Harness tore a 1/4" forged eye apart...

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what color was that rocket?

Dave,,
It was a very dark colored booster...
I thought it was black...
That pic you have of it coming down after it tore apart right over my EZ up is really hysterical...
I really think that's the correct rocket..
Zach would probably be able to tell..

Teddy

Hey,,
How the heck do you guys multiple quote ??
I need a lesson from Matt..lol..
 
Were you able to download flight data and look at the control traces? Might not be an alt problem--drag separation, payload pressure, etc. may be the culprit.

Hey,,
That's a great point...
Now that's a positive and helpful post right there...
Zach,, for sure,, take a look at these..
Did you have shear pins in the booster ??
A vent hole in the booster ??

Teddy
 
Dave,,
It was a very dark colored booster...
I thought it was black...
That pic you have of it coming down after it tore apart right over my EZ up is really hysterical...
I really think that's the correct rocket..
Zach would probably be able to tell..

Teddy

Hey,,
How the heck do you guys multiple quote ??
I need a lesson from Matt..lol..

this one? EDIT: nope this can't be it that's got a ripped harness when i zoom in
19111192708_549466f0a6_b.jpg
 
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Oh man,,
I really thought that was it Dave...
That woulda been really funny..

It still is,,,
It's comin to me for a harness that won't rip...lol...

Teddy
 
I zoomed in on that failed eye bolt. I have one like that, didn't use it because it was poorly forged. The base is not flat and the material looks porous. It's also made in China. I pulled it out and took a picture of it with the American made ones I get from McMaster-Carr:

044%202.jpg


045%202.jpg


The base that fits to the bulkhead is not flat on the Chinese eye bolt, whereas, the American made one is larger and well finished, even the threads.
It also looks like the failed eye bolt was pulled with a shear force and bent over before it failed.

You can destroy almost anything with enough mass and momentum, that's why we put these big rockets WAY out there!
 
Were you able to download flight data and look at the control traces? Might not be an alt problem--drag separation, payload pressure, etc. may be the culprit.

I was able to look at the data after the flight on the LCDT. One altimeter recorded an altitude of 3,290 feet and 1,320 feet per second speed. The other however had a reading of 593 feet and the insane speed of 1 foot per second. We had originally thought that the motor had blown the forward closure because the rocket made a banging sound that we had later learned was 8 grams (4 for the drogue 4 for the main)of 4f BP. Both charges fired at the same time because the main deployment altitude was set at 700 feet. Also, there was a ⅛ of an inch vent hole that was centered half way between the top of the MMT and the top of the tube. The booster was not shear pinned to the AV-Bay.

Zach
 
Zach,,
I'm all with ya building another rocket anyway,, but I thought the booster looked fine..
And the top half should have come down under the chute ,, no ??
Yeah ,, the quick link was twisted pretty bad in one of the pics you sent me..lol..

Teddy

Only half of the external fillet broke on the bad fin. The side that stuck pulled a couple layers of glass up by the slot. So, the tube is no longer round. The parts of the tube that are still in good condition will be cut off and used in another rocket. The payload tube came down under the main chute which was ripped in half.
Zach
 
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5 foot by 4 inch booster with 3 foot by 4 inch payload. The charges that fired were the larger backup charges.
 
Only half of the external fillet broke on the bad fin. The side that stuck pulled a couple layers of glass up by the slot. So, the tube is no longer round. The parts of the tube that are still in good condition will be cut off and used in another rocket. The payload tube came down under the main chute which was ripped in half.
Zach

I thought it wasn't damaged so badly Zach...
OK,, you win,,, you'll have to build another rocket....lol.....

Teddy
 
Fred, I totally agree. I am also working on a Wildman Extreme for my L3. I was going to go with 3/8" cast and shouldered eyebolts. I thought about that a bit and changed my mind and went with 3/8" U bolts.

It's definitely a good move. My first level 2 attempt had a cato which deployed the chute at 400mph. I was, of course, using one of Teddy's harnesses and U-Bolts on both ends. The weak point in that setup was the shroud lines on the chute of which all but 2 shredded. The U-Bolts and hardness (and rocket) came out fine and flew again on the successful 2nd attempt a few weeks later.
 
I was able to look at the data after the flight on the LCDT. One altimeter recorded an altitude of 3,290 feet and 1,320 feet per second speed. The other however had a reading of 593 feet and the insane speed of 1 foot per second. We had originally thought that the motor had blown the forward closure because the rocket made a banging sound that we had later learned was 8 grams (4 for the drogue 4 for the main)of 4f BP. Both charges fired at the same time because the main deployment altitude was set at 700 feet. Also, there was a ⅛ of an inch vent hole that was centered half way between the top of the MMT and the top of the tube. The booster was not shear pinned to the AV-Bay.

Zach

If the main and drogue charges fired at the same time it sounds like a wonky setting on the RRC3.
 
If the main and drogue charges fired at the same time it sounds like a wonky setting on the RRC3.

That is an interesting idea. I changed the altimeter's settings to put the altimeter in back-up mode (1 second apogee delay and main at altitude, in this case 700 feet).

Zach
 
If the main and drogue charges fired at the same time it sounds like a wonky setting on the RRC3.

Or the altimeter never reached the main altitude setting Dix...
If you have the main set for 700 ft and apogee is at 500 ft they are both set off at apogee...

Teddy
 
The rated strength of a 1/4" thread eyebolt is about 500 pound for a straight pull from MMC. Checking MMC's comments, the rating is reduced to 89 pounds at a 45 degree pull! 500 pounds is only 50 G on a 10 pound rocket, and a lousy 8.9 G at 45 degrees! A high speed deployment easily gives you that G loading level at 45 degrees so it is totally unsurprising the thread fails in shear before the Kevlar.

Bob
 
The rated strength of a 1/4" thread eyebolt is about 500 pound for a straight pull from MMC. Checking MMC's comments, the rating is reduced to 89 pounds at a 45 degree pull! 500 pounds is only 50 G on a 10 pound rocket, and a lousy 8.9 G at 45 degrees! A high speed deployment easily gives you that G loading level at 45 degrees so it is totally unsurprising the thread fails in shear before the Kevlar.

Bob

I completely agree Bob,,,
This is what I said from the beginning,,,
it is not surprising at all that the eye "gave" before the harness did,,
granted I have no problem believing the MMC eyes are stronger then the cheaper made eyes,,

but that doesn't change the fact that this is really no big deal...

And I still think it's really cool,,, lol...

Teddy
 
I believe the most important thing about this thread is that Teddy’s harnesses are not only strong but he has a lot of pride in them. As a result his workmanship is top rate. I probably have at least a dozen of his harnesses at this stage, and based on the price of the raw materials and quality of his workmanship, I am not even sure how he makes any profit.

Here is my personal One Bad Hawk success story from LDRS34 on my 3” PML Bull Pup, may the rocket gods rest it’s sole J.

My favourite motor to launch my Bull Pup is the AT I600 Redline. In case you don’t know the motor, it burns just under 600Ns in 1.1 seconds, almost a full “I”. Apparently it was AeroTech’s solution to the bowling ball launch competitions, so I was told and before my time in the hobby. That in a 4.7lb PML Bull Pup makes for an extreme launch, that is for this particular rocket.

Later on Friday I decided to launch my Bull Pup and as usual it took off in a blink of the eye. I was able to track it almost all the way, lost it for a second then I noticed a chute, and it wasn’t my drogue. At the time I simply thought it was a main @ apogee and I was in for a walk. I was visually able to track it until it disappeared on the horizon to the South East of the field.

Luckily I had a tracker in the nosecone, so I hopped in the car and tracked it down to a group of Mennonite children playing with it on their front yard. When they walked over and handed it to me, the first thing I noticed was that it was missing the body. Thankfully everything else was there, the nosecone, with the altimeter still beeping, the tracker, the 36” classic elliptical fruity chute, the 12” classic elliptical drogue/pilot chute and the cable cutter. Teddy’s harness was hanging from the U-bolt with the end loops still very much intact, but missing the harness it was connected to and the rest of the rocket.

A quick post mortem on the remains combined with how I set it up and what I have been told, leads me to the following conclusion. I assumed the AT delay was 14 seconds, it was not, it was the medium 10 second delay. For some reason I believed that I had always used a motor backup with this motor setup and I possibly have in the past but may have swapped out the delay for the 14 second one, if it fits, otherwise I just got it mixed up. Brain fart.

From the StratoLogger SL100 data below, it looks like the delay was pretty accurate and just after 10 seconds (10.65), while the rocket was still in it’s coasting phase @ 225’/s, the motor ejection popped. This caused the nosecone to swing around and strike something, resulting in a big gash in it. This appears to immediately deployed my drogue, which is normally held to the cable cutter and burrito wrapped main, also attached to the top loop of my main to act as a pilot.

Not surprisingly the cable cutter tie let go and the main must of deployed somewhere around .35 to .5 seconds after the deployment event. This caused a zipper from the top of the tube right down to the top CR. What happened next, I am unsure. Possibly the integrated harness that was glued to the MMT came completely off or the Kevlar stitching in the newly sewn top loop in the integrated tubular nylon harness let lose.

What I do know is that the loop in Teddy’s harness looks no worse for ware and that the stresses that the harness and other components must have been subject to would have been pretty high. Also worth mentioning, simply because I have heard many times about how expensive Fruity Chutes are, is that there is not a single broken stitch on either chute. This is definitely a case that you get what you pay for.

Riley Keller (AKA RKeller) sent me a PM to say that they recovered the remains and there was a zipper from the top of the body tube right down to the top CR. He also said that the motor hardware appeared to be fine. I will be interested to see what let lose when I get the remains back. In the end I lost the rocket but everything else looks to be salvageable.

One thing to mention is that I modified the stock recovery harness. It was a tubular nylon harness epoxied directly to the MMT and exited the top CR right against the top of the MMT. Using longer motors tended to cause one side of the nylon harness to get a bit crispy. My solution was to cut the harness just above the body tube and using Kevlar thread I had a seamstress permanently sew a Nomex sleeve on the remaining harness as well as sew a loop to the end of the harness to attach to my 11/32 One Bad Hawk Kevlar harness.

If I rebuild the kit I will likely use one of Teddy’s short harnesses and integrate it right into the MMT but extend the MMT a bit so it does not sit against motor. If you use a motor that does not exceed the length of the MMT, then you will likely not have the issue.

Below is a snip of the altimeter (SL100) data from just before what I interpret to be the motor ejection event to when it settled down to its average decent rate, which then took about another 7 min to land.

I would be interested to hear other opinions on anyone’s interpretation of the data points as well as what kind of forces it may have been subjected to.

The columns below are time, AGL in feet, and velocity in '/s, separated by a space.

9.90 4450 244
9.95 4463 243
10.00 4474 241
10.05 4487 240
10.10 4498 239
10.15 4511 238
10.20 4522 237
10.25 4534 235
10.30 4546 234
10.35 4557 232
10.40 4569 231
10.45 4580 230
10.50 4592 228
10.55 4604 224
10.60 4614 222
10.65 4625 225
10.70 4636 248
10.75 4646 319
10.80 4656 432
10.85 4670 573
10.90 4702 705
10.95 4770 760
11.00 4880 665
11.05 4979 434
11.10 4731 107
11.15 4708 -269
11.20 4666 -535
11.25 4672 -644
11.30 4679 -625
11.35 4715 -481
11.40 4672 -285
11.45 4680 -145
11.50 4687 -50
11.55 4686 9
11.60 4687 10
11.65 4688 11
11.70 4687 14
11.75 4688 9
11.80 4689 8
11.85 4689 10
11.90 4689 22
11.95 4690 27
12.00 4689 25
12.05 4692 13
12.10 4696 -21
12.15 4697 -43
12.20 4693 -51
12.25 4689 -45
12.30 4690 -28
12.35 4691 -17
12.40 4689 -10
 
First Michael,,,
Thank you very very much,,
I think the world of you, ( Not many can do 3 miles on a level 2 cert flight ) so to get praise from you means a great deal to me..

Now, with this statement I'd like to say a couple of things..

Possibly the integrated harness that was glued to the MMT came completely off or the Kevlar stitching in the newly sewn top loop in the integrated tubular nylon harness let lose.

You had a seamstress sew a loop in the nylon that came with the kit.. Madcow ships 9/16" Tubular Nylon...

OK,, here goes,,

It is possible to sew a loop that is stronger then the material,,
in other words,, sew a loop on both ends of a piece of material and stress / pull to catastrophic failure it will fail midstream,, the loops won't fail,, consistently....
It is possible,, with the correct materials,, machine,, and technique...

It is of course also possible to sew a loop that is not as strong as the material..

I am not a seamstress,, though I get teased about it by my nephew...lol...

I tried to sew a hem in a really nice and brand new pair of sweatpants..
I learned a lesson,, my sewing looks terrible in material that you wear,, getting the length correct takes practice,, you don't hit it right the first time you do it,, my came out too short,, and most importantly,, I didn't bother to change the thread or set up of the machine,, it is impossible to get the hem out,, it is permanent...

Now,, though this story may seam anecdotal,, there is a great point to it,, I'd like to see what the seamstress did to sew the loop,, there is a great possibility that I could tell you if it will retain 100% of the materials strength...

To each his own Michael,,
There are 2 things I would not have done..
One is having a seamstress sew the loop..
And the other ( oh man am I gonna get beat up over this one,, lol ) is gluing a piece of material into a motor mount..
No big deal,, I know that is that top most common method of creating an attachment point,, I am just not a fan of that...
For my builds,, and what I recommend when asked,, I'd rather put a welded stainless steel eye in the top centering ring....

Michael,, again,, you are the man,, no doubt,, I'll say it again,, 3 miles on your level 2 cert flight,,
What an honor for whoever was lucky enough to sign off on that cert.........

Teddy
 
It's only a 1/4" threaded rod. A forged eyebolt is only as good as the threaded rod diameter. And as mentioned, anything other than a perfectly straight pull will lower the rating.
 
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