There is a Hand Held Calculator on the website link below that can layout just about anything, and very user friendly, including Arc's and Large Radius's. See the two attached files from the Manual that comes with these Calculator Programs. You just input the dimensions it prompts you for, and it will give you all the layout dimension's you need for the layout. You don't need to know the math and its Dead Accurate. You can use the Layout Manual that comes with it like a computer monitor for visual instruction and direction. It will also layout Square to Rounds, Round Elbows, Intersecting TEE's at any angle including the HOLE layout, Conveyor Screws, Stair Cases, handrails and much more. It always reads dimensions in DECIMAL form 1st, then in FRACTIONAL form 2nd, to the closest 1/32",+/- 1/64". This is for the person that doesn't know his/her Decimal readouts. It also has Utility programs for FINDING the RADIUS of an Arc, the DEGREE of an Arc, the CORD across an Arc, the DEPTH of Cord and the LENGTH of Arc, using the same excellent formula's that "aevald" is showing above. I have to say, by everything he has posted,the man "aevald" knows his TRIG well. It also has Drill & Tap sizes, Metric Conversions, Pulley sizes, including RPM and Belt lengths and more. This is a hell of a tool for people that don't have any layout experience or know the math. The site shows all the pages in the manual, just click on each page. Be sure to read all the "NOTES" in the pages, it helps things make sense. This Calculator is a Real Tool, its not a gimmick or a toy. Its worth a look at.
The very 1st 2 programs that I wrote were for this Large Radius job shown below. I wrote them back in the early 80's for the Apple II Plus computer that are written in this Calculator today. (ARC'S & CORDS and TAPER or CONE LAYOUT,Multi Piece). After taking Cord & Depth of Cord Dimensions, top and bottom, shooting the heights with a builders level, knowing the width of the copper sheets to be used,(Allowing for Seam's) and measuring around the parimeter at the bottom, (All Field Dimensions), I quickly calculated the number of panels for the cone layouts. It took about 2 1/2 hrs. to completly Layout these copper roof's with Number of Piece's, full multiple piece total lengths, (5 piece's per length of panel) and O.D. width's of all panels from the bottom of the panels to the top of the panels, in 5 sections using 10 ft. stock sheet lengths and ready for fabrication.
http://www.sheetmetallayoutcalculator.com