In article . com,
Kingfish wrote:

On Sep 20, 2:36 pm, "Kloudy via AviationKB.com" u33403@uwe wrote:
here's more.
Indeed not plywood.http://www.check-six.com/Crash_Sites...crash_site.htm

Interesting the four-engine RB-50 (formerly B-29) was "much more
economical" for the photo recon mission than the XF-11 twin? I'm also
curious about the contra-rotating props on Hughes' plane - what was
the benefit? The article says he did have conventional props put on
the second prototype.

The contra-rotating props helped absorb the power of the R-4360s. Look
at the Russian Bear Bomber as another example. They also helped to
negate P-factor, as each prop had blades coming down on each side.