Nose Gear Bolt Failure. Argh!

[GalinHdz]

I feel your pain. This doesn't only happen to the RV clan. I just had almost the same bolt failure on my KIS4 nose gear assembly back in August.

[RKellogg]

Originally Posted by krw5927

You're right, Roger. I didn't look up the shear value and foolishly used someone else's stated number. According to the Skybolt document you referenced it does look like margins can be increased by using a NAS1100 (superceded by NAS6200, or for close tolerance NAS6600) series bolt here. Your calculation of 513 lbf at the tire to shear the AN bolt by a rotating load would be increased to about 640 lbf with a NAS6200/NAS6600 bolt at a 95ksi minimum single shear. Almost 25% stronger. I like those odds.

Given the relatively low factor of safety, it is a good place to add a bit of margin. I was surprised that the FS is that lean. My static empty nose gear weight was just under 300 lb. Will measure and order tomorrow.

Do the mains experience the same failures?

Roger

[LifeofReiley]

I think we will take this step up on the 7A to the NAS6605-27 standard bolt for now. Just makes me feel better.

[Bevan]

Genuine Aircraft Hardware has them, reamers too. Tom monitors these forums and is excellent to deal with. I for one would like to know more about chamfers helping to prevent bolts shearing.

http://www.gen-aircraft-hardware.com/store.asp

Bevan

[fstringham1]

I agree with Jim .... Nov. 1964 Flying Magazine says it all ....

Originally Posted by jrs14855

I am amazed at the number of times I read posts on this forum where builders seem to think they can ream, or much worse, drill to size a hole in a critical area using a fractional size drill or reamer. Nominal AN5 bolt would be considered 5/16" diameter. I just measured a few AN5 bolts, size varied from .3097 to .3119.
Obviously a bolt that is almost .003 undersize if not satisfactory for the nose gear. Furthermore it is not unusual to find substantial variation in the unthreaded portion of an AN4 bolt. This is especially true of the area immediately adjacent to the thread which may be substantially smaller than the rest of the shank. I compensate for this in critical areas by using a bolt that is one dash number longer than required.
A fractional reamer is very likely to cut slightly oversize, which further complicates the issue.
I have only a limited knowledge of the RV nose gears/mounts as to whether some or all are drilled/reamed to size by the factory.
When drilling a Wittman main gear, I drill in the heat treated condition. I use a clamp in place drill jig with removeable hardened drill bushings. I start with a 3/16 pilot drill, then a 1/64 undersize drill, then .309, 310, and 311 reamers. I select bolts that are a medium drive fit on an AN5 bolt.
If using a NAS bolt, these are usually .001/.002 over the fractional size, so would require a different set of reamers.
I use bolts that are one dash number extra length and use all metal lock nuts.

[rockwoodrv9]

Originally Posted by LifeofReiley

I think we will take this step up on the 7A to the NAS6605-27 standard bolt for now. Just makes me feel better.

Is this what you are talking about?

http://www.coastfab.com/php/proddetail.php?prod=0281

[LifeofReiley]

Originally Posted by rockwoodrv9

Is this what you are talking about?

http://www.coastfab.com/php/proddetail.php?prod=0281

Yes Sir... and Thanks!!!

[newt]

Originally Posted by vernh59

Here is another view from the crowd.

"Looks like that red one started aerobatics a bit early, son."



- mark

[fixnflyguy]

There is a bolt made that is far tougher than AN/NAS bolts. They are the "big plane" industry standard for ultimate strength..I have a few on my plane. They are 220KSI (220,000psi) tensile, and made from Inconel. They just don't break..period. The MFG designation is a Boeing trade designation, but you can google around and find them. Not knowing exact size for the A model application, I am only guessing you would be looking at a BACB30US5K27. The "BACB30" is the style, the "US" is the Inconel alloy, the "5" is the diameter, the "K" is for the coating of aluminum (long story I wont go into) and the "27" is the grip length. I don't intend to even try and re-engineer the current product, but that's what my day job is...and Len, stop out at 8A7 next time your around.

[Walt]

Originally Posted by fixnflyguy

There is a bolt made that is far tougher than AN/NAS bolts. They are the "big plane" industry standard for ultimate strength..I have a few on my plane. They are 220KSI (220,000psi) tensile, and made from Inconel. They just don't break..period. The MFG designation is a Boeing trade designation, but you can google around and find them. Not knowing exact size for the A model application, I am only guessing you would be looking at a BACB30US5K27. The "BACB30" is the style, the "US" is the Inconel alloy, the "5" is the diameter, the "K" is for the coating of aluminum (long story I wont go into) and the "27" is the grip length. I don't intend to even try and re-engineer the current product, but that's what my day job is...and Len, stop out at 8A7 next time your around.

Good idea, maybe GAHCO could track some of these down for us?