Failure of Nose Gear (now with bolt pics)

[flytoday]

I believe my bolt failed into three pieces. I'll call them the HEAD, BODY, and THREAD&NUT. Reference coin is US Dime.

I cannot find HEAD.

Here is a picture of the two pieces I have. THREAD&NUT was found under the plane at the failure place. BODY was in the strut and came out with a relatively light tap with a punch.



I believe these are the mating surfaces of THREAD&NUT and BODY



I believe this is the end of BODY that would have been attached to HEAD



And here are two lousy angle pictures with a temporary bolt to keep my strut in place while sitting in the hanger....

Top of temp bolt



Bottom of bolt (threads - no nut), odd orientation in upper right corner



Carl

[GAHco]

Depending on your model.

Nas6605-24 or Nas6605-29 standard diameters

add an (X) at the end for 1/64th oversize

We have the right reamers.

I do not know the hardware for the Ten model.

[Rootski]

Originally Posted by flytoday

I believe my bolt failed into three pieces. I'll call them the HEAD, BODY, and THREAD&NUT. Reference coin is US Dime.

I cannot find HEAD.

Here is a picture of the two pieces I have. THREAD&NUT was found under the plane at the failure place. BODY was in the strut and came out with a relatively light tap with a punch.



I believe these are the mating surfaces of THREAD&NUT and BODY



I believe this is the end of BODY that would have been attached to HEAD


And here are two lousy angle pictures with a temporary bolt to keep my strut in place while sitting in the hanger....

Top of temp bolt



Bottom of bolt (threads - no nut), odd orientation in upper right corner


Carl

That doesn't look like a ductile shear failure to me, especially that jagged edge on the head side.

If you're interested, PM me your address and I'll send you a titanium replacement, free of charge.

[DavidBurton]

Hi Carl,

It's somewhat difficult to see the fracture surfaces in the photos but at first glance it looks like the nut end failed from fatigue and the other end failed by tensile overload. We'd have to be able to examine the surfaces better to be positive.

If this was the failure mode I'm a little surprised to find the nut. What usually happens is that the strength of the fastener reduces as the crack progresses until there is a final tensile overload that causes the ultimate failure. I suppose that both failures could have happened almost simultaneously with the head end being torn off after the nut end failed.

David

[Taildrgr]

Here is my theory for the experts to diagnose.......I am guessing there were 2 separate failures. The first one was the head of the bolt failed in tension due to over torqueing and vibration in the engine mount. The bolt was held in place by friction but the sheer strength was significantly weakened. Some time later, due to all the sheer being transferred to the nut end, the nut finally sheared off.

[newtech]

As soon as the weather gets above 0 I'll remove the locking bolt in my nose gear for a look see. When landing at Larry Vetterman's fly-in last year my nose gear went into a violent grocery cart wheel shimmy; so bad that the front cap of the wheel wheel pant was thrown off. I don't expect to find anything but it was a pretty violent event.

[seattleworm]

From the pictures, it looks like the failure is a typical fatigue, about half of the fracture surface is smooth (fatigue zone), while the other half is rough (due to instant fracture). This is typically caused by repeated bolt bending. It is hard to say what really caused this since this type of failure is rare for RV fleet. If I have to guess, it is mostly likely the bolted joint was loosened due to vibration. Especially if the bolt is not re-torqued during annual.

[jrs14855]

Is the unthreaded portion of the bolt at least 1/8" longer than the od of the gear socket. The failure at the base of the threads is something that is relatively common on AN3 bolts, I have never seen it on a larger diameter bolt. The amount of thread below the nut is indicative of a bolt that was too short. Ideally the number of washers should be such that the nut is about 1-2 washers from bottoming out on the threads. The number of threads protruding beyond the nut is a very basic rule of thumb. The number of threads protruding will vary with the size of the bolt, the larger the bolt diameter the courser the threads. One thread protruding on an AN 3 is not equal to one thread on an AN8.
The technical name for the coating on bolts is dichromate (dip)> It is normally a brownish gold color but other colors could be used. Hydragen embrittlement is most problematic on chrome plating, especially 4130 steel. Not normally a problem with cadmium but I have my cadmium parts baked anyway.

[RV3bpilot]

I had trouble with an exhaust bolt that kept breaking just under the head. What I found was the bolt head was not flat on the surface it was clamping. Another words the hole was not perpindicular with the bolt surface.

[Mike S]

Originally Posted by RV3bpilot

I had trouble with an exhaust bolt that kept breaking just under the head. What I found was the bolt head was not flat on the surface it was clamping. Another words the hole was not perpindicular with the bolt surface.

They make special washers for that.



http://www.grainger.com/category/sph...ecatalog/N-8om