tailwheel main spring replacement

[robrien]

I did a quick search but did not see notice whether there are posts related to when you should replace the spring outside of a failure? I was told that these should be replaced every 500 landings, and my IA told me that you do not need to replace this unless signs of fatigue or failure. Any input on this? Thanks!

[bagarre]

Nothing official but folks around here say 500 hours.
IMO it'd depend on you flying/landings

[robrien]

Thanks for the response. I'm curious is this because of history of failures near the 500 hour point, or?
Is there any warning prior to failure? What is the typical damage if fails?

[swixtt]

I just replaced mine and the whole pack. I had no idea how old it was. you could see where mine had broke years ago... about 3" up from the tail end of the biggest spring.
http://www.cessna170.org/forums/viewtop ... =24&t=9642

[jmurtap]

If your in doubt, remove the spring pack and inspect the main leaf for a stress riser where the next spring ends. Changing the main leaf spring is very cheap insurance, and great piece of mind.

[Bruce Fenstermacher]

Robrien,

The problem is 99.99% of the time you can not tell the spring is about to break prior to it breaking. 99,99% of the time they break when the aircraft is in motion and when they do break in motion the tail wheel hangs on by the chains and destroys your rudder and elevator.

We won't even go into the amount of inconvenience and cost of stranding you someplace like 10 miles of the coast of Road Island on Block Island on a Sunday afternoon. Yes that was one place a tail wheel spring let loose with me, my wife my buddy and his wife in a borrowed 170. Because of the weight we had in the plane we choose not to fly out on the remaining spring skid. Instead we caught the last ferry to RI, found a taxi and hotel, bought clothes because we had nothing with us. Got a rental the next day to drive 8 hours home. That was the first day of my wife's new job she couldn't get to. I missed a day of work, his wife missed a day of work, he had to scramble to get more cloths and drive to the airport immediately when he got home to catch a plane to a week long work project he had to delay a day. He only made it because the flight was delayed. The next week we then had to have a friend fly back to Block Island with the new spring, pay a week long tie down, install the spring, return home and then pay to repair the rudder and elevator. We could have bought new tail wheel springs and had them installed for about 50 airplanes by the time we where done. But it was an adventure the 4 of us still talk about today, 15 years later.

On the other hand maybe you are as lucky as I was another time. My last tail spring broke just sitting at the tie down. Only messed with a day of fun flying for me. You see, I still have not followed my own recommendation. I even replaced that spring with another seasoned main spring we had. Just adds another element of excitement of surprise when we go flying.

The spring will look fine and perform fine, right up to the point it snaps. I have seen, but rarely, the spring get so relaxed, and the king pin pivot angle so bad the tail wheel could not possibly turn. I could not believe the pilot could taxi the airplane. I wouldn't leave the ground with it for fear of it snapping. Again seeing this and having the spring snap while not in motion are rare as hens teeth.

There is no science behind the recommended 500 hours in service. That recommendation is conservative in nature and only arrived upon because we have not heard of a spring with less than 500 hours snapping and we feel pretty good under normal circumstance they won't. And at 500 hours, between 5 and 10 years of flying for most of us, the cost of the main spring replacement is insignificant in the over all cost of aircraft ownership.

[daedaluscan]

Once you have asked yourself the question, the answer is to replace the spring. Its cheap.

[swixtt]

My thoughts on this centre around having a baseline, a starting point. Even if I knew the hours I still would consider replacing it. In my case like I mentioned I did the entire stack... Glad I did based on what I found.
Next are my axles.

[robrien]

Thanks all for the feedback - Bruce, a very compelling tale of woe! No wonder the numbers of aviators are dwindling with so many potential costs lurking in the shadows...
Ordering a new spring now (do not see anywhere in the logs that I have when it was last replaced).

[swixtt]

Good call, that's something you don't want to worry about!

[robrien]

I wanted to follow up on my earlier posts, as I bought a new main spring, and finally replaced it over the weekend.
It was a very timely replacement, as the bolt that secured the Scott 3200 tailwheel assembly was bent and partially separated (see attached image)!
Not sure how long that would've lasted before it finally failed, and I lost my tailwheel assembly... thanks for the advice to replace the leaf spring, as my IA told me not to worry about it!

[Bruce Fenstermacher]

That was close. You have a wise IA who must know EXACTLY the life left in a fatigued steel part.

You have now replaced the two most things in the tailwheel (maybe the entire airframe) that seem to break the most and cost lots of money to repair resulting damage. The last is the kingpin of the tail wheel itself but they seem to fail much much less often and when they do with less catastrophic results as the tail wheel departs the aircraft, not held on to beat the tail feathers to death. When this happened to me, I did not even know it until I parked the parked the plane after flight and noticed the nose had taken a odd high attitude.

[sreeves]

My tail spring looked great just before it broke the usual leaf at the usual spot while the aircraft was being towed by the tailwheel by a power tug up an incline into my hangar. When the mains hit the lip (2") of the hangar floor (city-owned) the spring snapped. The airplane lower rudder was damaged on the left side. So a replacement at the 500 hour mark is not excessive at all I don't think. But be prepared for some major fun while replacing the spring assembly. It was a pain. I have since built a set of homemade ramps so the airplane doesn't get stuck on the door tracks or on the hangar floor lip.

[Hineywheel Bill]

Having seen no evidence in the logbook that my main tail spring has ever been replaced, and given that it LOOKS to be the same age as the others above it, I plan to order a new main spring today. It seems like pretty cheap insurance to me.
I had a 1951 A model years ago that I just COULD NOT make taxi worth a hoot. Once I noticed what I should have seen on day one, that the spring was sprung allowing the tailwheel base to be tipped upward, it made perfect sense. A new spring made a whole new airplane out of it. No need taking unnecessary chances, especially over just a few dollars and a little work.

[TFA170]

I've seen no evidence mine has ever been changed either, so it's high on my "to do" list. What's the best place to source these main spring leaves?