# Eye-bolt failure: Myth or reality?

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#### Jeff

##### Well-Known Member
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.

#### ttabbal

##### Well-Known Member
I've never seen it either. I just add a few of the forged ones to my McMaster orders to be on the safe side though. Or use u-bolts.

On a nose cone, I wouldn't worry too much. Unless it's a really heavy nose cone.

#### MarkM

##### Well-Known Member
While I use 1/4" forged eyebolts or eyenuts, it would take a lot of force to open a 3/8" eyebolt. My first ebay was built with 1/4" standard eyebolts, and after many flights these eyebolts show no sign of failure. I use the forged simply out of habit and more definitive security, but, that being said, I have yet to see an eyebolt open up and fail.

#### cjl

##### Well-Known Member
I typically use forged eyenuts, but it would definitely take a ton of force to cause failure of a standard eyebolt. Of course, it never hurts to err on the safe side.

#### terryg

##### Well-Known Member
Yep, I have had a standard eye bolt fail, big time! I had an early delay on an I600 on a 10 lb L2 rocket and the 1/4 inch eye bolt was straightened like a piece of spaghetti (jbwelding the opening did no good at all). It can take as little as 120 lbs of force to open a 1/4 inch eye bolt. You can get by with it for mid and light weight high power rockets. I would never consider it for L2 rockets. Use U bolts, forged eye bolts, or have standard bolts welded shut. It is embarrassing after a failure to have to answer "no" to the question "did you use a forged eye bolt?"

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#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Yep, I've seen them come back straightened enough to let the recovery system fail.

The key to remember is that when the system gets overloaded, the first thing to fail is what's going to take the load. Also remember that the working load on a lot of standard eyebolts is in the hundreds of pounds, and it doesn't take much to generate that kind of load.

-Kevin

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Take a look at the acclerometer spikes that show up at recovery deployment in a lot of flights. I've seen numerous with two noticable events -- the ejection charge firing, followed by a pause, then another significant spike when the system hits the end of the harness.

Let's say your rocket weighs 10lbs (not all that big in HPR worlds) and your accelerometer shows a 20g load. Simple math shows that's 200lbs of force. Considering that the working load limit on a lot of the opened hardware is in the 200 - 250 range, you can see that it doesn't take much over that and you're starting to hit potential failure points.

The solutions to this are easy....

1) Use hardware rated for higher loads (forged solid, U-bolts, etc)
2) Don't use 300 mile long harnesses that allow the components to accelerate while the parachute is at a dead stop.

-Kevin

#### brianc

##### Well-Known Member

The solutions to this are easy....

1) Use hardware rated for higher loads (forged solid, U-bolts, etc)
2) Don't use 300 mile long harnesses that allow the components to accelerate while the parachute is at a dead stop.

-Kevin
Of course, the 3rd solution is to build the rocket lighter. Saves money on propellant, too. You can start by skipping the quick links and eyebolts altogether and just use knots. Instead of using a u-bolt, just use a tied loop of kevlar cord that goes through holes in your bulkhead. and/or goes all the way through your e-bay.

#### ben_ullman

##### Well-Known Member
Ive used non forged eye bolts on rockets up to 250lbs. I have the Terrier Boooster that is 9" in diameter and has a 6" mount in it. I have 2x 1/2" Eye bolts in the transition that I put my recovery harness to. That piece with the 4 1/2" dia. Steel rods weighs close to 15lbs by itself.

Ben

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
Of course, the 3rd solution is to build the rocket lighter. Saves money on propellant, too. You can start by skipping the quick links and eyebolts altogether and just use knots. Instead of using a u-bolt, just use a tied loop of kevlar cord that goes through holes in your bulkhead. and/or goes all the way through your e-bay.
That works great if you want to build small, high-altitude rockets. Not everyone wants that....

FWIW, finger-trapping is superior to knots, as it doesn't create the stress points that knots do. The figure-eight climber's knot is very good, as well.

-Kevin

#### cls

##### Well-Known Member
I've had a couple eye-bolts open up under duress, but in all cases they failed long after the other components and did not contribute to the recovery damage.

You gotta think real seriously about the order of failure of parts, and how one simple failure can protect other parts. Remember the definition of Fuse: a $0.50 part protected by a$300 assembly.

sufficient strength, weight, reliability: these days I am a big fan of kevlar loop & double-figure-8 knots. I think U-bolts are better than forged eye-bolts. I only use quicklinks where I can't reach in to tie a knot and don't want to run a big loop.

#### sylvie369

##### Well-Known Member
I flew with open eyebolts until I lost my rocket, with no issues. On the other hand, I have seen a couple of 3/8" open eyebolts straightened out completely in tough recoveries. The flights' problems began well before the eyebolts were stressed, though. These were flights with late deployments, no firing of the drogue, etc.

#### THier

##### Well-Known Member
I have had a 3/8 inch eye bolt straighten on me.

Here's what happened, I was flying my 90% Harpoon on its first flight, didn't put the forged eye on,, after all, this was a 3/8". Harpoon left on two of the three Ms, third came up late, as the first two burned out, the third kicked the rocket over for a very scale flight, :y: (Horizontal) the baro altimeters fired, (at somewhere around 300 feet per second) I had a four foot drogue, so it hit hard, the main forced its way out, and rocket looked good. We hiked to the rocket safely on the ground, and something wasn't right, the booster and payload seemed too far apart. When we got to the rocket, the eye bolt was now a J bolt, and somehow the strap held on, until it touched down. If you watch the video, it is obvious the payload had dragged.

Tom

#### Jeff

##### Well-Known Member
<getting out blowtorch for open eye-bolt removal project.

#### n5wd

##### Well-Known Member
FWIW, finger-trapping is superior to knots, as it doesn't create the stress points that knots do.
Kevin,

When you say "finger-trapping", you're talking about something similar to the old "Chinese handcuffs", correct? In looking through the TRF 1.0 archives this weekend, I found a thread that had a link to a page that described taking a tubular Kevlar piece, stuffing it into a brass tube, then folding that over into the thread of the piece, and pulling the brass tube out, trapping the other bit of Kevlar, making a loop. Is that what you're talking about? If so, do you happen to have that link (I apprarently didn't bookmark that page, but I did the one about the animated knot trainer).

Wayne

#### dlb

##### Sky Pyrate...
I stopped using Eyebolt and move over to U-Bolts on any rocket over 4 lb's
and to help stop hard yanks like that with extra long shock cord , wraped in a bundle like a spring. Kevlar shock cords get longer than Nylon by 50%.

Hate Failures:bangbang:

That works great if you want to build small, high-altitude rockets. Not everyone wants that....

-Kevin
A rocket of any size rocket can be overbuilt (or under-built). More rocket mass leads to higher recovery harness force and more destructive energy if something goes wrong. So a simple guideline for people making rockets of any size is to not make it heavier than it needs to be for its intended purpose. I don't think there's anything controversial in that.

#### cjl

##### Well-Known Member
Agreed. Actually, I was just finishing up my Wildman junior rocket, and I've been noticing how much that thing is built like a tank. Do I have any doubt that it will stand up to every 38mm load made? No. Did it need anywhere near a 1/8" thick solid fiberglass tube in order to stand up to every 38mm load made? Absolutely not - a thinner tube would have gone a long way to making this thing a LOT lighter. Of course, since it is on the heavy side, I'll just shove in more power

#### JDcluster

##### Well-Known Member
I use U bolts on 3" rockets & up ( only on FG 3" rockets though).
I feel better knowing both sides of the loop are connected to the bulk plate with a metal plate & loc nuts.

JD

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
When you say "finger-trapping", you're talking about something similar to the old "Chinese handcuffs", correct? In looking through the TRF 1.0 archives this weekend, I found a thread that had a link to a page that described taking a tubular Kevlar piece, stuffing it into a brass tube, then folding that over into the thread of the piece, and pulling the brass tube out, trapping the other bit of Kevlar, making a loop. Is that what you're talking about? If so, do you happen to have that link (I apprarently didn't bookmark that page, but I did the one about the animated knot trainer).
Yes, that's a finger trap.

It's heavily used in skydiving, because it doesn't create the weak (stress) points that knots do. It's also done on many ropes used to tie up large ships.

-Kevin

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
A rocket of any size rocket can be overbuilt (or under-built). More rocket mass leads to higher recovery harness force and more destructive energy if something goes wrong. So a simple guideline for people making rockets of any size is to not make it heavier than it needs to be for its intended purpose. I don't think there's anything controversial in that.
Agreed, completely!

There is a lot of overbuilding that happens in this hobby, just like composites are horribly over-used.

There was a day when folks flew Level 3 without composites. Now, there are people who advocate composites for basically anything high power.

-Kevin

#### bobkrech

##### Well-Known Member
I stopped using Eyebolt and move over to U-Bolts on any rocket over 4 lb's and to help stop hard yanks like that with extra long shock cord , wraped in a bundle like a spring. Kevlar shock cords get longer than Nylon by 50%.

Hate Failures:bangbang:
Dave

Kevlar(R) is more heat resistant than Nylon(R) but is doesn't stretch much. Kevlar(R) 29 has an elongation at break of 4%-5% whereas Nylon(R) 6-6 stretchs significantly more with an elongation at break of 16%-28%.

Bob

#### troj

##### Wielder Of the Skillet Of Harsh Discipline, Potent
I stopped using Eyebolt and move over to U-Bolts on any rocket over 4 lb's
and to help stop hard yanks like that with extra long shock cord , wraped in a bundle like a spring. Kevlar shock cords get longer than Nylon by 50%.

Hate Failures:bangbang:
My opinion? You're creating an additional failure mode, or two....

Long cords are MUCH more prone to getting tangled on deployment, causing problems.

Plus, a long cord can allow a parachute to bring part of the rocket to a dead stop, while the rest continues in free fall, until WHAM! It hits the end of the cord. saw that just this past weekend. That puts one heck of a shock load on the system.

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

Enough charge to reliably separate, but not so much that it blows things three miles apart, a bagged main with a pilot chute, and a short riser, and you're good to go.

We recover 150+ pound components this way.

-Kevin

Kevin,

#### dlb

##### Sky Pyrate...
My opinion? You're creating an additional failure mode, or two....

Long cords are MUCH more prone to getting tangled on deployment, causing problems.

Plus, a long cord can allow a parachute to bring part of the rocket to a dead stop, while the rest continues in free fall, until WHAM! It hits the end of the cord. saw that just this past weekend. That puts one heck of a shock load on the system.

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

Enough charge to reliably separate, but not so much that it blows things three miles apart, a bagged main with a pilot chute, and a short riser, and you're good to go.

We recover 150+ pound components this way.

-Kevin
Never use too long of shock cord, I've seen what can happen here.
also use a way of wrapping up the cord in a spring like way( using tape or rubber bands) to remove tangling, then it releases in a control fashion. never had a failure since I started to do that a few years ago, no zippers, no yanks, just a nice deployment. pictured below is a main starting to deploy after a double charge go's off. Proper size of the drouge help too! Works great
so far on rockets weighing up to 325lb so far, think I keep using it till a failure happens , then study why and correct it!
One thing people do need to learn is the proper amount on BP to use for charges and not go overboard, seen this alot, it's a ejection, not a cannon!

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#### Jeff

##### Well-Known Member
also use a way of wrapping up the cord in a spring like way( using tape or rubber bands) to remove tangling, then it releases in a control fashion

Can you illustrate this method?

#### Commonwealth.Net

##### Well-Known Member
Split Eye Bolts fail all the time in rockets that weight several pounds or more!

We have ones rated to 4000lbs
They have NEVER failed to date.

Check them out in our HARDWARE section

#### bobkrech

##### Well-Known Member
Closed end forged eye bolts with a shoulder are the only eye bolts that are load rated. They must be mounted against a flat surface or washer to carry their rated load, and they only fail by breakage. The rated load is significantly less that the actual breaking load (by about a factor of 10 IIRC) because you want to insure that you don't drop an overhead load on someone or something. Ever.

Wire eye bolts are never load rated. They don't fail by breaking, they fail by straighting out. They are never used in any overhead load situations because the failure point can not be accurately predicted.

Bob