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The curious case of the Coronado’s mixed propellers

8 November 2019

The sole example of Consolidated’s PB2Y Coronado is displayed within Pensacola’s National Naval Aviation Museum. And it is a monster! Four radial engines mounted on a high wing over a deep hull with no less than three fuselage decks. Each engine is a Pratt & Whitney R-1830 Twin Wasp which is a two row piston engine of which the 14 cylinders of each radial powerplant could collectively deliver 1200 hp. They were also employed in B-24 Liberators, C-47 Skytrains, PBY Catalinas and Short Bros. Sunderlands—among others.

The National Naval Aviation Museum’s Consolidated PB2Y-5 Coronado—©2019 Joseph May/SlipstreamPhotography

But the Coronado was different than the other aircraft with which it shared its engine and not because the PB2Y’s engines dispensed with superchargers (redundant since the aircraft was not flown at altitude). The outstanding difference is the inboard engines possessing 4-blade reversing propeller blades while the outboard engines utilized 3-blade non-reversing propeller blades.

Clearly the Coronado’s inboard Twin Wasp radial has four propeller blades yet the outboard Twin Wasp radial has three—©2019 Joseph May/SlipstreamPhotography

Such a difference! Asymmetric propellers and likely unique.

But why?

There isn’t anything definitive I could find but Ron Lesch and I have found that:

  • The outer propellers have a 6-inch greater diameter than the inner propellers
  • A pilot’s report stated the engines produced the same thrust when set at the same the rpm
  • The same pilot noted the inner props were smaller in diameter to reduce backspray from the fuselage eroding the propeller blades. He also noted that the inboard engines had to have the rpm less than 800 prior to reversing the blades.

Our hypothesis is the inboard engines could be used for braking (obviously) while keeping the outboards available for maneuvering while on the water. Also, the aircraft could pivot using the inboard engines without dipping the wingtips as easily.

Or, could it be that only two reversing propellers were required?

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