Competitor 3 Minimum Diameter build

[andrewlathrop87]

I got everything sanded down and scared. What do you guys think should I sand them down more and should I scar up the surfaces more before carbon?

Andrew

[jpummil]

Andrew,

While I haven't actually done this process (yet...), I believe everything should adhere fine to what you've done! I forget...are you using West?
I believe the most important part is the wetting to avoid dry spots and de-lamination. My $0.02, but eager to learn from my arm chair on this build as well!
Are you gonna be in attendance Sunday morning? If so...bring it with ya?

[flynfrog]

You need to sand the fins and booster tube between the fins much more than that. 60 grit and then score it with a sawzall blade. There should be no sheen on any of the parts. Once again to bring up the resources I provided in the last thread: http://groveraerospace.com/?page_id=826

After you sand and score, clean with acetone.

Sorry to interrupt someone else build thread but I feel the need to weigh in here. Scoring with a sawzall blade is something I have seen a few times on here. This is a bad idea. The deep scores are creating a stress riser and not doing anything to help the bond. Most aerospace epoxies have there maximum bond strength what abraded with 120-220 sanding in all directions so that you remove the resin on the laminate and leave the fibers exposed. Wipe with acetone until you get a clean rag follow with a alcohol wipe then bond within a few hours. Bonds should be clamped and held so that no air is entrapped.


I am sure the comeback will be that you have built dozens of rockets this way and never had a problem, I will counter that we did hundreds of thousands of dollars worth of testing on this.

[andrewlathrop87]

Thanks yea I sanded with 120 paper and the scoring was done with a putty knife. The scores are not very deep. I wiped clean with rubbing alcohol.

[BLKKROW]

It is looking really great. Keep up the great work.

[flynfrog]

Thanks yea I sanded with 120 paper and the scoring was done with a putty knife. The scores are not very deep. I wiped clean with rubbing alcohol.

my point being that the scoring is not really helping your bond and is weakening your fin. I dont want to derail your build thread anymore I was just trying to help out with others reading this.

Continue

[fineberg]

I just stumbled on this thread. This is really cool, I was thinking of doing exactly the same build. How did it turn out?

I have a couple of questions. Did you buy the CF fins seperately, or did they come with the comp3? I thought the C3 came with G10 fins. My biggest issue with the C3 is that it is a bit short for my CTI 75/6xl case. The case is about 42 inches with a full size load. No problem for the 54" mongoose 75, but it really doesn't work for the 48" comp3. I'd also be interested to know how the G12 holds up at Mach 2

Thanks for posting,
Sam

NAR 91047 / TRA 13293 L3
LUNAR Secretary

[MasonH]

I did all of the scoring on my DS DD with 60 grit sand paper. It really roughed up the surface for the fins, and nothing came undone, even after i dropped the rocket several times on the concrete basement floor (by accident of course...)

[andrewlathrop87]

The fins are just black G10 fins. I am having a guy in the process carbon fiber the rocket for me as I learn how to do it as I watch. I have never done it before so there is a learning curve.

[G_T]

Just FYI...

You want to be very careful about using rubbing alcohol for surface prep. Rubbing alcohol is typically 70% isopropyl alcohol and is not as good a degreaser as either methyl or ethyl alcohol - such as denatured alcohol. It is nowhere near as good as acetone. The rest is mostly water, which can soak into the part. If it has not evaporated out by the time a bond is desired, the bond will be weaker. Water is a solvent for the hardener part of epoxy, though not for the resin. But the really bad part is that most rubbing alcohol contains additives such as oils to prevent drying of skin. So by cleaning with many of the rubbing alcohol formulations, you are actually adding oil while removing dust. Frankly, I'd rather have the dust.

If your rubbing alcohol contains additives, then you'll need to acetone clean the surface to degrease, then denatured alcohol clean afterwards. That's a good idea anyway for critical bonds.

Gerald

[Burner]

I missed this thread as well, nice build. I really love these fiberglass kits.

Sorry to interrupt someone else build thread but I feel the need to weigh in here. Scoring with a sawzall blade is something I have seen a few times on here. This is a bad idea. The deep scores are creating a stress riser and not doing anything to help the bond. Most aerospace epoxies have there maximum bond strength what abraded with 120-220 sanding in all directions so that you remove the resin on the laminate and leave the fibers exposed. Wipe with acetone until you get a clean rag follow with a alcohol wipe then bond within a few hours. Bonds should be clamped and held so that no air is entrapped.


I am sure the comeback will be that you have built dozens of rockets this way and never had a problem, I will counter that we did hundreds of thousands of dollars worth of testing on this.

I should have a disclaimer on my site that mentions all “instruction” to be ingested with a grain of salt. Half the time I’m embarrassed of the things I post on my site not long after I put it up. However I think you bring up some good information that I'm fine to take as constructive criticism.

My thought on G10 is that rarely is there a strength issue when used as fin material, it’s almost always a stiffness issue when a problem arises. G10 will bend and flutter causing a shred long before it snaps and then causes a failure, hence the carbon tip-to-tip reinforcement for the stiffness. I think you bring up a good point about stress risers, however like I said I’m not worried about an 1/8” thick G10 fin snapping under loads as much as I’m concerned about the stiffness provided by the carbon reinforcement that needs to be well bonded to the G10 core. Your post does make me reconsider if there is any additional bonding benefit from rough scoring. I think this is some advice I may just heed, and stick with some low grit sandpaper. Besides, in the future I’m planning on nixing the G10 anyway and moving to all carbon fiber fin cans…so there

Anyway, back to the build.

[fineberg]

My first carbon fiber tip to tip was my L3 rocket, it worked out ok.

Sam

[flynfrog]

I missed this thread as well, nice build. I really love these fiberglass kits.



I should have a disclaimer on my site that mentions all “instruction” to be ingested with a grain of salt. Half the time I’m embarrassed of the things I post on my site not long after I put it up. However I think you bring up some good information that I'm fine to take as constructive criticism.

My thought on G10 is that rarely is there a strength issue when used as fin material, it’s almost always a stiffness issue when a problem arises. G10 will bend and flutter causing a shred long before it snaps and then causes a failure, hence the carbon tip-to-tip reinforcement for the stiffness. I think you bring up a good point about stress risers, however like I said I’m not worried about an 1/8” thick G10 fin snapping under loads as much as I’m concerned about the stiffness provided by the carbon reinforcement that needs to be well bonded to the G10 core. Your post does make me reconsider if there is any additional bonding benefit from rough scoring. I think this is some advice I may just heed, and stick with some low grit sandpaper. Besides, in the future I’m planning on nixing the G10 anyway and moving to all carbon fiber fin cans…so there

Anyway, back to the build.

Last post then I swear I am done. You will get better bond strength by abrading down to the fibers and removing the top coat of resin then you will get by using a rougher surface finish. Maybe I should make my own thread.

[andrewlathrop87]

I am new to Carbon fiber and I am learning. There is a gentleman that is from POTROCS that is teaching me how to carbon fiber. Since there is a learning curve involved he is carbon fibering the fin can of my rocket as I observe through pictures. He has sent me some information on how to do carbon fiber layout. Lets say it is a new experience for me. So I look forward to fibering my own fin cans in the near future!!

Thanks, Andrew

[andrewlathrop87]

[andrewlathrop87]

[andrewlathrop87]

[jpummil]

Lookin' GOOD Andrew!
Ready to go for Pawhuska? If so, what motor? I think our ceiling is 10K, right?

Edit: Oops, just checked...we have a 20K waiver

[andrewlathrop87]

Thanks Jeff I think it is 20'
I looked on the website!!

[bill2654]

Hey Andrew, I thought you were going to Airfest? Any tracking system? Cant wait to see that bad boy fly!

[andrewlathrop87]

yea bill i have a tracker. Have not tested it yet since the july launch was cancelled. Hope august is not cancelled. I am going to airfest but not going to launch the mim rocket b/c i am saving the M motor.

[DRAGON64]

Holy smokes, what an agressive project! I have considered a 76mm minimum dia build, but I hust do not have the air space to fly one. Your rockets is absolutely gorgeous, I wish you luck on your flight.

[Rhyno]

Looking good Andrew! For the August launch we got to be thinking rain..rain.. and more rain.

[prophecy]

Holy smokes, what an agressive project! I have considered a 76mm minimum dia build, but I hust do not have the air space to fly one. Your rockets is absolutely gorgeous, I wish you luck on your flight.

Johnnie,

Of course you have the airspace to fly one! A few years ago I built a 76mm minimum diameter rocket and flew it on a few 7600s to 29kish, but the same rocket only gets 18kish on a 4 grain 76mm motor, to say nothing of a 3-grain or a 2-grain. At Winterboro, you could easily fly anything up through a 4800 (maybe a 6000) and be just fine. I'll probably do just that at some point this winter.

[DRAGON64]

Johnnie,

Of course you have the airspace to fly one! A few years ago I built a 76mm minimum diameter rocket and flew it on a few 7600s to 29kish, but the same rocket only gets 18kish on a 4 grain 76mm motor, to say nothing of a 3-grain or a 2-grain. At Winterboro, you could easily fly anything up through a 4800 (maybe a 6000) and be just fine. I'll probably do just that at some point this winter.

Do we know each other? I'm not familiar with the username... And the fields that I have available to me; Manchester, TN and Childersburg, AL... do they have waivers capable now for a 29K flight?

[prophecy]

Johnnie,

The PMW field, whether you consider it to be in Winterboro or Childersburg, has standing waivers to 23k. I wasn't suggesting you could fly a 7600 in a 3" minimum diameter in the southeast, but my same rocket would get around 23k on a 6000 and 18k on a 4800ns 4 grain, so I was just suggesting that you have access to the best waiver in the southeast and plenty of room to fly some decent motors in a 3" minimum diameter project if that's the only reason you had previously decided not to build one.

Do we know each other? I'm not familiar with the username... And the fields that I have available to me; Manchester, TN and Childersburg, AL... do they have waivers capable now for a 29K flight?

[DRAGON64]

Johnnie,

The PMW field, whether you consider it to be in Winterboro or Childersburg, has standing waivers to 23k. I wasn't suggesting you could fly a 7600 in a 3" minimum diameter in the southeast, but my same rocket would get around 23k on a 6000 and 18k on a 4800ns 4 grain, so I was just suggesting that you have access to the best waiver in the southeast and plenty of room to fly some decent motors in a 3" minimum diameter project if that's the only reason you had previously decided not to build one.

That clears some things up, thank you.

[andrewlathrop87]

I got the rocket back from Texas. I have it basically done. Just add the shock cords and parachute and nose cone electronics bay!!!!

[andrewlathrop87]

[bill2654]

Beautiful!