Tailwheel issues

When I got the  Cub project the tailwheel was missing, so I rebuilt an old 1 1/4 inch Maule SFSA unit I had in stock. It was in pretty good shape but had a little wear on the main bushing, however I did not have the tooling to replace it. Lately I had been experiencing an occasional tailwheel shimmy on landing. Nothing you could not stop with a little forward pressure on the stick but annoying just the same. I thought this was due to the wear in the tailwheel so I ordered a new bushing from Aircraft Spruce and made the tools to do the job correctly. First I had to make a tool to remove the old bushing, my friends at Mid Atlantic Aviation let me use their lathe and I made this tool from some 4130 scrap.

The small end is 0.005 less than the ID of the bushing and the large end is 0.005 less than the ID of the pivot forging. Here is a shot of the new bushing.

Here is the old bushing still installed.

First you have to remove the two screws that hold the unlocking cam and the grease fitting. These extend into the bushing.

Then using the tool in a hydraulic press you can remove the worn bushing.

After cleaning up the forging , I used the tool in the press to install the new bushing.

After installing the bushing I carefully drilled through the threaded holes in the forging and through the new bushing. I then tapped the threads into the bushing. Since installing the bushing slightly reduces it's inside diameter, I reamed the ID to 0.875.

I cleaned and inspected all the other parts and reassembled the tailwheel. The old tire I had been using was worn funny so I installed a new tire.

Here is the completed tailwheel installed on the airplane, notice anything odd?

Notice the pivot axis of the tailwheel. It is actually tilted a little forward when it should be vertical or slightly aft ! This was a real boner on my part because I had installed a 1/8 inch rubber pad between the tailwheel spring and the airplane tail post , this changed the geometry of the spring and changed the pivot axis.

 I removed the pad and no more shimmy. While the tailwheel rebuild was very educational, the wear was probably not the cause of the problem after all. Here it is with the pad removed. I have decided to reinstall the pad and add a couple washers at the front attach bolt to maintain the correct angle. I think the pad does cushion the airframe a little from the tailwheel loads. Here it is all cleaned up , ready for a summer of flying.

 

Summer breather

I finally finished the modifications to the engine breather tube today. I had ordered a Baileigh tubing bender a while back and the UPS man left the 62 lb box on my front porch last week. I was a little disappointed to find it was made in China, but for $200 I guess it could not be made here. It is really made for steel tubing and conduit so I had to polish the 5/8 die before I could use them. Here is a couple shots of the tool.

It's a bench mounted device made of Chinese steel, the adjustable wheel dies are machined from steel and are acceptable, however the cast iron fixed dies were rough and I had to dress it down with my 5/8 carbide burr. Here you can see the assortment of dies.

Here is another view of the tool.

I ordered this tool because when I tried to bend the 5/8 x 0.035 tubing for the breather tube it came out really ugly with the cheap Harbor Freight bender I had. Here is a shot of the tube I replaced notice the tooling marks and kinked area.

Here are some trial bends using the new bender. One I made with the tube filled with sand and the other two were with the tube empty. When you measure the bend diameters there is only about 0.004 difference.

It does a pretty nice job for a relatively cheap tool.
All this effort was to replace the engine breather pipe. On the Cub the oil temp never gets above about 140 degrees F in the winter and you get a lot of oily water mix coming from the breather . My original installation had this dump out at the back of the cowl and the slop ended up all over the landing gear and bungee covers. My revised summer breather would extend aft along the bottom of the boot cowl and dump just aft of the landing gear. Here is a shot of a trial fitting.

Yes, I will buy some better looking hose clamps after a few test flights. I had resisted installing this because of the way it would look but you hardly notice it with the cowling installed.

I may paint it white after I'm sure it works OK. I flew it to Wakefield and back today and it seemed to work fine. The rest of the day was spent machining this tool. More on that tomorrow.

BC wanted to say Hi to his Mom.

Electrical System

I had resisted installing an electrical system in the Cub, operating with just a Icom handheld and a Garmin GPS III . After my cross country to North Carolina last month it was clear this would not be acceptable for the long trip to Oshkosh.  I found a really nice 3.4 AH sealed lead acid battery at Aircraft Spruce and I built a battery rack for it that fits just behind the seat. If this works out , I will use the same mount when I install the larger battery for the starter. I formed the rack from 0.032 aluminum with 0.750 flanged edges. I installed some angle for the forward and aft stops, and made a hinged strap from 0.032 for a hold down clamp. To make it easy to install the clamps they are installed first using AN 315 nuts then the rack is installed with AN 365 nuts. This saves a lot of fighting with the Adel clamps. Here are the clamps installed.

 
This is just behind the seat, you can see the elevator bell crank on the right. Here is a shot of the rack installed.

 
Here you can see the details of the rack. It's a bent up aluminum channel with fore and aft stops riveted on. The strap is hinged at the left and it's secured with a single AN 525 screw at the right. There is a nut plate riveted underneath. The battery weighs 3 lbs and the rack less than 1 lb. I think this same rack could be scaled up just a little to fit the PC 680 battery if I install the starter.
 I was tired of having the radio beside the seat so I made an angled mount up by the mag switch. Here is a picture of it.

This Icom A6 radio has no good mounting provisions, so I had to make my own bracket. The angle bracket I formed from 0.025 and it angles the radio so the screen can be seen from the back seat. The bracket attached to the radio is from 0.020 aluminum. It screws to the back of the radio where the Icom belt clip is installed. It clips over the top of the airframe angle bracket and then is held in place with a strip of 2 inch wide Velcro.  So far this works OK but it's a little hard to read the screen.
I made this bracket to hold the GPS.

It's just a formed channel held on each end by an Adel clamp. It is up on the cabin roof  just below the sky light. I have to look out the top of my glasses to see it . The Cub is so slow I usually just use it to get a compass heading then turn it off for 10-15 minutes.  You can see the red Icom push to talk switch, I have removed that and have it on the stick now.
The real problem is that every device runs at a different voltage, the radio at 11 volts, the GPS will take 12 volts and the headset needs 9 volts. I ended up using this 3 unit cigarette lighter plug I bought at Walmart.

It has nice little on off switches and had really nice LED lights but they sucked about 12 ma each so I had to disable them. Just behind the ELT you can see the voltage converter / filter for the headset. It drops the voltage to 9 volts for the noise cancelling headset. I know this looks a little cheesy but it was the easiest way to get a switch and fuse for each circuit. Here are some shots of the wiring, it looks like a mess but it's out of the way and is much better than what I had before.

I did some testing and the radio draws about 238 ma when receiving and 970 ma when transmitting. The radio still has it's internal Li ion battery as a back up and recharges from the lead acid cell at about 175 ma with the radio off. The GPS draws about 70 ma and the noise cancelling headset draws 11 ma. With everything on I should be good for about 6 hours, much longer with the radio off.
I'm still working on the antenna installation, more on the later.