I know most people will laugh at my struggle but I can't do simple math. I want to build my own PVC greenhouse. I know the height, width and length I want I just can't figure out the length the arc should be. Any push in the right direction is appreciated.
I'd have to dig out my math books... That's not going to happen. You don't want me working your equation anyway.
But maybe you could post the dimensions that you do know? Maybe somebody else remembers the formula. MAYBE some kind soul would do the math for you.
Say you want to build a hoop with a width of 12 feet, a length of 20 feet, and have your arc be 1/2 a full circle. Normal construction, I build small ones like this all the time.
The arc is the width, multiplied by 1 9/16 ths... or to be fancy... the width, times 3.1416 then divide that answer by 2. This will give you the length of the pvc you will be bending to make the arc.
Using this method, your height in the center is 1/2 the width. So if you have a 12 foot wide hoop, your pvc pipe length is approximately 18 feet 1 1/2 inches, and your center height will be approximately 6 feet.
I use 3 1/8 for the multiplier instead of 'pi' (3.1416) when doing the math, for hoops it comes out very close.
I usually use 3/4" thinwall white PVC for short season/short use hoops, you can use 1". Math will work about the same. I space the ribs 2 feet apart and use a center ridge (one piece of PVC duct taped to each rib under the center) pole to hold things in place. You can get fancier, use sections of PVC and cross/junctions and pvc-glue glue them together. I have also built large ones with a rigid metal pipe center ridge with two set in metal verticals, one at each end, to hold the ribs up. Then peg each rib end into the ground by driving rebar to about 4" sticking out and slip the pvc pipe end over the rebar.
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