Step 22: Propeller Pt 3/4 - End Cone

The end cone is the attachment to the hub that makes the assembly more aerodynamic (or hydrodynamic) when travelling through a fluid. The base diameter is 2" to match the hub diameter and the height is 2" chosen to give a streamlined surface without being too long. The overall shape is a parabola what has been reloved around a central axis.

To build it a plug was machined from 1" polystyrene foam in two halves (Photo #1). 0.05" was left at the bottom to stop the parts coming loose on the last pass (Photo #2, I need to learn how to use the holding tabs feature in CamBam when I get the time). The two havles were then glued together using a thin layer of white glue after the swarf was removed with a utility knif and some 220 grit sandpaper (Photo #3).

To give the endcone a hard durable shell I covered it in a layer of fiberglass using the vacuum bag method using the following steps:

-I assembled the materials in Photo#4. I was working outside with good ventilation to protect myself from the fumes.

-I measure out the epoxy in to 2:1 ration of resin to hardener using the measuring cups. Shown in Photo #5 is 15ml of mixed epoxy, I ended up using 30ml.

-Starting the fiberglassing I wetted out a piece of fiberglass cloth 3"x3" (larger than the cone's base) onto the piece of waxed MDF. Photo #6

-Next I placed the foam endcone plug in the middle of the wetted fiberglass. Photo #7

-and draped a piece of fiberglass cloth over it. Photo #8

-I wetted out the cloth until all areas were saturated with resin. In Photo #9 I still have creases in the cloth. These will not lay flush even after vacuum bagging so small slits will have to be cut in the fiberglass overlapping the edges to smooth the material out.

-Next an oversized piece of peel ply is layed over the fiberglass. Photo #10

-And then a layer of breather cloth (Photo #11). I put an elastic band around everything at this stage to hold it all together while I made the bag. Photo #12

-I placed everything on one side of the vapour barrier (Photo #13) and doubled the plastic over sealing the edges with duct tape while inserting an air line from underneath the breather cloth and out a corner (Photo #14)

-The exit point of the air line is the hardest place to seal. I used plasticine around the airline as shown in Photo #15. This takes a long time to get right an is quite frustrating. The next time I vacuum bag something I will take the time to make a proper sealed connection using brass fittings.

- A vacuum is now applied using a pump made from this instructable. With this setup I can pull up to 25" Hg.

-After 24 hours to let the epoxy cure the part was taken out (sorry, forgot to snap a picture of this step), the excess glass cutoff around the bottom, a coat of primer applied and sanded to be flush with the propeller hub. Photo #16

-When I was happy with the fairing (more a function of the time I had available than the results, it could have been a lot better) I gave it a couple more coats of primer. Photo #17

-I cut out a recess on the bottom and using autobody filler attached a #6-32 nut and washer. I covered a 1/2" long #6-32 machine screw in Vaseline to prevent the autobody filler from sticking to it and assembled it through the mounting hole in the propeller hub (Photo #18). This makes it possible to remove the endcone from the top side of the hub. I later decided that removing it wouldn't be necessary so I faired the hub and endcone together with drywall compound and made them one piece.

-Using metalic autobody spray paint I had on hand (Photo#19) I gave the endcone/top hub assembly and the bottom hub three coats of paint followed by a layer of clear coat. Photo #20