"Contents Under Pressure" - Static Test Cato

Aksrockets said:

Flynfrog, we might have to take you up on that offer to cast at your place pretty soon. :grin:

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just let me know

Jim would also be a good one to ask.

On a side note any idea when the uroc launches are the website has been down forever.

Aksrockets said:

Wow, we really need to get working on this.
We're currently at the motor design phase, so the stuff I can talk about on here is pretty limited. I would post about it on the Research section, but I'm not a member of it. Long story.
The propellant is still up in the air but we're narrowing down our options. On the table is David R's Turbo White, Tiger Tail, and 72/10. Each have their pros and cons. If you have a formula you think would be good for this application, PM me. I'd love to talk.

A few weeks ago, Clay and I made a trip down to RCS/Aerotech to pick up some chems. We got enough to make about 30lbs each. That should be enough. :wink:
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Flynfrog, we might have to take you up on that offer to cast at your place pretty soon. :grin:

If we're feeling confident, we might be able to static test at springfest.

Alex

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Ahem........ with 3k+ posts on the board here, I would suspect a request to post on the research thread would get positive attention. Tiger tail is a nice mix to work with. Carbon black is "always" fun to work with.:wink: Kurt

thobin said:

What did it cost to drive down there and back. I guess it beat the the shipping or you wouldn't have done it?


TA

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It was tons cheaper then having it shipped. Plus I got a tour of AeroTech!

flynfrog said:

just let me know

Jim would also be a good one to ask.

On a side note any idea when the uroc launches are the website has been down forever.

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That was posted on the UROC facebook page.
I'll ask Jim if he knows any good formulas that would fit the application.

ksaves2 said:

Ahem........ with 3k+ posts on the board here, I would suspect a request to post on the research thread would get positive attention. Tiger tail is a nice mix to work with. Carbon black is "always" fun to work with.:wink: Kurt

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It was an issue with my certs. My TRA prefect sent them in but TRA has no record of receiving them. I'll get this cleared up soon.

Alex

Alex, did you take any pics during you tour you can share?

Oh Alex! So jealous of the Aerotech tour! I've considered driving down there for a will call but I'm a couple hours north of you. Still, a tour! Someday I'm going to have to head down regardless of any savings or not just for that reason alone! Good work.
-Ken

Alex,

The next picture I want to see better be those chemicals in a solid state

Quick little update:
Almost ready to start casting. It's been a NIGHTMARE to work out grain geometry with this thing. Clay and I spent a few hours on the phone just talking about our options. I'm really not sure how much I can post about grain geometry here without interfering with the EX rules, but I can say its monolithic with parts of the core finocyl and parts of it being cylindrical. It took forever to find a happy medium between ease of casting and efficiency. Long story short, the motor works out to be about a 3700ns L1800 with a 2 second burn time. Crazy looking thrust curve too, but it generally doesn't deviate too far from the KN range we're comfortable with.

I through together a quick sim, using the burnsim estimates and using actual weights from my 54mm components. This is were things get interesting. Openrocket is giving me insanely high numbers as far as velocity goes. Mach 3.8-Mach 4. I double checked all my weights and even overestimated some of them (like my AV bay weight). I double checked the motor, but everything seems pretty realistic. Openrocket might be really overestimating or I was just vastly underestimating when I did initial calculations. Although it's likely it's that first one, I just got a huge boost of motivation toward this project.



Edit: Oooh, I forgot my favorite stat: Mass Fraction: .55 :dark:

More soon!

Alex

Aksrockets said:

Quick little update:
Almost ready to start casting. It's been a NIGHTMARE to work out grain geometry with this thing. Clay and I spent a few hours on the phone just talking about our options. I'm really not sure how much I can post about grain geometry here without interfering with the EX rules, but I can say its monolithic with parts of the core finocyl and parts of it being cylindrical. It took forever to find a happy medium between ease of casting and efficiency. Long story short, the motor works out to be about a 3700ns L1800 with a 2 second burn time. Crazy looking thrust curve too, but it generally doesn't deviate too far from the KN range we're comfortable with.

I through together a quick sim, using the burnsim estimates and using actual weights from my 54mm components. This is were things get interesting. Openrocket is giving me insanely high numbers as far as velocity goes. Mach 3.8-Mach 4. I double checked all my weights and even overestimated some of them (like my AV bay weight). I double checked the motor, but everything seems pretty realistic. Openrocket might be really overestimating or I was just vastly underestimating when I did initial calculations. Although it's likely it's that first one, I just got a huge boost of motivation toward this project.

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More soon!

Alex

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At those speeds, forget about paint on the fins. They'll be toasted anyways. Keeping them on will be a challenge. You'll have heating on the outside and at the end of the burn, heat coming out from the case. You welding the things on?:shock: Kurt

ksaves2 said:

At those speeds, forget about paint on the fins. They'll be toasted anyways. Keeping them on will be a challenge. You'll have heating on the outside and at the end of the burn, heat coming out from the case. You welding the things on?:shock: Kurt

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Welding to Fiberglass? :wink: Jb weld, maybe.
Fin construction schedule:
.1in CF fin core
3 layers 5.7oz CF
Edge sealing
Ablative, similar to AVcoat.

Oh, and I forgot to reply to some posts.

Grouch said:

Alex, did you take any pics during you tour you can share?

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I did, but I'm not sure I can post them. I never asked to take pictures and he never saw us take pics, so I dont know the policy. However, here's 1000 words about it to make up for the lack of pics. That equals one picture, right?: Imagine a room, about the side of your average living room - maybe 20 x 30 feet, with boxes everywhere, filled to the top with rocket motors, sealed and packaged. Stacks of M and N motors. There was some serious potential energy in that room. I walked through the rest of the factory and saw the propellant processing room and the place where they make kits, the machine that does mass tube slotting, the place where they cut shock cord, etc. Wasn't allowed in the mixing room. I probably couldn't handle it anyway. There were also shelves stacked high with motor components. Cases, closures, you name it. Upstairs was the R&D. There were experimental motor components and stuff that wont be released for a while. Out back was the motor testing stand, right out in the back next to a public road! They'd tested N motors in that little bunker, right next to buildings. Anyway, thats not quite 1000, but its about all I remember. I'll definately go back sometime. The guy who showed us around was super nice and generally really interested in what AT was doing. Maybe I'll ask to take some pics when I got back.

kenstarr said:

Oh Alex! So jealous of the Aerotech tour! I've considered driving down there for a will call but I'm a couple hours north of you. Still, a tour! Someday I'm going to have to head down regardless of any savings or not just for that reason alone! Good work.
-Ken

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Make sure you go on a day when they aren't busy! We were just barely able to get a tour. They were shipping out the last of the Wildman order that day.

Alex

Pics or it didn't happen! Just kidding man, sounds like a heck of an experience. Jelly.

So it's kinda like an Aerotech N4800? (Cylindrical core up front, 4 fins for the last 1/3)

Also, double-triple-quadruple check your stability.

I've been debating weather or not to post this for the past week, just because of how big of a complete failure it was on my part.
Saturday morning we drove up to Flynfrog's place to mix and pack propellant. We decided on only casting one motor, which was probably a good decision. That was about as much AP I wanted to handle for one day.
Mixing and packing was somewhat uneventful. Instead of using a release agent on our mandrel we used release tape because it would fill in all the imperfections on the mandrel. This had been a proven method (at least for cylindrical mandrels).
Everything packed down nicely, so I headed home with the AP.
I was in the process of removing the mandrel when the entire thing cracked.

This was entirely my fault. I was tapping the mandrel on the ground, trying it loosen it. I was encouraged because I could see the mandrel making progress through the propellant. I tapped it a bit too hard because entire grain split where I was holding it (just below the fins on the propellant).

Although this sucked, not everything's going to waste. I was able to save about 20in of propellant (we packed 30). I manually cut the fins, which was painstaking, but successful. Now this Saturday we'll be doing a slightly smaller version of the static test. We'll be using a redesigned shorter motor, running at similar pressures as the full length one.

Here's what I was able to salvage.


Huge, huge thank you to Flynfrog for letting us mix at his place!

Static test Saturday.

Alex

Might I suggest paper coupler tubes in lieu of phenolic? LOC will likely be able to hook you up. Sufficient for this size motor and less necessary to pre-coat with R45/curative.

Clay and I spent the last few hours getting the motor ready. We tapped and drilled 11.5 holes through graphite, fiberglass and aluminum, and made 3 separate trips to the hardware store. For "pins" we decided to use your run of the mill 1/4-20 machine screws. 6 of em for each closure. I did the shear strength calcs and these will easily hold the pressure. We'll be firing at about 9:00 tomorrow morning at the UROC tripoli research launch.
Now for some pictures.

Holes drilled.

And tapped.




Of course we'll switch out the pins for something a little sleeker for the actual fight, but we already had enough on our plate today.
T-12 hours!

Alex

good luck with the flight guys sorry I wont be able to see it.

[video=youtube;Z7Bkel0sLDE]https://www.youtube.com/watch?v=Z7Bkel0sLDE[/video]

So, Alex and I static tested our motor today.. This was the result. It's pretty safe to say we have a lot of brainstorming ahead of us. Case completely failed at the forward closure.

Man thats a bummer, the good thing is you tested it first.

Its important to note that the case itself is what failed. Not the pins or the forward closure. Ill take a pic of the case tomorrow.
We were able to recover everything else without damage.

Alex

I have a thought. The pins were in a single plane the same distance from the end of the motor, right? I would consider staggering the distance from the end of the holes. I might also consider two rows of pins.

Did you measure motor pressure?

I forget- is this off the shelf tubing? Fabricating composite cases has caused issues for others- namely Frank Kosdon and Dave Trianno.

If its going to be one time use any way why not bond on the closures?

How did the tube fail? Any pictures of the broken pieces?

If it is single use them by all means bond in the forward closure.

It could be that if you previously pressure tested the tube that you may have damaged it with the test.

Here is a photo of the failed section.


The casing itself isn't meant to be reusable. The nozzle and closures are, so we couldn't bond them. To add to the problem my lathe is broken and I wont the chance to get a new one until the end of my school year.

It's called experimental rocketry for a reason... You blow stuff up, you learn stuff.

As to the future of this project, I really don't know. Clay and I will have to discuss how we want to continue. There are several options. One is to improve our pinning design and cast more propellant. Another is to switch to an aluminum case or just slightly downside the project and use my Loki 54/2800 case.

Alex

that is a pretty impressive failure shear failure. The composite definitely didn't like having holes punched in it. What do you need turned?

I realize this is a little off topic, but what camera did you use to film that and what frame rate/resolution did you get?

I would use morepins than just six. Maybe twelve? The same size would be fine. I don't know if staggering would help in filament wound tubing.

Ive been thinking about adding more pins in my head I think he might be better off with less pins. If the area between the holes gets to small its a weaker assembly.

If the case is meant to be single use, why not bond a coupler piece on the inside to hold closure in and a similar one to hold the nozzle in. After you fire, cut the case open and retrieve those components.

That didn't look like a simple overpressure, it looked like the KN went exponential. How was the density of the grain compared with expected?

When I started doing fin-o-cyl motors and complex shapes I started using styrofoam mandrels. Cast the motor around them and melt them out with acetone. Works great.

Edward

AlphaHybrids said:

If the case is meant to be single use, why not bond a coupler piece on the inside to hold closure in and a similar one to hold the nozzle in. After you fire, cut the case open and retrieve those components.

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+1.

AlphaHybrids said:

If the case is meant to be single use, why not bond a coupler piece on the inside to hold closure in and a similar one to hold the nozzle in. After you fire, cut the case open and retrieve those components.

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That's a fantastic idea. I'll look into that, maybe do a few tests.

Theres evidence to believe the failure was caused by an O-ring blow by. There's the fact that the forward closure failed (with 1.25 in of tubing in front of it) and not the nozzle carrier (with .5in of tubing in front of it). The largest piece of evidence is the high speed. Aprox .0023 seconds before the failure, there was a leak. This was so close to the failure it's extremely difficult to tell. Even with the high speed camera. (watch the video again and try and catch it) Here's the frame-by frame:

The first frame, showing the leak.

.0023 seconds later (the next frame), showing the forward closure pushing out of the tube.

The next frame, with complete failure.

We think this may be an O ring blow by, but I'm still having a problem directly linking the failure to the leak. I'm not sure what would have caused the increase in force and there isn't nearly enough time for any heat transfer to the fiberglass enough to weaken it.
Thoughts?

Alex

wfcook said:

I realize this is a little off topic, but what camera did you use to film that and what frame rate/resolution did you get?

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wfcook, we used a Casio ex-fh20 and had it set to a frame rate of 420fps. Great for stuff like this.