Repair or retire?

Discussion in 'High Power Rocketry (HPR)' started by Steven88, Sep 4, 2019.

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  1. Sep 4, 2019 #1

    Steven88

    Steven88

    Steven88

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    [​IMG] I love my scratch build Estes/Apogee Mega Der Red Maxx. It was designed by Estes for 29 mm motors and I designed it to fly 38mm motors. I also lengthened it adding a Loc stiffy and regular coupler, longer body tube and extra parts in the motor mount area. I made the mistake of using wood glue originally like the instructions called for. This rocket weighs around 4 lbs without a motor. It can’t seem to take the landings without breaking the fin fillets or worse. Per someone’s suggestion, I added epoxy fin fillets after the first break and it worked great for the next flight. Now the other day at LDRS it popped a fin part way out and dented the outside body tube in upon impact. I was able to get most of the dent out, but my question is, is there is a way to fix this baby properly and keep flying or is it a lesson learned on my first HPR and time to build a stronger one and move on? Can this one by fiberglassed or long boat tail added or something to keep the fins from popping loose? I know rockets with fins that protrude below the bottom tend to have this problem if not epoxied correctly, but I love this rocket as it is big and the large fins give it a slow relistic flight and roar. Hate to retire it. But it is heavy for being an Estes build and perhaps I have built it it too heavy and the weight is more than it can handle.
     

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  2. Sep 4, 2019 #2

    Steven88

    Steven88

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    Here’s a pic of the whole thing upload_2019-9-3_18-30-42.jpeg
     
  3. Sep 4, 2019 #3

    Steven88

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    I should add that it had a 2’ drogue parachute and a 6’ main at 700’ on a Jolly Logic the other day when I flew and popped the fin
     
  4. Sep 5, 2019 #4

    jmmome

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    With that large of a main chute and still broken fins on landing- wow. My recommendation is to rebuild only the fin section, and keep the rest of the rocket that you love. I'm guessing that you don't have Thru The Wall fin attachment? That's where I would start. I use a Zona razor saw to cut through body tube- I like it better than using an X-Acto knife.

    With a good epoxy joint of the fins to the motor mount tube, and another epoxy joint at the Thru The Wall fin/body tube joint, I'd think your chances of damage would go down greatly. Seems like I recall that the Estes Pro Series II tubes are slightly different in diameter than the rest of the industry. You might consider using Blue Tube or fiberglass for that reconstructed fin section, and figure out a way to mate the slightly different body tube diameters.

    Assume your fin stock is plywood and not balsa? New fins will be a must, as they currently don't have the Thru The Wall tab.

    Just a few thoughts. Keep us updated as to your progress. Feel free to PM me if you may have any other questions.

    Mike Momenee
    TRA #12430 L3
     
  5. Sep 5, 2019 #5

    Nathan

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  6. Sep 5, 2019 #6

    Steven88

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    Thanks to both for the information and yes, purchasing that fiberglass Red Max is very tempting! Yes mine does have through the wall fins but I only used wood glue on the inside. I also had to modify em because I went up to a 38mm motor tube. I tried to get them tight tho, (to butt up to the motor mount tube). After the first break I used epoxy clay fillets and still popping fins :(
     
  7. Sep 6, 2019 #7

    jmmome

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    I do a little trick when creating TTW fin joints. For a 3" dia. tube, I extend the fin slots another 3" up the tube, and then cut the tube apart where the slots end. I epoxy the bottom centering ring to the motor tube in the proper final location. I've already drawn the three or four fin line markings on the motor tube. I put some epoxy on the first mark , slide the motor tube down the slotted tube and into position (where it's going to end up relative to the bottom of the body tube), and then insert the first fin through the slot, onto the epoxy, and make sure it abuts the bottom centering ring.

    When cured, I remove the motor tube with one fin epoxied in place, and repeat this process for each of the other fins. After all fins are epoxied to the motor tube, I remove the fin/motor tube assembly and epoxy the top centering ring in place- it should be touching the top of each fin. Now you can add generous epoxy fillets to each fin/motor tube joint, with the centering rings functioning as dams to hold the epoxy. Now slide the motor tube/fin assembly down through the slots, and epoxy the bottom centering ring to the body tube as you do..

    The last step is to epoxy a coupler to the fin/slotted body tube assembly- long enough to butt against the top centering ring, and long enough to fit the length of one body tube diameter into the upper body tube. Epoxy or screw all of these connections in place. Epoxy the outer body tube/fin joints, and you're good to go.

    Wish I had pics of all this- I've built almost all my HPR's this way. Fins have never come off, even when a shock cord snapped and the fin section freefell about 1,500 feet.
     
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  8. Sep 8, 2019 #8

    Jozef

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    Epoxy clay has no real bonding or structural strength. Don't know how Apogee sells that stuff. May I suggest grinding off the fillets and use some good bonding epoxy. You have to get down to the bare airframe for adhesion. It does appear that you have little or no bonding on that fin to the motor tube.
     
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  9. Sep 8, 2019 #9

    Sabrina

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    Here's what happened - You made the design heavier, and the fin joints can't take the strain of landing. To fix this correctly you must rebuild. No doubt about it.

    Get the x-acto and start cutting. :cool::D:eek:
    Let's save the nose and lots of the "un-kinked airframe".
    Motor retention and rail guides can be saved.
    Fins can probably be saved. :po_O:oops:

    I want to cut-up that fin can and see why the root pulled away from the motor tube.o_Oo_Oo_O - My guess is poor bonding of the fin root to the motor tube and little or no INNER filets between the fin and the INSIDE of the airframe. It doesn't really matter if you used wood glue or epoxy. (lots of folks might disagree - that's ok) When bonding paper and wood, a correctly bonded joint will be stronger than the surrounding materials regardless of the type of glue used. (really) :cool::cool::cool: (except epoxy clay - don't use epoxy clay for anything)

    Go to the hardware store. Get some Titebond wood glue or some 2-part epoxy. The epoxy you want comes in 2 separate bottles, not a plunger-syringe thing. You can use JB Weld for the retainer, but it's really too expensive to build the whole rocket with.

    :D:D:D Let's rebuild this with an Ebay so it splits in the middle. :D:D:D

    Fine print - By making a mid-break design - you greatly reduce the landing stress on those fins - this is the whole key right here and the reason why you must rebuild.

    If you are using LOC airframe - consider buying a LOC ebay kit - it makes things much easier.
    When building the new lower (fin can) section. Rough-up all the areas to be bonded so the glue can soak in. Every fin gets six filets. Bonus points if you can get the top and bottom centering rings glued to the fins.

    I always recommend keeping the build as light as possible.

    Have fun!!!
     
    SS/EA 6BBL 71 Cuda likes this.
  10. Sep 9, 2019 #10

    AlfaBrewer

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    No need to rebuild. I have a souped up Warlock-ish rocket (Same size, but 4 fins and a 54 central with 2 38mm outboards. It's a bit heavier than yours, about 15 lbs fully loaded.) that I broke a fin loose from the MMT on the maiden flight. What caused my failure was that I got out of sequence on my build and didn't properly bond the fins to the 38mm tubes.

    I fixed this by injecting internal fillets using US Composites 635 and milled fiberglass (chopped would probably be better). I drilled a couple of holes near the fin that would allow me to get decent fillets at the fin-MMT joint. I also drilled a hole in the rear centering ring to get a fillet on the fin-body tube joint. You can do the injections with a medicine syringe from the pharmacy. I covered the holes over with Superfil, but pretty much any thickend epoxy would work. You could probably get by with some Elmer's F'n'F. Flies great with no issues. Even survived a CATO that blew out the side of the rocket. Fin can bounced pretty hard, since the parachute ended up a melted mass of nylon.
     
  11. Sep 9, 2019 #11

    SS/EA 6BBL 71 Cuda

    SS/EA 6BBL 71 Cuda

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    I concur- A feisty one you are! ;)

    “Uncle Gus”
     
  12. Sep 9, 2019 #12

    SteveNeill

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    Repair!
     
  13. Sep 10, 2019 #13

    AHansom

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    I have always thought its better to re-glue a dislodged fin than snap it off inside the fincan..
     
  14. Sep 10, 2019 #14

    Steven88

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    Love all the great feedback guys! So much to learn, so many different methods
     
  15. Sep 12, 2019 #15

    caveduck

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    Rocket surgery! Looks like a good exercise in dealing with popped off fins. I had a recent case where that happened on a 38mm Darkstar 2.6 which has low aspect ratio fins with RocketPoxy fillets, on a nominal descent with fully deployed main. It also actually broke one of the G10 fins...broke the glass.

    Anyway I concur with the suggestion to remove the epoxy clay fillets and use something else. A diamond cutter in a Dremel is great for grinding off fillets. You have a choice of what glue to use for re-attaching the fins. I use Aeropoxy ES6209 for HPR and good old 5-minute epoxy for anything smaller (it's surprisingly decent). West System 105/205 is OK if you have it. At NARAM this year I was flying I motors in LOC kits built on the field with 5-minute epoxy, everything held through multiple flights. RocketPoxy is sort of OK for fillets but a bit brittle. If possible, pull the separated fin all the way out and glue it back in with the "double-butter" technique (slather epoxy on the fin root, insert it 'til it makes contact with the MMT, pull it back out, slather again and re-insert).

    For the tube I'd wrap a layer of 3oz glass cloth over the crinkle and brush some thin epoxy on it, blot with a paper towel. For more rigidity you can cut a 3-4" section of tube, slit it down the side so it will expand over the original tube, and epoxy that in place. Filled epoxy or pink 2-part Bondo in the gap and to fair out the ends of the tube. If you can get a length of coupler inside the tube (depends on the shock cord mounting method) it will be less finishing work.
     
    Last edited: Sep 12, 2019
  16. Sep 12, 2019 #16

    AlfaBrewer

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    If you can't get the coupler all the way to the crease, you can cut the tube at the crease, epoxy in a coupler, then either paint or use some automotive pinstripe tape to cover the joint.
     
  17. Sep 12, 2019 #17

    Steven88

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    That’s a lot of good, helpful information! Thanks for your time in explaining all that. I really want to fix and fly it again so maybe this winter I can find the time!
     

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