High Altitude Heavy Bomber for RAF (1 Viewer)

[wuzak]

Neither Gee nor Oboe could replace H2S in raids deep into the Reich. In the second half of 1944, the H2S was the primary navigational aid for long-range bombers.

Gee and Oboe could only operate on a few aircraft at a time, and were, therefore, mainly used for pathfinder aircraft.

Gee-H could be used for multiple aircraft, but not all bombers on a raid could use it - again, left to the pathfinders.

These were all limited in range by the altitude at which the aircraft flew. For the Lancaster, this was about 20,000ft.

H2S/H2X had the advantage that it could be operated by all the bombers in a raid, if they were fitted with the equipment. And it wasn't restricted by the altitude at which the aircraft flew.

There were experiments in extending the range of Oboe, using an aircraft as a relay. But it didn't go into operation.

 

[bf109xxl]

These were all limited in range by the altitude at which the aircraft flew. For the Lancaster, this was about 20,000ft.

The major problem was the insufficient range.

And it wasn't restricted by the altitude at which the aircraft flew.

I'm afraid the H2S developers would disagree with you.

The improved and more powerful strapped magnetrons gave greater frequency stability and the engineering design of the units enabled the system to be operated at 20 000 feet altitude without the problems of sparkover experienced in the earlier AI Mark VII.
...
But in the conclusions of this memorandum there was also a comment that tempered our euphoria after these first operations.
Some re-design of the scanner system is required to prevent gaps appearing at heights of 20,000 ft and above. (It should be noted that the scanner was originally designed for maximum operational efficiency at 15,000 ft).

 

[wuzak]

I'm afraid the H2S developers would disagree with you.

I meant that the range the system could operate over was independent from the altitude of the aircraft.

It didn't matter if the aircraft was at 10,000ft or 20,000ft, or even 30,000ft, it would still operate. Whether it was accurate or effective at those altitudes is different.

Gee, Oboe and Gee-H operational range was dependent on how high the aircraft flew.

 

[bf109xxl]

Can you please provide a little more detail on what you mean by "guaranteed" scanning quality?

Inherently, H2X offered a (roughly) 3-times improvement in resolution at a given altitude compared to H2S, due to its wavelength being one-third the length of the H2S system.

What do you mean by resolution? Range resolution is determined only by pulse length, azimuth resolution is determined by wavelength AND antenna length, so S-band will require a bulkier antenna, but resolution will not necessarily be three times different.
The H2X was tested on a B-17 at 30k feet, but how successful - I haven't reviewed the literature yet. I'll try to review the sources more carefully, maybe I've inappropriately extrapolated the problems with H2S.

Increasing the altitude will reduce radar resolution but H2X will still offer a substantive improvement over H2S.

And besides resolution, there's also contrast. This, to my knowledge, depended on the altitude of the flight.

Given the operational history, H2X offered a sufficient improvement for it to be used at higher altitudes…or am I missing something?

Honestly, judging from the PPI photos I wouldn't say the difference was that significant. But the photos may not reflect the perception of the radar operators.
From the same source:

The trouble was that Cherwell had visited the USA and had been given a demonstration of this American H2X comfortably fitted in a Boeing passenger plane with a full paraboloid as scanner giving an uninterrupted forward view. Naturally, the results when flying at 5000 feet altitude were quite impressive but bore little relation to the performance of a 3 centimetre equipment flying at 20000 feet in a cramped bomber.

 

[yosimitesam]

Beam-width for a parabaloid radar is roughly 70 x lambda / diameter, where 'lambda' is the wavelength and 'diameter' is the dish diameter, with both 'lambda' and 'diameter' in the same units, e.g. cm. The 10cm (9.8cm) radar and standard 29-inch diameter parabaloid (U.S. standard) gives a beam width of 9.3-deg. For 3.2cm wavelength this is 3.0-deg. This determines the angular "resolution", i.e. a lone reflective radar target will always show an "arc" on the scope of 9.3-deg for 10cm and 3.0-deg for 3.2cm radar, using the 29-inch parabaloid. (The further the range the "wider" the arc displayed on the scope, since it is an angle and the circle has a greater radius.) Range resolution depends on the pulse width. A 1-microsecond pulse will be about 300m "long" (984-ft), so no two objects, one behind the other in range, that are closer than this will show up as two separate targets. (The pulse will contain thousands of 3-GHZ or 9-GHZ "waves", if you try to visualize it.) So the shorter the pulse the better range discrimination, but the range of radar will be limited due to less energy being returned per pulse. Then, to fix this you have to increase PRF (pulse repetition frequency) so that more pulses (energy) are returned within the time the object is swept by the beam. But too large (fast) the PRF means to you have to slow the sweep down to get enough "returns" from the targets further down range to detect them. And so on, and so on... These and other compromises are what radar designers are always dealing with. For airborne navigation radar you also have to deal with the "line of sight" issue. The distance to the area more "under" the aircraft is shorter that the distance to something further away on the ground. (Airborne radar returns along the hypotenuse of right triangle.) Thus the center of the scope will be brighter (more energy returned) than the distant parts of the scope. The "co-secant-squared" parabaloid helps this to some degree, but they are difficult (=expensive) to manufacture using the standard metal sheet "spinning" techniques. The U.S. generally used co-secant-squared parabaloids when 3cm airborne radar became available, but the British were slow to incorporate this type of parabaloid since the end of the war was "in sight" and they were following the maxim "don't let the perfect become the enemy of the good enough." Radar is simple in conception but complex in execution.

For a good look at British radar during the war see: "Airborne Maritime Surveillance Radar, British ASV radars in WWII 1939-1945".

Published by iopscience.org/books Direct link to book

 

[MikeMeech]

Hi
The H2S was used in high altitude RAF bombers, but it was post war on the jet V-Bombers that operated at 50,000 ft., with H2S Mk. IXA.

Mike

 

[Dimlee]

Note that a picture on a radar screen in that era was very complex. Not a binary, so to speak, where you have a collection of symbols that either exist or disappear. The qualification and attentiveness of the operator are very important.

yosimitesam

provided a good description of the compromises that designers dealt with. Those were also compromises that the operator faced.
If I understand it right, the altitude limitation mostly referred to the blind spot centred around the radar position, i.e. the aircraft itself.
A large blind spot is very inconvenient, of course. Is it critical - depends on the mission. You can't see the objects covered by the spot, yet you can use the radar for general navigation.
On the radar models of the mid-1950s and later, we could manipulate the size and density of the blind spot. Whether it was possible in the 1940s, I don't know.
(My experience was limited to marine radars, but some of them were identical to airborne models, as old Decca types and their Soviet clones).

 

[nuuumannn]

Wasn't the Norden mostly vapourware rubbish?

Let's not forget that the atom bomb dropping B-29s used the Norden site; Little Boy was dropped from an altitude of 31,000 feet and a horizontal distance of five miles from the Aioi Bridge, the aiming point, while the bomb detonated less than 200 metres in horizontal distance from the Aioi Bridge at an altitude of just under 2,000 feet. Can't have been that bad a sight with that kind of accuracy.

 

[nuuumannn]

A note about armament for the new bomber, the British turret manufacturers had designed and built fifty calibre armed turrets as early as 1939; Boulton Paul had one ready for production, the Type T twin fifty-armed mid upper turret, but were told by the Air Ministry not to interrupt production of existing 303-armed turrets instead. Boulton Paul also developed remotely operated turrets in 1943, one of which entered service in the nose of the Avro Lincoln. The nose turret was remotely operated from the multi-faceted glazing below the turret rather than from in the turret itself.

 

[Alan Stevens]

the B-29 project was more expensive than the Manhattan project. Could the UK afford such an expensive project in the middle of a war?

Not a fair comparison, IMO. Built 3,950 B-29s during the war. Manhattan project created two atom bombs, Vast difference in unit costs.

UK doesn't need to build anywhere near that many planes, maybe just a few hundred,

 

[Thumpalumpacus]

Develop the GB-4 or equivalent and the B-17s will be up to that task. The challenge is we're seeing high altitude bomber aircraft being proposed or developed independently of the weapon. What was the point of Germany's Amerikabomber program if all you're going to get is a few aircraft dropping about 3 mt of bombs over a vast country?

Teleport those bombs back to 1937 and you might be on to something. Hindsightium aside, over the ocean the B-17 couldn't hit a moving target.

 

[muskeg13]

Teleport those bombs back to 1937 and you might be on to something. Hindsightium aside, over the ocean the B-17 couldn't hit a moving target.

As for the B-17s, it all depends on the attack altitude and the threat environment. The Army-Navy/Fleet Problems in the late 1930s proved that the B-17 could be very effective at locating and hitting maneuvering warships, BUT, no one was shooting live ammo and the attack altitudes were 200 feet or less. The USN was mortified and cancelled further joint exercises, but this solidified the notion of the B-17 as being a ship killer. A few years later, it was driven home that even with a Norden bombsight there's a big difference between 200 and 20,000 feet. However, the 5th AF under George Kenney did prove the effectiveness of low level attacks. This isn't to say that B-17s flying at 20,000 were useless. Even though they were unable to score hits from high altitude on moving ships, they were very good at locating Japanese naval formations, keeping them under surveillance and in distracting IJN attention so others could effectively engage. There were several instances of heavy bombers hitting stationary/moored ships from 20,000 feet, so it could be done.

 

[Geoffrey Sinclair]

While it is obvious the 20th Air Force had more logistical obstacles to overcome compared to Bomber Command, including longer range to targets, the US Aircraft industry was bigger, had plenty of enemy free areas to use with better average weather, operating in a less stressed economy. A common requirement was high altitude meant smaller bomb loads. Also monetary cost is not a perfect measure but the fact the wartime B-29 cost 2 to 3 times the B-17/24 indicates the reduction in other aircraft output to allow production of the new type. B-29 production was 92 in 1943, 1,161 in 1944, R-3350 production 917 in 1943, 11,321 in 1944, production of Stirling bomber (not transport) versions was 881 in 1943 and 239 in 1944 (plus 408 transports), 73 Griffon 60/70/80 series engines in 1943, 1,281 in 1944, 497 Centaurus of all types in 1943, 1,401 in 1944.

B-29 cost breakdown, GFE = Government Furnished equipment

Date	Type	Model	Airframe	Engines(s)	Propeller(s)	GFE	Ordnance	Communciations	Total	Notes
28-Feb-43​	VHB	B-29	$ 362,347	$ 101,685	$ 10,328	$ 125,341	$ 4,836	$ 34,738	$ 639,275	Costs based on weighted average of uncompleted contracts
30-Nov-44​	VHB	B-29	$ 434,512	$ 101,877	$ 13,628	$ 124,787	$ 5,531	$ 34,738	$ 715,073	Costs based on uncompleted contracts
31-Aug-44​	VHB	B-29	$ 469,269	$ 100,406	$ 12,433	$ 125,863	$ 5,526	$ 34,738	$ 748,235	Airframe and engine costs subject to revision. Costs based on uncompleted contracts
31-Jul-44​	VHB	B-29	$ 478,180	$ 100,406	$ 12,181	$ 125,919	$ 5,525	$ 34,738	$ 756,949	Costs are weighted average of all Army contracts from 1939 to date

The USAAF Statistical Digest gives B-29 average costs as in 1942 $893,730, in 1944 $605,360 and in 1945 $509,465.

Assuming the new British bomber arrived in the same way as the B-29, 20th Air Force figures, BC= RAF Bomber Command. Available is as of end of month, bombs in short tons.

Month	B-29 Available	Effective Sorties	Effective per a/c	Bomb Tons	Average bomb load	BC Bomb tons	B-29 as % of BC
Apr-44​	94​
May-44​	137​
Jun-44​	133​	131​	0.98​	547​	4.18​	64,139​	0.85​
Jul-44​	146​	102​	0.70​	209​	2.05​	64,529​	0.32​
Aug-44​	150​	145​	0.97​	252​	1.74​	73,758​	0.34​
Sep-44​	163​	199​	1.22​	521​	2.62​	58,897​	0.88​
Oct-44​	219​	279​	1.27​	1,669​	5.98​	68,548​	2.43​
Nov-44​	262​	514​	1.96​	2,205​	4.29​	59,385​	3.71​
Dec-44​	345​	787​	2.28​	3,661​	4.65​	54,925​	6.67​
Jan-45​	447​	887​	1.98​	3,410​	3.84​	36,874​	9.25​
Feb-45​	538​	1,189​	2.21​	4,020​	3.38​	51,396​	7.82​
Mar-45​	602​	2,892​	4.80​	15,283​	5.28​	75,753​	20.17​
Apr-45​	705​	3,246​	4.60​	17,492​	5.39​	39,148​	44.68​
May-45​	730​	4,226​	5.79​	24,285​	5.75​
Jun-45​	878​	5,243​	5.97​	32,542​	6.21​
Jul-45​	979​	6,168​	6.30​	42,551​	6.90​
Aug-45​	1,042​	3,145​	3.02​	21,029​	6.69​
Total	n/a	29,153​	n/a	169,676​	5.82​	647,352​	n/a

By the second half of 1944 Lancasters were routinely carrying over 5 short tons of bombs on average. The resources required to train on and debug the new type, plus probably extend airfields etc. Bomber Command war effort would decrease over historical and given B-29 arrival dates it is hard to see it made up by the end of the European war.

It can also be considered bombs dropped on Germany from March 1945 onwards had little impact on the fighting. To end February 1945 the B-29 dropped 16,494 short tons of bombs, in the roughly 24 hours of 14 and 14/15 October 1944 Bomber Command dropped 11,474 tons of bombs, including 10,122 tons on Duisburg as part of Operation Hurricane.

The Norden was a very good sight but it proved too difficult to mass produce in the numbers required to the specified pre war accuracy, standards had to be relaxed to 5.6 times more error than the precision specification. The situation was resolved mainly when the 8th Air Force started bombing in formation and so could leave the bomb sights out of some aircraft.

The nuclear strikes used the best of the best crews who were given extended training and the larger the bomb the better the average accuracy, I suspect they would also have been given the best bomb sights.

Given the issues over pressurisation there is a good case for all remotely controlled armament versus pressurising turrets. Trying for 40,000 feet says turbo, not mechanical supercharging

 

[Frog]

Not a fair comparison, IMO. Built 3,950 B-29s during the war. Manhattan project created two atom bombs, Vast difference in unit costs.

UK doesn't need to build anywhere near that many planes, maybe just a few hundred,

Project Silverplate (development and production of a special B-29 variant to deliver tha atomic bomb) was one of the sub-programs of the Manhattan project

 

[Jugman]

Wasn't the Norden mostly vapourware rubbish?

In short, no it wasn't rubbish.

View: https://youtu.be/PV_65rLWRa8?si=YKvawYk2ygQ8FOYu

View: https://youtu.be/9C1Zo1zKkAw?si=yon-1mtDS_p63S9n

 

[Frog]

Let's not forget that the atom bomb dropping B-29s used the Norden site; Little Boy was dropped from an altitude of 31,000 feet and a horizontal distance of five miles from the Aioi Bridge, the aiming point, while the bomb detonated less than 200 metres in horizontal distance from the Aioi Bridge at an altitude of just under 2,000 feet. Can't have been that bad a sight with that kind of accuracy.

That's true for Hiroshima, under excellent weather conditions and Hiroshima as prime target.
The Nagasaki mission went rather afoul with RV problems, poor weather, fuel pump trouble, target changed from Kokura to Nagasaki : contrarily to instructions they planed to the last moment a radar aimed drop when a clouds clearance enabled a sighted drop.

 

[Thumpalumpacus]

As for the B-17s, it all depends on the attack altitude and the threat environment. The Army-Navy/Fleet Problems in the late 1930s proved that the B-17 could be very effective at locating and hitting maneuvering warships, BUT, no one was shooting live ammo and the attack altitudes were 200 feet or less. The USN was mortified and cancelled further joint exercises, but this solidified the notion of the B-17 as being a ship killer. A few years later, it was driven home that even with a Norden bombsight there's a big difference between 200 and 20,000 feet. However, the 5th AF under George Kenney did prove the effectiveness of low level attacks. This isn't to say that B-17s flying at 20,000 were useless. Even though they were unable to score hits from high altitude on moving ships, they were very good at locating Japanese naval formations, keeping them under surveillance and in distracting IJN attention so others could effectively engage. There were several instances of heavy bombers hitting stationary/moored ships from 20,000 feet, so it could be done.

Right, there are exceptions to every statement. The -17s could hit from 200' -- if they were flown there. Problem is that, except in SWPA, they weren't.

Their value as recon assets was of course unquestioned.

 

[Alan Stevens]

Project Silverplate (development and production of a special B-29 variant to deliver tha atomic bomb) was one of the sub-programs of the Manhattan project

The 509th's 15 B-29s had Silverplate modifications and these are the only B-29s that should be charged to the Manhattan Project. The aircraft cost about $650,000 apiece.

While the 509th had more than 17 Silverplate aircraft assigned by the end of the war, only about 15 were operationally deployed to Tinian in time for the atomic missions.

 

[Alan Stevens]

Right, there are exceptions to every statement. The -17s could hit from 200' -- if they were flown there. Problem is that, except in SWPA, they weren't.

Their value as recon assets was of course unquestioned.

Flying a B-17 bombing mission at 200 feet AGL? Sounds rather reckless to me.

50cal and 20mm AA could get many hits on them and they could CFIT if they were not very careful.

 

[Thumpalumpacus]

Flying a B-17 bombing mission at 200 feet AGL? Sounds rather reckless to me.

50cal and 20mm AA could get many hits on them and they could CFIT if they were not very careful.

They were used for skip-bombing by 5th AF. Japanese merchant ships weren't festooned with guns.