I have built a 4x4 box blind (sq. tube covered with plywood). I want to elevate this thing 10-15' in the air. What angle do y'all recommend the legs be at?

i think the angle of the legs is less important than the reeeal tite 4 way guide wires that cant break or be pulled out or up !

mine are going to be 10 degrees each way, but ZZ is definately right about the guide wires.

I think I am going to use pipe so I [hopefully] dont have to use cross pieces between legs. 10 degrees doesn't seem like a whole lot

10º is a lot at 15 feet. I wouldn't go more than 15º anyway. The more the angle, the more the stability, but also the more weight on the metal/pipe/tubing. All you need is strength first and foremost, then stablize with cabling.

And welcome to THF, HHL

I would use some cross bracing, if you dont, the legs may bend when you stand them up.

I agree with the cross-bracing. Mine (was) 10 feet off of the ground, and when we moved it, the legs bent and we had to cut off 2 feet. I would suggest placing the cross-braces as low to the ground as feasible. While you are at it, you might as well put a hook in place to attach a rope or cable on the side you intend to pull it up from.

You will definitely need cross bracing at 15ft.

yes, weld on some type of attachment to hook your guide wires down with. I have one on each corner, and one in the middle on the very bottom.

Cross bracing depends on the size of pipe...we use 2 7/8 srill stem a lot and go up to 10-12' without bracing, but I would go any higher without. We built one with 18' legs and no braces, but it was about 4" pipe. (Big front-end loader and a big winch to get that one up!)
I agree with the 10-15 degrees. 10 degree for 10' or less, 15 degrees for 12'+
good luck!

I did the math. At 10 degrees the 10 ft. blind footing at the ground would be a little less than 90 inches squared, while the 15 ft. blind's footing would be a little over 110 inches squared. At 15 degrees the 10 ft. blind's footing would be nearly the same 110 inches squared, while at 15 degrees it would be a whopping 141 inches squared. My brother has a 4x6 blind 10 ft. tall at 10 degrees and it is extremely stable.

You could always leave them straight and use concrete and tie-downs.

I am building one 20' tall as we speek. I made the legs five degrees. It is a 10x10 blind. That makes the bottom 14'.