Airframes T/W spring bolt torque

[Aviator]

Just got my Airframes 1-3/4 2-hole T/W spring. The elongated hole in the 2nd leaf is at the airframe end. What's a good torque on this bolt? The standard torque doesn't allow the 2nd leaf to slide at all.

???

Thanks.

 

[barbwire]

I cannot answer the torque question on the bolt that holds the two springs together. I used a self locking nut and just cracked it tight and its been good. But find a piece of thin belting and cut you a piece to fit under the bracket that bolts to the frame. It will save you a problem in the future. As you tighten it the belting will compress and you can see when its about right. I had all kinds of trouble with that connection until I did that. There is a thread here somewhere on this very subject and the arguments about regs. etc. etc. are in there. I will just say I had all kinds of trouble with that connection until I installed the belting and then no problems since. It works and the original setup did not for me.
At this point I need to throw in a few legal disclaimers:roll:
I am an actress not a real mechanic.
Actual crash results may vary.
All research on this subject are blatantly flagrant.
Avoid alcoholic beverage while using this product.

 

[nanook]

If you impact hard enough, it will slide...

 

[mvivion]

If you impact hard enough, it will slide...

Talent and perseverance can overcome torque?

MTV

 

[Steve Pierce]

I tighten it pretty dang tight with a 3/8 long wratchet.

 

[Aviator]

Thanks for the info all. My issue is with the bolt at the fwd end where the #2 leaf is supposed to slide between #1 and #3. I didn't find a discussion on this. I did follow the thread on the T/W bolt (the other end of the spring).

I don't have a "U" bracket under the tail post, just a straight piece of aluminum with a pair of prongs on each side that holds the #1 leaf and about half of #2 (pic here: http://www.airframesalaska.com/category-s/1853.htm under tailspring bolt kit)

For the time being, I slipped two 1-3/4" x 8" x 1/16" sheets of that slippery (HMPE, UHMW?) plastic on the top and the bottom of the #2 leaf and snugged the 3 bolts (1 x AN7 and 2 x AN4) but not torqued to bolt specs. Will see how that performs.

 

[Steve Pierce]

I think you are over thinking the whole assembly. Install the tailwheel on the springs with an AN7-21 or 22 bolt. Install AN6 bolt through airframe and 3 springs, install the two 1/4" bolts at the tailpost and tighten everything. Installed many this way with no issues.

 

[Aviator]

I think you are over thinking the whole assembly. Install the tailwheel on the springs with an AN7-21 or 22 bolt. Install AN6 bolt through airframe and 3 springs, install the two 1/4" bolts at the tailpost and tighten everything. Installed many this way with no issues.

Thanks Steve. Is an AN6 adequate? Do you use a bushing? Both the springs and the airframe are drilled 7/16".

 

[Steve Pierce]

The spring has an oversized hole but the fuselage originally had a 3/8" hole.

 

[Aviator]

...the fuselage originally had a 3/8" hole.

That's good info. Thanks.

 

[skywagon8a]

Thanks for the info all. My issue is with the bolt at the fwd end where the #2 leaf is supposed to slide between #1 and #3. I didn't find a discussion on this. .....

Aviator, I believe that the elongated hole is for another purpose than to allow the spring to slide. Since the stack of springs are not precision built, without the slotted hole there would be a tendency for the bolt to shear in use. IF when stacking the springs the bolt holes were not in perfect alignment due to the arch of the springs the impact of landing and flexing of the springs could tend to shear the bolt. Thus the slot. The slotted spring is just sandwiched in the middle. The arch of each spring wants to nestle snug in the arch of the other springs in order to function properly. All of the sliding is at the tail wheel end. Loose springs can lead to other structural (cracks in tubing) issues.

 

[Aviator]

I appreciate the info, skywagon8a, but I have Airframe's springs. The T/W is attached to the #1 and #2 leaves with two AN7 bolts. No slot in the spring at the T/W end. It's at the front (airframe) end (in #2 leaf).

Neglecting the #3 (top) leaf for the moment, as I understand it, if both ends of a two-leaf arced spring-sandwich are fixed (by torquing the bots to specs), then the assembly can't flex and the airframe takes all the beating. Seen it before and it ain't pretty. Also, any bolt in round holes will be subjected to shear loads they can't handle (see pic of single hole Scott 3200 T/W bolt here: http://www.supercub.org/forum/showthread.php?43042-Broken-Tail-wheel-bolt/page5 post #172). Even if the slotted leaf does slip under a heavy load - e.g., when hitting the tail real hard, as nanook suggested(?!) - it won't return to its resting arced state, and the T/W caster will be lost or could even become negative.

Steve Pierce put the bug in my ear pointing out that the front bolt was originally an AN6. That opens up the possibility to put bushings in the 7/16" holes and separating the spring stack from the airframe with a 4130 plate drilled to 3/8". I could then torque the AN6 bolt to specs (on the spring bushing) without clamping the #2 spring leaf so tight it can't slip. Will try that sometime on my old 1-1/4 spring stack in a mockup.