Tailwheel Steering Springs and Chain Kit x

[Bruce Fenstermacher]

From Merriam-Websters online dictionary:

Main Entry: 1taut
Pronunciation: \ˈtȯt\
Function: adjective
Etymology: Middle English tought, perhaps from tought, toughth fierce, tough, alteration of tough tough
Date: 14th century
1 a : having no give or slack : tightly drawn <a taut rope> b : high-strung, tense <taut nerves>
2 a : kept in proper order or condition <a taut ship> b (1) : not loose or flabby <taut muscles> (2) : marked by economy of structure and detail <a taut story>
— taut·ly adverb

— taut·ness noun

Though the word taut can mean there might be some tension that is not necessarily the case.

This would all be more interesting if you could actually adjust the chains to have no slack without tenstion. Over the ten years I've had my 170 I'll bet I've rerigged the tailwheel 20 times. New main spring arch, new tension springs, new chain, with shackes, without shackes at the rudder horn, using eye bolts i.e. the Scott diagram, using shackes with the eye bolts. I have even messaged the chain links to lengthen them or shorten them in an attempt to get the illusive NO SLACK but NO TENSION but it is virtually impossible to achieve.

And so for most of the ten years my chains were just a pinch loose. Which of course is not one of the options given on any instructions. I've found it to work as well as the few times I'd adjusted the chains with a pinch of tension and I feel better about having them loose with the thought of avoiding wear.

Currently my chains are adjusted with a bit of tension. I won't admit that over the last 10 years George might have warn me down. Instead I like to think I'm just testing the adjustment as he interperates the instructions to be and I'll report back in about 10 years.

In the mean time you are on you own to figure out what works best for you. A pinch loose I've proven won't hurt on my airplane and I'll bet a pinch of tension won't hurt or make any difference either.

[GAHorn]

Do I detect a sly attempt to mollify?

Lookeehere.... I manytimes come across as a demanding guy when I don't mean to. I don't intend to be the tailwheel nazi, ...I just want to do my very best to give good info.

It's my personal belief that the intent of all the rigging instructions provided by all the mfr's is that no slack is to exist when the tailwheel is resting on the ground and aligned straight. I understand that due to minute differences among aircraft that the chain-links don't always cooperate with that exact length required, and that the amount of adjustment allowable is to shorten the chain to accomplish 1/8" to 1/4" of steering-spring stretch. That is the specific instruction for adjustment.

If anyone experiences tailwheel problems with the chains so-adjusted, then there is something else wrong with the installation. Look for that error and correct it. It's likely a worn tailwheel, a weak or bent-out-of-specs leafspring, damaged bellcrank, etc., etc..

I've remained silent on the 3200A "up-turned" steering arms, but I'll throw another wrench in the works: I don't believe that was ever intended for C-170 airplanes prior to SN26505. That steering arm was designed specifically for those Cessnas that have long steering cables that pull longitudinally such as the L-19 ... not short chains tied to rudder bellcranks that pull upward. That upward bend adds length to the "arm" and whenever an upward pull is exerted, the arm tends to bend. The only other reason a properly rigged steering arm should bend would be improperly mfr'd parts (such as the soft -A arms already discussed) or some failure (such as the internal pawl causing lock-up) or misapplication of parts such as using compression-type steering springs.
When the 3200-A unit came onto the scene and was used on the post-SN26505 aircraft, many owners and mechanics assumed it was OK to install on earlier aircraft ...because they did not consider/understand the geometry of the system. The 3200-A arms is not stronger than the 3200 arm. It some applications it is weaker because it is physically longer and magnifies any misaligned pull.

One of the problems dealing with this discussion is the wide variety of ad-hoc alterations which owners make in desperate efforts to change the system to their liking. One guy will complain about bent steering arms...and totally overlook the fact he installed a leafspring set different than the factory design for the aircraft. Another guy will complain about poor steering, because he's never operated a Cessna tailwheel before this airplane and is comparing it to a Maule or Stinson.
Another will completely forget/ignore the fact his mainspring is sagging and wonder why he has "shimmy"...so he re-bends and re-rigs to chase the problem, thereby even further aggravating the out-of-rig situation.
Let me remind everyone with a Scott 3200 that if you don't have C170- main leafspring sets, if you don't have the 3239 tension steering springs, if you have not inspected and kept your tailwheel properly maintained, ...then making further experimental alterations to the system is not likely to make it work any better. The factory spent a lot of effort getting it to work properly in the beginning and they had access to every tailwheel model and device and spring and mal-adjustments that we out here in the field have and MORE. They settled on what you see in the IPC, and any field-modifications are likely to give you something they'd already tried and rejected, or alternatively, something entirely unique and beyond the ability of anyone but you to deal with subsequent malfunction.
Quit trying to re-invent the wheel and you'll have a better chance of success, in my opinion.

[Bruce Fenstermacher]

Do I detect a sly attempt to mollify?

Absolutely not.




I will have to study the 3200A arm again to see what you are talking about George when you say it has a longer arm. I assumed the bent up arms were the same length as the 3200 series. It is obvious the 3200A bent up arms do slightly improve the angle of the pull of the chains but I think any improvement negligible. I also think the bent up arms would impart more or a rolling or twisting action of the arm regardless of the aircraft and control set up.

[canav8]

Hey george, can you send me a better copy of this picture please?

ScottBPrint.JPG

[GAHorn]

Sorry, can't help you as I do not have a better copy of that particular print. (Looking at the leafsprings, that does not appear to be a Cessna 170 installation.)

[rydfly]

So let me ask you this... assuming everything else was rigged correctly and such, what would one notice if the 2151 springs were installed w/ the 3200 Scott tailwheel instead of the 3239 "Heavy duty" springs?

I ask because I just checked and I do indeed have the 2151's on my 170B. I purchased the plane this past summer and the previous owner did tell me he replaced the springs, and that the replacements seemed smaller than the originals (of which he only had one), but that the person at A/C Spruce insisted the smaller spring was correct for his needs. The invoice included in my aircraft records confirms he received p/n 2151.

Now here I am months later having somewhat gotten used to a new-to-me aircraft with the wrong springs on it. My gut tells me to get the correct springs on it ASAP, but will I then be re-learning the ground handling characteristics of my plane?

[GAHorn]

The heavier springs will be more authoritative in turning the pnuematic tire which has greater footprint than the smaller solid tire of the Scott 2000, etc. They will also facilitate unlocking of the steering pawl when pivoting using brakes, due to greater "tug" upon the steering arm. (At least that's their intent.)

[blueldr]

For goodness sakes! As long as you are not using compression springs and you are able to steer the airplane reasonably well while taxiing, why worry about the spring type? Most C-170 airplanes do not react very well to rudder pedal inputs while taxiing and require some differential brake use.

[rydfly]

I'm not so much concerned about taxiing as I am those crutial seconds right after tailwheel contact on landing where the rudder doesn't quite have the authority it did prior to touchdown yet your forward momentum is enough to somewhat nullify inputs at the tailwheel. In that case, a little more pull on the tailwheel might help... or it could send me in the weeds if I over-correct!

I'm still getting used to being a full-time tailwheel pilot and am based on an airport with a single hard surface runway as the only landing option. I don't want to shoot myself in the foot by making my setup more sensitive than it needs to be, but I don't want to handicap myself with the wrong setup for the tailwheel assembly design either.

[Bruce Fenstermacher]

I'm thinking you won't notice the difference and if you do you will compensate just fine. I'd put on the correct springs to be correct but I wouldn't do it with my last maintenance dollar.

[CAVU Mark]

Wow... more info on tailwheels than I could ever image and now maybe I can add some more confusion. My 170A has a 3200 TW which was on the plane when a group of us purchased it. A one page Installation sheet included with the logs is all the information I found, Issue date: 4-8-49, Bulletin No. I-168 from Scott Aviation Corp, Lancaster NY (no zip code). The installation sheet shows eye bolts in the rudder horn which connect to the Spring Connector Assy, which is not what is installed, see pictures. A Note on the page clearly states: "Tension on the connector springs not required or advisable. Use sufficient chain links to remove slack in each connector assembly on installation." So there you have it, clear as mud, tension not required nor slack!

Regardless my concern is wear in hole which holds the spring to the rudder horn as well as the clips holding the springs to the tailwheel. The wear is obvious and will cause a problem if fails during a landing. Of course I watch it every preflight but my style is more precautionary. Perhaps the instructions are not for the wheel installed on my plane but the tension on the springs on my plane is more than I am comfortable with. The plane steers like a tailwheel, lands like a tailwheel, and now I just need a little more slack. Are people using the Eye-bolts or the tabs on the rudder horn? The instruction sheet I have may be throwing me into a tailspin!

http://www.flickr.com/photos/41488898@N ... 925773997/ I hope the link works or search for CAVU Mark SDM sets on Flickr.

P.S. Where do I find out how to embed images? Thanks.

[Bruce Fenstermacher]

Mark,

Your installation is the way it came from Cessna and would probably be considered the most correct method. I see the wear you point out in the photo. This can be repaired locally by making new tabs and attaching them to the horn as I discussed in the other thread. ( http://www.cessna170.org/forums/viewtopic.php?f=5&t=57 )

To be honest in reality it took about 60 years to wear that far and probably another 60 years till it wears through. Actually I haven't made it a priority to remember how big that hole is to start with so I can't say how much wear yours has. It is entirely possible mine has the same wear and I think nothing of it. I would suggest you look at others and compare. And perhaps someone can give us the original hole size.

The Scott instructions as far as the eye bolts go, well who knows how and why that is different than the way the factory did it. I've done it the Scott way and found no difference in performance. I think you could do it either way and as long as the work is documented be considered legal by most but maybe not by all.

As for wear the Scott method might eliminate the wear on the tab which is replaceable. But I feel over time the springs pulling on the eye bolt in one direction will cause the same type of wear on the horn itself. Eventually the horn will wear and to have to be replaced at a much larger cost than the tabs. I choose to change mine back to the factory method.

Yes the clips at the tail wheel end can and have worn slots in the tail wheel horn. I've never seen any though that I thought would break at any moment. I've seen some tail wheel horns repaired by having a washer welded over the hole to resize and reinforce it. I'm not advocating this as a good solution in all cases as these tail wheel horns have been made out of a few different kinds of aluminum and steel. The steel might be appropriate for weld repair, the aluminum maybe not.

I'll PM you about placing pictures at the forum.

[GAHorn]

A loose steering chain has NO capability to influence tailwheel steering. If you want your airplane to veer-off-course a while before you have sufficient input from steering chains...with the subsequent result of a panic-stricken over-correction in the opposite direction... then be certain to have slack in your steering chains.

Excessively-tight steering chains will create a sloppy steering input, because if both springs are significantly-stretched (with the tailwheel and rudder pedal cable-system in the straight-ahead position) then one spring will absorb considerable input from the pedals before it overcomes the power of the opposing overly-tensioned spring. (A small amount of spring-stretch is fine. Those pictured in the flickr pics are fine, but no more.) The ideal will be taut chains (not relaxed at all) with just-collapsed springs. Sometimes fresh springs are req'd to achieve this, but it's actually pretty rare for the heavy-duty springs elasticity to be lost. I don't think I've ever seen it except on a wreck which also exhibited other components broken/bent.

Remember, the tailwheel steering system is not a solidly-connected system. Pedal inputs move the rudder itself but the weight of the aircraft on the tire and the friction of the tire against the pavement all resist that steering-spring. The steering-spring/chain arrangement is deliberately designed to allow some amount of "disagreement" between the rudder and the tailwheel. Otherwise, how would things work without breaking something if the pilot had a momentary gust-of-wind that req'd opposite-rudder-deflection while aircraft weight and tire-friction prevented the tailwheel from rigidly-following the rudder?

Tailwheel steering should be thought of as "tailwheel encouragement". Liberal use of brakes to assist steering is to be expected. (Key-word: Liberal)

[robert.p.bowen]

A loose steering chain has NO capability to influence tailwheel steering. If you want your airplane to veer-off-course a while before you have sufficient input from steering chains...with the subsequent result of a panic-stricken over-correction in the opposite direction... then be certain to have slack in your steering chains.

Horse feathers.

After the earlier posts, I conducted an experiment to see if the steering chains...taut or loose...made any significant difference. First I adjusted my chains as per the Scott instructions, and went out and made multiple landings on a hard-surface runway. Then I put a link in each chain, causing the chains to now be "slack," and made multiple landings on that same runway (this time in a crosswind). I could detect NO difference in steering. By actual measure, with the tail jacked off the ground, the rudder pedal deflected 1/2 inch with slack chains versus taut, before anything happened at the tailwheel. Since there's a world more rudder pedal movement than that, it would take a pretty sensitive foot to detect that 0.5 inch movement, particularly since it is only a "tailwheel influencer." (That part I do agree with George.)

We'd find a better use of our time debating how many angels can dance on the head of a pin, than the true effect on tailwheel steering of taut--snug--or loose chains...in my humble opinion.

[GAHorn]

A loose steering chain has NO capability to influence tailwheel steering. If you want your airplane to veer-off-course a while before you have sufficient input from steering chains...with the subsequent result of a panic-stricken over-correction in the opposite direction... then be certain to have slack in your steering chains.

Horse feathers.

After the earlier posts, I conducted an experiment to see if the steering chains...taut or loose...made any significant difference. ...I could detect NO difference in steering. By actual measure, ..., the rudder pedal deflected 1/2 inch with slack chains versus taut, ...We'd find a better use of our time debating how many angels can dance on the head of a pin, than the true effect on tailwheel steering of taut--snug--or loose chains...in my humble opinion.

This may be a discussion without accurate comparison-data but.... I stand by what I said. A slack chain will not impart tailwheel steering input until the slack is taken-up. How MUCH slack we're discussing hasn't been specified.

If, on the other hand, you found 1/2" rudder movement took up the slack in your chain...then you didn't have much slack to consider....and my statement is still true, no horse feathers involved. Until the steering chains are taut, no input is made to the tailwheel. AND.... that is without regard to the health of your steering arm, or your pawl condition, or your detent and friction-discs, etc etc. All those items each have their own contribution to make. Until they receive input ... they make no effort to steer the wheel.

Still more to consider: A half-inch of deflection on a 4" tailwheel makes a pretty good turning-arc at the end of a 25-foot fuselage arm. It might make the difference between a steerable airplane and a ground-loop, depending upon a lot of other un-defined factors and levels of pilot skill, not to mention if the side-loads unlock that detent/pawl.

In any case, we are in agreement that tailwheel steering chains are one of the matters of lesser-import to a qualified tailwheel pilot. It's the tailwheel that is "steerable" by the pilot...not necessarily the aircraft steered by the tailwheel steering system.

PS: I wonder how many of us would happily fly around with slack in our elevator control or aileron control circuits?