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Junkers 1945 blended wing body (BWB)

Abraham Gubler

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From Herwig & Rode’s “Geheimprojekte der Luftwaffe” a Junker’s Fersntbomber (distance bomber) proposal of 1945. Designed by Heinrich Hertel in cooperation with the DLS (German Glider Institute). Post war passenger and freighter versions were planned.

Span: 51.3 m, Length: 31 m, Wing Area: 1,100 sq m, Wing Sweep: 45 degrees, Engines: 4 He S 109-011 or 4 Jumo 109-012, Range: 17,000 km, Speed: 1,030 km/h, Gross Weight: 90,000 kg, Bombload: 8,500 kg, Crew: 8-10

This is a very interesting aircraft because it’s of similar size and bombload to the B-47 but carries a lot more payload (extra crew and defensive weapons) to twice the range without the high wing loading and presumably ‘coffin corner’ performance. It’s also one of the first BWBs.
 

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Pioneer

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Love the design!
But would such long air-intake ducts have caused any trouble to the touchy German turbojets of the time?
Also these ducts look as if they would have taken up such vital internal volume/space for a strategic/heavy bomber of the day, which could have been better utilized for more fuel, especially for the fuel thirsty first generation turbojets?

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Pioneer
 

Abraham Gubler

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BWBs, lifting bodies and flying wings tend to have very large internal volumes for gross weight so the 'wasted' space of the long 'Luftkanal' (air intakes) is probably not as big a problem as insuring useable air for the engines at different AoAs.

I’m struggling to rationalise the Ju Fernbo 45’s performance figures. In order to reach the 17,000 km range the bomber would have to be able to cruise at a speed of 472 kph or 45 % of maximum speed while operating the engines on 13.5 % of maximum thrust (not even factoring in fuel consumption for takeoff, climb and attack). Using an estimated fuel fraction of 0.6 (very high) from a TOGW of 90,000 kg, SFC of 1.0 (kg/kg-hr) (Avon Mk 1 levels) with maximum thrust of 11,145 kgs from four Jumo 109-012.
 

Artie Bob

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If one follows the meeting minutes of Luftwaffe hierarchy during WWII, a recurring theme was the inability of designs to meet manufacturer's performance predictions. This was particularly true of the attempts to produce very long range bombers. The "Amerika" bombers at best probably would have been "Greenland" or "Ireland" bombers if they were to have carried any significant payload on a round trip mission. IMHO performance predictions of German aircraft that might have had first flights in 1947-50 need to be considered very carefully. BTW, much of the JFM engineering team went to the USSR for an extended period after capitulation. But, the first fairly successful long range bomber was the Tu-4 and I think we have a pretty good idea where the aerodynamics and technology of that design originated, The "Bear" is a lineal design and development progression from that base. I enjoy the variety and number of WWII period projects, but developing those concepts into useful weapons would not have been a fast or easy process with the resources available to third reich Germany.

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Artie Bob
 

Abraham Gubler

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The wing loading of the Ju Fernbo 45 is extremely low: at TOGW of 90 tonnes it is only W/S 16.8 lb/ft² or 81.1 kg/m²). Compared to the B-47’s 93.16 lb/ft² (454.8 kg/m²) or F-86 Sabre’s 58 lb/ft². So perhaps the 90,000 kg weight is an empty figure or it’s an amazing climber...
 

Abraham Gubler

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Artie Bob said:
BTW, much of the JFM engineering team went to the USSR for an extended period after capitulation.
Hertel went to France after WW2 and I'm not sure where DFS people ended up.
 

Abraham Gubler

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The more I look at this design the more feasible it looks but with just one change. The ‘Fluggewicht’ or flight weight of 90,000 kg (198,000 lbs) must be an empty weight with Herwig and Rode making a typo mistake. It’s a pretty reasonable empty weight for a bomber of this size with a heavy mission systems load (8-10 crew, multiple turrets defensive armament, 1940s tech radars) and aligns to a volume to weight ratio of contemporary bombers (like the YB-35).

Assuming a wing loading of 45 lbs/ft² (same as the YB-35 and pretty good) with the 11,840 ft² BWB of the Ju Fernbo 45 then we can have a takeoff gross weight (TOGW) of 532,000 lbs (241,800 kg). This minus the 18,700 lbs (8,500 kg) bombload gives us 325,300 lbs (143,300 kg) of fuel. Or enough to power four Avon Mk 1ish engines for 12 hours, 50 minutes at full power. This is very much in the realm of a 9,450 NM (17,000 km) maximum range at cruising speed.
 

Artie Bob

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Maybe I'm getting a little fuzzy in my old age, but taking off with 4 "avonish" engines at a gross of 532,000 #s seems like it would need a cold day in hell (low ambient and high air density). How long would it take to reach V1 and V2.
Best Regards,
Artie Bob
 

Abraham Gubler

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:D yeah that's the question I've been struggling to answer! Very long runways!
 

Abraham Gubler

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The TOGW T/W would be 0.046 with four Jumo 109-012s, which is well below that of the B-36B at 0.117 (props), B-36D’s 0.168 (props and jets) or B-47E’s 0.188. This is probably why the configuration picture above shows eight engines. This would help in over target altitude and being able to cruise on half your engines would be a good safety feature for very long range inter-continental missions. The Ju Fernbo 45 would need 85,000 lbs of thrust to have a reasonable T/W (0.16) for takeoff (combined with its low W/S). Avon Mk 207s would make it fly (and eight of these would weigh the same as four Jumo 109-012s).
 

Vahe Demirjian

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The wingspan and range of the jet flying wing bomber project are actually comparable to the B-52, B-35, M-4, and Tu-95. Had the Junkers design been conceived earlier, it would have been the ultimate Nazi flying wing Amerika Bomber. Are there any surviving drawings of the commercial variants of this flying wing project?
 
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