Tailwheel cables slack

[daedaluscan]

Tailwheel geometry is tomorrow.

My feeling is now that maybe my tailspring is starting to sag, and as it it "relaxes" that is allowing the chains to slacken? Or one of the tailwheel cables has slipped on the rudder cable, but both sides have two clamps ( I only see one in the parts book) The resolution of the borescope was not good enough to see tany signs of slipping.

I did find a crack in the bracket that has been stop drilled in the past.

[Bruce Fenstermacher]

The crack you found is common. You also have the thicker L-19 style main spring installed as do 80% or better I think of the 170s today.

[johneeb]

It maybe a optical "delusion" the cable in this picture does not appear to be tracking it pulley.

[blueldr]

Strangely enough, the tail wheel steering cabling on the '55 model C-170 looks like something added on in the field on some models. The attachment of the steering cables to the to the rudder cables often looks almost temporary with the use of "Kearney" bolts and I've seen a number of different inspection or access doors that look like field mods.
I have owned only one '55 model and it didn't steer any better than the earlier ones.

[canav8]

Charlie, reach in and turn the pulleys also to see if they are frozen.Since they are difficult to get to, they are often neglected by mechanics for lubrication.

[daedaluscan]

I wish I could reach in!

The only way I can even see in is through the elevator pushrod slot, and that is hard.

I think the pulley alignment is due to the extreme slackness of the cables, when they are snug everything lines up nicely.

If I can get to the plane today I will take photos of the spring/tailwheel pivot angle loaded and unloaded.

[daedaluscan]

I do have a bellcrank on the rudder with attachment points for tailwheel cables. I wonder if I should not just remove this entire system and got to the pre 55 (or whenever) system of direct of the rudder? Sure seems like a more simple solution, as Colin Chapman said "simplify, then add lightness".

[daedaluscan]

Tailwheel on the ground showing how slack the chains became

Here are some photos of the tailwheel/spring

[daedaluscan]

And some more.

I had to take out four links to get them snug off the ground, and they tightened significantly when they were back on the ground.

My parking spot is slightly sloped so the tailwheel is a little elevated.

The tailwheel seems to be locking and unlocking correctly, it was rebuilt by Alaska bushwheels about 50 hours ago.

I am still at a loss as to where all this slack is coming from, my best guess is that one of the tailwheel cables is slipping on the rudder cable.

Has anyone actually removed this system from their plane and gone to the pre 55 system?

[canav8]

Okay charlie, start chasing cables. Look at all the pulleys along the way for flat spots. Work your way forward. Hopefully you will get forward of the aft bulkhead.

[GAHorn]

Bruce, is that a subjective opinion (80%) or an observation of those you've seen?

The reason I ask is, the B-model 170 aluminum "alligator" bracket dispensed with the "pads, spacers, retainers" etc.. that the original steel "box" bracket used. (The Service Kit instructions for the conversion of earlier aircraft discards those parts.) The same spring-set is used in both versions.

The L-19A tailwheel bracket (referred to as the dash-3 bracket) closely follows the 170B bracket in design...but not exactly ...as it uses a different, rivetted-in pad to position the mainspring. This changes in the L-19D/O-1 BirdDog tailwheel bracket (the so-called dash-10 bracket). This -10 bracket uses a different "stiffener" which is that plate using multiple AN3 bolts to top the springset. The -10 bracket stiffener is shorter and does not have the "overhang" which fractures so commonly where the square U-bolt clamps the longer, 170B/L-19A stiffener.

Where I'm leading this is, I believe the late L-19E/O-1 BirdDog -10 tailwheel bracket uses the thicker mainspring, and that is why that -10 bracket and it's stiffener were changed from the -3 versions. IN ANY CASE, the owener who uses a thicker "L-19" mainspring should be aware that use of that spring in the original 170B hardware configuration may lead to cracks and failures of the bracket and stiffener.
If the thicker mainspring is installed then the installer must take into consideration those dimensional differences and make allowances. IMO.

I'll try to edit this msg post to include illustrations that might demonstrate the different profiles of the differing brackets.

L19Fig541.doc

170B bracket

(913.5 KiB) Downloaded 667 times

IPC B model pg 54 fig 29.doc

L19E/O-1BirdDog

(242.5 KiB) Downloaded 594 times

[Bruce Fenstermacher]

Bruce, is that a subjective opinion (80%) or an observation of those you've seen?

George, I don't know what others look at when they look at a 170, but there are certain things I always take note of on every 170 I look at. By now I have an above average knowledge of how these things came from the factory, what options where available, what changes where made through the production run, and popular changes that are made by owners. And these are the things I look at.

Probably because you and I had a very early disagreement in our friendship (over 12 years ago) with regard to the main tail spring it is almost always one of the first things I notice. Others might be ogling the polished finish but I'm inspecting the main tail spring and what parts are missing or installed correctly. So I've probably inspected every main spring on every 170 I've ever seen. And what I've noticed is it much more common to find the thicker l-19 spring than the correct original spring. If I felt it was more common to find the thick spring i might have said 60%. But since I fell it is much more common I assigned 80% to it. If it was most certainly to be found I'd likely have assigned 95%.

• BTW George in this time I have found at least two other renegade owner operators with two main springs installed and neither of them ever had a spring bolt shear. Not that i recommend that configuration.

Where I'm leading this is, I believe the late L-19E/O-1 BirdDog -10 tailwheel bracket uses the thicker mainspring, and that is why that -10 bracket and it's stiffener were changed from the -3 versions. IN ANY CASE, the owener who uses a thicker "L-19" mainspring should be aware that use of that spring in the original 170B hardware configuration may lead to cracks and failures of the bracket and stiffener.
If the thicker mainspring is installed then the installer must take into consideration those dimensional differences and make allowances. IMO.

I believe George is correct here. Even though the load seems to be placed on the part above the springs I'm beginning to think jamming the thicker spring in the pack and bracket, and that is what you have to do sometimes, is causing the cracks at the lower bottom. At least the thought it making me go hmmmmmm.

[GAHorn]

[...you and I had a very early disagreement in our friendship (over 12 years ago) ....

I hope that is not what you intended to say... I have never felt we had a disagreement in our friendship... only in our personal opinions as to the hazards of installing dual mainsprings.


(For those curious about this matter.... Long ago, when I hosted the "Classic Cessna One-Seventy Club" over at yahoo...predecessor to these Forums.... Bruce and I disagreed about the merits of installing dual mainsprings on our airplanes.
Bruce had dual mainsprings installed, through which the Scott tailwheel assy was bolted with that single bolt we all have.

Having personal experience with a failed tailwheel attach bolt (in a C-140 actually, while rolling out in front of an airliner which had to go-around), I opined that it was hazardous to the long-term health of that bolt because I felt than any flexing of the dual mainspring setup would subject the attach bolt to a cutting/shearing action by the springs as they "slid" during flexing.

Bruce expressed something to the effect that it'd take a long time before that would result in failure of the bolt, likely not within anyone's lifetime.

We disagreed strongly over the propriety of the matter and probably never expected to meet face-to-face, much less become good friends and co-horts in TIC170A.

Bruce's subject airplane was destroyed in a storm thereby removing my chance to prove him wrong as that particular airplane/mainsprings/tailwheel arrangement no longer flies..he never suffered my predicted failure of that particular assy....and he finds and points out to me similar examples he discovers over the years. (He's still rubbing-it-in.)

The real danger of course, is that a failed mainspring or tailwheel assy attach-bolt will likely subject the rudder to a bouncing, thrashing tailwheel retained by it's steering chains. This will be expensive.
Dual mainsprings are an effort to reduce the exposure to that hazard in the event of a broken mainspring.

I believe the risk is also that of a broken attach bolt, in addition...and that the best approach is to use the correct parts coupled with frequent inspections and timely replacements on the order of about 500 landings. This number was derived based upon all reported failures occuring beyond 750 hours (and usually many many years) of flight time, and making the assumption that one hour likely equates to one landing across the fleet.
Another suggestion, based upon inspections of failed mainsprings, is to radius or smooth the lower edge of that 3rd spring, the one just above the mainspring, where it contacts the mainspring. Mainsprings which have been inspected after failures have universally failed where they have suffered stress-risers from wear of the sharp, trailing-edge of the spring above them.

As for those who have dual mainsprings installed, I'd recommend you consider why the forward attach bolt is installed through the mainspring stack using a bushing/bearing/sleeve.

[Bruce Fenstermacher]

Well since George opened the can of worms a bit more I would just say I don't recommend two main springs because the combination may be two stiff for all those other delicate parts back there. And of course there is the approval thing. I was never worried about the bolt because Pipers have two main springs with a bushing on one end and a bolt on the other though they may not have the same load on the tail.

As for the way I constructed my first sentence. See here now, onest, that is just the way things are said here in Pennsylvania Dutch country. It wonders me if Texan's throw the horse over the fence some hay. I could go on but John Hess would show me up.

Seems to keeps the Texan's guessing though.

[n3833v]

You really want me to start. Come onest all to the convention and we can continue. See you all there.

John