R-1690 vs R-1820

[Zipper730]

I'm curious why the Boeing 299 (B-17) used the R-1690 in the prototype phase, whereas the Douglas B-18 and Martin 146 used R-1820's? The Boeing B-17 would eventually use the R-1820's eventually...

S Shortround6 , W wuzak

 

[bobm4360]

Boeing may have started the design while still part of United Aircraft and Transportation Corp., which also included Pratt & Whitney. As this was a private venture, they probably decided to keep as much as possible "in house". For the production aircraft, the Army told the aircraft manufacturer which engine they would use! Between-wars procurement, especially during the depression, was always about initial cost, not future growth.
Bob

 

[wuzak]

4 x 750hp engines vs 2 x 850hp engines?

Availability?

Preferred supplier?
The Model 221 Monomail, XF6B, Model 247, YB-9, P-12, P-26, and XB-15 (which flew after the Model 299/B-17) all used Pratt & Whitney engines. The Model 299 followed that trend.

 

[Zipper730]

Boeing may have started the design while still part of United Aircraft and Transportation Corp.

The break-up occurred in 1934, which was when the program was initiated.

As this was a private venture, they probably decided to keep as much as possible "in house".

You mean the prototype itself? In that case, I'm surprised they didn't pick the R-1830 if it was available. It was more powerful and would have extracted some extra speed out of it.

For the production aircraft, the Army told the aircraft manufacturer which engine they would use!

However, the prototype was more lax in what they could pick for available engines.

4 x 750hp engines vs 2 x 850hp engines?

That said, the top speed of the aircraft was said to be around 235 mph which was only 1-2 mph off the Martin 146. If preferred customer was an issue, then why not the R-1830? It was used on the XPBY (which flew in March of 1935).

 

[bobm4360]

For the prototype, cost and weight favor the Hornet. Lots of parts in common with the Wasp, and cheaper to build; also approximately 200 pounds lighter. For the production B-17, the R-1820 is lighter and less complex than the R-1830 with similar horsepower.
Bob