If expedited, when could the Mosquito have entered service?

[Admiral Beez]

October 1938, immediately after Munich, Geoffrey de Havilland pitches the Mosquito concept (two Merlin engines, wooden construction, speed as defence) to the Air Ministry. However, Serious Air Ministry interest didn't arrive until late 1939, resulting in later design and prototype completion, with first flight not until late Nov 1940, entering service a year late in Nov 1941. If the Air Ministry had shown earlier interest and support, how soon could the Mosquito have first flown and entered service? And what is the impact of an earlier Mosquito?

 

[MIflyer]

Mitchell was designing a new light fast twin engined bomber when he died. What if he had not passed away?

 

[Admiral Beez]

Mitchell was designing a new light fast twin engined bomber when he died. What if he had not passed away?

Another good what if. Why not post that thread?

 

[ThomasP]

So [Do] we know what the 1938 'Frog Biter' was supposed to look like and/or Mitchell's proposed specs?

The reason I ask is that the initial design might be significantly different from what the actual Mosquito turned out to be. Performance and potential improvement might be very different if the proto-mossi was expedited.

 

[Admiral Beez]

I ask is that the initial design might be significantly different from what the actual Mosquito turned out to be. Performance and potential improvement might be very different if the proto-mossi was expedited.

Maybe, but we're advancing at best six to twelve months, with the Air Ministry ordering a prototype in early 1939 instead of 1940. DeHavilland already had the wooden composite and monocoque construction sorted out on his DH.88 Comet and DH.91 Albatross, and by 1939 the Spitfire and Hurricane had demonstrated that the Merlin was clearly the engine to go for. I wonder if there's a sketch from 1938 in any archive somewhere.

 

[Shortround6]

Somewhere in an old thread we had a list of performance estimates of a Mosquito using Merlin X engines (same as Whitley's and some Wellingtons).
There were also 1-2 estimates with Merlin XX engines?
Bomb loads were usually 1000lbs (four 250lb bombs?)
I can't remember if the estimates separated out two speed props and constant speed or not.
Basic problem for early Mosquito service is the availability of engines and propellers. This is going to affect bomb/fuel loads. The plane is still going to be very fast for it's time but if it only carries 1/2 the bomb load and somewhat less (20?) fuel what is the combat effectiveness?

 

[Shortround6]

Mitchell was designing a new light fast twin engined bomber when he died. What if he had not passed away?

We have absolutely no idea.

This was the 317 heavy bomber and they were certainly not using a thin wing.
Mitchell was going to do what it took to meet the requirements and that includes taking off and landing on either existing airfields or the airfields expected be in service when the aircraft entered service.
Pictures of the type 327 fighter also do not show a thin wing.

Sleek for 1938-40 not quite Spitfire sleek.

 

[ThomasP]

Obstacles to earlier production, in addition to the already mentioned lack of Air Ministry interest and clearance to proceed.

1. The Mossi would not just have to be given the go-ahead but would have to be put on the 'Priority' list.
2. In order to begin Mossi production earlier DH would have to be able to offload production of the Tiger Moth and/or the Oxford (to de Havilland Canada?) and leave it there instead of having DH Canada gear up for the Mossi.
3. The Merlin XX was not available in any numbers until the 2nd half of 1940 at the earliest, so a decision would have to be made as to who gets the initial production - ie the Hurricane Mk II, Defiant Mk II, Beaufighter Mk II, or the Mossi. Or the Mossi would have to use the Merlin X initially and get priority over the Whitley and/or Wellington Mk II and/or Halifax Mk I.

If they managed the above then some effects would be:

1. Earlier long-range and more survivable high speed reconnaissance capability.
2. Earlier tactical use of the bomber version with associated advantages.
2. Earlier tactical use of the night fighter version in home skies (and maybe over France as intruder?) with associated advantages.
4. Earlier start on the continued development of more capable follow-on versions - with all that entails.

Not sure how much difference any of the effects would actually make in the grand scheme of things if they could be had 6-8 months sooner.

 

[EwenS]

There are a few other issues to be considered.

The proposal for the DH 98 Mosquito did not appear overnight as a concept let alone a complete design. In 1937 and the early part of 1938 DH were working on a twin Merlin / Hercules / Sabre engined development of the DH 91 Albatross air liner as an attempt to meet Spec P.13/36 (the Spec that led to the Manchester and Halifax). It was July 1938 before DH wrote to Freeman, Air Council Member for R&D arguing for wood construction in case of war breaking out and aluminium supply becoming short. It was out of this and other studies over the next few months that led DH to conclude that weights would need to be sacrificed to get a good bomber with decent performance on two Merlins with the then available power.

As for the Air Ministry in late 1938, they had a lot on their plate. Like trying to get types already ordered flying and into service, eight gun fighter production, and the shadow factory programme. So perhaps it is not surprising that the DH proposal for the Mosquito was not greeted with open arms.

But looking at DH itself there were issues other than those noted by ThomasP.

Their long serving chief designer, Arthur Hagg, resigned in early 1937. His last designs were the DH 91 Albatross airliner (first flight 20 May 1937 with 7 delivered to Imperial Airways 1938/39), the DH 93 Don trainer (first flight 18 June 1937. This was to be a three seat trainer with a turret so it could carry out all types of training. Its development proved to be a headache with numerous changes along the way. A production order for 250 was cut to 50 with only 30 aircraft fully completed before cancellation) and the DH 94 Moth Minor a monoplane trainer intended as a Tiger Moth replacement (first flight 22 June 1937 with about 100 built at Hatfield pre-war before production was transferred to DH Australia)

Hagg was replaced by a promoted R E Bishop. His first project was the first all metal stressed skin DH aircraft, the DH 95 Flamingo airliner (first flight 22 Dec 1938. The outbreak of WW2 saw the intended production run reduced to just 14 aircraft delivered 1939/40).

So DH had plenty of both design and production work in hand in 1937-38 both civil & military. Reduction in the Don contract freed up space for more Tiger Moth / Queen Bee (the pilotless drone version). Production of the DH 86 Express, DH 89 Dragon Rapide biplane airliner (& later the RAF Dominie) and DH 90 Dragonfly were in progress. This exposure to the civilian market had stood DH in good stead inter war, making it much less reliant on the vagaries of Air Ministry orders with their ever changing requirements.

So a initial question must be would DH have the design capacity to start DH 98 Mosquito work earlier? Then the question of manufacturing capacity?

Finally it is worth noting that the DH factory at Hatfield was a Luftwaffe target. Hatfield suffered severe disruption in summer / autumn of 1940. Not so much from direct hits as from the workforce having to take to the air raid shelters as bombs fell on the areas around it (in one two week period in Sept 1940 about one third of working hours was lost to this). On 3rd Oct 1940 it was bombed, killing 21 and injuring another 70 workers and disrupting production. About 80% of the raw materials and much work in progress for the Mosquito was lost to that lone attacker. You have to wonder about the effects of such a raid had Mosquito production been in full flow.

 

[merlin]

The spec. that resulted in the Albemarle, was for a bomber using non-strategic parts. De Haviland was at the start one of the companies interested but if memory serves dropped out. Seems plausible that they go for two options - the conventional bomber - that turned out the be overweight and that no one wanted. And a fast unarmed aircraft that became the Mossie, initially as a Recon, later options - could it have been in time for the Blitz, maybe.

 

[Howard Gibson]

Somewhere in an old thread we had a list of performance estimates of a Mosquito using Merlin X engines (same as Whitley's and some Wellingtons).
There were also 1-2 estimates with Merlin XX engines?
Bomb loads were usually 1000lbs (four 250lb bombs?)
I can't remember if the estimates separated out two speed props and constant speed or not.
Basic problem for early Mosquito service is the availability of engines and propellers. This is going to affect bomb/fuel loads. The plane is still going to be very fast for it's time but if it only carries 1/2 the bomb load and somewhat less (20?) fuel what is the combat effectiveness?

Mosquitos came out using two-speed Merlin engines. They were later converted to two-speed two-stage superchargers. The two-stage aircraft were not necessarily faster than the single-stage Mosquitoes at low altitude.

If Mosquitos come out in 1939/40, they would have single-speed superchargers, and they would have had to convert to the newer Merlins. But why shouldn't they? Probably, there is no need to extend the nose to accomodate the two-speed supercharger. Would they have enough aircraft in service to affect the Battle of France? Mosquitos were never used in this role. Would they have been effective?

 

[Shortround6]

Mosquitos came out using two-speed Merlin engines. They were later converted to two-speed two-stage superchargers. The two-stage aircraft were not necessarily faster than the single-stage Mosquitoes at low altitude.

If Mosquitos come out in 1939/40, they would have single-speed superchargers, and they would have had to convert to the newer Merlins. But why shouldn't they? Probably, there is no need to extend the nose to accomodate the two-speed supercharger. Would they have enough aircraft in service to affect the Battle of France? Mosquitos were never used in this role. Would they have been effective?

RR was making 2 speed engines in 1938-39, just not very many of them. They used pretty much the same supercharger as the Merlin II/III and were rated using 87 octane fuel.
As mentioned in earlier posts they were first used in the later models (Whitley V) of Whitley bombers and indeed in all Merlin powered Whitley's except around 33 (?) Whitley IVs which used Merlin IV single speed engines.
The Merlin X was rated at 1065hp for take-off instead of 880hp of the Merlin III. It was also rated at 1130hp at 5250ft in low gear at 5.75lbs of boost. High gear was good for 1010hp at 17,750ft. With 100 octane fuel things got somewhat better.
Engine.............................Merlin X...........................................Merlin XX..........................................Merlin XX/21 with higher boost.
take-off..........................1280hp/10lbs................................1280hp/12lbs........................................1280hp/12lbs
low gear........................1280hp/10lbs/sea level..............1240hp/9lbs/11,500ft........................1460hp/14lbs/6,250ft
high gear......................1010hp/5.75lbs/17,750ft...........1120hp/9lbs/18,500ft.........................1430hp/16lbs/11,000ft

By the time Mosquitos got into operational service in numbers the Merlins were allowed 12lbs of boost and then 14lbs in low gear and 16lbs in high gear and later 2 speed engines (not two stage, that is different) were allowed even higher boost. Ejector exhausts (not flame dampening) were good for 13-15mph with the 9lb boost limit.

Very few British aircraft aside from Spitfires were rebuilt/repowered with later versions of engines. A lot got replacement engines but not higher-powered versions.

Early Mosquitos should be looked at with these engines and boost limits depending on desired entry into service. Possible speeds and take-off weights/bomb and fuel loads.

 

[don4331]

RR built 310 Merlin X at Derby, 4,569 at Crewe per Mr. Sinclair, acknowledging that is through '43. Most, >3,200, used in Whitley production. Obviously, there is a ramp up/down at start/end, but almost 4,900 is quite a few in my books.

If an earlier Mosquito is available, most of the components (all except the 2 speed gear and block to fit them in?) from the Merlin II's found in Fairey Battles could be moved to de Havilland in '40, too. Battle production was continued well after they knew it was obsolete as there wasn't anything better available. With an earlier Mosquito, the better aircraft is there.

Convince Canadian government that they need to demonstrate they can build the "too small" Merlin (specifically Merlin X) pre-war before they would be granted contract to build "next generation" Sabre's would be another possible source of engines.

PR of the Siegfried Line by early Mossies rather than Battles would cut down losses...

 

[Shortround6]

f an earlier Mosquito is available, most of the components (all except the 2 speed gear and block to fit them in?) from the Merlin II's found in Fairey Battles could be moved to de Havilland in '40, too. Battle production was continued well after they knew it was obsolete as there wasn't anything better available. With an earlier Mosquito, the better aircraft is there.

Well this is damning with faint praise.
Mosquito junior (short pants.....Merlin III) has 1760hp for take-off total and two pitch props?
Mosquito junior (long pants......Merlin X) has 2130hp for take-off with 87 octane.
Mosquito adult (Merlin 21) has 2560hp for take-off.

A Mosquito with 69% of the take-off power of the historic planes with Merlin 21 engines is got to lift what payload off the runways?
Now try to figure out what the performance of a Mosquito at low altitudes is going to be with engines that are only somewhat more powerful than the engines in a Blenheim.
You need constant speed propellers and 100 octane fuel to make the MK IIIs work at all. As far as planning goes, neither is certain for most of 1939. We know they will show up in 1940 but they didn't know that in 1939.

Even Mosquitos with Merlin 21s would have failed in the Battle for France. Poor recon/targeting, poor or non-existent escorts, planes sent out in handfuls with bombs unsuited for some of the jobs? (250lb bombs are not bridge busters). Mosquito Juniors would have had little or no armor and not had protected fuel tanks.

 

[don4331]

Well this is damning with faint praise.
Mosquito junior (short pants.....Merlin III) has 1760hp for take-off total and two pitch props?
Mosquito junior (long pants......Merlin X) has 2130hp for take-off with 87 octane.
Mosquito adult (Merlin 21) has 2560hp for take-off.

A Mosquito with 69% of the take-off power of the historic planes with Merlin 21 engines is got to lift what payload off the runways?
Now try to figure out what the performance of a Mosquito at low altitudes is going to be with engines that are only somewhat more powerful than the engines in a Blenheim.
You need constant speed propellers and 100 octane fuel to make the MK IIIs work at all. As far as planning goes, neither is certain for most of 1939. We know they will show up in 1940 but they didn't know that in 1939.

Even Mosquitos with Merlin 21s would have failed in the Battle for France. Poor recon/targeting, poor or non-existent escorts, planes sent out in handfuls with bombs unsuited for some of the jobs? (250lb bombs are not bridge busters). Mosquito Juniors would have had little or no armor and not had protected fuel tanks.

Why are you so anti-variable pitch propellers in RAF aircraft?

You know Stoddard Hamilton was charging significant royalties for their propeller solution*. It was a very good system, but only going to be a matter of time before others got around their patent - Curtis had with their electric solution as had VDM with theirs's. So, Rolls-Royce and Bristol (Rotol) was going to come up with a solution sooner or later (which they did).

Secondly, UK gov't could hardly be preaching peace in our time and building a factory capable of supplying every RAF aircraft with constant speed propellers - UK doesn't have the same domestic market that may take advantage of constant speed propellers that the USA does.

Lastly, you know RAF bombers from Battles to Blenheims to Whitleys at least received variable pitch propellers - UK gov't wasn't complete naïve; they understood the benefits on heavy/twin aircraft.

So, the Mosquito early (Merlin X) has 83% of the power of Mosquito OTL (Merlin 21). The proposals were for 4-250lb bombs - history tells us that was too light, but that wasn't know at the time. Drop the self sealing tanks and armour and performance equal/better than the current Spitfires/Bf109E on the same 87 octane fuel. And by '40, 100 octane will be available.

Using the Mossie to get better recon is one of the roles I envision for the early version.

*Post war RR was charging $5k royalties for a Merlin, when Allison was building its V-12 for $7.5k. (numbers from Wiki). I have yet to see a number on how much Hamilton Stoddard was charging - was it a 65% or more uplift of the cost to manufacture one of their constant speed propellers?

 

[Shortround6]

Why are you so anti-variable pitch propellers in RAF aircraft?

You know Stoddard Hamilton was charging significant royalties for their propeller solution*. It was a very good system, but only going to be a matter of time before others got around their patent - Curtis had with their electric solution as had VDM with theirs's. So, Rolls-Royce and Bristol (Rotol) was going to come up with a solution sooner or later (which they did).

Secondly, UK gov't could hardly be preaching peace in our time and building a factory capable of supplying every RAF aircraft with constant speed propellers - UK doesn't have the same domestic market that may take advantage of constant speed propellers that the USA does.

Lastly, you know RAF bombers from Battles to Blenheims to Whitleys at least received variable pitch propellers - UK gov't wasn't complete naïve; they understood the benefits on heavy/twin aircraft.

I am not really anti-variable pitch propellers in RAF aircraft. It was the RAF that was that was anti-variable pitch.
Hamilton Standard had licensed their propeller to over a dozen countries by the late 30s including Italy, France and Japan. DeHavilland had the license in England but DH didn't have the production capacity needed. Rotol was formed because RR and Bristol (Fedden) saw the need while the Air ministry sat on their thumbs.
I have no idea how ordering thousands of warplanes with crappy propellers is "preaching peace in our time"?
There are 5 stages of propeller once you get past wooden sticks.
Ground adjustable. Mechanics can move the blades in the hub for best performance out of high airfields or in extreme weather. At least you have a factory making metal prop blades.
Variable pitch which was a fancy way of saying two pitch most of the time. Either course or fine pitch, nothing in-between.
Controllable Pitch in which the pilot can select any pitch between the upper and lower limits but any change has to be done by the Pilot.
Constant speed in which a governor automatically adjusts the pitch to keep the propeller/engine running at speed selected by the Pilot.
Full Feathering in which in the event of an engine failure on a multi engine aircraft the dead engine prop can turn it's blades parallel to the flight path for least drag.
Bragging that the RAF was using variable pitch propellers (2 pitch) in 1940 and later when H-S had demonstrated the full feathering propeller in 1938 just shows how behind the RAF was, or uncaring about their aircrews. A Lockheed Electra demonstrated a 6000ft increase in single engine ceiling using the full feathering propeller over the plain constant speed. It was a major safety feature on commercial aircraft.
The HS 2 Pitch propeller had been around since 1932. The RAF was not using 600hp Kestrels in first line aircraft any more in 1938.

So, the Mosquito early (Merlin X) has 83% of the power of Mosquito OTL (Merlin 21). The proposals were for 4-250lb bombs - history tells us that was too light, but that wasn't know at the time. Drop the self sealing tanks and armour and performance equal/better than the current Spitfires/Bf109E on the same 87 octane fuel. And by '40, 100 octane will be available.

Fair enough but will the Mosquitos get good propellers or poor ones in 1940?
Not all Beaufighters got feathering propellers and some did not make it back on one engine.

 

[Geoffrey Sinclair]

In any early war British aircraft production changes ideas an over riding consideration is to have the production line working at the latest in May 1940, otherwise it runs into the Battle of Britain freeze orders in a big way, something that did delay the Mosquito.

De Havilland pitched the idea for a military version of the Albatross airliner in mid 1938, wooden construction, twin Merlin but for bomb loads of 4,000 pounds or twin torpedoes, there were variations on this, size and armament, the October 1938 version with twin Merlin X, 3 crew and defensive guns was calculated to reach 300 mph. Also proposed was a twin Merlin version of the all metal Flamingo, smaller and faster. The pitch for an even smaller twin Merlin version was made in September. A year later the unarmed wooden design with 1,000 pounds of bombs was being quoted as reaching over 400 mph on a pair of 1,145 BHP engines.

The first production Mosquito PR.I were accepted in July 1941. That means starting the design process at least 14 months earlier than September 1939, that is mid 1938, to have first production by May 1940.

Next obstacle is the ramp up to mass production. To end June 1942 there were a total of 139 Mosquito built, including prototypes, 10 PR, 91 fighters, 29 bombers, 9 trainers, counting W4050 as a bomber. Production to end 1941 was 23 including 3 prototypes and a trainer. If you want the Mosquito around in numbers in mid 1940 start development in mid 1937 at the latest. Given the situation do not expect many bombers in 1940.

Rolls Royce Derby started Merlin X production in 1938, with 27 built by the end of the year, another 283 by end 1939 when production ended there, Crewe starting production in October 1939, with 108 by end of year, production ended in December 1942. The first Merlin XX were built at Crewe in July 1940, with 332 made by end of year, Glasgow 6 more November and December, Derby 1 in December.

Using Rolls Royce figures, 2,572 Merlin built in 1939, 2,196 being Merlin III, and as expected it was end loaded, 1,141 Merlin built in the final 4 months of 1939.

There were 33 Whitley IV (Merlin IV) built May to August 1939 then 7 IVA (Merlin X) and the first 8 Whitley V in August 1939. The report is only 73 Merlin IV built, all by Derby in 1938.

The RAF in France lost 34 Battle to all causes up to 9 May 1940, of these 8 were day reconnaissance sorties 20 to 30 September 1939, all shot down by fighters (including 1 joint French/German effort). After that it was all non combat and from 1 March 1940 all at night. Looks like reconnaissance was handed over to the Blenheim units, which lost 8 aircraft on the duty October 1939 to January 1940. Then come the losses from units based in Britain.

The RAF began the migration to 2 pitch then constant speed propellers pre war with its heavier aircraft first, the Hurricane changed over to constant speed end February 1940, it looks like the idea was the Spitfire I would stay 2 pitch, the mark II introduce the constant speed propeller.

Australia did not build any DH.94 Moth Minor as such, several had been ordered pre war by civil users, an initial production run was put in place to blend local wooden and imported metal parts to fill civil orders, with 4 being assembled when the war began. The cancellation of Moth Minor production in Britain offered the chance to acquire lots of now surplus parts and an order was placed in October 1939 via DH Australia for 50 under Overseas Indent 757, it was soon curtailed as it became clear the Tiger Moth was better. DH in Britain cabled in October 1939 that 22 finished machines and 20 incomplete sets were being shipped, in November 20 complete aircraft ready to sail, 3 more due to sail and 3 packed ready for shipment, there were 22 with dual control and "a few" with rudimentary blind flying instruments. The incomplete September 1939 to March 1940 British export reports have 30 Moth Minor sent to Australia. In the end 46 were around with 42 serials issued, including for impressed civil aircraft.

The RAAF ordered a total of 66 Avro Cadet as its trainer between 1935 to 1938 of which 32 were cancelled, then in 1939 it ordered 20 Tiger Moth fuselages and engines from Britain to be fitted with locally made wings, when war was declared more Tiger Moths were ordered from Britain and also DH Australia.

DH were building Tiger Moths for the RAF, 88 in 1938, 674 in 1939 and 663 in 1940 (production ending in August except 1 in December), plus overseas and civil orders. Add 59 Queen Bee in 1938 and 139 in 1939, 50 Don in 1938/39, 178 Oxford in 1939, all for the RAF.

 

[Shortround6]

In addition to the excellent post by Geoffrey Sinclair I would like to point out that the Merlin X was in high demand in 1938-40 for planned aircraft.

Design work for the Wellington II started in Jan 1938 but the first Wellington II didn't fly until March 1939, in part due to delays in the Merlin X engine program. eventually 401 Wellington IIs with Merlin X engines were built.
H-P Halifax was designed around the Merlin X engine and the first 75 (?) out of 100 ordered used the Merlin X engines. Later versions used the Merlin XX engines.
Air Ministry told H-P to use the Merlins in Sept 1937.
A few designs got shifted over to the Merlin XX engines as this was a fairly easy change. Main differences between the Merlin X and XX was the Merlin 45 style supercharger and carburetor and the new gear ratios (higher for the Merlin XX).

A lot is made of the 'conversion' of around 500 Spitfires from 2 pitch to constant speed propellers in late June of 1940 through August 16th (?) 1940. One claim is that 1051 Spitfires and Hurricanes (including some Defiants?) or perhaps it is that 1051 planes were either converted or built with the Constant speed propellers?
What is somewhat overlooked is that many of these planes should never have been built with 2 pitch propellers. Not to take anything away from the Men at DH who built the conversion units and/or the men, both factory and RAF fitters, who performed the work at the airfields. Basically, they fitted a new pump/governor unit to the engine and used the existing propeller hub. Which begs the question, why weren't they built that way to begin with? A constant speed unit for a H-S licensed propeller was about four years old (or more?) at the time. Building hundreds of two pitch props in 1939-40 knowing they were 2nd best is hard to swallow.