“Foam Core Wings” is meant to infer a complete airplane. The airplane needs not only foam core wings but also an airframe. In keeping with making very light and durable planes using relatively low tech methods, the airframes are constructed mostly of Liteply. Unnecessary material is removed from the components by using a router table to make them even lighter.
Templates are used to guide the router bits which results in a very light and durable fuselage. The templates are generally made of 1/4″, 1/2″ or 3/4″ MDF sheets. Hardwood such as oak is used to make some parts of the templates for router bit guides and sometimes spacers. 3/16″ dowels are used for alignment and holding pins to secure the materials that will be made into a part.
First make some router guides. 1/2″ x 1/2″ square oak sticks work well for the guides as long as they stay straight. The reason to use 1/2″ thick material is to allow for plenty of room for the router bit bearing to follow and set the width of the material to be left on the part. Thinner materials can be used but extra care must be taken to ensure the bearing runs along the guide. The oak guide sticks can be cut on a table saw.
Next a board wide and long enough to make the side profile of the fuselage is cut from 3/4″ MDF. The plan for the plane is used to draw the side profile onto the MDF. Add about 1/8″ at the firewall end to slide into a jig later. Cut the rough shape out with a band saw or jigsaw leaving extra outside to be routed off later. Use CA glue to attach router guide sticks exactly along the edges of the profile. Do not overdo the glue. All the guide sticks will be removed later.
Now decide where lightening holes can be made. BE CAREFUL not to remove material in areas that require extra strength. For example, fuselage former locations, the landing gear support area, firewall support areas, wing tube locations, strut attachments and the horizontal and vertical stabilizer attachments.
Triangle cutouts look fairly nice. Other shapes may also look nice. Decide how you want the part to look before laying out the areas to be removed. Symmetry is also something to consider. Again, BE CAREFUL to not remove too much but remove as much as reasonable to make the part light but strong.
Normally, the formers will be starting points for guide strip placement. The former should be in the center of the width of the guide strip. Cut a piece of guide strip to fit between the top and bottom edge guide strips and glue it in place. Make sure it is properly located so the former will be centered. Also be sure to make the strip fit close enough to be sure the router bit bearing cannot drop into the gap. This will ensure nice rounded corners.
Once all the guide strips are installed, drill a hole for the router bit through the MDF in the areas where material is to be removed. A 5/8″ or 3/4″ drill bit works well for this. To avoid tear out on the bottom, place a scrap under the MDF while drilling. I use a paddle bit for this and stop about 2/3’s of the way through. Then I turn the part over and drill where the point of the paddle bit made a small hole. This results in a fairly clean hole every time.
With all the holes drilled it is time to set up the router in the router table. The 1/2″ x 2″ flush trim bit is used to remove the unwanted material. IMPORTANT…adjust the bit bearing to the proper depth to allow it to ride along the guide strips. Be sure the router cutting edges are extended high enough to make a clean cut next to the oak strips. Place the router into the table.
SAFETY FIRST! Using the router table can be hazardous. It has a cutting bit spinning at high speed that will easily remove flesh and bone. You must be careful not to let that happen. Keep both hands on the part being routed with a firm grip and body parts away from the bit. That is why there is a foot switch on my router so I do not have to remove one hand to turn it off. I also turn the router off and wait for the bit to stop to move to the next area to be routed to avoid injury. Also, you may inadvertently nick the part while trying to move it with the router bit still spinning.
CAUTION! If a waste part is cut completely loose with the router bit, it can become a projectile or cause a jam that can unexpectedly and powerfully move the whole part being routed. Stop before reaching the point where the waste becomes a loose part. Turn the router off and wait for the bit to stop. Break out the waste piece. Then continue routing to clean up the area. There may be other hazards so do the routing at your own risk!
Routing of the template can now begin. A new bit spinning at the correct speed will cut through the material and not burn through it. If you are getting burned cuts, adjust the speed or if that does not work, get a sharp bit. Carefully follow each guide strip around the area to be removed. Break the piece out and clean up the edges before moving to the next area.
The outer strips were placed flush to the outside edge of the part outline. So now the outside edge can be flush routed for final shaping of the template. Again be careful of waste parts if any so they do not become projectiles.
A wood chisel and small hammer can be used to remove the oak guide strips from the template. There will be some tear out. Hopefully, it will not be a lot. The only thing this will affect is how the template looks unless it is excessive and would affect the bearing riding smoothly. This is partly why we use the 3/4″ MDF and try not to overdo the CA glue. Mike likes his looking nice so he runs the templates through a surface sander to smooth them out. I just sand the rough spots and leave it at that.
Now make some alignment pins out of the 3/16″ dowels. First test drill a scrap piece of MDF with a 3/16″ drill. Test fit the 3/16″ dowels to be sure they make a nice snug fit. If they are too loose the part will move around. My numbered drill set is where I had to go to find a perfect sized bit to drill the alignment pin holes. During testing, I found that some of the dowels fit differently in the same size hole. So, I made several size alignment pins. Some are very tight, some are tight and some are perfect fit. The very tight ones can be used later if the holes get too loose. Cut some 1″ pieces of the oak guide strips to make a head for the alignment pins. Drill a hole in the center of each head and glue a section of dowel into the holes. If you make several sizes, color code them for easy identification.
Finally, select locations to drill alignment holes into the template. These same holes will be drilled in the parts made by the template. So choose locations that are suitable and do not interfere with formers, wing tubes and etc.
Label your fuselage templates so when you have made several you can identify it for which plane. Make templates for all the parts needed for the airframes outside surfaces. Storage should be on a flat surface, or hanging to ensure they stay flat and straight.
Using the templates is “Super Easy”. Cut a piece of liteply of adequate size. If two parts are needed, both can be made at the same time.
Most liteply comes in 1′ x 4′ pieces or smaller. That was not long enough for the part need below. So using a fence on the router table and a 3/4″ plunge bit set to half the thickness of the liteply, a test lap joint was made. The two pieces were glued together with CA glue.
While this joint is not as strong as the rest of the liteply section, the area the joint is to be placed in will be part of a box where the horizontal and vertical stabilizer will be attached. Also, no lightening holes will be made in this area. No backer piece was use here but could be added if more strength is needed. So the lite ply piece was extended a few inches using this method.
Place the template over the liteply pieces. Use a hand drill and the same bit used for the alignment pin holes to drill holes in the liteply. Install an alignment pin after each hole is drilled to keep the part secure.
A few wraps of everything with blue painters tape will help keep the liteply firmly pressed to the template.
Drill holes for the router bit in each area to be routed. If you use a paddle bit drill partially through from the top side and turn the part over to drill through from the bottom side to avoid tear out.
BE SURE to properly align the height of the router bit bearing to ride on the router template. If you forget this step, you may damage the parts and templates. Use the same cautions when routing out the waste. Stop and remove the waste part before cutting it loose.
That is it! Be careful and have fun routing. As Mike likes to say, “This is ADDICTIVE”!