Author Topic: BB Level 3 project  (Read 15244 times)

Offline mdutch

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Re: BB Level 3 project
« Reply #15 on: January 14, 2016, 05:58:57 PM »

 Reinforcing fiberglass with fiberglass is just using a thicker fin isn't it?

I guess that's why I got into this... to learn things  :)

Dave, you should look over and read the link I gave you. By going from tip over to the next tip with fiberglass cloth especially if you use carbon fiber too gives you a stronger web over the whole section not just the fin to body connection point. I've seen this process done on a minimum  diameter 4" airframe using a 98mm "N" motor  and have the fins come back attached with no damage.
Seriously look at how it's done I'm sure you'll see the value in doing it.
Mike Dutch
TAP  L3CC
URRG & MRSI Founder
"I just Want to Fly ROCKETS"

Offline David Carter

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Re: BB Level 3 project
« Reply #16 on: January 14, 2016, 08:56:39 PM »
Dave, you should look over and read the link I gave you. By going from tip over to the next tip with fiberglass cloth especially if you use carbon fiber too gives you a stronger web over the whole section not just the fin to body connection point. I've seen this process done on a minimum  diameter 4" airframe using a 98mm "N" motor  and have the fins come back attached with no damage.
Seriously look at how it's done I'm sure you'll see the value in doing it.

This seems like overkill to me. Having done the calcs, I'm nowhere near the flutter threshold for my fins. And in terms of strength, it even says in the article that it generally isn't required for G10 fins. I can see this being of great value for surface mount minimum diameter, but I've essentially got reinforcement on 3 surfaces with the through the wall fin design. It's not something I've seen done in similar level 3 projects either (admittedly I haven't seen many), except where they had non-fiberglass materials.

My reluctance is simply that this is a significant amount of work if it's not necessary, not just on the rocket but the tooling as well. I've not done any fiberglass work before so in my mind this adds another element of risk. I respect your opinion, and if you really think it's needed I will, but are you sure this is necessary?
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline mdutch

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Re: BB Level 3 project
« Reply #17 on: January 15, 2016, 08:41:26 AM »
Dave,
As your L3CC I'm not going to tell you that you have to do things one way or another. My job is to review what you present to me with your project to make sure you are building everything properly, and if I see a possible issue I will make recommendations to help you as I can.

Right now based on Img0836 and Img0837 you do not have enough epoxy reinforcement on your internal or external fin to airframe connections. If you have not installed your final centering ring or your Aeropac retainer yet, you can still do something about that. I would also appreciate a final description on what you did to improve that along with follow up photos showing what you did.

I'm not saying that you must do a tip to tip fiber glassing, but it is something that can be done after the motor mount, fin assemble is completed to beef things up if necessary.

Please remember I'm trying to help you succeed in achieving your Level 3 and help you learn something as well.

If you lose a fin during your flight you will fail the cert attempt. And with 95% of the fin out side of the airframe you WILL have fin flutter, (something you will see with your rearward facing camera).
Mike Dutch
TAP  L3CC
URRG & MRSI Founder
"I just Want to Fly ROCKETS"

Offline David Carter

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Re: BB Level 3 project
« Reply #18 on: January 15, 2016, 10:23:44 AM »
Dave,
As your L3CC I'm not going to tell you that you have to do things one way or another. My job is to review what you present to me with your project to make sure you are building everything properly, and if I see a possible issue I will make recommendations to help you as I can.

Right now based on Img0836 and Img0837 you do not have enough epoxy reinforcement on your internal or external fin to airframe connections. If you have not installed your final centering ring or your Aeropac retainer yet, you can still do something about that. I would also appreciate a final description on what you did to improve that along with follow up photos showing what you did.

I'm not saying that you must do a tip to tip fiber glassing, but it is something that can be done after the motor mount, fin assemble is completed to beef things up if necessary.

Please remember I'm trying to help you succeed in achieving your Level 3 and help you learn something as well.

If you lose a fin during your flight you will fail the cert attempt. And with 95% of the fin out side of the airframe you WILL have fin flutter, (something you will see with your rearward facing camera).

I definitely don't have enough reinforcement yet... that's just begun. :)

While I may challenge your recommendations, that doesn't mean I'm not listening. You definitely have more experience in this than I do so I take your advice seriously. Looks like I'm about to build a glassing jig!
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline mdutch

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Re: BB Level 3 project
« Reply #19 on: January 15, 2016, 11:14:41 AM »
Why don't you do your reinforcing first and we'll go from there before you build a jig.

Here, let me make a point based on my experience; I have two Wildman Eagle Claw rockets in my fleet. One is stock with the 54mm motor mount, the other was modified with a new tail cone and a 75mm motor mount. Neither rocket has 'TtT' reinforcing, yet.

I have flown the modified Eagle Claw twice with a 2 grain and 3 grain research motor respectively, with no issue with the fins. But then it hasn't flown on a 'M' yet either. I have also flown the stock version several times and a few times on a L1300BB by AMW, (a very hard hitting motor), And I did lose one of the large fins once, though that might have been due to a hard landing.

On the modified Eagle Claw I did fill the inner cavity by each side of the fins with about a 1/2" of epoxy. I also have a decent fillet on the exterior of the airframe at the fins. Some day I will fly the rocket on a "M" motor, but I'm also sure that I will be doing a 'TtT' application before then.

Based on this and a few other L3 cert attempts I've witnessed I'm sure you can see I'm trying to help you succeed. Again for now, finish beefing up your attachment points and we'll go from there.
« Last Edit: January 15, 2016, 11:17:58 AM by mdutch »
Mike Dutch
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URRG & MRSI Founder
"I just Want to Fly ROCKETS"

Offline David Carter

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Re: BB Level 3 project
« Reply #20 on: January 17, 2016, 03:38:18 PM »
Well, since it seems important, I've decided to post my fin flutter calcs. Not just to satisfy Dutch, although that's important too, but to satisfy myself. Feel free to review and comment. Also, if you use a different method for fin flutter calcs, then by all means let me know.

I based my analysis on the contents of this article https://www.apogeerockets.com/education/downloads/Newsletter291.pdf

I've attached the spreadsheet I used with my calculations. With the expected maximum speed (from rocksim) I have a 47% safety margin using G10 fins

I've also found some other spreadsheets that claim an even higher error margin, but they come with no explanation of their calcs. One claims I can go to Mach 10! I decided not to use that one...
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline David Carter

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Re: BB Level 3 project
« Reply #21 on: January 24, 2016, 02:25:06 PM »
Well, I've been kind of quiet this week. Dealing with a clogged extruder in my 3D printer... a common thing but my first so it's a learning curve. In the meantime I've been receiving parts... ejection charge canisters, eyebolts, all threads, teathers, and more.

I also have my main recovery chute. It's a SkyAngle Cert-3 XL, which should bring this to a soft 17 fps landing. Unfortunately this required a change in my design. The original design had a forward airframe that was 24". However, when packed for a 4" airframe it requires 25". So I also received my new 36" fibreglass tube. I've tried to pack a chute into too small a space before and it's not fun (I also got a new forward airframe for that rocket. Ain't got time for that sh*t!)

So no assembly last week, and probably not the week coming up... but more to follow!

In the meantime feel free to review the flutter calcs from my last post.
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline RKeller

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Re: BB Level 3 project
« Reply #22 on: January 24, 2016, 05:42:09 PM »
I've been using Aero FinSim for flutter analysis. http://www.aerorocket.com/finsim.html There used to be a download link but I think you have to email and ask for it now. I plugged in your design and came up with slightly lower numbers, but over 1300fps for flutter velocity and 1700fps for divergence velocity. FinSim is known to be conservative.
Riley Keller
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I'm addicted to building stuff, rockets are just a way to get high

Offline David Carter

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Re: BB Level 3 project
« Reply #23 on: January 28, 2016, 06:32:47 PM »
Really nice build! what 3d printer are you using?

Robo 3D R1+. (http://www.robo3d.com)

Not to derail, but what are you're impressions of it?  I've been toying with the idea of getting one myself.  There are bunch of parts for various scale projects that I want to build that it would be really handy for, especially with the largish build volume compared to a lot of the other small printers.

I really like it. I took it out of the box and was printing in minutes. Some printers require a lot of DIY to get up and running, but this was pretty much plug and play.

I printed a few things, left the country for a couple of months, and when I came back and printed some more without issue. It was printing pretty much non-stop for about a week and a half doing prototypes and builds. I love it. There are contract services that will print for you using your model files, but if you require a series of prototypes then nothing beats having your own.

That being said, last night I seem to have gotten a clogged nozzle. I went to bed. I'll let you know how easy it was to clear that, but I can't imagine it being any worse than any other printer. Their online help is quite good, and by all reports so is their phone support. I have no first hand knowledge of that. Other companies though are notoriously bad about after sales support.

As I mentioned earlier, the article I wrote about 3D printing for PSC is now available online at http://www.psc473.org/Newsletters/Issue185.pdf. I wrote this a couple of months ago.

I'm still dealing with my clogged nozzle. Apparently the print head I received (referred to as the hot end) was not the latest design. Clogs and jams are not uncommon, but none of the standard fixes seemed to work for me. I have a free replacement on the way as we speak (under warrenty) and I spent the $40 for a spare just in case.

There are some ways to minimize these issues, including oiling the filament with canola oil. I'll be printing an oiler as soon as my replacement hot end arrives.
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline David Carter

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Re: BB Level 3 project
« Reply #24 on: February 25, 2016, 12:22:29 PM »
Signs you are deep into a build: boxes for wood and tools for a tip to tip jig, laminating epoxy, fibreglass, carbon fiber, and various other materials filling the living room.

I took a break for some work travel but should be back at it this weekend  :)
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline mdutch

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Re: BB Level 3 project
« Reply #25 on: February 25, 2016, 12:41:08 PM »
Looking forward to seeing you continue on your L3 project Dave.  :D
Mike Dutch
TAP  L3CC
URRG & MRSI Founder
"I just Want to Fly ROCKETS"

Offline David Carter

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Re: BB Level 3 project
« Reply #26 on: February 28, 2016, 11:55:20 PM »
A few things going on this weekend, including starting the tip to tip jig, but I'll share more about that later.

Since I'd never done any fiberglassing before, I thought I should practice. The rocket is 3 finned, but 4 were made, so I had one I could practice with. I also had an old cardboard tube. So I added a layer of glass to the tube and glued the fin onto it.

The technique I used is based on the tree layer method shown here, with each layer being a slightly larger piece of material.

So each layer is in fact two, one of carbon fiber, and one of fiberglass. Prep time is far more significant than I expected. It was about three hours before I started mixing the epoxy. I made a lot of little mistakes, but that of course is the point of practicing. I also learned the value of making a jig!

There's a lot to be done still... the internal fillets, making the tip to tip jig, and of course the tip to tip reinforcement.
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline David Carter

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Re: BB Level 3 project
« Reply #27 on: February 28, 2016, 11:56:54 PM »
And some more...
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline David Carter

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Re: BB Level 3 project
« Reply #28 on: March 23, 2016, 11:15:50 PM »
Continuing the build... back to the internal fillets.

This has been the biggest thorn in my side in quite a while. I've alternately called this phase "Murphy's Law of Epoxy", "Why do I enjoy rocketry again?", and at many points just "F***! F***! F***!" The basic problem is that there's not a lot of room when you have a 75mm motor in a 98mm (4") tube. It sounds like more room than it is, especially with fat fingers like mine.

My first approach was to use RocketPoxy straight up. It flows albeit slowly, but not in my case. It just clumped up near the top of the tube. So I tried thinning it. And then some more. It did flow, just everywhere but where I wanted it. Eventually, I got it thin enough that I was able to inject it with a syringe. I placed a modeling clay dam over the end, and was able to get it to where I wanted it, albeit with quite a bit of colourful language.

I've done a lot of bad fillets in the past, but these are by far my ugliest.

This has definitely convinced me that tip to tip glassing is required, but also to use expanding foam in the fin can. So next up is the tip to tip reinforcement, then I'll put the rail buttons in place, fill the can with X-30 foam, and finally put the rear centering ring in place.
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!

Offline David Carter

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Re: BB Level 3 project
« Reply #29 on: March 23, 2016, 11:20:04 PM »
In the meantime, I've been working on my tip to tip jig. Absent a lot of wood working tools, this involved a bigger shopping spree than I wanted, but that's rocketry right? It's not pretty (I really hope any self respecting shop teacher would give it a failing grade), but it will do what I want.

I think this was as much work as the fin can so far!

I really shouldn't be allowed near a router.
David Carter
NAR 98850, Level 3

90% of rocketry is sanding!