Eye-bolt failure: Myth or reality?

[Chrisn]

For any equipment: safety margin of 10 for lifting people, safety margin of 6 for lifting loads, IIRC

A sudden shock is enough to go beyond what the max load rating of the eye bolt is, even if your rocket weight is nowhere close.

 

[WOOSHPREZ]

I had a PML D region tomahawk that I purposely built with a 3/16" eyebolt years ago. It's just a 3" phenolic critter that might weigh 4 lbs.
Intended to test the beast until failure of the eyebolt but never really wanted it to fail so I flew the thing in every mode possible including adding an e bay and extra section to fly skyripper hybrids in it. It is still going strong.
Why? I must have been either lucky or a good altimeter that popped out the laundry at just the right time to inflict as little damage as possible. Electronics are so nice that way.

One of our new members didn't get so lucky. He built a LOC Warloc zipper proof but only used a regular 3/8" eyebolt. The eyebolt straightened out on it's first flight dooming the rocket. Since then he rebuilt the warloc. It was a pretty rocket until last weekend when the wildman sold him a new Cesaroni K675 skid. Used motor deploy. They shortened it down from 18 to 14 seconds.
The delay grain never burned. Down it went. My video of the flight was 24 seconds from motor ignition to ramming speed and impact. His U bolt looks like a pretzel now.

 

[MarkII]

...
The delay grain never burned. Down it went. My video of the flight was 24 seconds from motor ignition to ramming speed and impact. His U bolt looks like a pretzel now.

The strength of the hardware is rather irrelevant at that point...

Without discounting the potential harm that can be caused by even one such incident, just how often do such eyebolt-straightening recoveries happen, anyway? (1 in x individual launches at your field?) In many of those incidents, aren't there other design flaws in the rocket or other major malfunctions during the flight, too (which set the stage for the eyebolt failure)? I am referring to rockets that only have apogee deployment.

MarkII

 

[DeWain]

This is pretty timely advice... I am building my first HPR kit. The Mad Cow Rocketry Big Fizz (the kit that I am building, which is basically a 4x Alpha upscale) comes with two open eyebolts. One is used as the attachment point on the upper centering ring, and the other is screwed into the base of the nose cone (to attach the NC to the shock cord).

So here is the question: if there is the possibility of enough force at the centering ring attachment point to cause an open eyebolt to straighten, wouldn't the eyebolt at the base of the NC also be a problem? And given that the NC eyebolt just screws into the opening in the base of the nose cone (no washers or opportunity to epoxy both sides), wouldn't the interface between he nose cone and the shaft of the bolt fail long before the open eye bolt would straighten out?

 

[troj]

So here is the question: if there is the possibility of enough force at the centering ring attachment point to cause an open eyebolt to straighten, wouldn't the eyebolt at the base of the NC also be a problem? And given that the NC eyebolt just screws into the opening in the base of the nose cone (no washers or opportunity to epoxy both sides), wouldn't the interface between he nose cone and the shaft of the bolt fail long before the open eye bolt would straighten out?

Yes, the one on the nosecone could straighten, but as you said, it's more likely that it will strip out, given that it's just into plastic, and has no nut behind it.

In regards to Mark's question about how often it occurs, I couldn't tell you -- most people I know toss any open eyebolts they get, and replace them either with forged, or with a u-bolt.

-Kevin

 

[cjl]

Besides, the nose cone is usually fairly light, so it is less likely to cause extreme loads than a heavier component.

 

[troj]

Besides, the nose cone is usually fairly light, so it is less likely to cause extreme loads than a heavier component.

With the "blow it up or blow it out" mentality many seem to use, it can generate amazingly high loads, even when relatively light.

-Kevin

 

[cjl]

Agreed. I will admit to using somewhat heavy charges in some cases, but I also try to lessen the loads by bundling the shock cord with fairly heavy tape wraps so the pieces can slow down progressively, rather than in one large impact. So far, it has worked quite well.

 

[DeWain]

Yes, the one on the nosecone could straighten, but as you said, it's more likely that it will strip out, given that it's just into plastic, and has no nut behind it.
-Kevin

Sooo... do you recommend a different way of attaching the harness to the nose cone? Any ideas (or any references)?

Also... are there good rules of thumb for how much ejection charge to use? I plan on using Cessaroni and/or Aerotech 38mm reloads with motor ejection.


Since this kit is a gift from my wife, she is liable to do this >> :bangbang: if she watches it plummet to the ground on it's first flight.

 

[cjl]

It is true that you always would rather have too much than too little, but don't take that idea too much the extreme. What size is your chute compartment?

 

[troj]

Sooo... do you recommend a different way of attaching the harness to the nose cone? Any ideas (or any references)?

A couple options come to mind...

1) Use an expansion bolt, instead of the eyebolt provide.
2) Cut a hole in the shoulder of the nosecone which allows you to reach in from behind and install a fender washer and nut.

The second option is common and would work well.

Also... are there good rules of thumb for how much ejection charge to use? I plan on using Cessaroni and/or Aerotech 38mm reloads with motor ejection.

The ejection charges that come with them are usually reasonable, unless your rocket is small, in which case they can pack quite a wallop.

Since this kit is a gift from my wife, she is liable to do this >> :bangbang: if she watches it plummet to the ground on it's first flight.

Don't let her be there for the first flight.

That was easy.

-Kevin

 

[DeWain]

Thanks for the rapid advice!

The Big Fizz is a 4" rocket. It doesn't have a separate chute compartment, but the amount of space between the upper centering ring and the nose cone is about 14" long.

Are closed eyebolts and the quicklinks used for attaching chutes commonly found at hardware stores?

 

[cjl]

Some hardware stores, but definitely not all. If it's a 4", the included charge will be about right (perhaps slightly on the energetic side, but not bad). I'd just use the entire included charge.

 

[troj]

The Big Fizz is a 4" rocket. It doesn't have a separate chute compartment, but the amount of space between the upper centering ring and the nose cone is about 14" long.

You should be fine.

Are closed eyebolts and the quicklinks used for attaching chutes commonly found at hardware stores?

Depends. Around here, the forged eyebolts are not, at least not that I've found yet. I can find a limited selection of U-bolts. If I wanted to scavange stores in Omaha, I bet I could find a better selection.

Quick links, yes, at least around here. A trick to shopping for them -- look for French. Literally.

Reach in the bin and grab a handful; if it says "Maillon Rapide," it's a good quality link that you can trust. If not, put it back -- quality is questionable, unless it has a WLL marked on it.

Some of the stores here will have a mix in the same bin, so it's worth checking.

-Kevin

 

[patelldp]

The "blow it up or blow it out" mentality is part of the problem, as are long cords.

-Kevin

I swear by this method.

 

[troj]

I swear by this method.

I've seen recovery systems get yanked hard by excessive charges, even when the harness is exceedingly long.

Neither one is necessary, and both create their own risks.

-Kevin

 

[als57]

Thanks for the rapid advice!

The Big Fizz is a 4" rocket. It doesn't have a separate chute compartment, but the amount of space between the upper centering ring and the nose cone is about 14" long.

Are closed eyebolts and the quicklinks used for attaching chutes commonly found at hardware stores?

Typically you can find them at most of the big box stores. Prices are cheaper on line thru McMaster-Carr.

Are you going to fly this beast at Nypower? If so stop by and I'll be glad to help out.

BTW the 1.3gr charge in a CTI 38mm reload should pop the cone with no problems. Ditto for the Aerotech 38mm.

BTW if your going to certify I will have the paper work with me.:bangpan:

Al

 

[cjl]

I've seen recovery systems get yanked hard by excessive charges, even when the harness is exceedingly long.

Neither one is necessary, and both create their own risks.

-Kevin

True, though I've had great success with quite long recovery harnesses combined with packing the cord in bundles wrapped pretty thoroughly in tape - as the bundles break apart, they absorb some of the shock, and it doesn't hit the end nearly as hard.

As for good quality recovery materials, the hardware store I normally go to has load rated quick links and shackles (up to larger sizes than I would ever need), as well as large amounts of tubular nylon and forged eye nuts. They might have forged eyebolts too - I wouldn't know (I prefer the eye nuts). It isn't exactly your standard hardware store though. Still, you could look - you might get lucky.

 

[epickett]

I often read that it is better to use forged eye-bolts, and as I have regular eye-bolts on a couple of my nose cones I am wondering: has anyone ever actually had an (un-forged) eye-bolt fail? I figure that there are several recovery points that would fail way before a 3/8" eye-bolt would unbend.

I've never had it happen personally, nor have I witnessed it happen. But there are a couple of guys in my main club who have. I use regular eyebolts in most of my stuff, and haven't had a problem, even with hard deployment. But my heaviest bird is only about 10 lbs... If I ever do a Level 3, I'll be using u-bolts for anchors on the fincan, anyway.

Eldred

 

[Handeman]

I think the whole argument about open or forged eyebolts is relative. It all depends on the rest of the rocket design. A five or six pound rocket with 3/8 tubular nylon shock cord could probably use a 5/16 - 3/8 open eyebolt with no issues. If there are ever any loads that could straighten the eyebolt, you have a lot of other things to worry about like broken shock cords, shreaded chutes, etc.

There is no way to make every component unbreakable unless you build something so heavy it won't fly. You need to match the components to each other. You don't need to over do one item and you don't want one item to be a weak link either. It's all about design.

 

[BobH48]

I've been reading this thread because it's interesting. I personally don't have any rockets that weigh over a pound. There has been plenty of discussion about overbuilding and adding excess weight.

My questions are:

What is the difference in weight between a 3/8" open eyebolt and the same size forged closed eyebolt? I'm assuming it can't be much.

What is the difference in cost between a 3/8" open eyebolt and the same size forged closed eyebolt? Is the money you save worth the risk when you factor in the cost of the entire rocket?

 

[Sailorbill]

I've been reading this thread because it's interesting. I personally don't have any rockets that weigh over a pound. There has been plenty of discussion about overbuilding and adding excess weight.

My questions are:

What is the difference in weight between a 3/8" open eyebolt and the same size forged closed eyebolt? I'm assuming it can't be much.

What is the difference in cost between a 3/8" open eyebolt and the same size forged closed eyebolt? Is the money you save worth the risk when you factor in the cost of the entire rocket?

Pulled from McMaster-Carr

Light Duty Eyebolt with Nut-Not for Lifting Zinc-Plated, 3/8"-16 Thread, 1" Shank, 7/8" Thrd Length
In stock at $6.55 per Pack
This product is sold in Packs of 10

or in 1/4"

9489T18
Light Duty Eyebolt with Nut-Not for Lifting Zinc-Plated, 1/4"-20 Thrd, 1-1/2" Shank, 1-1/4" L Thrd
In stock at $3.14 per Pack
This product is sold in Packs of 10

Forged

Steel Eyebolt Without Shoulder for Lifting 3/8"-16 Thread, 1300# Wll, 1-1/4" Thread Length
In stock at $3.48 Each

or in 1/4"
3013T45
Steel Eyebolt Without Shoulder for Lifting 1/4"-20 Thread, 500# Wll, 1" Thread Length
In stock at $2.76 Each




Eye Nut
3274T41
Heavy Duty Forged Steel Oval Eye Nut 3/8"-16 Thread, 1800# Wll, 7/8" Eye ID, 5/16" Thickness
In stock at $6.59 Each

or in a size I think is pretty sufficient for a 4" rocket
3019T14
Forged Galvanized Steel Oval Eye Nut 1/4"-20 Thread, 520# Wll, 3/4" Eye ID, 1/4" Thick
In stock at $6.03 Each

 

[troj]

What is the difference in weight between a 3/8" open eyebolt and the same size forged closed eyebolt? I'm assuming it can't be much.

Negligible.

What is the difference in cost between a 3/8" open eyebolt and the same size forged closed eyebolt? Is the money you save worth the risk when you factor in the cost of the entire rocket?

Not just risk from a cost standpoint, but also risk from a safety standpoint, which is even more important.

-Kevin

 

[DeWain]

Are you going to fly this beast at Nypower? If so stop by and I'll be glad to help out.

BTW if your going to certify I will have the paper work with me.:bangpan:

Al

Al,

I was hoping to have it ready by NYPOWER, but it won't be ready until August :bang:. I'll PM you later with more questions on the certification.

Thanks,
DeWain

PS. My kids are here with me as I write this, and for some reason, they want me to put in the marshmallow guy >>> :marshmallow::marshmallow: and the smilie ducking: :duck:

 

[DeWain]

Well the Big Fizz is s-l-o-w-l-y going together. Before I epoxy the motor mount assemby into the main body tube, I want to make sure that I will properly attach the tubular Nylon recovery harness to my newly-acquired forged eyebolts.

Some sources recommend attaching the harness to the attachment point via a quick link. I picked up a quick link on the weekend to attach the chute... and now I am wondering if I should have picked up more. The big question now is... what is the best way to secure the harness to the attachment point (eye bolt)? If I use the quick link, will this create a new "weak link", or are the threads on the quick link strong enough to bear any reasonable forces. If I tie the harness to the eyebolt and epoxy the knot, will I later regret making this a permanent attachment if the harness wears out (or will it take a *lot* to wear out the harness)?

 

[Handeman]

I've had good luck with quick links, but I've never had a problem with eye bolts either.

I would NOT recommend putting epoxy on a knot. The point where the fibers leave the epoxy is a lot like the point where the wire leaves the jaws of a pliers its being held by. Then start flexing the remaining fibers or wire and you see what happens. I think your better off just tying the knot and checking it every flight then putting epoxy on it.

 

[5x7]

Well the Big Fizz is s-l-o-w-l-y going together. Before I epoxy the motor mount assemby into the main body tube, I want to make sure that I will properly attach the tubular Nylon recovery harness to my newly-acquired forged eyebolts.

Some sources recommend attaching the harness to the attachment point via a quick link. I picked up a quick link on the weekend to attach the chute... and now I am wondering if I should have picked up more. The big question now is... what is the best way to secure the harness to the attachment point (eye bolt)? If I use the quick link, will this create a new "weak link", or are the threads on the quick link strong enough to bear any reasonable forces. If I tie the harness to the eyebolt and epoxy the knot, will I later regret making this a permanent attachment if the harness wears out (or will it take a *lot* to wear out the harness)?

A figure eight loop is a high strength knot, (then tie a tied a stop knot on the loose cord.) Use it with the quick link.
https://en.wikipedia.org/wiki/Figure-eight_follow_through

I use these knots with everything now, model to L3.

 

[Adrian A]

I like to avoid the mass of quicklinks, so I just use knots. If I have two harnesses I tie a permanent loop at each end of the harness and then connect the two by putting one through the other. Or you can use a double fisherman's knot. It's nearly as fast to connect and disconnect a s a quicklink, it weighs a lot less, and there's no hard, heavy lump to put a dent into anything during the deployment.