Airborne Awesomosity

Boeing XB-39 Spirit of Lincoln

Boeing’s liquid cooled XB-39

[image from the San Diego Air and Space museum]


With the production lines having problems with the B-29 itself as well as its complex R-3350 engines it should be no surprise that alternates to each were looked for. We have already looked at replacement bombers so now lets take a look at a replacement engine option for the Superfortress.


The Boeing B-39 Showing Off Its New Watercooled Engines


Unlike replacing the engines on the Flying Fortress with V-1710’s this had a reason for being. The Wright R-3350 was having its own teething problems. Plus there was a real question as to whether enough of them could actually be produced to power all the B-29’s needed to fight the war and inevitable invasion of Japan.

Into this void steps our friend the Allison V-3420 coupled engine. This engine is at the heart of a lot of failed prototypes. The Allison inline watercooled twenty four cylinder engine is actually two of the standard V-1720’s coupled together. This makes this XB-39 effectively an eight engine bomber.  Remember this was meant as a way to lower the complexity of the air cooled R-3350 engines.


Speaking Of Complexity This Is The Engineers Console. Today We’d Get Three Warning Lights.

[image National Air Force Museum]


During war time every day matters in aircraft development. Although they were able to get the B-29 working with the coupled engines it was already past the time that Wright needed to iron out the R-3350’s issues. So the project never moved forward past the prototype.

  • Number_Six

    Ewwww! No!

    • fodder650

      How do you really feel?

      • Number_Six

        I forgot to mention I don't like it. But I do love the post! Could you follow this up with some KB-50 love? Jet engines and radials!

        • fodder650

          There were several odd B-29 variants plus the B-50. Also Pima Air and Space Museum is nearly finished with their B-50 restoration.

          So yeah I can do a writeup on it since very few people have ever heard of it.

          • CaptianNemo2001

            The B-50 is quite the odd ball the more and more I think about it. Its just obscured by its more famous cousins and neighbors of the times.

  • CaptianNemo2001

    Notice how it will do 405 mph.
    Second the Allison V-3420 coupled engine had "issues". Not always with just reliability, cooling and parts demand.
    Third "This makes this XB-39 effectively an eight engine bomber." the Germans has "Issues" with their multiple-engine designs as well. Heinkel He 177.

    • fodder650

      I was going to talk about the Griffin in the article and completely forget this morning. Allison actually had a production ready engine in the V-3420 where the Griffin's coupled BMW's (wasnt it two 601's becomes the 610?) had far more problems.

      • CaptianNemo2001

        Yah the 610 is a real mess of a design. They could not cool the rear engine well enough (key problem).

  • Conversely, the Handley Page Halifax in various iterations could be had with either Bristol Siddely Hercules radials or Rolls-Royce Merlins. My Grandfather flew both types and universally the radials were seen as superior, for reliability, performance and character.

    • fodder650

      Yeah I read that the radial Halifax's were the better choice but it was the Air Ministry that was against air cooled radials in their Air Force for some reasons. It is a rather brute force method of powering an aircraft but that would seem to be a good thing in a time of war.

      • Yep; wartime production lines lose any interest in refinement and the battle against noise, vibration and harshness.

        You can bet that the interior plastics were lousy, too.

        • Vairship

          They just didn't make Bakelite like they used to!

          • fodder650

            Yeah it feels all plasticy now 🙂

      • CaptianNemo2001

        Radials can take more damage, in terms of number of rounds, before they are Atomic Toast.

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