What we don't know

Discussion in 'Engines' started by RayB, Jul 13, 2010.

  1. RayB

    RayB New Member

    Joined:
    May 31, 2008
    Messages:
    8
    Likes Received:
    0
    Trophy Points:
    1
    Occupation:
    Retired
    Location:
    Arlington VA
    After a lifetime interest in military aviation, I “discovered” this site a while ago and have learned a great deal from it. Some contributors are somewhat argumentative but that seems a small price to pay for the knowledge that they have. Still . . . I have lots of questions remaining.

    For example,

    Why the Wright R-3350 for the B-29 - why not the P&W R-2800? The 3350 produced 2200 hp at takeoff while the 2800 produced 2100 hp; not much of a difference. And choosing as undeveloped an engine as the 3350 for such an important project was very risky and almost lead to the failure of the program. The one idea that has occurred to me is that the cruise power of the 2800 may have been inadequate as compared to the 3350 with its much larger displacement. I haven’t seen cruise power curves for either engines.

    Any thoughts?
     
  2. Geedee

    Geedee Well-Known Member

    Joined:
    Dec 5, 2008
    Messages:
    3,292
    Likes Received:
    210
    Trophy Points:
    63
    Gender:
    Male
    Location:
    Wiltshire, UK
    Cant help with your question Ray, but welcome aboard.
     
  3. Colin1

    Colin1 Active Member

    Joined:
    Jan 2, 2009
    Messages:
    3,541
    Likes Received:
    0
    Trophy Points:
    36
    Occupation:
    Engineer and overgrown schoolboy
    Location:
    United Kingdom
    It's a zero price to pay
    if people didn't get involved in the debate, it wouldn't be a forum, it would be a bulletin board
     
  4. davebender

    davebender Well-Known Member

    Joined:
    Jan 18, 2009
    Messages:
    6,418
    Likes Received:
    64
    Trophy Points:
    48
    Location:
    Michigan, USA
    The larger engine had more development potential. And I suspect the U.S. Army Air Corps wanted the larger engine to power other aircraft also. It's the same reason the Luftwaffe paid to develop the Jumo222 V24 even though the DB603 and Jumo213 V12s were perfectly adequate for WWII era aircraft.
     
  5. Shortround6

    Shortround6 Well-Known Member

    Joined:
    Jun 29, 2009
    Messages:
    9,770
    Likes Received:
    801
    Trophy Points:
    113
    Occupation:
    retired Firefighter
    Location:
    Central Florida Highlands
    At the time work was started on the two engines the power difference was a lot further apart.

    Initial estimate of power for the R-2800 was 1650hp which improved to 1850hp when first production models came out.

    It took 4 to 6 years to bring an engine from initial drawing board to squadron service. Initial work on the R-3350 started before the R-2800 was started. It seemed low risk, use two rows of 9 cylinders instead of the two rows of 7 on the R-2600. But use the same cylinders, heads, valves, pistons, etc.
    Engine development wasn't always as easy at it seems.:lol:
    With the B-29 starting to take shape on paper in July of 1939, predicting which engine would be more reliable or even putting out what level of power in 1943 was also a bit beyond the abilities of most men.
     
  6. krieghund

    krieghund Member

    Joined:
    Sep 25, 2006
    Messages:
    611
    Likes Received:
    21
    Trophy Points:
    18
    Occupation:
    Avionics Engineer Advisor to RSAF
    Location:
    Riyadh
    Hi RayB

    I posted my engine info in the technical section
    http://www.ww2aircraft.net/forum/engines/r2800-vs-r3350-25485.html#post692342

    Basically from a performance stand point at that time in the war The B-29 with 20,000 Lbs of bombs cruises at 67% power (about 1340 HP each) at 18,000feet for 258 mph consuming approximately 433 gals/hr with the R-3350

    With the R-2800 there is a weight savings per plane of about 800 lbs give or take. However to produce the same speed performance the engines would have to be set at 78% to 81% power with the greater rise in fuel consumption of about 550 gals/hr. To approximate the same long range fuel consumption would mean cruising somewhere between 200 and 215 mph.

    In summary it could be done, just speed performance would suffer as would time to target would increase which in turn would increase your vulnerability to fighters.
     
  7. Jabberwocky

    Jabberwocky Active Member

    Joined:
    Jul 24, 2005
    Messages:
    1,090
    Likes Received:
    16
    Trophy Points:
    38
    Occupation:
    Teacher
    Location:
    Japan
    When the B-29 was being designed, in early 1940, the R-2800 had only just been certified for 2,000 hp. Despite its teething problem, the R-3350 was producing 2,200 hp from the get-go and promising 2,400 hp with a little more development. Three of the four designs submitted for the very heavy bomber contract were powered by R-3350s.

    Another major consideration was the lack of spare production for the R-2800. The R-2800 was selected to power the P-47, the F4U, the F6F, the C-46, the Ventura and the B-26 (maybe a few others as well). That's a lot of major aircraft for the one engine type.

    Wright, on the other hand, had no major order for the R-3350 in 1940.
     
Loading...

Share This Page