Sikorsky engine nacelles
Our slight detour: more work on Walter Treadwell's Sikorsky S-38 project.
Last month we made some new parts for Walter Treadwell's Sikorsky S-38 amphibian project. As you may remember, we made four fuel tanks back in the beginning of the year. This time we made engine nacelles which form a streamlined area behind each radial engine. Walter provided us with a nacelle "plug" for us to make a mold. Since he has two engines, his project requires 4 nacelle halves. Chuck and I made a few minor modifications to his plug and made a trim fixture and a mold from it.
Here is a picture of the engine nacelle plug. This is formed into the shape
of the final part. The plug is used to make the mold for making more parts.
In order to make a mold from a plug, you first have to apply 3 or 4 layers of wax to its surface. I use Minwax, which is easy to apply and buff out by hand. After the wax has been buffed, a smooth and even coating of PVA (polyvinyl alcohol) is sprayed onto the plug surface. The PVA is a mold releasing agent, which makes it easier to remove the mold from the plug, after the part has fully cured.
While forming the mold off the plug , we learned how to make a "gel coat" surface. We made our own gel coat by mixing a type of glass powder called "cab-o-sil" into the epoxy resin. The resulting mixture makes a very thick slurry of resin which does not run or drip when applied to the plug. After the gel coat had a chance to "set up" and thicken for a couple of hours, we then began adding pieces of fiberglass cloth. We used quite a few layers and several different types of cloth that we had on hand so that a fairly thick and stiff mold was produced. After allowing it to completely cure, I was able to pop it off the plug fairly easily. Here is a picture of the new mold:
Brand new mold mounted on sawhorses. Note the smooth shiny gel coat
surface.
We also made a trimming fixture which was formed off the plug as well, but unlike the mold, we did not need to use a gel coat.
This is the trim fixture. As you may be able to see, it still needs to be trimmed.
As of the week ending Friday, September 18, we have completed 3 of the four nacelle halves. Two of them were trimmed and delivered to Walter. After test fitting he determined that the trim line needed to moved 1/2 to 5/8" on each longitudinal edge. Because of this 3 more nacelle halves were made (total of 6 parts made).
Here is one of the 6 completed nacelle halves.
Here is a picture of one nacelle being test fitted onto the Sikorsky.
On October 12th, the last part was molded for the Sikorsky engine nacelles. We are now ready to move to the new hanger and start working on our project 100 percent!
Last month we made some new parts for Walter Treadwell's Sikorsky S-38 amphibian project. As you may remember, we made four fuel tanks back in the beginning of the year. This time we made engine nacelles which form a streamlined area behind each radial engine. Walter provided us with a nacelle "plug" for us to make a mold. Since he has two engines, his project requires 4 nacelle halves. Chuck and I made a few minor modifications to his plug and made a trim fixture and a mold from it.
Here is a picture of the engine nacelle plug. This is formed into the shape
of the final part. The plug is used to make the mold for making more parts.
In order to make a mold from a plug, you first have to apply 3 or 4 layers of wax to its surface. I use Minwax, which is easy to apply and buff out by hand. After the wax has been buffed, a smooth and even coating of PVA (polyvinyl alcohol) is sprayed onto the plug surface. The PVA is a mold releasing agent, which makes it easier to remove the mold from the plug, after the part has fully cured.
While forming the mold off the plug , we learned how to make a "gel coat" surface. We made our own gel coat by mixing a type of glass powder called "cab-o-sil" into the epoxy resin. The resulting mixture makes a very thick slurry of resin which does not run or drip when applied to the plug. After the gel coat had a chance to "set up" and thicken for a couple of hours, we then began adding pieces of fiberglass cloth. We used quite a few layers and several different types of cloth that we had on hand so that a fairly thick and stiff mold was produced. After allowing it to completely cure, I was able to pop it off the plug fairly easily. Here is a picture of the new mold:
Brand new mold mounted on sawhorses. Note the smooth shiny gel coat
surface.
We also made a trimming fixture which was formed off the plug as well, but unlike the mold, we did not need to use a gel coat.
This is the trim fixture. As you may be able to see, it still needs to be trimmed.
As of the week ending Friday, September 18, we have completed 3 of the four nacelle halves. Two of them were trimmed and delivered to Walter. After test fitting he determined that the trim line needed to moved 1/2 to 5/8" on each longitudinal edge. Because of this 3 more nacelle halves were made (total of 6 parts made).
Here is one of the 6 completed nacelle halves.
Here is a picture of one nacelle being test fitted onto the Sikorsky.
On October 12th, the last part was molded for the Sikorsky engine nacelles. We are now ready to move to the new hanger and start working on our project 100 percent!
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