P-47 Thunderbolt

Ziroli 1/5 scale 92" span

 

 
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Tail wheel, and tail feathers:
   

I've decided to concentrate my next efforts on the tail section of the airplane. I feel that the most complex parts will be in the tail, simply because of the limited space I have to work in. I figure before gluing in any formers, or sub flooring, that I should first figure out how everything will fit, and function.
The first thing I've done so far is to cut out the tail wheel doors from the fiberglass fuse. But before I attach the doors, or attach the tail wheel, I still want to test fit the stab, rudder, pushrods, etc to see if anything will interfere.
Note: I will be jumping from one section to the other as I proceed through the tail section.

Since the fin is part of the fiberglass fuse, I only need to build up the rudder. The rudder is basically built like the elevators. A built up, sheeted surface and like the elevators, I had to draw out the scale hinge lines, then build them into the leading edge.

Before I completely build the rudder, I've test fit the stab, rudder post, and tail wheel to see where my push rods are all going to go. I want to have hidden elevator, and hidden rudder linkages to give it a more scale appearance, so my next steps will be to figure out how that will all function.

After looking at numerous ways to do the rudder linkage, I came up with the following: I decided to make a rudder rib out of some circuit board, sandwiched between balsa, then drilled and tapped to accept ball links.
   
I then took the rib, and glued it into the rudder structure along with the other ribs. I reinforced the area around the rib with some balsa to give it a little more strength and rigidity. I then took the rudder post and cut slits that will allow the ball link/pull pull wire to pass through, to the eventual servo. I also added a hinge in between the two ball links to add a little more scale realism, and further rigidity in that location.

After looking at the scale P-47, I noticed some sort of slit that is in the same location to where my linkage is. I believe that is where the scale linkage for the rudder control is, so it should work out well.
I also noticed that the rudder line is not completely straight, in that as you reach the point where the rudder hinge line, intersects with the stab, the hinge line moves further into the rudder.
  
I compensated for this, and cut the rudder post, in the same location. This should hopefully give my P-47 a more scale outline. There are other curves and features that I've noticed in the rudder, but will do them at a later stage when I have more of less figured out how the rest of the tail section will fall together.

Now that I have somewhat figured out the tail section, I want to switch my efforts to the tail wheel, and tail wheel door assembly. I want to first install the tail wheel, before I glue in the tail feathers. This way I will have as much room as possible to wok in. In the picture above you can see the Robart tail wheel assembly and former. That whole assembly will eventually be glued into the fuse, once I've calculated how the doors will function and operate.
  
I had already cut the doors out in earlier steps to make more room to maneuver in.  Now I wanted to better fit the doors, for their eventual installation. I used some 1/64 ply to create a door stop that was glued into the fuse. This way the doors would have something to rest on. I also didn't like the way the doors lined up, so I added a small lip of West System Epoxy, mixed with fairing filler to fill the edge of the door. This filler when dry, sands quite easily.
  
Since I wasn't sure of the geometry required to make the tail wheel doors function properly.  I decided to just temporarily tack glue things in place, to see how they work. I temporarily glued some offset door hinges, using some thin CA. Then I also temporarily glued in a piece of hardwood that I could hold the cylinder in place with. I drilled a few holes along the hardwood, and tried different arms on the door, to see which combination worked the best. The cylinders I'm using have a 3/4" throw and are made by Ultra Precision Valves. Eventually after a little fooling around, I got the doors to work rather nicely.

Since I am waiting on a few parts to finish off the tail wheel assembly, I decided to switch back to the stab, and  finish off the linkages.
Originally I wanted to have hidden linkages in the stab, but the more I looked at it, and thought about it, the more I convinced myself that having positive direct linkages in the stabs was the way to go. At least for me, in that I would feel more comfortable about it, and since the linkages will be underneath the stab, the likelihood of people noticing them will be very slim.
JR makes some very small relatively powerful servos that work well in my situation. They have a servo called a JR3421, which is roughly 1/2" thick X 1" X1.25" yet has 65oz of Torque at 4.8 volts. Plenty of power for each stab half, and will fit nicely in my stabs.
  
I decided to make servo bays at the trailing edge of the stab. I cut the stab skin with an exacto, then made a hatch cover out of some 1/8 light ply. Once I had cut out the skin, I needed to make some ribs that will support the edges of the already cut skin.
  
It may be hard to see, but where I made the cuts, I had to use a little scrap balsa to make some supports that will finish off the rest of the servo bay.  Once I had a nice bay, I then used some hardwood tri stock to make a ledge that will eventually be used to support the plywood plate.

My next step is to finish off the plate. Again I used some hardwood to make mounts that will hold the servo in place. I then cut a slit in the plate to allow the servo arm to move freely.  I also drilled some holes that will be used to hold the plate in place.

Now that the plates were complete, I placed them back in their positions to see how they fit. I purposely recessed the hatches  by about 1/16th in the bay.
  
The reasoning for recessing the hatches, is because I wanted to add a piece of balsa on top. I do this because plywood is very flat, and hard to shape, yet balsa will shape quite easily. So once I glue the balsa on, I can put them back in the stab, and finish sanding the hatches to perfectly match the contour of the stabs. I then glassed the hatches to give them some hardness..

I finally received some hardware, I had been waiting on, and finished off the linkages for the stabs. I used Nelson Hobby, RCL linkages, that utilize a 6-40 screw as a horn. They worked out rather nicely, and are very positive.

Since I'm waiting on some products to come in the mail, I have to put finishing off the stabs till my supplies come in. I have a specific order of how I would like things to go, and not having certain items, sort of puts a curve in that schedule. So I've decided to jump around and do some other small jobs while I wait.
     
Since I'm using a pull pull system for the rudder, and a pull pull system for the tail wheel, I had to make some sort of servo tray for those servos. I decided to make a tray that has two levels. This way, the wires will not interfere with each other. I made the tray out of light ply, then reinforced the edges with some carbon fiber tube to give the tray some rigidity. The tray will sit right behind the wing saddle, and directly in line with both the tail wheel, and rudder linkage.
         
Well after checking my mail every night, I finally received a delivery, and can now finish off the tail wheel assembly. I had been waiting on some BVM off set hinges, and now they had finally arrived. Since I had already calculated how the tail wheel doors would operate, I just basically had to copy them, and make a more permanent installation. As I had the proper geometry from my trial fit, I made some light ply blocks, to hold the cylinders. I then glued them into the fuse at the right angles so they would actuate the doors. In the process, I also routed the air tubing for later on. Since I still want to be able to take the doors off and on for finishing, I used some BVM flush mounted panel screws to hold the doors on. This way I can remove them later on if needed. I also added a little scale detail to the inner parts of the doors. I just figured it would be easier now.

Construction Page 1

Construction Page 2

Construction Page 3

Construction Page 4

 

 

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Last Updated 03/01/2007