Expert RC scale designer, builder and pilot Sal Calvagna is known for his love of the hobby especially when it comes warbirds. A member of the Long Island Skyhawks RC club, Sal is a regular at most warbird events and in particular, you can count on Sal showing up at any WW1 jamoboree, gaggle or meet. One of his favorite planes is the WW1 Fokker Triplane and he has built several from kits and plans. Most have ridged landing gear setups that are soldered up from bent music wire. But, Sal wanted something better, so he designed a simple way to add shock absorbing axles to help smooth landings and make his vintage models look and react in a more scale like way. Here’s how he did it!
I have always admired early aircraft, especially those used during the war to end all wars, more commonly known as World War One. The evolution of aircraft from 1914 to 1918 is simply amazing. Balsa USA of Marinette, Wisconsin is one of the well known manufacturers of WWI kits in an array of sizes. Their kits are well designed, fairly priced and always result in good flying models. I have built many of their offerings and enjoyed hours of drilling holes in the sky. Since my landings can be less than perfect at times, I wanted to design a way to increase the shock absorbing capability of the landing gear. Some time ago I came up with a design that not only reduces stress on the airframe, but can be fabricated without having to solder any of the parts together. Here’s what I did for the ¼ scale Fokker Dr.1 Triplane:
Since a picture is worth a thousand words, I will describe the landing gear build by using a sequence of photos.
First the materialsyou will need are:
- 3/8 inch aircraft grade plywood.
- 1/8 lite plywood.
- ¼, 1/8 and 3/32 balsa sheets.
- ¼ and 1/16 inch music wire.
- CA and epoxy glue.
The first three parts needed are the most difficult pieces to make in the entire construction process. So once you get through this step, the remaining build is pretty straight forward. These are the three knuckles or plywood supports that are 1 3/16 inch tall, 1 3/8 inch wide and ¾ inch thick. In order to make the three supports, I started with a sheet of 3/8 inch aircraft grade plywood and glued two pieces together to make a ¾ inch thick block. Using a band saw, I cut the three identical pieces 1 3/16 inch high and 1 38 inch wide. I tack glued the three blocks on top of each other and used my drill press to drill a ¼ inch hole in the bottom center of all three blocks, about 1/8 inch from the lower edge (photo 1). Refer to the photos and you’ll have no troubles with the descriptions.
I then separated the top ¾ inch block and continued to drill out the remaining two blocks to form a slot that is just shy of 1 inch (photo 2). You will need to use a slightly larger drill size for the slots or use whatever tool you like to enlarge the ¼ inch slots so that the ¼ inch axle freely moves within the slot.
Cut two lite ply pieces that are 1 3/16 inches by 15 inches. These will form the sides of the landing gear box. Mark the center and 1 inch inboard on each end (photo 3).
Glue the blocks onto the lite ply as pictured (photo 4).
Make sure the center knuckle is lined up with the slots properly. Glue on the the second lite ply piece, refer to (photos 5 and 6).
Measure across the top of the gear box (photo 7) to get the correct width for the top cover. Make sure you glue the cover on the top side. The top side is the furthest distance from the axle (photos 7 and 8).
Photo 8 also shows the completed landing gear box. Mark the location of the outer support blocks (knuckles), (Photo 9). This is the finished landing gear support structure, everything else that is added just goes along for the ride!
(Photos 10 and 11) show the 1/8 inch balsa ribs that will form the sub wing shape. You will need to make these slightly higher than the box structure (photo 11). Make 7 balsa ribs around 6 inches in length.
Trial fit (photos 12 and 13), do not glue the ribs onto the box structure at this time.
Now it’s time to install the ¼ inch music wire axle. You can leave the axle long for now. Mark the center of the axle and roughen up with some sand paper. The axle should be a tight fit in the center block. Use a piece of hard wood to tap the axle into position. Use your favorite epoxy to glue the center of the axle in place, refer to (photo 15).
Okay, take break from building, it’s time for a little explanation. The operation of this shock absorbing landing gear depends on the flexibility or memory of the music wire. I have found that in the case of the ¼ scale Fokker Dr.1 or the ¼ scale Fokker D-VII, the ¼ inch music wire provides just about the right amount of spring or flex without adding any bungee material for additional support. However, if you would like to use a smaller diameter music wire axle, or you are building a larger model, then the 1/16 inch pins installed into both outer gear blocks (knuckles) are used to wrap the bungee material around the axle for additional support, see (photo 14).
Now it’s time to make and install the outer lite ply ribs and the balsa ribs, see (photos 16 and 17). The outer lite ply ribs have a slot for the axle and are laminated to the outer balsa ribs.
Using the existing landing gear wire from the kit, use a dremel to cut off the ends and grind to a point as in (photos 18, 19 and 20). Rough up the ends as they will be epoxied into the gear box in a later step.
(Photos 21 and 22) show the position where the landing wire will be installed. You may have to bend the existing angles on the gear depending on how wide you decided to make the whole assembly.
The next step is to install the bottom 3/32 balsa sheeting, remember to not cover the area where the bungees are accessed. See (photos 23, 24 and 25).
While manufacturing the knuckles or aircraft grade ply supports was the most difficult step, this next step is probably the most important, the proper installation and alignment of the landing gear. Mount the gear wire onto the fuselage as shown in the kit instructions. Support the fuselage, make sure that it is level to your work surface.
I used a small level which sat on the upper longeron (Photos 26 and 27). Using a slightly larger diameter drill bit than the gear wire, drill out the four holes at similar approximate angles where the gear wire will enter the landing gear structure. Since you are using a larger diameter bit you do not have drill the exact angle where the wire enters the gear structure.t Like they say, “close enough for government work” will be just fine. The epoxy used to glue in the gear wire will fill in any voids. Drill the holes approximately 3/8 inch deep, but please stay away from the center of the block where the slot is located. You must not penetrate the slots in the gear blocks, see (photo 26). You can accomplish this by wrapping some masking tape around the bit as a guide, 3/8 of an inch from the tip.
Now you can insert the landing gear wire into the four holes in the gear structure. Use a straight edge to make sure the gear is aligned properly. You may have to adjust the length of the gear wire to accomplish this, see (photo 28). Once you’re happy with the fit and alignment, epoxy in the landing gear wire and let set, (photo 29).
When dry, you can remove the gear assembly and sheet the upper surface, install the leading edge and sand to shape, (photos 30 and 31).
You can refer to the kit instructions to complete the gear by encapsulating the gear wire and mounting your wheels.
In closing, this gear can be adapted to any size model that has a sub wing. You just need to adjust the dimensions of the material used. Happy landings!