Any math to calculate resultant stress is meaningless, because we have no data on how uniformly dense the wood is.
Not to mention it looks flimsy to the point of being cartoonish.
I just felt the need to dispel this rumor that is quite dangerous that I see all the time at work where people use 1/4 wire rope slings with unrated hardware as part of rigging instead of 1/2 inch Manila rope because “That rope doesn’t have any rating, it’s natural”. (It does, about 1/2 the wire rope, but needs knots or splices to attach it to thing being lifted, not the unrated hardware that comes with the wire-rope.) Like someone posting further down, I’m more immediately concerned that there is no brace to prevent racking or the use of ratchet straps as a lifting device.
[1] https://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr11...
What he showed is the crane is plenty strong enough to hold the engine--the failure mode is tipping, not strength.
> This whole article is a largely pointless exercise in figuring out how strong some random dude’s wood crane is, even though I have no clue what the load case is.