The International Cessna^® 170 Association

It is a question

Many owners of C 170 know to be vigilant about condition of main leaf tail wheel spring.

Some will simply order replacement part from Aviation catalog company.

My question is . Are we simply purchasing the same ages old metallurgy technology ?

Could there be a better metal spring to help the C170 fleet to continue forward?

Grady, the truth is, it is spring steel and the fatigue process of the spring will happen no matter what the material is. you are getting newer material but using the same process for making spring steel. It lasts the longest. If you wish to preserve your life of your tail main spring, consider being mindful of the tail when flying. That means, always wheel land instead of 3 point. Do not taxi on rough unimproved surfaces. do not load your airplane to the aft CG limit. All of these will increase the life of the tail main spring. Does it sound practical? It isnt except the wheel landing part, all the rest is normal wear and tear. Doug

There is no life limit placed on the tailwheel spring and no requirement to replace it before it shows signs of failure.
But they do break from time to time.


You could also IRAN the part with whatever process you think is appropriate (dye penetrant?)
Whatever process you think is appropriate because there is no requirement to test or inspect the part at any given regularity (other than visual at annual and before each flight but that will rarely reveal anything)

Being a $100 part, it's easy enough to replace it at some interval that you are comfortable with.

The 500 hour recommendation is an arbitrary number of hours and based on no real measurement other than being half way between 0 and 1000.

All this to say, there doesn't seem to be enough evidence of regular breakage to necessitate improving the material.
Having said THAT...I believe Tom Anderson has a titanium tailwheel spring which will increase your useful load by removing weight from your wallet.

The 500 hr recommendation to replace the main tailwheel spring and bolt/eyebolt is not based upon speculation or being halfway to 1000. It was based upon a "poll" taken years ago by myself. Of the relative few who responded with believable data, (dozens responded but less than that had any real data from logs to confirm) the figures pointed to 700 hrs and 12 years being the lowest amount of time which could be documented as having experienced failure. (One corporate pilot actually had counted cycles, but could not differentiate between paved vs unpaved or wheelies vs 3-points, so I arbitrarily decided to convert cycles to hours and leave it at that.)

In an attempt to be conservative on the side of safety, settled upon 500 hrs/cycles or 10-years, whichever came first, and having been appointed parts/mx guy, posted that info., and it was generally accepted. (There's a lot of foolishness that goes on around here.)

I am keeping accurate logs on my own mainspring purchased from Spruce (but carrying a Univair PMA tag.) If it breaks prematurely (<500 hrs/cycles) I will let everyone know. It is presently at 236 hrs, 157 cycles, and will be 8 years on Sep 26. Previous spring was 11 years old, had 761 hrs, and estimated 500 cycles (which is why I asked Del to replace it while in his shop for other work.)

500 hours was 200 hours less than the lowest number of hours of the relative few people that you polled years ago.

How many people responded to the poll? What was the max, min, mean of the numbers? How may are over 1,000 hours without a failure?

If someone had a documented failure at 200 hours would the recommendation be to replace it every 100 hours?

That's all still arbitrary in my book and is the equivalent of a wet finger in the wind.

David, if I told you those actual numbers would it change your mind?

Your statement said it was "based on no real measurement other than being half way between 0 and 1000."

I only wanted to clarify it was not based upon something that arbitrary.

It's your airplane. You get to decide when to change your spring.

"Of the relative few who responded with believable data, (dozens responded but less than that had any real data from logs to confirm) the figures pointed to 700 hrs and 12 years being the lowest amount of time which could be documented as having experienced failure."

You said what your data was right there in your post. Also that the 500 hour value was arbitrarily selected because is was a nice round number that twas lower than the 700 hour lowest documented...out of a few dozen responses.

I dont want people around here to get the false impression that 500 hours is some value derived by scientific or engineering practices or is anything more than the opinion.

That's correct. It was only a WAG based on anecdotal evidence. (Not entirely arbitrary.)

Thanks.

Geeze George, your recommendation having been questioned, I am now really concerned about your "many" previous posts regarding the virtue of a RED airplane being faster than a GREEN one! Who can we trust any more? Just when I "might" have thought you had some actual documentation regarding vrs speeds of vrs colors of airplanes, now this

170C wrote:Geeze George, your recommendation having been questioned, I am now really concerned about your "many" previous posts regarding the virtue of a RED airplane being faster than a GREEN one! Who can we trust any more? Just when I "might" have thought you had some actual documentation regarding vrs speeds of vrs colors of airplanes, now this

George is correct on that issue. Most everything else is debatable.

Frank, you...and I... and most others who've known you for more than a decade... think we know why your call-sign is "Ol' Pokey". They also know that in the only "official" TIC170A contest-of-speed* scheduled between Members who owned red or green...which took place April, 2002 at Many, LA* ... the green airplane failed to even make it! (and we also know why your avatar photo shows your airplane from the front. Unlike Bruce's business-card, which demonstrates his well-published, self-admitted Photoshop capabilities.)

Typical view of a red 170.

Two 180hp airplanes were trailing me, the Decathlon pictured, and the 170 from which that picture was taken.

George, that contest you mentioned probably took place and the green 170 was so fast you never saw it And to give credit where credit is due, that photo of Ole Pokey was taken from a white & orange 170 by our historian SG.

Bruce, I need some help here

Ryan Smith wrote:Typical view of a red 170.

Two 180hp airplanes were trailing me, the Decathlon pictured, and the 170 from which that picture was taken.

If you know anything about flying formation, you know you always put the slow guy in front.

Bruce Fenstermacher wrote:

Ryan Smith wrote:Typical view of a red 170.

Two 180hp airplanes were trailing me, the Decathlon pictured, and the 170 from which that picture was taken.

If you know anything about flying formation, you know you always put the slow guy in front.

Shhhh.

It was a race. I totally promise.