Installing the tail gear

June 18, 2006

Coming up with a vertical axle assembly

The width of the JDM FW190 tail section is a little narrower than most, especially inside the fuse as the foam walls take up most of the space. This makes installing the static/fixed Shindin scale tail gear a little tricky and would make installing the retractable version virtually impossible in this specific kit.

As a matter of fact, the fork of the tail gear is actually wider than the fuselage exterior by a fair amount, so getting it to retract up inside would not be possible. This combined with me wanting to keep the installation very simple and lightweight drove me to choose the static/fixed option.

I began my making the "axle" for the vertical column of the gear from a standard metal screw. I filed a flat spot on one side for the two set screws to seat onto. I painted the bolt so that I could easily see the flat spot once this was buried up inside the fuselage.

I then took a large hardwood dowel and drilled out the center, sliding the screw down inside with plenty of free movement. I also added a nlyon washer on the top which was made from a servo wheel. I filed two large flat spots on either side of the wooden dowel.

The photo at left shows how the whole assembly comes together and the set screws are drawn down to hold everything together.

Installing the assembly

Next I used a Forstner bit to drill a recession down into the styrofoam inside the fuselage tail. Half of the wooden dowel will seat down into this recession. I also drilled a small hole in the top of the fuse directly above this area. This allows me to access it from the top and hold the screw head in position when gluing it together.

Next I lowered the assembly down into the recession (without the set screws in place) and epoxied the wooden dowel solidly into the fuse. The screw wants to fall down into the plane when you do this, but I hold it in place via the small access hole in the top side. The dowel was positioned such that the flat spots face the front and back of the plane.

Once the epoxy sets up, I glued two 1/4" aircraft ply formers up against the two flat spots on the large wooden dowel. This supports the dowel and keeps it from rotating. When that dried, I then added two large but light balsa blocks in, butting them up against the ply formers. These were glued in with Gorilla Glue.

The finished assembly is extremely strong but relatively light weight. More importantly, it was possible to pull off in the extremely tight constraints of the fuselage tail walls.

Finishing up the install

Once all was good and dry, I added an additional cover plate made from aircraft ply. This piece not only covers the hole up, but provides another "bushing" of sorts to support the vertical tail gear column. This will help eliminate excessive torsional stress. I then sealed the open remaining styrofoam by adding a quick fillet of epoxy and microballoons. I'll clean this area up a little more when I glass and detail the plane.

To access the set screws that hold the gear into the plane, I made an access hole that will get a hinged hatch door after glassing. The only thing left to do here now is go ahead and plug the small hole in the top of the fuse with a dowel rod.

The pics here show how the finished assembly is positioned. Side to side it is perfectly straight up and down. Front to rear there is a slight angle rearward as was so in the full scale plane. The vertical position is such that it would be in the fully extended position, allowing the gear clearance for full rotation without hitting the fuselage.

What I failed to mention earlier was that before installing anything, I of course had to open a large hole in the sheeting and stryrofoam to begin working the gear down into. When opening the hole, you can see that the hole extends up into the sides of the plan in a way that creates somewhat of a "crescent shaped" cutout in the belly of the tail area. This cutout gives you additional clearance for the gear without having to have the gear extend any further out of the plane than necessary.

Steering arm and shaping

Next I pulled the gear back out, and began making some sort of steering arm mechanism. I drilled and tapped a hole in the side of the vertical gear column to accept a 6-32 bolt. I then screwed a steel screw into the hole, cut the end off and added a nylon horn. This will later allow me to control the gear rotation via a pushrod from the rudder, connected to this steering arm with clevises or ball links.

The Shindin tail gear are very close to the shape of the full scale gear, and are of excellent quality. However, the corners and edges are a little sharp in comparison to the full scale so I decided to go ahead and round them down to look just a little more like the gear on the real 190. It's a subtle change but turned out very nicely.

That's pretty much it for now. I have a set of 2-1/4" Dubro Lite Treaded main wheels on order, one of which will become my tail wheel if it works out as I hope. The shape of the wheel and hub aren't too far off and the size should fit well.

Actually, the tail wheel should be just over 2-1/2" to be exact 1/5 scale, but all wheels I found at that size were too wide to fit the forks. Unless of course I decided to go with very expensive custom machined wheel, but that's not going to happen. Besides, 2-1/2" just seems huge for an RC tail wheel, and 2-1/4" is a little more tolerable for me in terms of size and weight.

"building the wing fairing"