Tailwheel assemblies are probably the most overlooked part of a model, especially scale models. Although many hours may go into construction of a model, a crude plastic tail wheel bracket is typically used to mount the tailwheel. Usually, this attachment method results in damaging stresses being placed on the rudder during the inevitable hard landing. However, for little additional effort, a scale-like leaf spring tailwheel assembly can be constructed out of readily available materials in a very short time.
Although the materials and construction shown here are aimed towards a .40 size model, they can easily be scaled to any RC model. A little ingenuity goes a long way in adapting this design, so feel free to experiment along the way.
Construction begins with proper selection of building materials. For a typical .40 size model, all the materials can be readily found off-the-shelf in local hardware and hobby stores. For example, the leaf springs can be made from a single tang of a leaf rake. This material is stiff enough to make a good spring yet soft enough to be drilled. The eyelets and washers can come from excess servo parts. The aluminum, brass, and wire may be purchased from a hobby or hardware store, but more often can be scavenged from materials left over from other building projects. The tiller springs can be made from old ball point pens. The descriptive illustration shown comes from Howard Sullivan and is briefly summarized in the following paragraph:
The tailwheel caster assembly is bent to shape based on the size of the tailweel being used. In this case, 3/32" (2.4 mm) music wire is used with a 1" (2.5 cm) tailwheel. The wire is bent to clear the tailwheel with a minimum of clearance. It is affixed to the leaf springs by eyelets and washers, the latter of which are soldered in place. The upper stem of the caster may be oversized initially and then cut off after final soldering.
The length of the main (longest) leaf spring must be determined first. A cardboard template can be cut 1/4'' x 6'' (6 mm x 15 cm) and held in place to determine the location of the tailwheel. The main spring is cut with about 1/2'' (13 mm) extra which will be removed after final adjustments are made. The curve can be bent into the main spring with the end bent so that it is approximately parallel with the ground when installed. The other springs are cut progressively shorter, and their lengths are not critical.
After all of the springs are bent to mating contours, they are clamped together and two (2) 1/16'' (1.5 mm) pilot holes are drilled for mounting holes. The springs can be separated and each hole drilled out with a 3/32'' (2.4 mm) drill. The holes should be slightly larger than the screws that are to be used for mounting. A 3/32'' hole (2.4 mm) hole is drilled in the main spring for the caster assembly.
The tailwheel should be assembled to the model and test fitted before the final assembly. The caster assembly is placed through the hole in the main spring. A washer is placed on the stem of the caster onto the top of the main spring, then an eyelet then the tiller. The caster can be turned upside down with the stem in a vise and the tiller on the top of the vise. Finally, the tiller, the eyelet, and the washer are soldered by allowing the solder to wick between the parts. When this is complete, the assembly may be painted to match the model.
The tiller springs can be stretched to achieve the right amount of tension. The tailwheel is installed on the caster and a pushnut is pressed on. The excess length of the axle and the stem can be trimmed off. The flat of the main spring should be bent so that it is parallel with the ground and the excess trimmed off.
This tailwheel assembly looks good and it is functional. The weight that is added by these modifications is surprisingly low. One can even save some weight by making one's own tailwheels, using liteply for the wheel center, and a thin layer of rubber scavenged from old RC wheels or even old bicycle tires. A 3/4'' tailwheel made in this fashion weighs only a few grams, or a fraction of an ounce. The assembly is functionally far superior to plastic tail wheel assemblies and will outlast almost anything that is commercially available. Try it!