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Pilottonny

Well Known Member
Hello out there,

I am concerned about the bolt and screw quality supplied with the kit.

In Europe we are used to "8.8" quality bolts as being the, sort of, least quality, every day average, off the shelve, house and guardening, bolts being used for anything ordinary in Automotive, Construction, Bicycle, Steel erection, etc. Better quality bolts used for "high tensile" connections are "10.9" and "12.9". So far I have never been able to break a bolt tightening it, using the appropriate screwdriver/spanner! (Hey, I do not do fitness nor powerlifting)

Now I am very worried, because I broke a screw, tightening one of the tank cover plates using a normal screwdriver! and just recently broke an AN3 bolt when thighthening one of the bolts of the Tie-down bar "W933" on the RV9 wing-spar, with a 1/4" ratchet. OK, against the specifications, I did not use a Torque-wrench for these screws and bolts:

-1: because I thought if they are tight that would suffice (tight is tight, right?).

-2: I can not find a torque wrench that will go below "5 Nm", which is higher than what is specified for these screws/bolts, anyway (but is very, very, low !?).

I am wondering what the quality of the screws and bolts is, supplied with the kit, compared to the ordinary "8.8" quality we use in Europe? Obviously the bolt-strength has been considered in the design, but, if the bolts are as soft as they seem, the tightening is very crucial, because they might be over-torqued easily and break when stressed in flight.

Anyway, I am worried !!! Can anybody share data on the bolt-strength and give advice?

Thanks in advance,

Pilot Tonny.



 
bolts

Hi Tony,

The bolts need to be tightened with a torque wrench until you are comfortable with the "feeling" of torquing them. The torque required for an AN3 bolt is very low, and if you don't use a very small wrench, it is very easy to overtighten them.

Clearly with 4000 RVs flying, and hundreds of thousands of other aircraft flying with these bolts, they are strong enough. Keep in mind that most of the time the material between the bolt and the nut is aluminum, so you really don't need or want a lot of torque on there.

I know you are a strong fellow, but these nuts and bolts are not the right place to show off all that power! :)
 
I've done it

I broke one last night too. Mine was a tie-down assembly also. I used a torque wrench, the kind that "clicks" when you've reached the proper load.

Apparently I missed the click. As soon as I thought to myself. "Hmm, this seems to be a little tight for an AN-3, where's the click?" I heard a pop and the nut was on the floor.

They take very little strength to tighten, definitely use a torque wrench. I had a hard time finding one in inch-lbs as well, but eventually did, it was about $30 if I remember correctly. You may be able to find one on the internet.

On that note, the AN-3's do seem very lightly tightened. Does anyone know if these should be safety wired? What are others doing to attach the tie-down brackets to the spar?
 
They are good

Pilottonny said:
I am wondering what the quality of the screws and bolts is, supplied with the kit, compared to the ordinary "8.8" quality we use in Europe? Obviously the bolt-strength has been considered in the design, but, if the bolts are as soft as they seem, the tightening is very crucial, because they might be over-torqued easily and break when stressed in flight.

Anyway, I am worried !!! Can anybody share data on the bolt-strength and give advice?

Thanks in advance,

Pilot Tonny
Click to expand...

Tonny... US AN hardware is well made and of a known strength. Vans designed to the specifications of the AN hardware charts.

The 8.8 Metric specification bolts you mention are made of steel that has an ultimate strength of 116,000 psi and a yield strength of 93,000 psi (all units normalized to US standards for comparison).

The AN bolts are certified bolts that exceed a SAE Grade 5 specification with an ultimate strength of 125,000 psi and a yield strength of 93,000 psi

Some NAS bolts are stronger, but are not necessary for our planes (unless specifically called out by Van, of course).

An office mate of mine has a "souvenir" bolt he kept from an autogyro crash on El Mirage Dry Lake. It's a AN 6 bolt that was in his rotor system, and it has a 90 degree bend in it, but it didn't fail! Bolt substitution for stronger hardware may have different effects when failures occur... stick with what the designer called out.

Rest assured, the AN hardware is good, and is right for the job. They have been around unaltered from at least the 1940s... Get a torque wrench with the right calibration - even if you have to get a US one - and use that for your project. Follow the torque requirements of the "bible" AC 43.13-1B and you'll have a correct joint and be able to satisfy whatever inspectors you have in your home country.

gil in Tucson
 
Bolts

Tonny,

This is my favorite subject. I feel a responsibility to reply to your post because I have some professional experience with bolting in general, and have built an RV-4, so have experience in using AN hardware. I am a mechanical engineer, and early in my career became the bolting guru (expert) at an oil refinery where every bad bolt can kill you. There is much more to bolting than just strength, although that is what everyone ultimately needs in a bolted joint. The AN hardware also has to meet rigid requirements for ductility, which is another way of saying that it won't fail the second it is overstressed. It will yeild first, and become severely distorted before it finally fails. The problem with torqueing bolts past the recommended amount is that you eat into the failure margin, and the bolt will fail under load sooner than it would if it was torqued correctly.

For some reason, I am not sure why, many people do not take the torque requirements and other bolt standards seriously when they build their airplanes. Maybe it is because of the hardware's ductility, which causes The hardware to be very forgiving of the typical problems associated with bolting, so it is unlikely you would ever have a failure in flight. However, that being said, overtorqueing is playing with fire. If you severely over torque a bolt it has already yeilded. When will it fail? How can you know for sure? Follow the torque requirements religiously on every bolt, especially those in the control system and you can sleep at night.

Secondly, Van's, at least on the RV-4, called out some bolt lengths incorrectly. Check the standards for how to tell if you have the correct length bolt installed. Make sure the nuts are not bottomed out on the threads and eating into the shank. Make sure there is one complete thread visible on top of the nut, etc. You can not blindly put in bolts that are the wrong length without risking cracking in the shank, or the nut not staying locked in position.

The bottom line to your original question, use a torque wrench, and do NOT over torque any bolt. I would recommend replacing any that you feel you may have over torqued, because very likely they have stretched into the danger zone already, and there is no way to know for sure without doing sophisticated testing to them. And bolts are inexpensive.

Brent Travis
N999BT
RV-4 Flying
 
vmirv8bldr said:
On that note, the AN-3's do seem very lightly tightened. Does anyone know if these should be safety wired? What are others doing to attach the tie-down brackets to the spar?
Click to expand...

BP:

Those bolts are torqued into K1000-6 anchor nuts right? Bolts into anchor nuts "don't need no stinking safety wire". More gererally, bolts or screws with self-locking nuts, including anchor nuts, don't require additional safetying. Ensure you use the right bolt without the safety wire hole or folks in the future may think something is missing.

Jekyll
 
Thanks

Thanks.

I was thinking that, but just wanted to be sure.

I'm using the regular ones, no holes for safety wire, as called-out in the instructions. The ones that hold the tie-down bracket on are into self-locking nuts (Nylok?) The one's that hold the bellcranks on are into nutplates.
 
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