Presented by: Joe Goffin and Gordon Nichols
Joe Goffin and Gordon Nichols were looking at some of Joe's airplane plans some time ago and decided to build a RV-6 Model off of the plans he had. We started looking at the plans and it immediately became apparent that we needed to start by designing the cowling mold and the plan to make the large canopy.
There are a number of ways to construct molds for fiber glassing a cowling. You can use a large amount of balsa, glue pieces together and sand them down to the desired shape, you can use a wood block with a LOT of sanding, and you can also use Plaster of Paris and sand it down to the shape. I am sure there are many other methods we did not consider.
We chose the cheapest method and are gambling that it will work. We chose to use PINK FOAM pieces (2" thick), cut close to the shape we want, and glue multiple pieces together to get the total thickness desired, and then sand it down to the desired shape, using light weight SPACKLING to fill area. The foam and spackling were very easy to sand to shape.
After the sanding to desired shape was complete, we coated the mold with multiple coats of EPOXY RISEN, which is foam friendly. The result was a very smooth surface which was fairly hard. We chose not to use glass cloth due to the joint problem and added sanding.
Pictured here are both the canopy and cowling plugs. The canopy plug was changed to solid wood for stability.
The next step was to look into the construction of a Vaccuum forming box. Looking at the Internet and talking to Fred Guilfoile resulted in a decision to make the box the size we did. The box was constructed with 1 X 4 material for the sides, and ¼" thick plywood for the bottom. The top is Pegboard material with holes already in the material. It is important that this box be airtight in all areas except the top, so each joint was glued and then the inside edge area was coated with Silicon Seal to make a good joint. The top Pegboard was screwed into place and then the silver tape was applied to the top and edges to complete the seal. Then we cut and applied a rubber sealer tape to the top edge of the box to make the vacuum seal complete. A hole was drilled into the end of the box and a cutoff piece of the Shop Vac extension hose was cut and glued into the hole. The Shop Vac is used in making a part as the vacuum source. To control the amount of Vacuum needed, a good idea is to install a hose faucet on the side of the box. This way, it can be left closed for maximum vacuum, or opened to the desired amount to reduce the vacuum on smaller projects. We have not done this as yet, as we are working with .040 materials.
The next step was to make a pair of frames to hold the clear plastic material. We used some old oak trim that was laying around in constructing two frames, which are held together with wing nuts. The two frames hold the plastic in place while it heats and then is transferred to the vacuum box for shaping. Since the frames and plastic have to be placed into an oven for heating, We put a couple of handles on the top frame for handling it to and from the oven.
We purchased a 4 X 8 foot sheet of .040 PETG material and cut pieces 16" X 19" for fitting onto the frame. Shown here is the material with the protective coating still in place, as it looks in the frame. The handles were added for ease of inserting the material, and taking out of the oven, HOT STUFF.
The picture below shows the material in the frame, sitting on the vacuum box.
The picture below shows Joe holding the frame over the canopy as it will look when it comes out of the oven. He will be holding onto the handles with gloves of course, and the Shop Vac will be plugged into the end of the box.
When heating in the oven, the material will sag quite a bit. When this happens, it is ready for removing and placing over the canopy plug. When it is pressed down on the edges of the vacuum box, the vacuum is turned on and VIOLA, a new canopy is formed in an instant. Instantly press around the edges of the mold for a sharp break in the material.
The following pictures are taken showing the making of the canopy with a wooden master, which is much more stable. We found that it takes about 55 Seconds to heat in the oven.
Pressing heated material onto the vacuum box.
Taking new canopy out of the frame and reloading (blue stuff) for another one.
Not all of them turn out super. This one is junk.
Really nice work. Next step is to build the plane.
Another consideration is to tackle the cowling, which is a different process. We will use regular glass cloth and resin to make a master mold out of the cowling plug, resulting in the following picture. From there, we can make multiple cowlings from the master easily.
Since our cowling plug is made of foam, covered with Epoxy Resin, we have decided to use Plaster of Paris for the first female mold, and then make a fiberglass mold out of the first cowling produced from the Plaster of Paris mold. This will make a lighter and stronger mold for multiple copies to be made from. A typical mold is shown here, which is our master for a Senior Kadet Cowling.
This is a lot of fun, and we encourage you all to try this during this nice rainy winter weather.