Vought Kingfisher and American floatplanes

Does anybody know about the design criteria and choices made with this machine in regard to the engine and the requirements. This plane was certainly seen as a success when compared to certain other designs like the Seamew. but if you look at the Seagull, Seamew and then even the Duck, their engines were all far more powerful - 600hp and plus. The Kingfisher used a 450hp junior but the respective aircraft weights were all similar, though the Duck certainly was slightly heavier.

So why choose an engine 25% less in power compared with current or even older designs. This also affected the bomb load which was half that of the older Seagull. Looking at the air frame it could, I assume, accept in diameter, say an R1340. So why do we think a 450hp engine was chosen for a newer design?

There is the incident were one taxied 40km's after picking up a downed crew - if it had 150hp more could it have taken off and flew?. It seems an odd engine choice. The range doesn't seem to be that much better - if that was a consideration. The Duck was 750 miles with 850hp and the Seamew 1150 miles with 600hp. Any thoughts.

Cheers,

Lee

Interesting...

See: os2u

There is often more to requirements than speed/range/bomb load.

ANd then you have the Kingfisher that saved ten men.

sos2u3

And No you probably don't want to try to take off with 2-3 men holding onto to the wing because they won't fit it in the fuselage even if you have the power to do so.

BTW, when I was a kid one of my friends' father had flown a Kingfisher from the Battleship Colorado.

Yes, what he said about men on the wings, but also consider that a floatplane can not take off from open ocean unless the water is very calm. It has nothing to do with power. They can land on the ocean, but then they are stuck.
Navy recon planes are intended to be low, slow and cheap. They aren't supposed to be combat planes. I would bet that the Navy told Vought to "make us a plane about the same size and weight as the SOC, so we can use the same catapults and hangars. It should be at least as fast as the SOC, but give it an extra couple hundred miles of range. We want a monoplane, with metal construction and floats that can be swapped with wheels. Also, give us good radio equipment and take-off performance. Oh, and try to use an engine that no-one else wants for anything."
So Vought figured out a plane that could do all that, but with a smaller, cheaper engine than the SOC uses, to boot! A smaller engine costs less, and uses less fuel (although that depends on whether you have to run it on full power all the time to stay flying!). That is likely how they achieved greater range (which is the important thing for a recon floatplane) with a aircraft that weighs the same.
There are also strategic considerations. There were likely many R-985's sitting around, while they needed powerful twin-rows like the R-1340 for "real" combat planes. Why waste it on a pokey little floatplane when a little old R-985 will do "good enough"? That might even have been the primary consideration. It may well have been in the specification, that the plane had to use the R-985 engine.
In any case, the OS2U did it's job perfectly well. I don't see that a larger engine would have been a great help, and may have even hurt things (would use more fuel, would raise weight, increasing takeoff and landing speeds, etc).

Maybe they used the R-985 because of its reliability versus the single row R-1340. In my experience, the R-985 can fly with a lot of damage; I have seen them arrive with a cylinder head blown off (one of the upper ones, of course), and I have also seen an R-1340 grounded due to a cylinder failure.