I am certain that I have NEVER seen a mechanic put a TQ wrench on a tail wheel spring.. The only time I have ever seen a TQ wrench used was on the prop and the engine. Putting a Tq wrench on the tail spring and getting off into the pickers on possible moments and stresses and all the other stuff seems to take the fun out of building and makes it work.. with big head aches.. unless your an engineer who lives for numbers, loves to crunch them, and not make much forward progress on building, but you have one impressive stack of scratch paper with more formulas on them than you can shake a stick at LOL

I have a AN7-bolt on my 3 leaf (non RANS, for a J-3 I think, from Spruce anyway and for a similar weight airplane) tail spring. It came with a bushed hole for a AN 5. I go tight, but not "too" tight, just tight, and don't use a TW. The first one broke (one leaf, caught it in time) at about 900 hours, I plan to replace the current one at 700 hours, as cheap insurance. They take a beating no matter what.

I also, at the time I upgraded that bolt, using some info from the Cub guys, added some additional cross bracing back there. Yes I may be transferring the stress, but at least it's spread out over a much larger area, so far so good. Finally, I cut back the fabric, permanently, leaving the entire spring and attach hardware exposed, for easy pre flighting. Before it was only visible after I took a inspection plate off, even then you almost needed a mirror. Now it's all exposed and much easier to get to when needed.

akavidflyer wrote:I am certain that I have NEVER seen a mechanic put a TQ wrench on a tail wheel spring.. The only time I have ever seen a TQ wrench used was on the prop and the engine. Putting a Tq wrench on the tail spring and getting off into the pickers on possible moments and stresses and all the other stuff seems to take the fun out of building and makes it work.. with big head aches.. unless your an engineer who lives for numbers, loves to crunch them, and not make much forward progress on building, but you have one impressive stack of scratch paper with more formulas on them than you can shake a stick at LOL

You just read the number off a list, for the size of bolt, then pull the wrench.

If you don't torque tailwheel bolts, they can crack over time. Mine did.

THAT leaves you doing tricky and risky field repairs, about a day's walk from the nearest road. With passengers looking pretty uneasy.

It's easier for everyone just to do the job right the first time. If your engineer isn't using a torque wrench, maybe he has a calibrated arm from experience.

In case you're interested in some light reading this nasa spec is fairly new and we use it as a reference in both space and faa programs...

https://standards.nasa.gov/documents/detail/3315811

With the aid of some 2x4s and a Toyota bottle jack I've attached my tailwheel, just using the AN7 for now but I think I may go up to the 1/2" bolt per Wup's suggestion before braving any rough stuff. Nothing torqued yet though. It's in "noncommittal build mode."

Zzz wrote:With the aid of some 2x4s and a Toyota bottle jack I've attached my tailwheel, just using the AN7 for now but I think I may go up to the 1/2" bolt per Wup's suggestion before braving any rough stuff. Nothing torqued yet though. It's in "noncommittal build mode."

How much do you have to torque a Craftsman screwdriver in a rudder installation, anyway?

Are you saying I shouldn't be using screwdrivers in lieu of AN4 for permanent rudder attachment? Did I do something wrong?

BazzLow wrote:In case you're interested in some light reading this nasa spec is fairly new and we use it as a reference in both space and faa programs...

https://standards.nasa.gov/documents/detail/3315811

This thread was already on its way to convincing me that tailwheel bolt tightening was rocket science. This NASA link seals the deal.

Just removed, inspected, repacked with Mobil 28, and reinstalled my 3200. Found a great series of Youtube videos from "Steve Johnson", though as zzz points out the presenter is actually Steve Pierce. ACA says to torque the AN7 attach bolt to 41 ft lbs.

But it is a castellated nut with a split pin, so good maintenance practice is what - torque to 41 then increase until the split pin goes through, or to 41 and then back off until the split pin lines up?

Karmutzen wrote:using Steve Johnson's YouTube videos.

Steve Pierce is the knowledgable mechanic who made those videos.

Zzz wrote:

This photo is a good example of something I've always wondered about. Looks like the t/w bolt goes through two springs. Those two springs have to be able to slide against each other, since at different radius's they will flex differently. I've seen where the upper leaf has an oval hole, supposedly to allow that--
yet tightening the t/w attach bolt would compress all three parts (two leafs & the t/w head) into one unit. Also, the two springs trying to work (slide) against each other would tend to put a lot of shear pressure on that bolt.

IMHO bolting the t/w to a single thicker leaf would seem to be a better idea.
My C170 had that arrangement, although my C150TD had the double leaf.

hotrod180 wrote: This photo is a good example of something I've always wondered about. Looks like the t/w bolt goes through two springs. Those two springs have to be able to slide against each other, since at different radius's they will flex differently. I've seen where the upper leaf has an oval hole, supposedly to allow that--

Hence the original post: https://www.backcountrypilot.org/commun ... 54#p211982

Oops.
I went back & read through the entire thread, it doesn't look like that issue was ever addressed?
I've seen lotsa small Cessnas have the 3-point angle-of-attack modified by cutting the main leaf off even with the second leaf and bolting through the whole works, my C150TD might have been similarly modified. In any event, it did have the double-leaf thing going on. As I recall, when I pulled it apart one time the bolt seemed to have a slight curve to it. I replaced the bolt, I think it was a 7/16"? Also I seem to recall that it didn't want to stay put-- maybe because of the springs working on each other and the bolt. I ended up dabbing some torque-seal on the nut to check for loosening.

I've got a little experience with tw springs on ag planes doing around 1,000 to 1,500 landings per 100 hours... These things get an absolute beating. Has taken some trial and error, but we've had great reliability over the last 3,000 hours or so and only two AN4 bolt failures in 30,000+ landings, no damage, just new bolts fitted. We have a local spring works manufacture a 4 leaf setup and have the oval holes at the very front attach bolt so the tw knuckle bolts are torqued to max recommended (with a torque wrench). We replace the 3 front bolts every 100 hours and rear ones on condition. I also spray the sliding surfaces with Molykote dry lube rather than greasing. We get between 500 and a 1,000 hours from a set of springs before they sag enough to affect steering..