Bell 47B-3 crop dusting helicopter from the 1940s.
Fullsize image: https://diqn32j8nouaz.cloudfront.net...3_fullsize.jpg
https://diqn32j8nouaz.cloudfront.net/bell_47_b3.jpg
Previously:
https://www.homemadetools.net/forum/...340#post231019
https://www.homemadetools.net/forum/...790#post229405
https://www.homemadetools.net/forum/...066#post210768
https://www.homemadetools.net/forum/...464#post208788
https://www.homemadetools.net/forum/...181#post203724