800 m), and a cruising speed of 230 miles per hour (370 km/h) at 18,000 feet (5,500 m). De Havilland believed that such a concept was too much of a compromise, and that getting rid of some surplus equipment would lead to a better design. On 4 October 1938, for example, de Havilland projected the performance of another design based on the D.H 91 Albatross, powered by two Merlin Xs, with a three-man crew and armed with six or eight forward firing guns, plus one or two manually operated guns and a tail turret. Based on a total loaded weight of 19,000 pounds (8,600 kg) it would have a top speed of 300 miles per hour (480 km/h) and cruising speed of 268 miles per hour (431 km/h) at 22,500 feet (6,900 m).
Still believing that this performance could be improved upon, and after examining more concepts based on the Albatross and the new all-metal DH.95 Flamingo, de Havilland settled on designing a completely new aircraft that would be aerodynamically clean, of wooden construction and powered by the Merlin, which offered promise of substantial future development. The new design would be faster than all current or foreseeable enemy fighter aircraft, and could dispense with a defensive armament, which would only slow it down and make interception or losses to anti-aircraft guns more likely. Instead, high speed and good manoeuvrability would make it easier for the design to evade both fighters and ground fire.
Also, the lack of turrets meant that production would be simplified and production time reduced, with a delivery rate far in advance of any competing designs. Without armament, the crew could be reduced to a pilot and a navigator. This was in contrast to contemporary RAF design philosophy, which required well-armed heavy bombers and was much more akin to the German schnellbomber concept" (. However, it also damned the acceptance of the Mosquito to a very rough reception, and a long aceptance perios. it was simply too radical and too much of a departure to be easily accepted for the war winner that it could be).
"During a meeting held in early October 1938 between Geoffrey de Havilland, Charles C Walker (de Havilland's chief engineer) and Air Ministry officials, the latter showed little interest in de Havilland's concept and, instead, asked de Havilland to build wings for other bombers as a sub-contractor.
By September 1939 de Havilland had produced preliminary estimates for both single- and twin-engined variations of light-bomber designs using different engines, while speculating on the effects of defensive armament on their designs. On 20 September, in another letter to Wilfred Freeman, Geoffrey de Havilland wrote "...we believe that we could produce a twin-engine bomber which would have a performance so outstanding that little defensive equipment would be needed." (Those pre-design estimates proved to be prophetically accurate. DeHavilland estimated their design could achieve a top speed of around 360mph, the actual dewsign was found to be 367mph). "By 4 October work had progressed to a twin engine light bomber with a wingspan of 51 ft 3 in (15.62 m), and powered by either Merlin or Griffon engines, with the Merlin being favoured because of its immediate availability."