My L3 Project...A 7.5" LOC Goblin...AMA

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DAllen

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It's kind of amazing how many public figures will respond to tweets by some random dude on the internet (no offense to DAllen here).
Haha no offense taken I am definitely a rando in Toreys world
 

firemanup

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In reference to John’s video here is another, clearer video, shows flutter clearly, vibration from the flutter also appears to make the road “squiggly”, and the smoke trail does the exact same thing.

Initially i wasn't sold on the flutter diagnosis but i am now, seeing John’s video and comparing to this one.

In this video the build is able to survive the flutter.

 

Reinhard

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What can be seen very nicely in your video are the yellow tips of your fins. Rolling shutter artifacts alone are not sufficient to make those visible. Only the twist in the fin can make those visible from the cameras point of view.

Reinhard
 

FredA

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Rolling shutter doesn't change the motion - it just doesn't capture all motion at the same time.

The excursions you see are very real.
 

DAllen

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In this video the build is able to survive the flutter.
Survived yes but I sure wouldn't trust any of those fins or fillets to another flight. Probably hundreds of micro cracks all over that structure just waiting to catastrophically fail on the next flight.
 

wsume99

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In reference to John’s video here is another, clearer video, shows flutter clearly, vibration from the flutter also appears to make the road “squiggly”, and the smoke trail does the exact same thing.

Initially i wasn't sold on the flutter diagnosis but i am now, seeing John’s video and comparing to this one.

In this video the build is able to survive the flutter.

Very interesting video. The white fin, which is a very different shape, experienced no noticeable flutter. Is it the same thickness as the other fins and attached similarly??
 

AfterBurners

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AfterBurners

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Survived yes but I sure wouldn't trust any of those fins or fillets to another flight. Probably hundreds of micro cracks all over that structure just waiting to catastrophically fail on the next flight.
It's time to retire to make it a shelf Queen
 

Dustin Lobner

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Haven't read the whole thread, but I was standing next to DAllen when this one went up. Sad to see, but...dang, it was interesting to watch. As someone planning for an L3 cert attempt, it was one heck of a learning experience.

Also - Talked with DAllen a couple of times, both at the flight line before and after the flight and then at his car afterwards (with half a rocket and a pile of confetti sitting there on the ground) and I would like to compliment his great attitude - "these things happen in rocketry", you could tell bummed (as anyone would be) but certainly not beaten. It was an excellent attitude that I will look to emulate in my own pursuits.

Plus, "It's Round, we checked.... :D:p:cool:😁
 

ThirstyBarbarian

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Sorry about the mishap. That’s too bad. It sounds like your plan going forward with the fiberglassed fins should fix the flutter. Good luck!
 

ThirstyBarbarian

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Looking at the video I have of the flight everything looks good until about a second before destruction when the smoke trail from the motor sorta ripples or spirals maybe (rocket doesn’t appear to be spinning that much). Those with more experience maybe can tell if this is evidence of flutter causing the rippled smoke trail?
Here’s the first pic from my video showing everything normal:


View attachment 418313
Milliseconds later some rippling of the smoke trail:
View attachment 418314And then right before destruction:
View attachment 418315Zoomed in picture right before:View attachment 418316and Bad things happening:View attachment 418317
That is a really interesting series of frames. I’ve never seen that before.
 

OverTheTop

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Getting the stiffer parts of the wood further out from the center improves the stiffness. For non-isotropic materials the stiffness will vary in different directions. Basically the material provides more stiffness the further from the middle it is. It is a cubic law so the effect increases quite quickly. The closer material is to the neutral axis the less effect it has on the stiffness.

Doubling the thickness of a homogenous fin will increase its stiffness by around a factor of 8 (cubic function). You don't have to get too lost in the maths, just trust me ;).
 

DAllen

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Haven't read the whole thread, but I was standing next to DAllen when this one went up. Sad to see, but...dang, it was interesting to watch. As someone planning for an L3 cert attempt, it was one heck of a learning experience.

Also - Talked with DAllen a couple of times, both at the flight line before and after the flight and then at his car afterwards (with half a rocket and a pile of confetti sitting there on the ground) and I would like to compliment his great attitude - "these things happen in rocketry", you could tell bummed (as anyone would be) but certainly not beaten. It was an excellent attitude that I will look to emulate in my own pursuits.

Plus, "It's Round, we checked.... :D:p:cool:😁
Wow thanks for the nice comments!
 

firemanup

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Haven't read the whole thread, but I was standing next to DAllen when this one went up. Sad to see, but...dang, it was interesting to watch. As someone planning for an L3 cert attempt, it was one heck of a learning experience.

Also - Talked with DAllen a couple of times, both at the flight line before and after the flight and then at his car afterwards (with half a rocket and a pile of confetti sitting there on the ground) and I would like to compliment his great attitude - "these things happen in rocketry", you could tell bummed (as anyone would be) but certainly not beaten. It was an excellent attitude that I will look to emulate in my own pursuits.

Plus, "It's Round, we checked.... :D:p:cool:😁
I hear ya, i was standing there as well waiting to send up my L2 flight. It was sad yet interesting.

Planning on my second L3 right there at the same spot as well, see ya at midwest power.
 

Not Quite Nominal

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Survived yes but I sure wouldn't trust any of those fins or fillets to another flight. Probably hundreds of micro cracks all over that structure just waiting to catastrophically fail on the next flight.
In the spirit of post-mortem, do you have pictures of the rest of the fin can and are you willing to open it up?

I'm willing to bed it's in good condition.

I feel like we often suffer from a case of Wald's Planes here - we keep reinforcing the parts we get back, without realizing those were the parts that survived, hence the glue wars, etc.

We keep reinforcing the strongest links we get back, and not the weakest links we don't get back.

As an example, there's the "one caliber" rule for gluing in a coupler.

It's necessary to a full caliber for a sliding joint, but a glued-in coupler has enormous glued area and very little shear loading. I never use more than 1/4 caliber, I've had some spectacular shreds, and those coupler joints have never failed, even after some deep core samples.
 

DAllen

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In the spirit of post-mortem, do you have pictures of the rest of the fin can and are you willing to open it up?
If we could have found it then yes I'd have pictures. ;) The outer fin can from a couple of inches above the fins to the aft end is gone. The internal MMAS system is sort of in okay shape and the centering rings are shattered. If I think of it later I'll post pictures.
 

HVArcas

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You flew on the M1297 right Dave? I think Loc has a video of this kit on that exact motor




Never stepped foot in NY state, I'm from Texas and work in Rocket city (H-ville Alabama). How to fly the big stuff? Same as everyone else, take a trip out west.
ah, i misunderstood your e1337 k-r4d spelling :)
 

LOC

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For $0.02 worth, ours flew on the 1297 and a 1315. The only thing I can tell that is different is we did NOT bevel the fins and used US composites 3:1 thin resin epoxy. Certainly not wanting to start a "glue war". But, we have seen wood glue fail several times on these kits that we've drag raced. From the 4" to the 7.5". If there's anything else you need for the booster let us know!

Oh, and we do cut the fins with the grain perpendicular on all the Goblins. I think the photo is showing the top layer ripped off and you're seeing the next layer in line... You'll get the L3 next round!!!
 

DAllen

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Oddly enough, this photo came up on my FB time line from exactly 11 years ago. This was my first failed L2 flight that came in ballistic because of a bad ejection charge. This happened at Bong at NSL 2009.
 

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LOC

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4" Goblins on K-535. His held together, but a fin was loose when recovered... I can't recall the 7.5" exactly but I want to say a Patriot or Bruiser and a small L?
 

Speaknoevil

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Did my L2 and L3 on LOC designs, both of which I know would survive any motor you stuffed in them. Cannot blame LOC, their kits are fabulous.
IMG_4272.jpgmy-level-2-rocket_2267150036_o.jpg
 

Speaknoevil

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That L2 rocket looks VERRRRY familiar... Almost exactly like one down in my basement... ;) ;) 🤪
Yep, helps prove the point then. 15 year old LOC kit still alive and kicking after multiple owners and many flights.
 

Speaknoevil

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Tim, what is the Hope N' Pray kit, a custom or an original LOC kit?
I worked with Barry (former owner) on modifying a Bruiser EXL which I originally purchased from Ken Herrick at Al's Hobby Shop in Elmhurst, IL. Barry cut new fins based on my Rocksim modifications.
 
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