Propeller question

[P-40 Admin]

I received an e-mail and part of it was a question on propellers and I wasn't completely sure about the answer so I thought I would post a question here for you guys.
 
I have also two question about propellers used on P-40s (D-N variants):

From photos it is evident, that at least two types were used: one narrow with more pointed tip, and other more rectangular with rounded tip (mostly on N, but also some F,K,L,M series). This is not mentioned in the popular literature on P-40. I would like to know of what types (manufacturers ) they were and if there were any rules of application?

[GatorDude]

I'm bumping this topic with an additional question.  What is the propeller of a P-40 made of?

[Mark Joyce]

As to what the propellers were made of, I believe they were hollow steel.  Here's a link to learn everything there is to know about their construction:

http://www.enginehistory.org/Convention/2005/Presentations/FeyTom/P08%20Curtiss%20Electric.pdf

As to the two types; yes, this appears the case although I too haven't seen it described in very much detail.  In the book, "Flying American Combat Aircraft of WWII," Bruce Holloway of the 23rd FG mentions that the P-40M and N models were fitted with a paddle-blade propeller instead of the previously used "streamlined" (his word) one in an effort to improve climb and altitude ratings.

I assume both types were manufactured by Curtiss (Curtiss Electric).  Hopefully someone else has a definite answer.