bolt torque

[wannafly]

Tail wheel spring assembly. Front bolt is AN-20 and bottom that attaches the wheel is a AN-7.

who knows the torque value for these.

thanks

[jtpitkin06]

Wow!!! you have an AN-20 bolt for the tailwheel? That has to be a misprint. An AN-20 bolt is 1-1/4 threads. That's as wide as the spring.

My front bolt on the tail spring is an AN-5
Torque is 100-140 in-lb or 11 -16 Nm in tension.

My tailwheel to spring bolt is also an AN-7
Torque is 450-500 in-lb or 51 -56 Nm in tension

I consider both these bolts to be in tension. Shear torque values are lower.

John Pitkin
Greenville, TX

[PapuaPilot]

I agree, the front bolt isn't going to be an AN-20. Find out what size the bolt really is before you torque it.

The reason I am chipping in is to clear up one very common misunderstanding that John brought up; and that is whether to use tension or shear torques. Most of us think that the shear/tension torque decision has to do with the application or what type of load the bolt is under. It doesn't!

To choose which torque to use you need to consider the hardware that is being used. You only need to use the shear torque when you are using low profile (i.e. shear) nuts. You should use the tension torque for everything else. The reason is very simple: the thinner nuts have less threads and need to be torqued at a lower value so they don't strip out.

I didn't understand this correctly for many years working as an A&P. I taught the wrong way to other mechanics too. Finally a friend (old timer A&P, IA, maintenance instructor) pointed out the truth using the torque table in a Cessna maintenance manual. Take a look, the Cessna MM only shows shear torques under the column for nuts, not bolts, and all of the nuts in the shear column are low profile nuts.

I bring this up because the Kitfox uses lots of low profile nuts and it would be good if we know how to torque them properly. Remember: think hardware, not application!

[t j]

Wannafly,
Looking at my Classic 4 builders manual tail wheel instructions. The page is a little blurry. It does look like the front bolt is labeled as an AN-20. It is actually an AN5-20. The rear bolt is AN7-10A. It does have a torque range for the rear AN364-720 shear nut...270-300 in/lb.

The front nut is an AN310-5 castle nut.

[t j]

Here's more to add to the confusion.

My Kit came with an AN364-720 shear nut on the rear bolt. That bolt goes through only one spring leaf. The maule tail wheel documentation that came with the tail wheel in my Kit shows that bolt going through two spring leafs and using an AN310-7 nut.

I guess you need to check which nut you have to determine the correct torque.

[jtpitkin06]

When considering shear or tension torque on a bolt think BOTH application AND hardware.

The bolt application on the tailwheel spring is clearly in tension. Thus, one should use appropriate tension hardware.

Because the tail spring is subject to a lot of abuse and vibration it needs a secure, high torque connection to both the fuselage and the tailwheel assembly. No thin nuts here. Use the tension torque settings.

You can find torque charts in AC43 or simply do a Google for AN bolt torque. Print out a copy and hang it on the shop wall.

John Pitkin
Greenville , TX

[PapuaPilot]

I think John and I are saying the same thing in different ways.

Like he said, there are high tension loads on a tailwheel spring. Therefore you need to use hardware for tension (standard nuts not a low profile ones). If you use a standard nut you want to use the tension torque.

As the builders we don't really make the decision about hardware. This information is given to us in the assembly manual. The engineers have calculated what hardware needs to be used throughout the plane. For each application they chose the right size bolts and nuts to handle the loads (tension and/or shear). The nut is the only factor in choosing the correct torque though.

FYI There is no problem using a standard nut in place of a shear nut as long as the nut goes on the bolt far enough. The bolt can handle the higher torque. You may need to use a longer bolt though, which means extra weight from both the bigger nut and longer bolt.

To summarize this:
Application determines your choice of hardware.

The choice of nut (tension/shear) determines the torque required. This is because the low profile nuts have less threads and can't handle the same torque as a standard nut.