b 17 with allison motors

Discussion in 'Engines' started by mike siggins, Dec 29, 2012.

  1. mike siggins

    mike siggins Member

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    does anybody know the top speed was compared to a stock one millage range etc
     
  2. FLYBOYJ

    FLYBOYJ "THE GREAT GAZOO"
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  3. wuzak

    wuzak Well-Known Member

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  4. wuzak

    wuzak Well-Known Member

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    Didn't see the range question.

    From Joe Baugher's page:
    Vega XB-38: Range 2400 miles with 3000 pounds of bombs, 1900 miles with 6000 pounds of bombs. Maximum range 3600 miles.
    Service ceiling 29,700 feet
    Weights: 34,748 pounds empty, 56,000 pounds gross, 64,000 pounds maximum.
    Maximum speed 327 mph at 25,000 feet.
    Cruising speed 226 mph.

    Boeing B-17E Fortress: Normal range 2000 miles with 4000 pounds of bombs. Maximum range 3300 miles.
    Service ceiling 36,600 feet
    Weights: 32,350 pounds empty, 40,260 pounds gross, 53,000 pounds maximum.
    Maximum speed 318 mph at 25,000 feet
    Cruising speed 195-223 mph.
     
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  5. wuzak

    wuzak Well-Known Member

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    I think the thing that really killed the XB-38 concept was the engine installation.

    The nacelle contained the intercooler but not the radiator, which was mounted in the wing leading edge between the engine nacelles. The installation did make use of the standard turbo (both R-1820 and V-1710 used the B-series turbo) and its location.

    But the need to change the leading edge and install radiators would have required delays in production for the changeover. If the engine installation was designed as a self contained module with radiators and intercooler, still using the standard turbo location, airframe modifications would have been avoided.

    For the XB-38 to succeed as it was it would have needed to give much more performance advantage than it did.
     
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  6. johnbr

    johnbr Well-Known Member

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    XB-38_engine.jpg XB-38_engines.jpg
     
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  7. wuzak

    wuzak Well-Known Member

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    Nice photos John.

    Shows how much space was available inside the outline of the firewall of the radials normally used.

    You could just about fit a V-3420 in there!
     
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  8. GregP

    GregP Well-Known Member

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    I think what killed the XB-38 was that it was developed as an alternative aircraft to see what was possible with V-12 engines, and the incremental improvement wasn't deemed worth the extra training for mechanics and the changeover to the production lines. It DID carry 50% more bomb load to Berlin, but that must not have been deemed all that important at the time versus the changeover costs and everythng else added up.

    It is very possible to have changed the basic B-17 airframe to be considerably faster, but the intent was to see what just changing the power would accomplish with the already-designed airframe. They did and they saw.

    Allison may have had some input, too, as they had patented many bearing designs as proprietary and may not have been willing to share the technology with everyone freely. I wouldn't have been so disposed if I had been in charge of Allison, wartime situation or not. I'd have insisted on supplying all bearings for any Allisons made by other companies, without drawings being available except for dimensional checks and any final inspections, and I'd have insisted on supplying Allison go-no go crankshaft bearing gauges as well. Almost everything else was rather ordinary in technology if not design, except maybe the Stellite valves and sodium-filled valve stems.

    What they SHOULD have done was to design an integral 2-stage supercharger themselves, and never did. It was a smaller company and the resources just weren't avilaable for taht design in parallel with the design already taking place at government expense and contracts.
     
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  9. wuzak

    wuzak Well-Known Member

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    Did it?

    You mean it had the potential to carry the extra load.


    Ultimately it was the changeover time for production which killed the project, the performance increase not being sufficient to justify production.

    Part of the issue with that was the decision to use an adapted P-38 nacelle (I think that was the case), with core type intercooler up front and leading edge radiators between the inner and outer engines. If Vega or Allison too the time they could have come up with a quick change module which contained the radiator as well as the intercooler (or they could have used the B-17s current intercooler location, but that may not have been sufficient for cooling).

    The turbo was located in the same place as the B-17, so the exhaust manifolds would just have to meet up.


    The B-38 program had nothing to do with an alternate manufacturer of the V-1710. So all that is moot.


    This is also moot, as the B-38 was based on a B-17 and would, therefore, use the B-series turbo already specified for use with the R-1820s and already in use with the V-1710 in P-38 aircraft.
     
  10. GregP

    GregP Well-Known Member

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    #10 GregP, Nov 3, 2016
    Last edited: Nov 3, 2016
    Hi Wuzak,

    For your second quote, I said exactly the same thing. Is there a point?

    The B-38 DID have something to do with a second or further manufacturer. If the B-38 had been selected for producrion, Allison could nver have made the required number of engines and the government is rather famous for asking many manufacturers to produce an item, including engines. Look at how many manufacturers built the Wright R-1820, including Studebaker.

    The last quote is also not moot. The Merlin was successful because of an integral 2-stage supercharger with intercooler in later versions. It had almost the same design as the Allison, but had an updraft carburetor instead of a downdraft carburetor. Not many other design differences in the single stage versions other than the strength of the connecting rods, which was in Allison's favor by a damned LONG shot. An Allison with a Merlin 2-stage supercharger would almost certianly have perfromed as well or better ... very probably about as well. The 60 cubic inch difference in dispalcement wan't a big factor to speak of. The difference is less than 4%, which is nothing in big engines.

    They never made an integral 2-stage, supercharged engine of the V-1710 variety and really should have. All their real 2-stages engines were with an auxilliary supercharger driven by a shaft that made the engine system much longer than necessary.
     
  11. wuzak

    wuzak Well-Known Member

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    Just expanding on your point - and making the point that the installation didn't make for an easy change-over.


    Allison expanded its facilities with government money. And if it came to other manufacturers building them I am sure GM (owner of Allison at the time) would have lobbied hard for it to be done in-house.


    The use of an integral 2 stage supercharger was not going to help the B-38 since it was a single stage supoercharged engine plus turbocharger installation.

    The integral 2 stage supercharger would have been more applicable to P-39s, P-40s and P-51s. And, perhaps, the P-38.
     
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  12. wuzak

    wuzak Well-Known Member

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    A picture of the XB-38 showing the leading edge radiators.

    [​IMG]
     
  13. tomo pauk

    tomo pauk Creator of Interesting Threads

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    The actual demand for the V-1710s shrinked a bit in 1944 vs. 1943, with cancellation of production of P-40 and P-39, with P-63 being low on the priority list. So methinks that by late 1943/early 1944 Allison would've met the demand for the B-38 had it been pursued. By early/mid 1944 the P-38 is also not the sole LR fighter, so here is another opportunity to have more V-1710s for the B-38s.
     
  14. Capt. Vick

    Capt. Vick Well-Known Member

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    Being water cooled, I don't think as many of these would have come home with the type of damage the Fort was legendary for.
     
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  15. Shortround6

    Shortround6 Well-Known Member

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    It was one prototype. A different version might have separated the radiators, like moved the outer engine engine radiators outboard of the engines. Traded larger target area for less likelihood of loosing both radiators?
    B-17s could fly fairly well on two engines IF they had one engine left on each side. Loosing both engines on one side made things a LOT harder and while it was done on occasion getting home on two engines on one side was pretty rare.

    B-17 ranges and bomb loads are all over the place and without actual range charts for the XB-38 the commonly listed figures for the XB-38 don't mean much.
    The XB-38 having a max gross weight of 64,000lbs and an empty weight of 34,748lbs.
    The B-17G having a max gross weight of 72,000lbs (dropped to 67,860lbs post war) and an empty weight of 32,720lbs (?).
    weights are all over the place too.
    Once you put in the crew of 10, 144 gals of oil and over 1300lbs of .50 cal ammo, plus guns, radios etc. the amount of weight for fuel and bombs drops a bit. B-17G went about 41,048lbs without fuel/bombs. Granted a production XB-38 might very well have had a higher gross weight than 64,000lbs. But the engine installation was heavier than the Cyclone installation which cuts into either the Fuel or bomb load for a given max gross weight. XB-38 didn't have the chin turret, it could be added but was more weight/drag.
    Could the better aerodynamics make up for the greater weight?
     
  16. wuzak

    wuzak Well-Known Member

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    They could have separated the radiators by having them in the QEC with the engine - either as a chin radiator or an annular radiator.

    By doing it that way they would cut down on the plumbing and reduce the area that needed protecting with armour (if that is what they chose to do).

    Some consideration was given to using the V-1710s in the XB/YB-40 bomber escort to make up for the additional weight making them slower than the standard bombers, particularly on the return journey.
     
  17. Shortround6

    Shortround6 Well-Known Member

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    Something else to consider is that the Cyclone in the later B-17s was rated at 1200hp for take-off and for military power, it was rated at 1380hp for war emergency and for 1000hp "normal" or max continuous, like a long climb. Allisons varied a bit but were either 1000hp or 1100hp "normal". Always subject to temperature limits of course. .
     
  18. michaelmaltby

    michaelmaltby Well-Known Member

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    #18 michaelmaltby, Nov 4, 2016
    Last edited: Nov 4, 2016
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  19. Denniss

    Denniss Active Member

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    According to Wiki the XB-38 was 30-40 mph faster in both max and cruise speed. This may have been problematic for operational use. They would either have to throttle back to keep formation with B-17s or USAAF would have to create separate groups solely equipped with them to create large and fast bomber streams with a modified escort relay system.
     
  20. Shortround6

    Shortround6 Well-Known Member

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    Well, it is Wiki but you have to make sure which B-17 you are comparing. The XB-38 was a modified B-17E airframe.
    Depending on weight B-17E/Fs were good for 317mph (Light) to 307/9 mph at 56,000lbs. The G's were slower but then the XB-38 didn't have the chin turret either. Difference was more like 20mph if you are comparing like to like.
    XB-38 first flew on May 19, 1943 and was lost on June 16, just 28 days later on it's 9th flight. I am afraid that some of the published performance figures may not be backed up by test data. Again, a second or 3rd prototype might have been tweaked to go even faster but we just don't know.
     
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