Paperback juvenile fiction from the 1970s about kids who install a fan in their tree house and accidentally turn it into a helicopter. Among the kids is the son of the ambassador from a fictitious Latin American country.
Stump the Bookseller
New format, same book stumper solving.
Could it be “The Blackmail Machine” by Felice Holman? (First published 1968)
https://www.kirkusreviews.com/book-reviews/felice-holman-2/the-blackmail-machine/