Luftwaffe's ideal night fighter: you are in charge

[Siegfried]

The Ar240 showed very poor handling all her lifetime with three or four different prototypes with 3 different engines and was in a "permanent correction" to get a better handling. I doubt that the Ar 240 was a promising design, it was too much destroyer and light bomber then heavy fighter or night fighter.

Rudiger Kosin, who designed the Ar 240 and the Ar 440 as well as the Jet bomber the Ar 234 talks of some of the issues that confronted the Ar 240 in an essential book he wrote called "The German Fighter".

Basically a Fuhrer order when the battle of Poland and latter France started froze the resources to the project and directed them to productivity weapons for the immediate war effort.

Due to this the Ar 240 was starved of funds and the following requirements could not be met:

1 The contra-rotating engines, which had been planed from the start to ensure stabillity around the vertical and roll axis.
They were not supplied due to the restrictions
2 It had been designed to use flow through spinners for radiator cooling, this was not supplied so the aircraft ended up with propellers spinning in the same direction instead of opposite in large extension shafts (due to the wrong gearbox) which put the spinning propellers in the wrong spot. (latter fixed when Db603 and 605 engines fitted)

3 Basically the wing profile was poorly designed.

The Ar 440 seemed to fix all of these issues, the cabin was moved forward, the tail extended, wing span increased, new wing profile used larger DB603A engines used.

Notable with the A3 440 was its speed of 660kmh (410mph) with bomb racks and 670kmh (416mph) without. This was exceptional speed, much faster than the Me 410 though unlike the Me 410 it seems to lack a bomb bay so its penetration speed with bombs 'may' have been lower (it was 360mph for the Me 410)

The speed as a night fighter would have been useful though its high wing loading would require good runways and runway length, takeoff run became a huge issue for the Luftwaffe. It may also have suffered from lack of space issues as well.

It's hard to get passed the Junkers Ju 88. The Ju 88C was the first of the fighter series, the Ju 88R added BMW 801 and the G series improved the aerodynamics (tail size).

Getting a high power engine onto the Ju 88 as quickly as possible would seem the most sensible course. The Ju 88, like most German night fighters was slowed down by the use of external gun packs. These were important in that they kept gun shock away from the avionics and more importantly protected the pilots night vision from gun flash but perhaps it might have been possible to develop a cleaner installation.

 

[Siegfried]

German firms had magnetron patents during the 1930s. Were captured British magnetrons different then what they already had?

There are several types of Magnetron. The magnetron is a "diode" it only has two functional terminal (ignoring the heater). The basic type is the split anode magnetron invented by Habann of Jena IN 1924 based on a primitive magnetron developed by Hull of GE in 1922. The type Randall and Boot developed is the multicavity magnetron however this was known to the Germans, Russians and Japanese.

A basic vacuum tube diode has a heated cathode at the centre to boil of electrons and has a cylindrical positively charged anode surrounding the cathode to attract them. In a split anode magnetron the concentric anode cylinder is split and a magnetic field run down the axis. The electrons traveling out from the cathod to the anode are curled around by the magnetic field and interact with the anode segments to form a resonant effect.

Another type is the mulitcavity magnetron, known as a 'rad' or 'wheel' magnetron to the Germans and Mandarin to the Japanese. In this the anode is metal and looks like say 8 or so cavities in the shape of say gear teeth or mandarin segments. French were using these to develop radar at the outset of WW2.

Randall and Boots magnetron had a very efficient cavity, it was a hole with narrow slots rather than relatively open mandarin are square gear tooth like segments.

The story goes that Randall frequented a second had book shops on Saturday afternoon, found a book on Hertz's experiments and a formula which gave the resonance of a loop of wire as 7.94 times its diameter. He wondered whether he could make the loop of wire 3 dimensional along with Boot and they came up with the idea of boring a hole and having narrow slots.

The British magnetron was actually based on a 6 shot revolver cylinder which had the correct dimensions for 9cm radiation (with minor adjustments) and was made on the same tooling. (9cm produced 15 degree beam width with a 75cm dish aerial, this is why 9cm was chosen as the beam was narrow enough to avoid sweeping the ground and till fit in a Mosquito or Beaufighter)

So it was the efficiency of this arrangement that was stunning.

The Japanese at systematically studied their 'mandarin' and 'chrysanthemum' multitcavity magnetrons and came up with exactly the same arrangement actually ahead of Randall and Boot about 1 year earlier. Their M3 magnetron of 10cm 10kW water cooled (glass envelop) magnetron was productionised as the M312 and used in the Type 22 radar in 1942 on the cruisers Ise and Hyugu in mid 1942. In 1943 it was in mass production and about 300 produced. Some were given extra side antennas for fire control. These radars only stayed in the Japanese Navy.

The Japanese moved much much slower than the British despite their primacy, some researchers were even arrested for buying the magnet materials on the black market! They never introduced PPI.

So the British innovations were:
1 efficient cavity configuration
2 later developed 'strapping' which quadrupled power (the Japanese also developed)
3 British immediately recognized the technical and tactical value of their invention and had the researchers to develop the receivers. This was unique.

They had taken 80 physicists before the war and introduced them to Chain Home so that they could be used if war broke out.

The Germans were fairly successful with their 50cm radars and were really left wanting for little till 1943 when Wurzburg was jammed by windows.

The Germans became obsessed with developing tunable magnetrons, also started to run out of resources to engineer new radars.

As I pointed out a 18kW 18cm magnetron is respectable and could have made a radar as is a 3.7cm tunable 4kW unit. In 1940 the Sanitas company had a 100W continuous wave 18cm magnetron that probably could have done about 4 kW in pulse mode. (power goes up with either number of cavities or magnet power) but they didn't recognized its potential.

There was one other factor. The Germans developed standard triodes to the max to the point they could produce microwaves at considerable power.

What prevents normal triodes (with a control grid between cathode and anode) from working at ultra high freqencies is
1 The transit time of the electrons between anode and cathod exceeds the period of the wavelength.
2 the leads become highly inductive and capacitive and block and short out high frequency signals.

To overcome 1 they developed techniques to get electrode gaps down to a few thousands of an inch.
To overcome 2 they made the whole tube in coaxial technology using anular electrode entering through ceramic seals.

These tubes could produce about 12kW, perhaps 18kw in a gas atmosphere) at 9cm, greater powers at higher wavelenghts.

The idea was to go to radars operating at about 25cm and 110kW. These radars were about 80% complete when they were suspended due to resource issues in 1942 though the 3m dish track locking Mannheim K radar did eventually get built for the German navy as a 1.5m dish version known as FuMO 231 Euklid FLAK radar (for German destroyers).

These disk triode tubes such as the LD6 are STILL in production and formed the backbone of soviet radar till 1970.

See here.

http://www.cdvandt.org/BIOS-30.pdf

If you can read German:

http://www.jogis-roehrenbude.de/Buecher/Hist_Leseprobe.pdf

See page 13 at the end of the page.

"So entstand bereits im Jahre 1940 ein Impulsmagnetron einer Leistung
von 18 kW bei 18...20 cm. Und bis 1942 schaffte man ohne Kenntnis des
späteren Beutegutes, des Rotterdam-Tastmagnetrons CV64, eine Eigenentwicklung für
4,5 cm/3 kW zu bauen, brach dann jedoch eine konsequente
Weiterentwicklung ab."


"The result was as early as 1940, a Impulse magnetron of power of 18
kW at 18 ... 20 cm. In 1942 they managed without the knowledge of the
later captured Rotterdam-magnetron CV64, developed a 4.5 cm / 3 kW but then
terminated from a logical development. "

From You can check Review article: Microwave tube development in Germany
from 1920-1945 by H. Döring. (Pay document unfortunately)


"The most important tube, the multi-cavity magnetron, was already in
existence in Germany in 1937. For example, Telefunken built an eight-cavity
magnetron operating at 1.5cm and capable of delivering 50mW ouput CW. At Sanitas
a water-cooled magnetron was developed to deliver I00W CW at 25cm. At
this time, such tubes were called 'Radmagnetron' ('Rad' meaning 'wheel' in
German). A tube developed in 1'938 at Lorenz A G by F. Herriger for a wavelength
of 8cm is shown in Fig. 18. However the advantages of this particular design
for pulse operation were not fully appreciated in Germany at the time."

A 100W CW can probably be produce to about 4kW impulse (1 microsecond or so) and greater if more powerful magnets or more cavities used.

Note: Lovell pointed out that the British almost canceled their magnetron work due to resource issues at the height of the battle of Britain.
http://rsnr.royalsocietypublishing.org/content/58/3/283.full.pdf

video of Bernard Lovell (H2S developer) talks about how the British magnetron was almost canceled !)
Bernard Lovell - A secret report by Hackenberg on the Cavity Magnetron - Web of Stories (Lovell talks about magnetron development and German knowledge of it)
Bernard Lovell - Differing attitudes towards science between Germany and the Allies - Web of Stories

 

[Siegfried]

Seigfried - thanks for the analysis of radar. Interesting stuff. I don't claim that Britain invented radar - nor is radar the principle component of Britain's air defense planning -- back to the Zeppelins of WW1. I was thinking of much more - national mind set - as exemplified by this (for example): Listening for the Enemy: Giant Ears on the British Coast - SPIEGEL ONLINE - News - International

Is it easier to defend an island than a "patch" of territory not surrounded by a large "moat"? Well yes, I guess it is. That's why moats were invented isn't it.

Yes, I realize you never made that claim.

The British of course were highly organized and Wattson Watt promoted a long wavelength technology that could be quickly introduced into service; this is what ensured Britain won the battle of Britain since a half implemented solution of better technology would have lost the battle for them. (the 1.5m stuff developed by the British Army for Coastal Artillery eventually became Chain Home Low and almost could have matched CH into service). It seems the German Navy was on the ball ahead of the Luftwaffe.

The introduction of 80 Physicists to Chain Home radar prior to the war to ensure an adequate R+D potential was of course also critical to British success.

 

[michaelmaltby]

"...The introduction of 80 Physicists to Chain Home radar prior to the war to ensure an adequate R+D potential was of course also critical to British success."



MM

 

[davebender]

The He-219 night fighter was effective and well liked. Historically the program was hamstrung as this relatively large aircraft required relatively powerful DB603 engines that were in short supply. Consequently historical production numbers were tiny.

11 He-219 produced during 1943.
195 He-219 produced during 1944.

But what if RLM were convinced to produce the Me-210C light bomber (DB605 engines) ILO the Me-410A (DB603 engines)? This would free up additional DB603 engines for the He-219 program.

291 Me-410A produced during 1943.
722 Me-410A produced during 1944.

Possible He-219 production.
302 during 1943. ILO the historical 11.
917 during 1944. ILO the historical 195.

1,000 additional He-219 night fighter aircraft produced during 1943 to 1944 won't completely solve the problem but I think their presence would be felt by RAF Bomber Command.

As for the Me-410A, most were used as bomber interceptors rather then their design role of light bomber. I doubt anyone would notice if they were replaced with Me-210Cs.


BTW, great information on the magnetron. Makes my head spin but I'm glad we have techno geeks who understand this stuff.

 

[tomo pauk]

Many thanks indeed

 

[Erich]

The He 219 was well liked by I./NJG 1 only. NJG 3 were not impressed and nor was NJGr 10 even into 1945 with the Stab.

Having built more Uhu's would not of effected anything, most likely building existing Ju 88G-6's would have as it could carry more electronics and had the additional rear arms and tail warning radar as standard which the Uhu did not.

 

[davebender]

11,200 kg. He-219A7 empty weight.
13,109 kg. Ju-88G7 empty weight

I think the purpose built and lighter in weight He-219 night fighter would be inheritly superior to the Ju-88G light bomber if both aircraft have the same engines and electronic equipment. But perhaps not superior enough to justify placing a new aircraft type into production.

In any case there will not be enough DB603 and Jumo213 engines for the entire night fighter force before 1945. So we still need a DB605 powered night fighter to bulk out operational numbers.

What about upgrades to the existing Me-110G? Perhaps new wings and a new nose similiar to the Me-210C would increase speed a bit. GM-1 might be useful for catching high flying RAF Bomber Command pathfinder aircraft.

 

[The Basket]

If given 18 months or even 2 years there isnt much that can be done. Cant develop a new machine so would build up numbers of Bf 110s or Ju 88s and train crews.

One idea is to build a light nimber single engined 2 seater that can be used on Wilde Sau missions. Enough performance to take on the bombers which would be no big deal and enough endurance to stay aloft. A German Defiant with the rear gunner as a navigator. Or maybe a two seat version of the 109 Emil.

 

[tomo pauk]

Like the German Defiant idea

 

[The Basket]

The He 118 would have been a great starting point.

The Yokosuka D4Y had great performance for a large machine and the 118 was very similar.

 

[davebender]

Doesn't 1942 Germany have enough problems already? 8)

 

[johnbr]

Remember the He 219 was designed for the Ju-222 engine.

 

[The Basket]

Doesn't 1942 Germany have enough problems already? 8)

The Defiant was the most successful night fighter of the 40-41 period in RAF service. That may have been worth copying if I was looking for ideas.

 

[davebender]

920 kg. DB603A engine. 1,750 hp. 1,900 hp for version using C3 fuel.
1,088 kg. Jumo222A engine. 2,465 hp.

Perhaps a bit of airframe weight can be trimmed if the He-219 is designed for the smaller and less powerful DB603 engine. Power to weight ratio is still as good or better then the highly regarded Ju-88G.

 

[pbfoot]

The Defiant was the most successful night fighter of the 40-41 period in RAF service. That may have been worth copying if I was looking for ideas.

Thats not saying much ,IIRc and I may be very wrong but they had next nothing in kills , a single digit number I believe

 

[vanir]

The RAF had little in the way of night fighters because right up to that point the universal doctrine was fast day bombers in europe. The British-German air war got literally chased into the night skies by attrition, not by choice, the Luftwaffe simply didn't have the aircrews let alone the industry to waste on continuing a daylight campaign.

So nightfighters were a novelty that suddenly turned deadly serious overnight. For the RAF in 1940-41 they were smack in the middle of a panic and were still ramping up and refining Hurri and Spit production, most of these didn't have self sealing tanks and only just got bullet proof windshields, a good number were still using watts props including all the overseas hurricane squadrons, whilst reserve units were things like Gloster Gladiators.

The Air Ministry had just made some recent, massive errors in judgement which included series production using limited resources of superfluous aircraft types. It had stockpiles of Fairey Battles, Boulton Paul Defiants and scores of other models produced in limited, but significant numbers that were victims of the changing technological battlefield. These aircraft no longer had the mission survivability for daylight operations in enemy territory, the Luftwaffe had gone and put Messers in every damn fighter squadron in record time. These aircraft were designed for a world where this would've taken ten years to do.

So the RAF just had a lot of useless obsolete models laying around by the squadron, too obsolete to use and too expensive to scrap given replacing them took time. So I wouldn't call the Defiant a successful nightfighter so much as an available one. By early 1942 there were enough surplus day fighter production that Hurri II's could be used and they were welcomed, but night fliers were all holding their breath until things like the Beaufighter came onto the scene, when was that, 1943 before the RAF had any dedicated night fighters? It would make sense that would be the same year it was really picking up pace in Germany.

Hey in 1941 everybody went paranoid over 30 bombers, 300 were "as far as the eye can see" whilst fast forward to 1945 and Brandenburg saw something 5000 sorties in one afternoon from one soviet air army. There were three in the vicinity.

The scope of warfare changes so much through the war that it's like lots of different wars inside one big war.

 

[The Basket]

The Bf 110 was not a good nightfighger either. It was available. And you can wait for the Me 262 to appear or build something now.

If your prey is big and slow then you dont need a jet...just a 20mm cannon and docile handling and you're going to get kills.

 

[The Basket]

About obsolete and bad ideas then everything from the 1930s would be obsolete. The Spitfire would have been hopeless if the prototype had been the main fighter in 1942. The Bf 109B would have been not much either.

109B bad idea 109F good idea and yet same concept same name. Had the B-29 flown against jets in ww2 then it would also have been shown as obsolete in short order. One can argue had the Defiant been developed in the same way then it would have been a better machine rather than the dead end it became.

 

[stona]

The Defiant was the most successful night fighter of the 40-41 period in RAF service. That may have been worth copying if I was looking for ideas.

That's not saying much. It was the complete inability of the RAF to make night time interceptions that cost Dowding his job.
Cheers
Steve