Cierva W.11 Air Horse three-rotor helicopter from the late 1940s. Two were built.
https://diqn32j8nouaz.cloudfront.net...e_fullsize.jpg
Previously:
https://www.homemadetools.net/forum/...946#post210446
https://www.homemadetools.net/forum/...616#post234897
https://www.homemadetools.net/forum/...831#post229517
https://www.homemadetools.net/forum/...449#post231345
https://www.homemadetools.net/forum/...107#post214380
