Overpitched:
I thought the 47 had something to do with the year it was originally produced.
Many people assume so. And we have to ask: Did Larry Bell "jump" from the Model 30 to the Model 47 to coincide with his intended year of certification (like Sikorsky did later with the S-76)? It's possible.
History does record that Bell was messing around with the Model 30 as early as 1943. The Model 30 was readied for "mass production" as the Model 47, and the first "Bell 47" flew in December of 1945. Production actually began in 1946, and of course the first commercial helicopter type certificate was issued to the 47 on March 8, 1946. So were there actually 16 different experimental models between the Model 30 and Model 47? It would appear not!
It must have been an incredible, hectic time at the Bell factory in the years immediately following WWII. Because also in 1946, Bell wanted to produce a larger version of the Model 47. They called it the Model 42. You can look at a picture and read about it here:
http://avia.russian.ee/~star/vertigo/bell_42-r.html
Five seats and a Wright R-985 radial behind the back seats? And you thought a 47 was noisy! And how 'bout that very R-44ish profile, eh? And three-blade tail rotor?? Without a civilian market, Bell must've said, "Hey, let's put a P&W 1340 in it and see if we can sell the damn thing to the Air Force!" The Model 42 then morphed into the Model 48/XR-12, also in 1946.
As the five-seat original Model 42/48 was not successful either for the civilian or military markets, it was apparently the Air Force that spurred the development of the Model 48A, a larger version designed to carry up to 10 people. And if you look closely at both the Model 42/48 and the Model 48A, you can clearly see the basis for what would later become the Model 204/YH-40/HU-1.
Man, I would've loved to have been around Bell in 1945. I guess I was just born too late
What were those times like, Lu?