Original drawing released into the public domain by Pearson Scott Foresman.
http://commons.wikimedia.org/wiki/File:Cloud_seeding_(PSF).jpg
I figure it is an A-26 or something, but I don't know anything about planes, lol.
I'm not too happy with the propellers...
This image was donated by Pearson Scott Foresman, an educational publisher, to Wikimedia Commons, and is thereby in the Public Domain.
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See http://commons.wikimedia.org/wiki/Category:Pearson_Scott_Foresman_publisher