What we don't know

[RayB]

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?

 

[Geedee]

Cant help with your question Ray, but welcome aboard.

 

[Colin1]

...Some contributors are somewhat argumentative but that seems a small price to pay...

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

 

[davebender]

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.

 

[Shortround6]

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?

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.
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.

 

[krieghund]

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.

 

[Jabberwocky]

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?

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.