01-30-2016, 09:55 AM (This post was last modified: 02-24-2016, 01:00 PM by MarkH.)
I'll be cutting new fins. I took some liberty with the fin shape in order to increase the span and stability margin. Stock span is about 4.25. I'm going with a 5.5 inch span. The increased span along with using four fins will add necessary stability margin to fly with a 4 inch motor. [Edit: I later scaled down the fin size about 5%, going with a 5.25 inch in span. Attached is the .pdf I sent to the laser cutter]
I have access to a laser cutter at work, so I lasered up some fins. These were cut from 1/8 " 5 layer Finnish birch. They will be laminated with multiple layers of carbon fiber.
Well the fins were a failure. The plywood sheet I ordered from Aircraft Spruce had some pretty good warp to it. I bagged one fin with 3 CF layers per side against a marble tile, expecting it to remain flat after curing. End result was less warpage but not totally flat. So I'm looking for some flat ply. Will probably go to Hobby lobby and look for some flat Midwest 3 ply. Even balsa as core will work if it is flat since all the strength will be coming from the CF.
02-14-2016, 05:35 PM (This post was last modified: 02-14-2016, 05:37 PM by MarkH.)
Cut out some new fins.
One fin down, three to go.
I used 4 layers of plain weave on each side. It looks like this one came out perfectly flat.
Weight is 126 grams in comparison to the original fin which weighs 197 grams. So in total four fins will weigh less than the three original fins 504 grams to 591. The new fin is also stiffer than the original.
02-23-2016, 11:58 PM (This post was last modified: 02-24-2016, 12:06 AM by MarkH.)
I was posting from a desktop and had trouble getting all the pictures from the cloud. Here are the rest of the pictures. Fins lost some weight and are now about 110 grams each. The bevels turned out pretty much perfect, although they look a little funny with the carbon fiber to wood transition. I need to sand the face of the fins smooth. Then bond them, finishing it off with probably two layers of CF tip-tip.