Fast bombers again

[tomo pauk]

My favorite flavor of the bombers
How real were they an asset (if a country had them), were they neglected or maybe too much emphasized, what were the options if a country wanted them. How to forestall the attack undertaken by fast bombers, how well they performed against an opponent with decent fighter and/or AAA force? How good were by day? The types that didn't made it in service? Install the guns or not?

 

[nuuumannn]

Mine too, Tomo. Looking forward to this.

 

[Shortround6]

You have to remember that the British got lucky, very lucky, with the Mosquito. Expecting the same amount of "luck" with a variety of other designs may not be realistic.

A current generation "fast bomber" could always out run a previous generation fighter, the problem comes in with current fast bomber vs current fighter or last generation fast bomber vs current fighter.

Blenheim was the fastest aircraft in RAF service when introduced.

Fast bombers worked well with good crews, in small raids. What happens if you tried to put 500 fast bombers over a target in the space of a a few hours?

 

[tomo pauk]

They would saturate the defenders? Plus, the faster flying bombers will spend less time in enemy airspace than slower ones, that has more than one benefit. 1st, the defending fighters will have had trouble catching them if they are not in suitable position. The AAA will have harder time to hit a faster target than a slower one. It will expand fewer shells, further decreasing the possibility of hitting a bomber.
Not all countries have had the extensive radar-assisted HQs, positioning even a few fighters to thwart a fast bombers' raid would be next to impossible for them.
Against fighters, and beside speed - a fast bomber does not automatically mean it can't have defensive guns.

We might recall that DB-7 have had quite a low attrition vs. Luftwaffe fighters Flak in 1940, despite not having the top-notch engines. LW never bragged about shooting the Pe-2 and Tu-2 in droves. Of the four B-26 attacking Japanese carriers during Midway, only one was claimed by Zeroes.

 

[Shortround6]

Getting the defenders into suitable position/s is hard when it is a small raid. A lot easier when it is a big raid, you don't get the first wave ( or first few) but the following waves are in trouble.

And it is not about a one battle or raid, it is about being able to sustain a campaign over many raids or even sustaining a campaign over several years which means the bombers and fighters may swap back and forth several times as to has the advantage.

Making fast fighters is easier than making fast bombers.

 

[tomo pauk]

For coming out with fast bombers, there are several thing s that can help out. Like forgetting about a dozen of HMGs, for starters. That not just cuts drag and weight, it also cuts down the crew requirement. So the weight is further down. Less crew also means that smaller fuselage will do - again cuts down weight, along with required size of the aircraft. The lighter fuselage means that smaller wing can be used, for same wing loading. Current technology flap system can help.
Having an engine that is as good as one's current fighter have also can help. Do we really need 4 crew members for a bomber aircraft to do it's mission (during a day), plus the gunners?
Yep, I'm referring to the B-26.

 

[Shortround6]

Having an engine that is as good as one's current fighter have also can help. Do we really need 4 crew members for a bomber aircraft to do it's mission (during a day), plus the gunners?
Yep, I'm referring to the B-26.

It kind of depends on what the "mission" was doesn't it?

Original specification that lead to the B-26 included " a bombload of 3000 pounds was to be carried over a range of 2000 miles at a top speed of over 300 mph and at a service ceiling exceeding 20,000 feet. The crew was to be five and armament was to consist of four 0.30-inch machine guns. The proposal called for either the Pratt Whitney R-2800, the Wright R-2600, or the Wright R-3350 radial engine."

Please note that this is before the R-2800 even flies in a test mule.

This on March 11, 1939. Now even at 250mph 2000 miles takes 8 hours so perhaps a relief pilot was wanted? 1939 radio perhaps needed a dedicated operator?

And once again, Timing is everything. 500th B-26 is rolled out the door within a few weeks of the 5th F4U Corsair and the 1000th B-26 is rolled out within a few weeks of the 5th F6F.

IF you can afford to delay production of the B-26 for about year perhaps you could have used the same engines as the fighters.

BTW "Further orders for 719 B-26Bs on September 28, 1940 brought the total B-26 order to 1131 aircraft"

max bomb load of the B-26 as ordered was 4800lbs (?).

The First B-26 actual flew for the first time the same day the Mosquito prototype flew. The Mosquito at the time was planned to have a 1000lb bomb load.
This site has 3 large pictures of the first B-26
Factsheets : Martin B-26

They didn't get quite what they requested.

 

[nuuumannn]

You have to remember that the British got lucky, very lucky, with the Mosquito. Expecting the same amount of "luck" with a variety of other designs may not be realistic.

I don't think 'luck' has anything to do with it. There was a pre-disposition at the time (contrary to what the popular view would have us all believe) within the British Air Ministry that fast bombers offered much and although the Mossie was initially not what the chaps had in mind, they certainly got it once it was demonstrated, pretty much within days of its first flight. There were a few ideas on what a fast bomber should be wihin the RAF and much discussion was done on the idea, particularly after George Volkert produced his paper on fast bombers in 1937. The thing that turned the decisions against the unarmed bit was the success, or at least the promise of the power operated gun turret and all the bomber specifications underway at the time (B.12/36, P.13/36 and so on) stipulated them for defence. Few other countries truly embraced the concept of a true fast bomber ('Speed Bomber' as Ludlow Hewitt called the armed fast bomber); the Luftwaffe did and the Ju 88, whilst not possessing the all out performance of the Mossie, proved a very competent and versatile machine that gave excellent service.

As for its design, the Mosquito was a sound, well thought out machine with little advance over contemporaries. Nothing that had not been tried before, just current technology done really well (unlike the Whirlwind!), so no luck involved at all.

 

[pbehn]

With the mosquito I believe some luck was involved in the choice of engine, if they had chosen any other British engine it would not have been as good and in choosing the merlin its production was ramped up so much that engines were eventually available.

 

[tomo pauk]

Thanks for the data, Shortround6.
The Baugher's site mentions already for the B-26 (no suffix) that bomb load of 3000 lbs is to be carried through 1000 mile range, a 50% decrease over the proposal. The gun armament grew heavier, 2 LMGs and 3 HMGs, 2 of them in a turret, also the crew was at 7 already.
For the engines: install 2-stage engines when they are available. Won't help much the historical B-26, though.

I don't think 'luck' has anything to do with it.

Agreed. De Havilland have had plenty of experience with streamlined aircraft, eg. Comet (racer) and Albatros. What they lacked, namely the powerful engines, the Mosquito got.

 

[Shortround6]

I don't think 'luck' has anything to do with it. There was a pre-disposition at the time (contrary to what the popular view would have us all believe) within the British Air Ministry that fast bombers offered much and although the Mossie was initially not what the chaps had in mind, they certainly got it once it was demonstrated, pretty much within days of its first flight. There were a few ideas on what a fast bomber should be wihin the RAF and much discussion was done on the idea, particularly after George Volkert produced his paper on fast bombers in 1937. The thing that turned the decisions against the unarmed bit was the success, or at least the promise of the power operated gun turret and all the bomber specifications underway at the time (B.12/36, P.13/36 and so on) stipulated them for defence. Few other countries truly embraced the concept of a true fast bomber ('Speed Bomber' as Ludlow Hewitt called the armed fast bomber); the Luftwaffe did and the Ju 88, whilst not possessing the all out performance of the Mossie, proved a very competent and versatile machine that gave excellent service.

As for its design, the Mosquito was a sound, well thought out machine with little advance over contemporaries. Nothing that had not been tried before, just current technology done really well (unlike the Whirlwind!), so no luck involved at all.

The "Luck" comes in with the Mossie actually exceeding initial performance estimates instead of failing to meet them by 20-40mph like the Beaufighter and early Typhoons. Next bit of luck was that they could shorten the tail fins of the 500lb bombs with little or no loss of bombing accuracy and double the bomb load without having to redesign the bomb-bay. Another bit of luck was that the Merlin proved very adaptable to increased power levels over time and allowed for increased performance and/or loads (bombs or fuel) without major redesign. Mosquito also benefited from an ongoing development program. Like replacing the saxaphone exhaust system with multi stub exhausts on certain models. Worth 13-15mph in level speed with no other change to the engines. Later Mosquitoes got the benefit of newer "technology" unlike the Whirlwind which was stuck in 1940 (early 1940 at that).

From Wiki; foot noted to Martin Bowman.

" . The original estimates were that as the Mosquito prototype had twice the surface area and over twice the weight of the Spitfire Mk II, but also with twice its power, the Mosquito would end up being 20 miles per hour (32 km/h) faster. Over the next few months, W4050 surpassed this estimate, easily beating the Spitfire Mk II in testing at RAF Boscombe Down in February 1941, reaching a top speed of 392 miles per hour (631 km/h) at 22,000 feet (6,700 m) altitude, compared to a top speed of 360 miles per hour (580 km/h) at 19,500 feet (5,900 m) for the Spitfire."

 

[tomo pauk]

The reason why the Mossie prototype exceeded the expected 20 mph difference over Spitfire II is that it was powered by engines that were making almost 20% more power at 20000 ft than Merlin XII.
Against the Spitfire V, that have had about the same power per engine, it was indeed about 20 mph faster. Choosing what was maybe the best engine of 1940 to power it's bomber prototype was a sign of good judgement on d-H part, rather than luck.
The choice of exhaust system was rather a 'bad luck', or bad decision when the saxophone exhausts were designed, the simple exhausts were no rocket science long before 1942.
Mosquito was not 'luckier' than Spitfire or Mustang. It was luckier than many other aircraft, though. Merlin was not the only engine that grew in capability without paying much of the price in weight and/or size.

 

[Shortround6]

20% seems like a pretty high estimate. A MK II Spit held 9lbs (8.8) in level flight to 17,750ft under test. A Mosquito held 9lbs ( actually 8.5 and 8.3lbs ) to 21,400ft.

Mosquito Performance Trials.

This is for level speed with RAM

Prototype Mosquito went faster than expected. This could be traded off in various ways, Heavier bomb load being one. Matt black night fighter finish being another

Saxophone exhausts may have been intended for flame damping?

As far as improved engines go, The A-20 kept pretty much the same engines after switching to the R-2600s (last few batches got 1700hp engines) B-25s had 1700hp engines all the way through, B-26s went from 1850 to 1920-2000hp engines.

None of them got WEP ratings or boosted ratings. A Mosquito flying over Europe in 1944 with single stage, two speed Merlins limited to 9lbs boost might not have had quite the reputation that the ones that did fly over Europe then did.

Luck has to do with the way somethings developed and reputation. It sometimes took a lot of sweat, 12-14 hour days to make some of that "luck" actually pan out.

 

[tomo pauk]

Indeed, I've went a bit overboard with the 20% figure
Per this chart it is ~1060 HP at 20000 ft, vs. the Mk.XII making ~940 HP (here). Or, some 12% more.

As far as improved engines go, The A-20 kept pretty much the same engines after switching to the R-2600s (last few batches got 1700hp engines) B-25s had 1700hp engines all the way through, B-26s went from 1850 to 1920-2000hp engines.

The Bf 110 and Ju 88 went from 1100-1200 HP engines to 1400-1500, even more if we count the Ju 188 and 388 under Ju 88 family. Mosquito vent from 1280 HP to 1610 HP (for take off), or from ~1400 to 1700 on combat setting. 25-20% increase, not that far away from German stuff. The P-38 saw quite a jump, from 1150 to 1425 HP for TO, plus up to 1600 WER, and was tested for 2000 HP on 150 oct fuel.

Luck has to do with the way somethings developed and reputation. It sometimes took a lot of sweat, 12-14 hour days to make some of that "luck" actually pan out.

A fitting description to many of my wife's my summer days

 

[pbehn]

I would say the most important thing for a fast bomber is that it must be fast at all altitudes. For a bomber flying at 350mph/30,000ft the defence must climb to that altitude it is difficult to vector a fighter to a plane travelling at 350mph at 30,000ft when he is climbing. By the time they are up to 30,000ft the bomber may be a huge distance away. For a bomber at low level the defence has completely different problems of finding tracking and distribution of resources.

 

[nuuumannn]

The "Luck" comes in with the Mossie actually exceeding initial performance estimates

Again, I don't think it's luck, I think its very clever design, streamlining, drag reduction. Although I agree with you, pbehn in that the choice of Merlin was good fortune, but there really was no alternative and again, low drag came into the equation; the engine having a relatively low frontal area and possessing the power output to take advantage of the drag reduction measures applied to the airframe. Sometimes, designers just get it right, despite delays, technical difficulties and so on, so the machine, once the problems are sorted really comes into its own because its a great design to begin with. It's not luck.

A fitting description to many of my wife's my summer days

 

[pbehn]

Again, I don't think it's luck, I think its very clever design, streamlining, drag reduction. Although I agree with you, pbehn in that the choice of Merlin was good fortune, but there really was no alternative and again, low drag came into the equation; the engine having a relatively low frontal area and possessing the power output to take advantage of the drag reduction measures applied to the airframe. Sometimes, designers just get it right, despite delays, technical difficulties and so on, so the machine, once the problems are sorted really comes into its own because its a great design to begin with. It's not luck.

I agree completely, the luck is that things went the way of the merlin, it worked and was produced by thousands if the BoB went differently or, for example, the vulture worked, the mossie may have been in the same position as the whirlwind, promising AC but the engine is yesterdays news. In some accounts they say that the Vulture/sabre were considered but that must be a complete re design.

 

[wuzak]

I would say the most important thing for a fast bomber is that it must be fast at all altitudes. For a bomber flying at 350mph/30,000ft the defence must climb to that altitude it is difficult to vector a fighter to a plane travelling at 350mph at 30,000ft when he is climbing. By the time they are up to 30,000ft the bomber may be a huge distance away. For a bomber at low level the defence has completely different problems of finding tracking and distribution of resources.

The most important thing for a fast bomber is to be fast at the altitudes it operates at. Or more correctly, it is operated at the heights where its speed relative to defending fighters is at its best.

Alternatively it is best to operate the fast bomber at altitudes where interception is difficult (30,000ft as you say above) or where detection is difficult (ie 0ft).

It is a happy coincidence for the Mosquito that at low altitudes its speed was comparable to the main defending fighters of Germany, the Bf 109 and Fw 190. At these low levels radar detection was less likely if not impossible.

 

[nuuumannn]

Yes indeed, although as you probably are aware, the Merlin was not without its troubles, but its basic design was sound and since Rolls had the experience, brains and work force to work through the issues, it became what it did. The same with the Mossie, Fw 190, Mustang etc etc...

Data was prepared for the DH.98 proposal before it was built as powered by Sabres and Vultures, although after the Mosquito had flown for the first time de Havillands prepared a proposal for a Griffon engined variant (or DH.101, DH.102). The two-speed, two-stage Merlin in the Mossie, distinguishable by the extra intake directly below the spinner gave it the performance and lifting ability that de Havilland wanted if powered by the Griffon though, so it wasn't worth the extra effort.

 

[pbehn]

Just a thought, was the mosquito the only British bomber actually designed to use merlins from the start?