Hey Guys,
Whats the advantage or disadvantage to using 'direct' linkage to the tailwheel vs. using springs? Have a model which has only 30 degrees max. on the rudder. I've tried 4-5 different springs with different tensions, but there's always too much play in them to give this plane any reasonable ground steering. I'm considering using ball links and rods to tie the steering arm to the tailwheel. I don't see that done often and wanted to know if this is a good idea or not. Thanks!
HM

Con: weight. Need to add 4x to the firewall

Option: pull-pull wire rather than control rod. leave a "teanse" bit of slack to allow some small movement.

Thanks SeamusG... weight not a problem. Have considered the pull-pull wire approach. I am curious tho, are springs more a matter of convenience or is there a specific function they fulfill beyond just moving the wheel?

There are two separate issues here:

1) Springs are used to absorb any lateral shock produced by stones, etc. and prevent the instant high forces to reach the gears of the servo (or the rudder, if it is part of the linkage's chain).
That is achieved at the expense of the solidness of the command.
To use springs or not depends on the strength of the servo and linkages.

2) The deflection of the wheel can be made bigger than the deflection of the rudder, simply by choosing a different layout of arms (more arm for the servo and less arm for the wheel).
That makes the servo "feel" the lateral shocks stronger, though.

Much appreciated. Good point on the length of the arms. The steering control arm is fixed, its tig welded to a steel rod that fits within the rudder and exits the bottom of the fuse. But, the J&J tailwheel does allow me to position the linkage within an 1" outboard or inboard. I'll try setting up the spring closer to the wheel and see what that does.

I'd post a pic but am getting some '500 internal server error'... when attempting it.

Yes, as Juan said, one of the biggest reasons to use springs is to avoid stripping the servo gears.

If you use a solid pushrod, put a reasonable bend in it to act as a shock absorber

I was using a setup with the steering arm tied to the rudder and I had a hard time keeping it straight on takeoff.  I switched to a spring system and it tracks alot better.  I cant say why this is, I just know thats my experiance.

My 4Star60 uses a length of fuel line fixed to the tail wheel "stanchion" and then "machine screwed" to the underside of the rudder. My 1st attempt put the screws too far away from the stanchion resulting in a very sloppy TW - looked like a drunk sailor on the deck of an aircraft carrier (at least that's what an ex-carrier club member called it). I moved the machine screws nearer the stanchion and control was greatly improved.

Here is an example of using a second tailwheel pushrod (carbon fiber). There is a nosewheel steering arm just above the notch in the ordinary Dubro tailwheel bracket for the external arm.

This Hellcat Beater I use for genuine arrested landings and as a paint ball target. The tailwheel was neccesary to beef up considerably for this as it was often caught in the arrester Line.


http://www.youtube.com/watch?v=M2WIVHZaSHA


John

Hey John - you usin' 2 collars to tie a dual elevator pushrod system (DEPS)? That would make ensuring that the elevators are in sync pretty easy.

Ya, that makes things real simple. Those rods are the rods used by most of the pylon folks and the inside ID is a perfect slip fit for the 2-56 sized rod ends. I use these rods in the vast majority of my airplanes.

Its so easy just insert a a piece of rod with the threads on one end and epoxie or insert a bare rod like that elevator yoke with the collors as well as a rod end with the S bend already bent. adjust it to length and epoxie.

I picked that airplane up cheap and the horrible solid full length steel rods was a complete mess. It had actually had been flown a few times with the rudder rod force to the outside of a bulkhead about half way back pinched between the bulkhead and the fiberglas of the fuselage.

The elevator rods had so many deliberate bends in it that you almost flatten the elevator just by blowning on it with your mouth. All of my airplanes have straight fuselage pushrods and never any fuselage exit bends. I just let the rods out of the fuselage wherever that needs to be so they are never bent and thats not neccessairly where the outlets may be on some arfs and well as indicated on the plans of some kits.

John[8D]

Springs on the tail wheel, amongst other things, allow the tail wheel to "castor" on cross wind loandings, without throwing the plane all over everywhere that you dont want.

Les

"JohnBuckner; ...This Hellcat Beater I use for genuine arrested landings and as a paint ball target."

Sweet!!!

Thanks for all the info., am a bit more educated on tailwheels. Finally got a pic posted....

Cool, now that you have a picture up the reason you are having trouble with soft springs is two fold the primary reason is the design of the tailwheel it self. It has considerable trail (caster) designed in.

Note the further back from the steering axis the wheels footprint is the greater the trail i.e. moment arm. The effect of this is with any side force such as the start of a ground loop the this strong moment arm will put far greater loads on the spring than what you might expect. A tailwheel with less trail can use springs with less tension.

This brings us to the other option here and that is the spring itself. Yes you definately need more resistance to tension but the real answer is not just a heavier spring its a different type spring.

Its likely you have been using tension springs, springs that pull apart. compression springs are more desirable with a larger airplane. Sorry I have no picture but these have rod claws inside that the links attach to and all loads compress the spring. This type spring is used on most more modern full scale taildraggers.

Using this type will increase the springs strength with larger loads untill it is fully locked. Yes I beleve the steering should never be free wheeling.

Yes I am aware most full scale airplanes have a full swivel feature but this is for a different purpose to make very tight manuvers while parking or pushing the airplane backward, we simple do not need this.

Indeed many full scale airplanes that have this automatic full swivel feature also have a rigid pilot operated tailwheel lock to prevent sudden loss of control on takeoff due to the wheel suddenly going to full swivel if side loads are high.

You will find these compression springs at many good hardware store in their spring selection bins.

Another option I recently did with a fifty CC ship which is a Yak something or ruther ARF. I used a tailwheel similar to your but installed a steering arm fixed rigidly to the bottom of the rudder. The steering arm on the tailwheel was behind the arm on the rudder. Now rather than use springs at all I choose to use wire links that provided rigid connection between the two steerring arms. This arraignment provided extremely pleasent ground handling to this larger taildragger in other words it handels on like the proverbial piece of cake and on takeoffs or landings, its a delight.


John

HM,

Solid rods cannot be used in this layout.
An elastic connection is needed on each side because the up-down flexing effect of the supporting strap would be annulled, and/or the rods could be bent under a heavy landing.

As John explained, the caster of the wheel makes it more powerful respect to the linkage, and stronger springs are needed.

"...the rods could be bent under a heavy landing."

That was pretty much the conclusion I came to messing around with it. Think for the moment I'm just going to move the compression springs I have on it closer to the wheel and see if that gives me a bit more turn area...