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Thread: Rocket Fins

  1. #1
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    Rocket Fins

    Hello everyone just a quick update on the state of my rocket relating to the fins. Originally as in a previous post i was going to use poly-carbonate sheets for the fins, however i found PVC in sheet form and decided to give it a try. It is quite light in weight and very strong for being in the plastic family. Here is an image as of now of the fins I cut out. [ https://imgur.com/T3m8ZJz ]. ***A few things to note about this. First off the image is a bit distorted and gives the illusion of the fins being wider than they really are, I apologize as the images was just taken off my phone. The other thing is cut of the fins themselves, I have only rough cut the fins out and the lines are not true yet, I will finish them off before attaching the fins. I did use a formula to calculate around what the area should be for my fin. For my project I chose the clipped delta wing style for my fins. I realize the shape of the fins does have correlation to the height, speed, diameter, and cg of the rocket. However between builders there is also personal preference. I know apparently the elliptical shape is theoretically the best, but I would rather build my rocket around something tried and true, especially since this is my first build in this class.

    Now to my question which has to do with attaching my fin. Obviously I will have to sand some of the paint job I did off to attach the fins, no big deal. Since it will be PVC mounted to PVC it will make it easier than the original poly-carbonate I had planned on using. I was wondering what yall's thoughts were on plastic welding the fins to the body. Also I would have to support it in such a way so that the body and fins do not warp. My other option was to to use the tried and true (Thru the wall) and bond with PVC cement to permanently attach the fins into place.

    let me know your thoughts on these options or if you have any other suggestions for mounting techniques for my particular situation.

    Cheers ,
    Ed


  2. #2
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    Quote Originally Posted by TheSpartan_300 View Post
    Hello everyone just a quick update on the state of my rocket relating to the fins. Originally as in a previous post i was going to use poly-carbonate sheets for the fins, however i found PVC in sheet form and decided to give it a try. It is quite light in weight and very strong for being in the plastic family. Here is an image as of now of the fins I cut out. [ https://imgur.com/T3m8ZJz ]. ***A few things to note about this. First off the image is a bit distorted and gives the illusion of the fins being wider than they really are, I apologize as the images was just taken off my phone. The other thing is cut of the fins themselves, I have only rough cut the fins out and the lines are not true yet, I will finish them off before attaching the fins. I did use a formula to calculate around what the area should be for my fin. For my project I chose the clipped delta wing style for my fins. I realize the shape of the fins does have correlation to the height, speed, diameter, and cg of the rocket. However between builders there is also personal preference. I know apparently the elliptical shape is theoretically the best, but I would rather build my rocket around something tried and true, especially since this is my first build in this class.

    Now to my question which has to do with attaching my fin. Obviously I will have to sand some of the paint job I did off to attach the fins, no big deal. Since it will be PVC mounted to PVC it will make it easier than the original poly-carbonate I had planned on using. I was wondering what yall's thoughts were on plastic welding the fins to the body. Also I would have to support it in such a way so that the body and fins do not warp. My other option was to to use the tried and true (Thru the wall) and bond with PVC cement to permanently attach the fins into place.

    let me know your thoughts on these options or if you have any other suggestions for mounting techniques for my particular situation.

    Cheers ,
    Ed
    The only thing I've used to glue PVC is normal pvc cement. Then again, my PVC stays underground/behind walls and doesn't fly anywhere.

    Blackjack responded previously indicating he's flown pvc rockets, so he may chime in soon.

    Either way, a fin Jig or fin template will be handy for keeping things straight. payloadbays.com has a tool where you input your tube diameter, fin thickness and span, and it'll create a template you can print out and transfer cut to foamboard or cardboard.

    If you're doing thru the wall, one board is fine, but you'll need two for surface mounted fins.

    "I'm at least 70% confident about whatever I say (90% of the time)"- college me

    NAR 101195
    Level 1: Big SAM, 9/10/16

  3. #3
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    I stated what to use on your other thread...did you read it?

    Loc-Tite plastic weld epoxy in syringe at big box stores....works

    http://www.loctiteproducts.com/p/epx...tic-Bonder.htm

    Quote "Recommended For:
    Bonding substrates such as: PVC, polycarbonate, acrylic, ABS, FRP, Nylon™, Mylar™, Delrin, phenolic, aluminum and stainless steel".

    I've used everything building PVC rockets...this is the best.



    Regarding this:Out of curiosity what do you build most of your rockets from nowadays? and I am not worried about breaking this rocket its just a starter custom rocket and i will be moving on to much bigger rockets soon enough.

    Fiberglass for sport flying [thin wall] carbon for high performance where fiberglass won't do.

    Even my tiny mini's [38mm airframe with 29 motor mount] are glass. Cheap, take a beating & keep on going.
    every size up to 12in diameter.

    Click my name & search for my " latest threads"....that will show you what I build.

    Working on a 3/4 scale 12in diameter Nike Smoke.
    2-stage Nike-Apache
    2-stage Mach-2 project as of now all glass.

    Heck the Mach-2 kit is 54mm airframe minimum all glass spiral wound tube & Von Karmon nose cone for eighty buck & included the high temp/high performance epoxy.
    There is a sticky at top of high power called "how to build a DarkStar" which is really how to build any high power rocket in super great detail...read it.

    Good luck...have fun.
    Last edited by blackjack2564; 11th February 2018 at 01:11 AM.
    Jim Hendricksen
    L-3 Tripoli 9693
    [ICBM, Orangeburg,SC R.I.P.] - QCRS ,Princeton ILL - MDRA , Price Maryland - Woosh, Bong Wisconsin- ROCC, Charlotte NC , ICBM Camden SC
    "Made" member of Chicago & Carolina Rocket Mafia
    Rocketry...........an exact science.......but not exactly !!!

  4. #4
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    Quote Originally Posted by blackjack2564 View Post

    I've used everything building PVC rockets...this is the best.
    I'm curious about Pvc rockets. Many avoid them due to their brittleness.
    What extra measures do you find helps mitigate that downside?

  5. #5
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    Quote Originally Posted by Nytrunner View Post
    I'm curious about Pvc rockets. Many avoid them due to their brittleness.
    What extra measures do you find helps mitigate that downside?
    Only fly them on dirt fields/sod/crop field.....playa/hard surface is a killer.
    Use a larger than normal chute to mitigate damage. [for same size fiberglass rocket]
    Small light ones aren't too bad.
    Get near 3in or above and the thin wall can flex and crack.
    ALSO BE SURE to wipe clean after every flight any BP residue from ejection....it reacts with plastic over time & degrades/makes it brittle.

    I had several of the "BaddAzz" kits. The little ones fly fantastically well, the 24mm motor version [airframe barely larger] would hit 45-4800 ft every time on F-85's!

    I hard landed [use a streamer on it.] on a gravel patch in the field...that was the end of that. Shatter city.
    3in. lasted couple years when finally same size charge always used, [1.5 grams] blew hole on the side. Pretty sure due to residue degradation.
    Jim Hendricksen
    L-3 Tripoli 9693
    [ICBM, Orangeburg,SC R.I.P.] - QCRS ,Princeton ILL - MDRA , Price Maryland - Woosh, Bong Wisconsin- ROCC, Charlotte NC , ICBM Camden SC
    "Made" member of Chicago & Carolina Rocket Mafia
    Rocketry...........an exact science.......but not exactly !!!

  6. #6
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    I still think you're building this backwards, and giving other 'newbies' wrong or misleading information..

    Can I ask you about your fleet? How many rockets have you've built / own / currently fly? Can I ask about your flying habits?
    -paul

    NAR# 101258 - L1
    www.CRMRC.org
    I don't know the same things you don't know..

  7. #7
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    I would also suggest that the Beginners forum is not the place for this. ===> Techniques.
    In progress: something completely different / recent: Accur8 Ragnarok Orbital Interceptor
    My design thread / Fleet pics /
    My OR Renderings

  8. #8
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    Quote Originally Posted by dr wogz View Post
    I still think you're building this backwards, and giving other 'newbies' wrong or misleading information..

    Can I ask you about your fleet? How many rockets have you've built / own / currently fly? Can I ask about your flying habits?
    To answer your last question, currently I am just getting back into rocketry after about 5 years, used to fly more than one can count, including low and mid powered rockets, whether bought as a kit or cardboard/paper rockets I made. So as of right now this is the only rocket I have at the moment, other than a rocket I will probably buy for certification. Now to your first statement, if I may ask in what way am I giving wrong or misleading information in this post? In fact I have not given any information but simply asked a question about bonding techniques to PVC, so I am not exactly sure at what you are getting at. I am relatively new here and the only informational post I have given is about painting techniques, which I am fairly skilled in painting. Now I do realize that it would have made more sense to attach the fins before painting the rocket body. However at the point in time I am replying all four fins have been attached. Also in order to attach the fins I did not have to strip a whole lot of paint on the body, only the surface of fin attachment. I also realize I have not posted a lot about the other work being done to the rocket, but if i may ask how am I doing this backwards? with the exception of the parachute and the launch accessories and the addition of the motor and parachute everything else is finished on the rocket, I will post the finished product in a later post, including information on how I chose to attach motor mounts, etc.

  9. #9
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    Mr. Spartan,

    I mean no disrespect, or malice towards you. As stated, I feel you doing this in a bit of a reverse order, and this is the beginner’s forum, where people who have little to no building or flying experience come to ask what we might consider to be a “basic” question.

    Traditionally, your first rocket is an Estes or Quest kit, an LPR thing. No custom / scratch work (so no figuring our CG/CP relationships, fin sizes, placement etc..) And, it’s traditionally a paper/cardboard tube, wood (balsa) and a plastic nosecone all glued together with white or carpenter’s glue, maybe even a bit of epoxy. Painting is a rattle can from the local hobby or hardware store.

    Building the rocket also traditionally starts with the motor mount assembly. This assembly is then affixed in the rocket body tube. Then fin prep, and fin attaching. Lastly the recovery system is added. I think everyone (mostly!!) will agree that painting is always the final step, outside, on a nice day. (The first few rockets anyone builds rarely have primer, or a clear-coat.) LPR to level 3 stratospheric mach busters all seem to follow this progression on building. Look at a lot of the build threads here..

    Once they get a taste; the rocketry ‘bug', and start to ponder larger & bigger birds, Rocksim or Open Rocket start to come into the picture. And here, a ‘sim’ becomes ‘step 1’ with motor choices being pondered.

    Your post here, one of your first, seems to be jumping right into painting a tube, a PVC 3” tube. Granted, the thread is titled “Painting a Custom Rocketry”. There is no mention of what the rocket is, what it is going to look like, whether it’s been simm’d, what motor choices you made, recovery details, etc. It’s just painting a tube. So, a newbie might get the impression that they can pre-paint all the parts beforehand. They may not have the experience or understanding that gluing (with white glue) onto a painted surface is not going to last long. And, it might be overwhelming for said newbie to see the work you’ve put in, and the size of your project.

    As Neil_W mentioned, this is best placed in the ‘techniques’ or ‘scratch’ forums. You can ask a moderator to move the post to the appropriate forums, where it is better suited, and will garner more feedback other than what you’ve received here.

    To delve deeper into my meaning of the ‘backwards’. Again, I’ll reiterate you’re building a rocket (scratch built) but have yet to mention anything else about the rocket, other than it being blue and PVC.. We don’t know anything about you, where you’re from, what you’ve done, what you’re experiences are. So it’s hard to judge your level or expertise & knowledge.

    May I suggest you also start a thread in the watering hole to introduce yourself, say something things about yourself, your goals, experience, etc.. And, also start a thread in the MPR forum about your build, and do a “build thread” on the rocket. (That would gain lots of credit!) That way we have more of a reference as to what you’re doing, what you’re trying to achieve.

    Let’s also ask the moderator to move this post to the ‘techniques' forum where it is better suited & will get more views..

    Again, no ill intent towards you, just that your build differs from what most typically do.
    -paul

    NAR# 101258 - L1
    www.CRMRC.org
    I don't know the same things you don't know..

  10. #10
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    Quote Originally Posted by dr wogz View Post
    Mr. Spartan,

    I mean no disrespect, or malice towards you. As stated, I feel you doing this in a bit of a reverse order, and this is the beginner’s forum, where people who have little to no building or flying experience come to ask what we might consider to be a “basic” question.

    Traditionally, your first rocket is an Estes or Quest kit, an LPR thing. No custom / scratch work (so no figuring our CG/CP relationships, fin sizes, placement etc..) And, it’s traditionally a paper/cardboard tube, wood (balsa) and a plastic nosecone all glued together with white or carpenter’s glue, maybe even a bit of epoxy. Painting is a rattle can from the local hobby or hardware store.

    Building the rocket also traditionally starts with the motor mount assembly. This assembly is then affixed in the rocket body tube. Then fin prep, and fin attaching. Lastly the recovery system is added. I think everyone (mostly!!) will agree that painting is always the final step, outside, on a nice day. (The first few rockets anyone builds rarely have primer, or a clear-coat.) LPR to level 3 stratospheric mach busters all seem to follow this progression on building. Look at a lot of the build threads here..

    Once they get a taste; the rocketry ‘bug', and start to ponder larger & bigger birds, Rocksim or Open Rocket start to come into the picture. And here, a ‘sim’ becomes ‘step 1’ with motor choices being pondered.

    Your post here, one of your first, seems to be jumping right into painting a tube, a PVC 3” tube. Granted, the thread is titled “Painting a Custom Rocketry”. There is no mention of what the rocket is, what it is going to look like, whether it’s been simm’d, what motor choices you made, recovery details, etc. It’s just painting a tube. So, a newbie might get the impression that they can pre-paint all the parts beforehand. They may not have the experience or understanding that gluing (with white glue) onto a painted surface is not going to last long. And, it might be overwhelming for said newbie to see the work you’ve put in, and the size of your project.

    As Neil_W mentioned, this is best placed in the ‘techniques’ or ‘scratch’ forums. You can ask a moderator to move the post to the appropriate forums, where it is better suited, and will garner more feedback other than what you’ve received here.

    To delve deeper into my meaning of the ‘backwards’. Again, I’ll reiterate you’re building a rocket (scratch built) but have yet to mention anything else about the rocket, other than it being blue and PVC.. We don’t know anything about you, where you’re from, what you’ve done, what you’re experiences are. So it’s hard to judge your level or expertise & knowledge.

    May I suggest you also start a thread in the watering hole to introduce yourself, say something things about yourself, your goals, experience, etc.. And, also start a thread in the MPR forum about your build, and do a “build thread” on the rocket. (That would gain lots of credit!) That way we have more of a reference as to what you’re doing, what you’re trying to achieve.

    Let’s also ask the moderator to move this post to the ‘techniques' forum where it is better suited & will get more views..

    Again, no ill intent towards you, just that your build differs from what most typically do.
    Yep we can move this thread to wherever it is more appropriate. And soon or later I will officially start a build thread and an introduction thread about me. Thanks for the latest post, clarified many things up.

    Cheers
    Ed

    P.S. in the meantime enjoy the update on my rocket build [ https://i.imgur.com/TK1izJs.jpg ]

  11. #11
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    So, the whole thing was painted a nice sparkly blue, now it's all all primer grey? Maybe I missed something as there appears to be multiple threads on this one rocket, but what's the point in a) painting before setting fins, b) primering over paint?

    I don't call myself smart, but I'm pretty sure the primer is supposed to go under the paint.
    NAR #98114

  12. #12
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    Quote Originally Posted by kyle View Post
    So, the whole thing was painted a nice sparkly blue, now it's all all primer grey? Maybe I missed something as there appears to be multiple threads on this one rocket, but what's the point in a) painting before setting fins, b) primering over paint?

    I don't call myself smart, but I'm pretty sure the primer is supposed to go under the paint.
    Thanks for the question, sorry for not clarifying but there is a lot of work going behind the scenes, I will post the full project when i finish it. Because I was impatient I originally painted before attaching the fins I had to strip the paint clean on the bottom to attach the fins. However when getting ready to paint, being a perfectionist I personally do not like the look of blended paint so I stripped all the paint off to bare plastic and started the process over again. So to answer your question I did not primer over paint. The only thing that remained painted was the nosecone.

  13. #13
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    Cool, thanks for the clarification.
    NAR #98114

  14. #14
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    What class motor are you planning on stuffing into it? Just curious. Fin design and material sometimes depends on Mach numbers and epoxy can depend on temperature at that Mach number at least when you start into high powered rocket motors class H and up. Some HPR PVC tube fins have survived, but many prefer fiberglass, CF, or even phenolic/wrapped cardboard. Depends on tube diameters and motors once you venture outside of Walmart or Estes E motors it applies more engineering tactics and math or other forum members experience on what really works to insure survival of rocket airframe. PVC is a wonderful material as long as it's used within its limits. Many lower powered models use tubes almost toilet paper roll thin. You can practice with open rocket to find how stable ANY rocket is. Kit or scratch. Most like stability margins between 1.5-2.0 which tells you how to size fins. Below 1.5 under stable. Above 2.0 Overstable as long as not going Mach 2.5+. There the rules change and other dorks know more go ask L-3 nerds. You'll want CG ahead of CP or it crashes. Apogee has articles to size parachutes by how much the rocket mass is for a controlled descent speed. High powered rockets also need a waiver launched site/club and generally vent holes sized for leftover tube volume so nose doesn't pop off in flight. Also ground in test parachute charges which are volume calculated then experimentally verified to work. Shock cords on HPR are nylon or Kevlar versus lpr could use lesser quality material.

    Or you could lobb it skyward Von Braun style and cuss when it explodes but that's not normally TRA\NAR approved but it is rocketry... Sometimes you do all that math and sims and it still fails. Welcome to rocketry.

  15. #15
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    If this thing goes supersonic you can use a inverse sin function to size the fin sweep angle based on Mach from chapter five wing design a university technical document in google to reduce oblique shocks. But hey we don't know the specs or design goals on your rocket so we can't help you much.

  16. #16
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    The fin span and thickness with material strength affects the maximum Mach number that the fin will survive before flutter. AeroFinSim is a common HPR fin design tool or you can try a NACA4197TN equation and expect 20% error or more. When flutter velocity is exceeded then fin vibrates itself to pieces and fails in flight. Additionally the fin fillet size radius determines the maximum angle of attack away from launch rod until the fin shears off. This depends on epoxy tensile strength. If epoxy TG is lower than temperature rocket reached then the "glue" melts and you cry much as rocket crashes.

    Designed two HPR multistages L-1 for SEDS last year. It was a big skill jump from a Estes lpr Kit. Just tossing some crap out there for you to think about in the future and why what motor matters.

  17. #17
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    Its certainly a bigger rocket than I have ever made before, I will clarify a few things now and some in the final build post. The epoxy I used to attach the fins to the rocket is rated, according to the label, to 6000psi tensile strength and a temperature durability of around 100C or 200~ Fahrenheit I believe. It is actually more likely for the PVC to shatter or burn up than the epoxy lol, it will for sure stay together in one piece during the first half of flight anyways. Also one thing I just thought of doing is to apply a extreme heat ceramic coating to the bottom of the rocket, and to where the motor mount is, so that it has the durability to survive at least a few flights heat from the motor. That being said I wouldn't dare put above an impulse I motor in it. As for the rest of the questions I will answer in a final build post.

    In the meantime here is an update on the rocket, as I am waiting for a few parts to come in such as the recovery gear (parachute, etc..)
    [ https://i.imgur.com/ZS3xDy9.jpg ] Needs some finishing work but I am waiting for the paint to fully gas out.

    Cheers,
    Ed

  18. #18
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    Quote Originally Posted by TheSpartan_300 View Post
    Its certainly a bigger rocket than I have ever made before, I will clarify a few things now and some in the final build post. The epoxy I used to attach the fins to the rocket is rated, according to the label, to 6000psi tensile strength and a temperature durability of around 100C or 200~ Fahrenheit I believe.

    The main problem with PVC is that it resists either mechanical or chemical levels of bonding with most epoxy adhesives. Most of the glues designed to work with it actually slightly dissolve or melt the surface to get the bond. This is why a bit of PVC pipe is great for shaping fillets, if you have mess left on the pipe most of the time after the epoxy sets you can just pop it off. If your glue is rated for 6000psi tensile strength bonding PVC that is different, but if that is for wood or fiberglass it's likely to be much weaker on PVC.

  19. #19
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    Nope not a single piece of wood on my rocket, I did get epoxy specifically meant for this application, was not able to pop it off like you say. One important thing that people mess up with plastics in general is that first the surface is not roughed up, Especially for PVC, use PVC cleaner first of all, and another trick is to apply a thin layer of PVC cement then put the Epoxy on top of the PVC cement, which acts sort of as a primer promoting adhesion. I definitely learned a lot of things building with PVC after a couple failed attempts everything worked out just fine in the end.

    Here is some more photos

    [ https://i.imgur.com/nS82yZu.jpg ] [ https://i.imgur.com/gi2HnIB.jpg ]

    Cheers,
    Ed


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