Through-the-wall fin attachment?

Discussion in 'High Power Rocketry (HPR)' started by Rail Dawg, Nov 24, 2018.

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  1. Nov 24, 2018 #1

    Rail Dawg

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    Getting back into rocketry after 10 years.

    With the advancements in carbon fiber and epoxy technologies is it ok not to attach fins through the wall?

    My previous rockets up to 8” diameter all had through-the-wall but am now building a 12” and don’t want to do this.

    Is there acceptable strength at the fin joint by using carbon fiber and epoxy? I do need maximum strength as this will be a couple hundred pounds of rocket.

    Thanks!

    Chuck
     
  2. Nov 24, 2018 #2

    BDB

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    You can definitely reinforce surface mounted fins with carbon fiber lay-ups. The technique is usually called tip-to-tip. Just search for that term; you’ll surely find lots of threads about it here.

    The other option is to use an aluminum fin can (if allowed at your launch site). Check out some of Mike Fisher’s beautiful work here:
    http://binderdesign.com/store/page22.html

    Are you planning a 12” minimum diameter rocket? That’s incredible, insane, and definitely not inexpensive!
     
  3. Nov 24, 2018 #3

    Rail Dawg

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    Well that’s the plan lol. Got away from the hobby but after 12 years am finding myself pulled back in again.

    There’s a lot to relearn but this forum has good participation with a lot of experts. I plan to ask a lot of questions.

    I like the idea of carbon tip-to-tip. Will also look into aluminum.

    Thanks!

    Chuck
     
  4. Nov 25, 2018 #4

    BDB

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  5. Nov 25, 2018 #5

    Rail Dawg

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    My goal is to build a large rocket that can be seen for the entire flight... if possible.

    Those who make rockets that almost reach space have worthwhile goals. However we only see those rockets for a few seconds.

    I’d like to build a real big rocket and with the “Q” casing I have make it the kind of flight where you really see the power of the “Q”. And then watch the recovery sequence.

    Correct me if I’m wrong but the biggest G-10 tubes are 12” right? If they make them bigger I’ll go for that. I’ve always enjoyed building G-10 rockets. They can really take a beating.

    Lots to re-learn but I’m excited to be back in the hobby again.

    Thanks!

    Chuck
     
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  6. Nov 25, 2018 #6

    dhbarr

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    SShotS is 12in
    gofast was 10in
    qu8k was 8in

    Keeping any Q subsonic and visible is going to require a tremendous amount of drag and mass. I'm honestly not sure it's possible, but it should be interesting in any case
     
  7. Nov 25, 2018 #7

    grouch

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    Why wouldn't you want through the wall fins?
     
  8. Nov 25, 2018 #8

    Tyler P

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    Looks like he wants to do 12" minimum diameter, so I'm thinking that through the wall isn't possible.
     
  9. Nov 25, 2018 #9

    Rail Dawg

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    Yeah I’m picking up the “Q” casing tomorrow and will see what will/will not work.
     
  10. Nov 25, 2018 #10

    blackjack2564

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    We did the Mega DarkStar [12in 26ft tall 325lbs] wth foam fins dense core...covered with 2 layers of 5 oz carbon, then vacuum bagged.

    These were for slotted fincan with central 6in O motor and 3 54's.
    Then another fincan with surface mounted fins [same ones] for minimum diam fincan for P motor. Fins were attached with strips of carbon going tip down fin...across airframe...up to tip of next fin. T-T.

    fins only weighed 7lbs for all 6....great way to save ton of weight from rear...where you don't want it.
    Metal fincan for a 12in rocket would be VERY expensive.
    These foam fins are stiff as steel. There is another way now we have used. Just cover the foam with 1/16 g-10 plate...cheap and VERY strong...we took a test strip 8in wide 14in long 1in thick..set between 2 cinder blocks and jumped up/down on it....never budged.
    Scary strong and no flex whatsoever. Have made fins for a couple large projects this way.. one was a 24in tube Jay-Hawk....

    Score the surface of foam and epoxy the G-10 plate on after wrapping the beveled edges with 2 layers of 6oz [if there are bevels]

    100_4955.jpg 100_4957.jpg 100_6181.jpg
     
    Last edited: Nov 25, 2018
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  11. Nov 26, 2018 #11

    Joe Rocket 97

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    CJ, that is awesome
     
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  12. Nov 26, 2018 #12

    Rail Dawg

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    That is outstanding work on that rocket!

    I'm not going to go the foam/vacuum-bagging route although I know it's a superior way to build lightweight/strong fins.

    But I am going to use G-10 fiberglass for the fins and run the carbon from tip-to-tip for strength. There's a weight penalty but I'm not concerned because the goal is to keep the rocket relatively low and slow.

    Thanks for taking the time to post the explanation and the pics... those are very helpful.

    Again outstanding work!

    Chuck
     
  13. Nov 26, 2018 #13

    grouch

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    Still not getting why you are opposed to through the wall. At the weight and power you are talking about, you will need all the help you can get. Losing a fin on a heavy rocket is just asking for trouble.
     
  14. Nov 26, 2018 #14

    Tyler P

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    Replying as a noob here, but can you do through the wall on a minimum diameter rocket? The way I understand it, you would only be getting the depth of the tube itself, which on a tube this big probably offers some extra support, but the fin will be butting directly against the motor can.

    I suppose you could cut the tube to insert the fin and then lay in some carbon rod in the fillet to give some extra bonding surface area, or just do the tip-to-tip carbon layover as they've been discussing. Again, total noob to anything this size, so take it for what it's worth (maybe not much, haha) but I'm also trying to learn here.
     
  15. Nov 26, 2018 #15

    grouch

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    It's a proposed 12" rocket. The largest cases I know of are 6". If he had a 12" motor and wanted to do a minimum diameter then yeh, you would be spot on but it appears this is not even remotely the "case"....see what I did there?

    You would want all the strength and help you could get. This means through the wall at the very least and possibly foamed and tip to tipped. The thought of a fin letting lose at max Q is not cool.
     
  16. Nov 26, 2018 #16

    Tyler P

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    Ah, I see. I thought a Q case might be larger. Now I understand. Then through-the-wall makes sense, then.

    Thanks!
     
  17. Nov 26, 2018 #17

    blackjack2564

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    There are situations where surface mount is a must. When done correctly there is no problem with strength. WHEN DONE CORRECTLY.
    The rocket above flew 3 times in different configurations weighing from 300-375lbs.
    Cutting slots in a tube this size would compromise the tube strength & is not needed for any reason. You want the strongest tube possible and with several layers of carbon Tip-Tip,,,,,,the fins ain't going anywhere.
    You must figure what stresses are involved and design around them.

    When you build rockets this large.....it IS rocket science! You better have weight and thrust profiles figured correctly or your project will fail disastrously.

    If you have never been part of a project like this, I can see why the skepticism. In our case the P-motor was bell shaped 9in at the nozzle and 10.5 at the top. No motor tube can be used.

    The motor forward end had a ring receiver with 6 threaded holes. There was an aluminum 1/4in BP in the airframe. The bolts go through the BP and into the ring on motor to hold in place.

    Here are the pics of minimum fincan; Looking down see the Aluminum CR with motor bolted on [through center]
    There is a wood ring around motor on nozzle end NOT a CR..it's just glued on motor to prevent base drag pulling flame and heat up into fincan around the hanging motor.

    Motor in ship box see how wider on top.
    Top of motor [carbon tow wrapped around the grain, no metal case] showing built in metal ring to mount.]

    100_9355.jpg 100_9358.jpg 100_9373.jpg 100_9374.jpg

    There are times you need all the open space for other reasons.
    You may do several motor mounts that fit into the 12in airframe. [removable]
    6M's around a N.
    6in mount surrounded by 54's
    4 cluster M's
    8in mount. [P & Q}

    You can make these internal mounts interchangeable of different flight profiles.
    all that being said...it is a rarity to see a bird this size A: survive intact without damage and fly again. B designed for multiple flights.

    Big Rockets with huge motors are usually designed around that motor and looked upon to be one time use.

    _LLS0686.jpg
     
    Last edited: Nov 26, 2018
  18. Nov 26, 2018 #18

    grouch

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    I get all that. While impressive, I'm not sure this is what the OP had in mind considering the 10 year hiatus.
     
  19. Nov 26, 2018 #19

    blackjack2564

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    What are you up to Dawg? Building what.
     
  20. Nov 27, 2018 #20

    Rail Dawg

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    IMG_4737[1].JPG IMG_4736[1].JPG
     
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  21. Nov 27, 2018 #21

    Rail Dawg

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    OK you guys are making some good points!

    Got the "Q" casing and nozzle today. It stands 7 1/2 feet tall and is 9 inches in diameter.

    So through the wall is going to work along with foam if I go with a 12" diameter rocket.

    My last rocket was a two-stage "O" to an "N" and that was 10 years ago.

    But it's kind of like riding a bike right lol?

    I'm going to be listening to all of you so please don't hesitate to throw out ideas and suggestions.

    I do want to fly the rocket more than once hence it's going to be built like a tank. Not shooting for super-high altitude but a solid, stable flight that perhaps can be seen it's entire flight.

    Going with 12" G-12 fiberglass tubing but am going to have to give a lot of thought into the fins.

    Shooting from the hip I'm thinking of going extra thick on the G-10 fins with carbon tip-to-tip. Maybe a 30 ft tall rocket to get the CG forward. Haven't started the RockSim yet though.

    I'll probably fly this at BALLS next year so there's time to do it right.

    I'm pretty sharp on rockets like most of you but there is still a learning curve for sure. That is what is going to make it fun.

    Have been thinking of this rocket scaled-up:

    AGM-33 Pike.jpg
     
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  22. Nov 27, 2018 #22

    grouch

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    Gonna be sweeeet man!
     
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  23. Nov 27, 2018 #23

    Steve Shannon

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    Don’t forget that for anything larger than an O (40,960 Ns) you’ll need a Class 3 COA.
     
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  24. Nov 27, 2018 #24

    Rail Dawg

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    I'm excited to be doing this!

    I remember launching small Estes rockets and looking at videos of folks launching the really big stuff. "There's just no way!" I used to tell myself.

    Maybe we sometimes forget just how difficult all this can be lol.

    Chuck
     
  25. Nov 27, 2018 #25

    Wallace

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    Jim: I'm looking at ideas for my future (7.5 diameter)L3 projects fins and since they will be large,foam/carbon was pretty much at the top of the list. What specific foam/weight per ft. did you use? Can I just cut/bevel the foam and layer carbon directly over the whole mess (vacuum bagged of course)? Then apply epoxy to the leading edges after trimming? Would end grain balsa be a better option $ wise? And before I forget are there any suppliers in the Chicago area that anyone's aware of, oversize shipping charges are insulting?
     
  26. Nov 28, 2018 #26

    Ez2cDave

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    Pardon me, if I'm mistaken . . . Am I the only person here with "warning bells" going off ?

    ( 1 ) 10 years out of rocketry . . . First rocket is a "Q" motor.

    ( 2 ) The motor hardware is purchased before the rocket is even designed.

    ( 3 ) A "30-ft long / 12" diameter" rocket is under consideration . . . ( A "Fineness Ratio" of nearly 30:1, allowing for nose cone taper ).

    ( 4 ) The desire to "ballast" this long, thin, Q-powered rocket to attempt to keep it subsonic ( Sub-transonic, I hope < 950 ft/sec ), and limit its altitude to keep it visible throughout the flight.

    ( 5 ) "Disturbing" questions about fin attachment methods and talking about a "learning curve" . . . ( Perhaps that should occur somewhere well "South" of the "Q-Motor"impulse range ? )

    etc, etc, etc . . .

    Dave F.
     
  27. Nov 28, 2018 #27

    eggplant

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    +1. I'd be willing to believe that this level of project is appropriate for someone who has been out of the hobby for 10 years if they actually flew a "O to N two stage" to some level of success, but based on the questions being asked here I have a hard time believing that happened. Is the OP L3 certified? Does anyone know them?
     
  28. Nov 28, 2018 #28

    dhbarr

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    I'm not particularly concerned, although I trust OP will open up the Class III discussion sooner rather than later. Nothing about this design is particularly exotic, although substantially larger than usual.

    Also, mean culpa. I was the one who guessed massy and subsonic, but I have no idea what characteristics OPs motor will have. In any case, 9" in a 12" with overthick FG fins and CF overlay is going to be quite stout, which will require a fair bit of noseweight, leading to a large chute.
     
  29. Nov 28, 2018 #29

    Rail Dawg

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    The rock-throwing came a little sooner than I expected lol.

    Still it’s disappointing.

    This is going to be a fun project and I certainly have the ability to do it right. This isn’t my first rodeo around big rockets. Perhaps my attempt to be humble comes across as ignorance. Who knows.

    And yes I’m building the rocket around the motor. My motor designer/builder is one of the best in the business.

    Going from building an “O” rocket to a “Q” isn’t that much of a leap.

    My mistake for throwing numbers out there before I’ve had a chance to crunch them.

    I’ll have to ignore the negative folks and encourage those with constructive advice to give their opinions as every successful rocket is the result of the collective wisdom.

    We’ve set certain goals and parameters but like every worthwhile big project there will be modifications to the plan.

    To those with a positive attitude... thanks!!

    Chuck
     
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  30. Nov 28, 2018 #30

    blackjack2564

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    Ignore the "fake concern".
    I say full speed ahead matey! There probably aren't half dozen on here that can relate/been part of big project, nor do they realize it usually a group effort of very knowledgable fliers.

    AND it's way more fun than any adult should legally be allowed to have!!@#$#
    I'll be following all way.

    I have a 3/4 sale Nike Smoke [12in tubes] sitting out back] cost originally 2400 bucks . Ya can have for 500 bucks and part it. everything 100 % except 2 fins came off clean...no damage to tube. hell the Nose cone which is a perfect fit...RARE for Curtis] cost is 650 alone. You probably have the skills to put the 2 fins back a semi difficult task for a knowledgable type.

    Any how fully usable 2 ft av-bay coupler [ 2- 48 in tubes] 6ft nosecone with built in chute cannon for a 28ft man rated chute. etc etc. if interest just message me.

    Here's the build so you can see all the parts & it's a 8inch motor mount you can bust out if need be:
    https://www.rocketryforum.com/threads/excelsior-the-3-4-scale-nike-smoke-success-flew-today.144294/

    Like to see it go to good use. it was built just to fly a P motor once..Heck ya can have the motor to for just pick up. It's a pinned case but ya can cut it down and use again 6 ft long. LOl

    For that matter [shameless plug] anyone interested in high quality parts cheap...contact me.

    Screen Shot 2018-11-28 at 12.26.13 AM.png Screen Shot 2018-11-28 at 12.30.00 AM.png
     
    Last edited: Nov 28, 2018
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