Punisher 4 Kit Bash - Minimum Diameter Build

[MarkH]

[I deleted the original thread in Construction and re-started it here under Your Projects.  Seems like a better fit.]

After debating how to build this rocket (3 inch or 4 inch motor), I've decided to go sans motor mount, and 4 inch.

In other words, I am building a minimum diameter (98 mm) Punisher 4;  the  kit comes with a 75mm motor mount. 

Here are a few pics to get started.

Filling in the slots.  There are three fin slots, and since I will be building this as a 4 fin rocket these had to go.

[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]

[MarkH]

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.

[MarkH]

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.

[Viking]

I have access to a laser cutter at work, so I lasered up some fins....

Massive envy!
One day I'll finish building mine(serious lack of space) or I'll just cheat and buy one.

Nice build so far, shame about the fins.

[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. 

...now I need to order some more carbon fiber.

[MarkH]

Another day another fin down.

[MarkH]

Finished the fin layups. Cut off the excess. Squared them up.

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Finished the fin layups. Cut off the excess. Squared them up.

[MarkH]

Bevels.  I copied the router table setup from one of the Honey Badger threads on TRF.  Cut the jig to produce a 10 degree bevel.

[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.

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