[grosbeak]

When I converted my Hobbistar to a tail dragger I tried a couple of methods of steering the tail wheel via the rudder. Trouble is, the bottom of the rudder is a LONG way above the tail wheel and both methods failed rather quickly.

I have no desire for a castering tail wheel; the rudder is small and I think I would have trouble getting the plane to turn on the ground. What I would like is to drive the tail wheel with a push rod connected to the rudder servo. However, I have yet to find a tail wheel assembly that's well suited for this approach.

Here's what was on the plane before:



Any suggestions would be appreciated.

[grosbeak]

It's been a productive if sleepless night and I think I have answered my own question.

While browsing through the Great Hobbies website I came across this Du-Bro Steering Arm.



In the description: "The Du-Bro Steering Arm assembly includes a 1-1/4" (31.7 mm) steering arm with brass bushing and socket head set screw. Fits a 5/32" (mm) nose gear wire."

I'd noticed that the wire of my current gear is soldered onto the post. First thing I did was measure the wire thickness. Whaddaya know - 5/32". I put the post into a set of helping hands, brought out my soldering station and turned it up to eleven (aka 900º F).




Applying the tip of the iron to the post for less than a minute allowed me to separate it from the assembly.






Plenty of wire above the block for the steering arm to clamp to.

[grosbeak]

Turns out I actually have a leftover steering arm very much like the Du-Bro model, but there must have been some middle-of-the-night confusion because the wire on the tailwheel is 5/64", not 5/32". I decided to go with a different product altogether:



Here's how it looks partly assembled.




Notice the horn on top - it's in just the right position for a push rod to exit the fuselage. I'm adding a little ply to the bottom of the fuse for extra strength.

[grosbeak]

Here's the plate with the tail wheel assembly shown in place. Note the rudder push rod exit below my finger - there another on the other side of the fuselage that's perfectly positioned for the tail wheel rod.

[michaely]

Originally Posted by grosbeak

Here's the plate with the tail wheel assembly shown in place. Note the rudder push rod exit below my finger - there another on the other side of the fuselage that's perfectly positioned for the tail wheel rod.

John,

In this picture, your setup appears to have eliminated the coil in the music wire axle/end strut and if that flat metal strut is aluminum you may be sacrificing any vertical shock absorbing capacity....

Probably not a big deal but there are some flat metal tail wheel struts made from tempered spring steel that will provide this vertical shock absorbing. Ohio Superstar comes to mine.

Years ago there was a "how to do" article/paragraph w/ picture in one of the magazines on using 1/2" wide flat spring steel baling (used to secure containers, etc.), arranged in three layers of decreasing length, a la truck leaf springs, to make such tail wheel assembly with shock absorbing capacity.

good luck,

[grosbeak]

Originally Posted by michaely

John,

In this picture, your setup appears to have eliminated the coil in the music wire axle/end strut and if that flat metal strut is aluminum you may be sacrificing any vertical shock absorbing capacity....

Probably not a big deal but there are some flat metal tail wheel struts made from tempered spring steel that will provide this vertical shock absorbing. Ohio Superstar comes to mine.

Years ago there was a "how to do" article/paragraph w/ picture in one of the magazines on using 1/2" wide flat spring steel baling (used to secure containers, etc.), arranged in three layers of decreasing length, a la truck leaf springs, to make such tail wheel assembly with shock absorbing capacity.

good luck,

I'm pretty comfortable with this plane and I think there'll be enough spring in the tail wheel assembly, but I do appreciate the input.

[grosbeak]

Here's the tail wheel push rod tube through the exit on the starboard side of the tail.




Here's the control over-ride servo saver on the servo horn.




And here's a view of the push rod support plate, glued and curing.




The push rod is in perfect position to connect to the tail wheel control horn.

[waynepinke]

The "servo saver" springs at the servo is a great idea. I think your tail wheel bracket might have enough stiffness to also prevent too much shock to the servo plus the tail wheel wire on the wheel will still have a bit of spring/flex to help limit shock to the servo.
The only way to see how it works is to try it out. It should be OK.

[grosbeak]

Originally Posted by waynepinke

The "servo saver" springs at the servo is a great idea. I think your tail wheel bracket might have enough stiffness to also prevent too much shock to the servo plus the tail wheel wire on the wheel will still have a bit of spring/flex to help limit shock to the servo.
The only way to see how it works is to try it out. It should be OK.

Hey Wayne, that servo saver was not original equipment when the plane was a trike but at the advice of an instructor I added it soon after I started training. Lots of hard landings - I'm sure it helped preserve the servo!

For (slight) additional cushioning I've put small O-rings on the wire above and below the post... and I'm using Sullivan Gold-N-Rod which will also absorb a little. I think it will be fine bus as you say, the only way to see how it works is to try it out!

[grosbeak]

This morning I cut the push rod tube shorter at the rear exit and applied some medium CA to the at both ends to help hold it in place. I was planning to use Gorilla glue but it's not safe for some plastics and I don't know the tube is made of. In any case the fit in the forward tube is very tight and I don't expect it will shift.






I added a third hole to the tail wheel bracket and mounted it.




Hardening the threads with thin CA.