The Radial Engine P-40

Sorry, I misunderstood what you were asking. The B-26 RFP was issued 11 March 1939 and called for an aircraft using the P&W R-2800, the Wright R-2600, or the Wright R-3350. All were new engine designs. Planning for possible future aircraft had to take into account engine production as well. The design was completed in June and the prototype flew on 25 November 1940.

What would have been risky would be adding a radial-engine version of the P-40 into the production mix before engine production was sufficient to supply them. Further, the P-40 was considered state of the art for its generation. It was an earlier generation aircraft, being a modification of the P-36 in February 1937 as the XP-37, which then morphed into the P-40. It was effectively almost two years older than the P-47, B-26, or F4U in its heritage.

 

Yes, it was flown then, it was a prototype.

I am unsure how you see airframes without engines as being a useful development Terry. Something has to give, either the F4U program, the B-26 program, or the P-47 program planned to utilize the production of the R-2800 has to either go away or be reduced. Its robbing Peter to pay Paul to put up-to-date engines in an airframe design that was two to three years older than the airframes that were designed to use it. The XP-60C was actually an attempt to salvage the market they were losing to North American, Republic, and Lockheed, which only existed because the original plan, to put the Alison V-1710 into it failed.

 

Initially, Curtiss would need just two engines for prototypes. Those would require testing and working out any issues that arose. So, I would expect to see that process done by say June 1941. That would put the R-2800 version in production a few months before the US enters the war. But, it also places the P-40 in a position that would allow it be far more effective as a fighter in 1942 than it actually was.

The P-60 series started out as a cleaned up version of the P-40 with possibly a Merlin or Continental XIV 1430-3 engine to improve performance over the Allison version. With a bottleneck in Merlin production, and the Continental not working out, Curtiss suggested the P-60A receive the Allison V 1710-75 with a GE B-14 turbocharger that offered similar power. This ran into development problems at Curtiss' end.
Then in mid 1942 Curtiss offered an alternative version, the C, with first a Chrysler XIV 2220 engine but that fell through because the engine's development was very questionable. That led to a switch to the P&W R-2800. Curtiss screwed the pooch on that by wanting to use a counter-rotating airscrew. That led to the XP-60E with a conventional 4 blade prop. Testing went satisfactorily with this machine and two YP-60E were ordered, one built. It was tested in mid 1944 and because it was no better than stuff in service at that time, the USAAF dropped the whole program.

Historically, Curtiss simply proved really lousy at designing new aircraft after the P-40. They needed a new design in 1939 to replace the P-40 to stay competitive. They didn't produce one.

One might note that the USAAC did place an order for a Curtiss prototype, the XP-62, in January 1941 to use the Wright 3350-17 engine. The resulting plane was overweight and not a particularly good performer. Development was further slowed as the USAAF didn't want it to interfere with Curtiss' manufacturing of P-47G fighters so by the time it was really being tested, it too was just not better enough to make it worth producing.

 

One thing to remember about those high flight speeds set by prototypes is that they were often in level flight, and without awkward little things like pilot armour, guns, toolkits, first aid kits, dinghies, ammo loads...(there's a LOT of weight in brass)....and even on occasion without radios! Pared right down. They'd also be set in optimum weather and heght/barometric conditions - not the heat of a dogfight furball.