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GOT: The Boeing XB-39


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#1 Romantic Technofreak

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Posted 28 January 2018 - 03:12 PM

Long time gone since the last GOT, I know and am sorry. The more as it is really difficult to write something about this big bird what is NOT found in Wikipedia.

 

Only thing I can do is to construct this GOT as "Duel": between this one and its predecessor, the B-29, and what became the latter's successor, the B-50.

 

The main, or say only, difference between B-39 and -29 are the former's Allison inline engines. And the difference in performance is impressive:

 

Speed: 648 km/h vs. 570 km/h

Range: 10,060 km vs. 9,100 km

Ceiling: 11,000 m vs. 9,170 m.

 

The B-50 is nearly equal in ceiling (11,200 m), a bit better in range (12,472 km) and, slower in speed (634 km/h) than the B-39. The B-50 runs again on radial engines. It looks like the use of inline engines of highest power was then near to a close, while the one of radials still continued for a while.

 

To conclude is that the B-39 had a much higher speed than the B-29, which would have made its use favourable had WWII went on or led to an inter-Allied conflict. It might have become the USAAF standard big ship of 1946/47.

Regards, RT



#2 Ricky

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Posted 28 January 2018 - 04:02 PM

Interesting... if it hadn't been for the Fisher Eagle then we'd likely have had B-39's rather than B-29's

#3 Rick65

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Posted 29 January 2018 - 01:33 AM

The big question on the XB-39 was the engines.

The V-3240 was two tried and proven V-1710 engines geared to a common crank.

Coupled engines are not always successful, harmonic balance can be an issue, but for example the concept was extensively used in racing two stroke motorcycle engines. The DB 606 and 610 engines are the best know examples of unsuccessful coupled aviation engines and their failure effectively removed the He 177 as a viable strategic threat.

 

No planes using the V-3240 reached production and hence the long term reliability and performance of the engine was never fully proven.

The giant XB-19 was re-engined with V-3240 in 1943 and flew with them until 1946. However unlike the earlier XB-15 the XB-19 wasn't used much as a transport plane and data on the effectiveness of the engines is scarce.

The V-3240 was used in hydroplane racing post war but this involves much shorter running periods than in a long range bomber.

If anyone (Greg?) is aware of data on the performance/reliability of the V-3240 I would love to see it as for me it remains a classic "what if" engine.



#4 Ricky

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Posted 29 January 2018 - 07:32 AM

The big question on the XB-39 was the engines.


While this is true, the B-29 definitely did have issues with its engines...

#5 Rick65

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Posted 29 January 2018 - 09:30 AM

Unquestionably.

The early R-3350 general unreliability was a problem, particularly when being worked hard carrying heavy loads for long range missions. The tendency of the engine to overheat, catch fire and set the alloy (incl Magnesium) crankcase on fire and then burn through the main spar was a terminal one for that plane and crew.

It is no coincidence that both FiFi and Doc now fly with custom created composite R-3350's based on  later engine models that were very different from the early R-3350s and far more reliable.
The V-3420 could have had it's own problems, for example each engine had to be rotated from the vertical which could have caused oiling problems but the point of my post is that there were not enough produced (150? only) and used for us to know.



#6 Romantic Technofreak

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Posted 29 January 2018 - 05:26 PM

The big question on the XB-39 was the engines. The DB 606 and 610 engines are the best know examples of unsuccessful coupled aviation engines and their failure effectively removed the He 177 as a viable strategic threat.

There is nothing known about the V-3420 having been troublesome, at least quick googling gives no hint. About the DB coupled engines in the Heinkel He 177, please consider miy friend's and my text here: https://www.warbirds...d-lemons/page-3

 

 

The V-3240 was used in hydroplane racing post war ...

Gives me another kick towards my proposed hydroplane fighter... ;)

Regards, RT



#7 Rick65

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Posted 30 January 2018 - 09:33 AM

No I haven't found any indication of the V-3240 being troublesome either but neither have I found anything that states that it was a refined and reliable design that was ready for the trials and abuses of operational service without modification. i suspect that not enough engines did enough hours for a clear picture.

As the R-3350 in the B-29 and the DB606/610 in the He 177 prove an excessively low drag cowling can extract a heavy price in engine cooling and reliability.



#8 CORSNING

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Posted 30 January 2018 - 08:50 PM

XB-39-three-quarter-view.jpgXB-39-Undernearth-San-Diego-Air-and-Spac300px-XB-39_Superfortress.jpg


Edited by CORSNING, 30 January 2018 - 08:52 PM.


#9 Rick65

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Posted 30 January 2018 - 11:56 PM

Like the photos, they underline how big the V-3420 engines were though the nacelles being a different finish from the rest contributes to this perception.

The following link is a good article on the V-3420.

https://oldmachinepr...ircraft-engine/






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