SeamusG

I'm in the process of converting a built trainer with tricycle gear to a tail dragger. My question has to do with controlling the tail wheel. As you can see from the plans the rudder is not exposed at the bottom of the fuse. I'm going to use the Dubro tail gear pictured with a 1" wheel. My plan (until I change it) is to bend the wire above the block so that it exits 90 degrees to the side - perpendicular to the fuse. As you can see in the picture the wire has 2 collars and a white "horn" between them. The horn is a candidate for a control rod terminus using a clevis.

My $64 question is "How would you control the tail wheel?"

Btw, this plane is already a bit on the "big butt" side so weight in the back pocket is an issue.

TIA

airbusdrvr

http://www3.towerhobbies.com/cgi-bin...?&I=LXHDJ3&P=7 and http://www3.towerhobbies.com/cgi-bin...&I=LXD671&P=ML . If you have room to use a two legged(180 degrees apart) control arm on your rudder servo like the one on the right side of that servo parts T, you could then install a pull-pull tailwheel control.

SeamusG

I've used a pull-pull from the rudder servo on a Kadet Senior ARF tail dragger retrofit. I've also used a mini servo on a Senior kit with a really short pull-pull.

You included a link to a Dubro servo arm product. How would you attach a servo arm to a tail gear mechanism?

I have a Great Planes device (same as used in the Senior ARFw/ pull pull). Might be that the overall weight of the GP gear & pull-pull would be less than other options.

SeamusG

Just thinking - how about a dual rudder push-rod system? I've done a dual elevator push-rod system before. In this case there would be a primary push-rod to the rudder and an ancillary push-rod to the tail wheel. I have a Dave Brown glass push rod that includes single and double ends - single to the servo, one of the double wires to the flexible tube / rod assembly for the rudder and the other double wire to a tail wheel push rod.

Your thoughts?

blvdbuzzard

If the hinges are the thin CA type, cut the rudder off, make a new piece of wire long enough to reach through the fuse to where the rudder control arm mounts, drill a hole in the rudder for the longer wire? You can make the wire as long or short as you want. A little bending of a new wire and you are all set. The weight of the plane will be on the mount and the wheel collar you put below the mount, not the rudder.


Dru.

ARUP

Lots of ways- here's one!

SeamusG

Hey ARUP - interesting.  What did ya use to connect the various metal parts?

Insanemoondoggie

Heres how I'mgoing to do mine. I think this is what Dru was talking about. Sorry for the poor illustration ,my first attempt at paint.

SeamusG

Hey insane - thx for the graphix.

I understand the approach and would have used it if I had decided to add the tail wheel during the initial build.

I'm not sure what the hinge material is. Why? Well, I read RCKen's build thread for his TL-40. He used a covering technique that includes a first step of covering the hinge line. I'm not keen on rehinging & recovering the fin/rudder assembly. Actually, the hinges are probably CA hinges as they are not visible through the hinge line covering. My normal hinges are Dubro standard pinned hinges - they would show.

blvdbuzzard

That is about what I was talking about. I would run the rod straight down to the tail wheel. Move the tail wheel mount forward so it is a lined up with the rudder. You will have a little bit of fuse behind the wheel, but that is not a problem. You can also bend the tail wheel wire so the wheel is farther back.


Dru.

SeamusG

Here's a pic of the tail gear on my in-progress Bridi Killer Chao 60. I would use this approach for the LT-40 during the initial build like you suggest.

The nylon parts are Dubro and Great Planes pieces. They are inserted into the fin post and provide for a very secure installation - keeps the tension off of the rudder.

ARUP

Silver solder and liquid flux heated with torch is used to hold everything together. Ideally the main tailwheel strut could be let into the fuse which would have a block to receive it but I forgot to build a mounting block into mine, thus the brackets. I drilled for a dowell and then glued dowell into fuse. Then I drilled dowell to receive bolts to hold tailwheel brackets. Crush proof and strong. If the main tailwheel strut is a straight run it is very strong and is difficult to get torqued and broken. I do that for my CL ships- strong, simple and lightweight! The horns on the rudder are 2 wires soldered together, bent at 90 degree angle (which is let into the rudder). One end was curved- just to look 'purty' and the ends are brass tubing with a hole drilled to take linkage. Springs are highly engineered for ball point pens but they work for my model, LOL. The linkages spring together so ball point pen spring can be slipped over them. The little 'bend ups' at their ends capture the ball point pen springs. Flat brass used to make other parts. A bench vise is handy to make these parts. 'Gap' the vise and hammer the wire into the brass sheet that is lain across the vise normal to its gap, drill holes then separate from stock. Hope this helps.

SeamusG

Ok Dru & Insane - here's my attempt at "the picture" my way (using my best old-blue-eyes swagger) ...

If you use Robart hinge points things get a bit simplier as they don't take up so much terrain.

ARUP- thanks guy. There are soooo many skills that are useful in this darn hobby!!!!

Btw Insane - move the elevator horn off to one side 'cause there's gonna be some interferance between the tail wheel wire and the elevator control rod. Just sayin' ...

Insanemoondoggie

Your paint skills are better than mine for sure. The reason I'm doing mine the way I am , is to take all the load off the rudder. I use mine for training and am afraid a few hard bumps might tranfer the shock to the rudder. Kind of a pull-pull set up with springs between the tail wheel and rudder rod. If it was just me flying, I could go with your design, less hardware and weight.

SeamusG

Insane - my LT-40 is also a club trainer. Part of our "approach" is that the students only fly around with club planes. They need to kick in a bit of skin before solo'ing by providing their own plane for the take offs and landings. That's not to say that no one else will land mine.

Now that you bring the "stress issue" I'm going to take a re-look at the Chao's approach. Hey, it's a kit that hasn't been covered yet. And I have a saw, a big saw, a really really big saw ...

Oh, btw - the collar under the tail gear is secured to the tail "wire" and will transmit the vertical load to the tail gear rather than the rudder.

Oh, btw btw (that's old school) pps - I didn't use Paint. I have Microsoft's Visio - more an engineering tool. Ya outa see MinnFlyer (Mike B) - he's got some serious Adobe Photoshop skills.

SeamusG

I think (subject to change) that I'm going a bit old school on the push rod arrangement for the elevator, rudder and tail wheel. SIG Kadet Senior used 11/32" (9 mm) balsa dowel push rods with 2-56 wire ends secured with heat shrink tubing. This will work for the elevator (the Senior shares the same "open fuse rear with centered elevator horn" as the LT-40). For the rudder / tail wheel I'm going to use a wood dowel / 2-56 wires as the primary control for the rudder with a mid-run flexible "control rod in tube" with 2-56 wire to control the tail wheel wire. The flexible control rod will be either a Sullivan yellow / blue rod or CF / blue rod. The joints between the wood and the wire will either be "whipped" with kevlar fishing line and CA or heat shrink tubing.

The tail wheel will be the Dubro "simple" support with the wire bent 90 degrees to the side with a horn attached.

Time to find a 1" tail wheel.

Cheers,

airbusdrvr

It is preferable to have some dampening in the linkage between your rudder servo and the tailwheel. This precludes jolts and impacts to the tailwheel from being transmitted directly to the rudder servo. That is where a pull pull system with springs at the tailwheel end will prevent this from happening. You asked above how I would attach the servo arm I referenced. That arm is for your servo. The tailwheel kit comes with the necessary horn, wire, springs, etc.

SeamusG

Gotcha! Sometimes the brain just ain't in gear ... [8D]

On planes with an exposed rudder I use a lengh of fuel line screwed to the bottom of the rudder. Depending upon how taut you make it more or less energy is transmitted to the servo.

I added a pic of my Kadet Senior tail wheel.

blvdbuzzard

That is what I had in my head. One thing with a wire that long, it will act as a stress relief for the shock to the tail wheel. It will bend and twist a little and not transfer it all to the rudder.

I think the beef up of the ply would is good too. A lite weight foam wheel and you are all set.

You could just use a long 2-56 rod for the rudder and run it through a tube where it would exit the fuse. The rudder is not going to be putting that much force on it. If this was an aerobatic plane, yeah it needs to be a little stronger. I flew my Goldberg Cub for many years with a long 2-56 rod pushing the rudder. Never had an issue.


Dru.

P.S. Pictures of finished setup would be nice.

SeamusG

Hey Dru - I have another thread going specific to my LT-40 update in the kit building forum. But, I went ballistic this evening and stripped all of the covering. I found out how challenging it is to add aileron servo wire access thru the ribs on a completed wing. Ain't completed any more. [:'(]

SeamusG

Here's another option as provided by Great Planes. The example given shows a wire-with-clevis to the tail wheel attached to the torque rod horn. That assumes that the rudder control exits the fuse very near the tail wheel. Not the situation with an above-the-stab rudder.

If access is available to the rudder control rod inside the fuse (like during the build) ANDa rod-in-tube control rod is used, a section of the tube can be cut out exposing the rod. The "shock absorber"can be installed in the "missing" section. The torque rod horn can be attached to a rod-in-tube-clevis that is connected to the tail wheel. No doubt that this approach would be heavier than a pull-pull approach. But, if there is no straight line shot between the servo (and arm) to the tail wheel's steering arm then this might be a decent "shocked" approach.

Here's a mock up of the approach.

blvdbuzzard

It is always fun to try and change it AFTER it is covered. I just finished adding dual aileron servos to a wing that is covered. I had to put all of the new support pieces through the servo sized hole I cut in the covering.

Talk about build a ship in a bottle. If it was easy any one could do it.


Dru.

SeamusG

Life will be soooooo much easier when they come up with wireless servos! How did ya route the servo wire? Enquiring minds just gotta know.

Dzlstunter

SeamusG: Do you Y-harness the tail wheel servo to the rudder servo on your Senior? Dzl

SeamusG

No, just a really long servo extension. I have a DX7 with an AR7000 Rx. Truth be know - the Senior has not been flown and it's been finished for over a year. What kind of father am I? The servo out back is intended to accommodate a float rudder as well. There is a rear float mount just behind the former at the rear of the wing. That was the plan.