Is overbuilding turning into a thing we should reconsider?

Discussion in 'The Watering Hole' started by muddymooose, Feb 18, 2019.

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  1. Feb 25, 2019 #91

    Ez2cDave

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    There are people who "flood" their models with epoxy, thinking it adds strength. It doesn't, only excessive weight and expense.

    If you were building an MMX-powered (1/8 A) rocket from rolled bond paper with poster board fins, the use of epoxy might be considered "over-building".

    Here is a definition :

    https://www.thefreedictionary.com/overbuilt
    ( See #3 & #4 )

    1. To build over or on top of.
    2. To construct more buildings in (an area) than necessary.
    3. To build with excessive size or elaboration.
    4. To make more sturdy than would ordinarily be considered necessary.

    Dave F.
     
  2. Feb 25, 2019 #92

    DaveW6DPS

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    Why would epoxy be over-building, exactly?

    As for your definition, it is subjective to the point of adding no clarification.

    Define "excessive size or elaboration". Does anything over 1.5 KG launch weight constitute over-building? Does adding scale details constitute overbuilding?

    What, exactly is "more sturdy than … ordinarily … necessary"? Specifically, what does "ordinarily" mean?
     
  3. Feb 25, 2019 #93

    jlabrasca

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    Somebody who thought "well, if internal epoxy fillets are good and filling the space between the fin tabs with foam is good, then filling the fin can with epoxy must be double good"

    Again. Don't want to speak for the OP, but I get the impression that this is not a question about experienced and/or thoughtful fliers.

    How about this:

    Building to withstand stresses that the rocket will not see unless if fails.

    Adhering CF rods to the inside the paper airframe because you are afraid the rocket will buckle under the axial stresses during the thrust phase.

    Or building from FG only because it is zipper-proof (sorry Nathan -- not trying to call you out).

    Or doing whatever it is going on in the link to which Ez2cDave posted

    http://web.mit.edu/mouser/www/rocketry/fleet/nerdmagnet/

    Seriously -- that is a LOT of threaded rod for a rocket that flew on H motors. The description of what he did, and why he did it, is a quick -- and depressing -- read.

    The Nerd Magnet
    Length: 151.8cm
    Diameter: 5.4cm
    Dry Weight: 1.5kg

    Flight Date Motor Comments
    1 2002.04.20 H128-W Perfect flight. L1 HPR Certification flight!
    2 2002.04.20 H165-R Perfect flight. First use of Redline propellant.
    3 2002.06.16 H128-W Perfect flight.
    4 2002.06.16 H238-T First use of Blue Thunder propellant. Ejection failed to pull out parachute, heavy damage on impact.​
     
  4. Feb 25, 2019 #94

    Ez2cDave

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    Mr. Smith,

    Really ?

    I'm tempted to "define" something else here, but I don't want to get banned from the forum . . .

    Think of it as using a sledgehammer ( "full swing" ) to kill a fly on a glass tabletop, rather than using a plastic fly-swatter ( "full swing" ).

    If you can't figure it out from that illustration, you're either "dense" or a "troll" . . . Either way, it doesn't matter !

    Dave F.
     
  5. Feb 25, 2019 #95

    DaveW6DPS

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    "Building to withstand stresses that the rocket will not see unless if fails."
    I think building with a margin above anticipated stress is a good idea.

    "Adhering CF rods to the inside the paper airframe because you are afraid the rocket will buckle under the axial stresses during the thrust phase."
    Carbon Fiber is very light weight and can add a lot of stiffness. I don't see the downside there.

    "Or building from FG only because it is zipper-proof"...
    I like fiberglass for a number of reasons. It is zipper resistant, and I don't see the problem with that either.

    "Or doing whatever it is going on in the link to which Ez2cDave posted"
    Okay, I don't know what the actual thought process was there. That was a lot of hardware. A dangerously overbuilt amount of hardware? Would I disqualify the rocket if I was RSO? No.

    "Fiberglass, carbon fiber, 30-minute epoxy with fillers, 2-part expanding foam, brick shithouse fin cans, aluminum-tipped FWFG nose cones, etc."
    Sounds like the rockets I like to build and fly. I currently am partial to Wildman kits. My flights do consistently break mach and approach 50 Gs.

    I haven't seen anything in this thread to change my mind.

    I am more interested in ensuring a rocket is stable, the recovery system is robust, and the flight path will take the rocket away from people and other things that should not be in the impact area.
     
  6. Feb 25, 2019 #96

    jlabrasca

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    Fair enough. We seem to be an an impasse.
     
  7. Feb 25, 2019 #97

    DaveW6DPS

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    Yes, really.

    I still haven't seen a definition that is practical or useful.

    I have seen posts with examples of over-building that are practices considered quite normal by many flyers. I have not seen a justification for the concern.
     
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  8. Feb 25, 2019 #98

    Rex R

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    I'm of a mind that the 'nerd magnet' is over complicated, and would fit my theory that people tend to over think things that shouldn't need overthinking.
     
  9. Feb 25, 2019 #99

    Ez2cDave

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    Pray that you never do !
     
  10. Feb 27, 2019 #100

    kevindcornwell

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    When I'm teaching rocketry, I stress to the kids to build carefully. To learn to build accurately (per the design) and to strive to achieve a clean end result: Clean lines, Clean surface. It would seem to me that a reasonable definition of overbuilding is to build any rocket such that it's strength far-exceeds nominal flight stresses. Is doing this a bad thing? Absolutely and categorically no. If that's part of your design criteria, then it's not over-built. Rather, it is built to design parameters. However, with students who are yet learning the value of putting the fins on straight, of not using more glue than the joint needs (which is defined as a joint that has far greater strength than the material itself), of what to expect when their shroud lines are unequal lengths. In these cases, overbuilding, defined as adding more strength than the material needs, can be a crutch to compensate for poor building practices. The all-thread Nerd rocket. That's just nuts. (get it...) The inherent strength of the structure so far exceeded the expected stress forces that it was no an engineering marvel. It was an overbuilt marvel that became so heavy that there was no chance of survival due to impact loads. That's the compromise: it could withstand enormous 'up' (and by appearance, lateral) loads, but not severe 'down' loads. I hold to two definitions of Over-Building: 1) Adding strength to compensate for poor build technique, 2) Adding strength in an effort to survive a catastrophe when such an event will inevitably destroy 'something'. (ie. you can't build strong enough to survive 'anything' and still get off the ground.) And, on that latter, the caveat is only when the catastrophe could have been avoided. I'm reminded of a YouTube video where the 100k attempt showed them prepping the rocket. You wouldn't believe how much effort they were expending stuffing the parachute into it's tube. Red Flag!!! If it takes two of you to force it in the tube, there's a good chance it won't come out. It didn't, and the ballistic impact was impressive. An avoidable catastrophe. Over-strengthening in order to avoid a thoughtful approach to the build or to the flight, should then be a reasonable definition of over-building. Every glue has its place, every shock cord material has its place, every chute material has its place. Etc. Dismissing one or insisting on another 'just because' cannot yield a thoughtful approach. Accidents do and will still happen (man that RTF puncture in the trailer roof is also impressive) but a thoughtful approach with good technique following well-considered design parameters should result in minimal collateral damage when the oops'es do occur.
     
  11. Feb 27, 2019 #101

    kevindcornwell

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    Yeah, that was particularly unfortunate. And your point was made in a terribly poignant manner. How do we avoid such tragedies? *sigh* While there is no perfect solution, I for one, have become even more vigilant at launches to do my best to implement proper launch rod angles, appropriate spectator distances, etc., etc. Every rocket launched must have spotters - no spotters, no launch. Especially in the case of drag-races. I had one chap get upset at me awhile back, I finally simply said, "Calm down, we're here to have fun, nothing more." Perspective, in this case, is everything.
     
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  12. Feb 27, 2019 #102

    jeffjblack

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    Right building is good. Define the mission. Define the parameters. Give 110% or whatever you are comfortable with. Build by design.
     
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  13. Feb 27, 2019 #103

    jlabrasca

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    How do you compute the 110%? And 110% of what?

    edit: Not trying to be provocative. I am curious what folks measure, and how folks spec their rockets when defining "the mission".
     
  14. Feb 27, 2019 #104

    DaveW6DPS

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    A couple of examples:

    I build for at least 150% of expected load and prefer 200%. A five pound nose cone at 50 Gs of boost applies 250 pounds to its mounting, to the nose cone itself, and to the body tube. So I would build for at least 375 pounds of force and try for 500. So a four inch filament wound fiberglass nose cone with 1/8" wide shoulders to mate with a four inch filament wound fiberglass body tube would not have enough mating area for me to fly it. I reinforced with an added internal collar for the actual edge of nose cone rather than chance it being pushed into the body tube under boost. This took my mating area from just under 1.6 square inches to about 4.7.

    If I am using a K1440, which has a peak thrust of 411 pounds, I am going to ensure the motor mount can withstand 822 pounds of force. I don't settle for less here, and actually is doesn't take much to ensure that level of shear strength with three centering rings and three 1/8" fins, with a ten inch root epoxied to the MMT and epoxy fillets to the body tube.

    Maybe the exhortation to 110% effort applies. I find a 10% engineering margin to be unsatisfactory.
     
  15. Feb 27, 2019 #105

    kevindcornwell

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    Because I haven't done _all_ the material tests on every material I use, I, for one, must rely on published data, and sometimes seat-of-the-pants guesstimating. In most cases, I follow breaking-strength parameters and rocketry rules of thumb. For example, I use 100# kevlar on my 12oz rocket. It exceeds the rule of 100x vehicle weight (and this primarily for practical reasons - smaller kevlar is fiddly to handle and the weight difference is negligible) so is quite adequate. However, I don't then use an eyebolt with 1000# load strength, fitted into a piece of plywood that breaks at 50#. In other words, I do my best to follow the advice of seasoned rocketeers, and to keep it consistent -- 100# line, 100# attachment, on a 100# mount. Okay, I get that it's not realistic to be perfectly consistent, so I get as close as I can with available parts without going (too far) under the rules of thumb.

    Let's go with another example: If your building criteria was to see just how lightweight you could go, then the 'mission' criteria would include recovery system deployment precisely at apogee. In this case, the recovery system in its entirety would need breaking strengths of nothing more than 110% of the weight of the rocket. Nice and light. We can have loads of fun with that watching the recovery system fail over and over again. Not because our math was wrong, but because we can't control everything (like horizontal velocity.) So, in our example we need to go to 150%, or 250%, or whatever our experiments dictate.

    And sometimes I just plain guess. And stand behind the car at launch time. ;-)

    That's just how I do it. I'd love to hear from others as well so I can learn something new. :)


    I find this quote to be particularly instructive:

     
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  16. Feb 27, 2019 #106

    cbrarick

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    then we'd all be back to cardboard. Fiberglass is over-build by definition for the mission, unless you want to account for survival in my truck bed or trailer :> then it may be necessary. I have a whole fleet of LOC rockets, all unmodified, that fly just fine. We see paper rockets take all sorts of abuse at any major launch.

    <sigh> I wish the "strength of HPR materials" website was still up and running. I was rather shocked how well cardboard did on axial loads and how strong wood glue was on paper to wood joints.
     
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  17. Feb 27, 2019 #107

    Maxout

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    Oh for Pete's sake this is silly.

    He's a fresh college grad who wanted to flex his engineering education on a fun project. Let him overdo it if he wants to.

    He did far better than many--passed L1 on his first try. So before you go bashing him or anyone else who overengineers a project, give some consideration to the outcome. There's more than one way to fly an airplane, and there's more than one way to build and fly a rocket.

    And that's truly the rebuttal of this entire thread: there's more than one way to build and fly a rocket. Focus on actual safety--correct procedures, correct flight prep, and correct launch direction.
     
  18. Feb 27, 2019 #108

    jlabrasca

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    I don't know which smiley/emoji/emoticon to insert here to indicate that I am not trying to win the internet -- that I am asking these questions honestly and without an agenda.

    Why?

    Is this static loading? What are you using as the limiting criterion?

    How?

    ---

    That's interesting. There are, I expect, different sets of considerations when thinking about what counts as overbuilt recovery and what counts as overbuilt airframe.

    The seat-of-the-pants thing is, I think, the question.

    I'm not a materials scientist or a mech. e., so I don't have a lot of background in strength of materials. But I think I know enough to estimate the depths of my ignorance on the topic. I am not sure I would be able to parse the problems DaveW6DPS is trying to solve in #104. I am not even sure that I speak the same dialect of engineering (I think in terms of stresses rather than forces, and I wonder -- fruitlessly -- about the difference between rupture under quasi-static loading and rupture under dynamic loading, etc.)

    When the OP asked about overbuilding, it brought discussions like these to mind

    Centering Ring Thickness, Calculating Shock Cord Size and Lengths, Newbie here: How can I figure out the point at which body tubes buckle?

    The NAR High Power Safety code comprehends construction materials. "...or when necessary ductile metal..."

    It would be interesting to ask the builder of the nerd Magnet rocket why he used all of that steel, and to ask him if he'd looked at the construction of any of the commercially available L1 kits.
     
  19. Feb 27, 2019 #109

    Maxout

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    I'm not even the person who mentioned using a safety of factor of 2, but the answer to that should be apparent: a safety factor of 2 accounts for a variety of things, not least of which is that we aren't commercial operators and hence lack quality control and NDI procedures to ensure that our structured designed to withstand a minimum of x load actually can do so, nevermind what thermal cycling might do to it as the thing sits for months or years waiting to take flight.

    To the first question, a certification team and an RSO signed off on it. End of story.

    Why? Frankly, because he could. Which is why most of us build rockets.
     
  20. Feb 27, 2019 #110

    Ez2cDave

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  21. Feb 27, 2019 #111

    Bat-mite

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    Sometimes with threads like these, I wish "rocket science" could just be "rocket fun." :(
     
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  22. Feb 27, 2019 #112

    jlabrasca

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    what's the difference between science and fun?
     
  23. Feb 27, 2019 #113

    Bat-mite

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    When things get tedious, they cease to be fun for me. I like working with FG; I don't like working with cardboard. I tend to trip and fall on cardboard things. I need an HPR material strengths list to know that I like to build FG rockets. And who cares if I am overbuilding? The rocket goes up, it comes down, I go get it, and next month I do it again.
     
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  24. Feb 27, 2019 #114

    Tyler P

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    The only reason I can see for "overbuilding" on a kit is if you're intending to fly it on motors that are not recommended for it. If you're going to overpower it, then you have to factor the greater forces and weights involved.

    However, if a manufacturer (insert any popular one here) has spec'd a kit to work on such-and-such a motor, then why not trust that they've done the math for the biggest motor they suggest and use the materials and equipment they've supplied? I think that's what I was trying to get across in my numerous long-winded posts before.

    If you're building from scratch, researching other known kits in similar size and motor usage probably would help to ensure you're not overdoing a build.

    I particularly liked this post by kevindcornwell: "I hold to two definitions of Over-Building: 1) Adding strength to compensate for poor build technique, 2) Adding strength in an effort to survive a catastrophe when such an event will inevitably destroy 'something'. (ie. you can't build strong enough to survive 'anything' and still get off the ground.)" This is basically hitting the nail on the head for me.

    They are made for flying, not for crashing, so build it right and enjoy the flight.;)
     
  25. Feb 27, 2019 #115

    afadeev

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    Yeah, but this is the price we pay for taking the beer and wine out of a hobby!

    Without proper lubrication, folks start treating this hobby as if it was a job, bringing science and material tests and strength analysis into a recreational activity.
    :eek:

    I like my #3, below, even more:
    (3) Adding strength because I don't care to analyze the $@#% out of this rocket's components - I just want to fly it on a weekend with friends and family, without needing to interject repair sequences into the process.

    Yeah, my rockets could be lighter, though a few of mine were built for lightness. Those could be lighter still.
    But mostly, I drive to a middle of nowhere to both fly the rockets, and hang out with other similarly minded rocket hobbyists, and BS about rockets. And stuff.

    We do more talking than flying.
    Sometimes, some of us neglect to even fly the damn things ... ;)

    YMMV,
    a
     
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  26. Feb 27, 2019 #116

    cwbullet

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    If you ask ten rocket folks their opinion on how to do some thing, you will get at least 15 difference responses. I recommend you make the rocket as safe as you can.
     
  27. Feb 27, 2019 #117

    Tyler P

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    Amen to that.
     
  28. Feb 27, 2019 #118

    Ez2cDave

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    "Science" is flying with "someone looking over your shoulder" the whole time . . . "Fun" is "running like Hell", after you lit the fuse !
     
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  29. Feb 27, 2019 #119

    Nytrunner

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    Don't forget that a segment of the sport population do derive recreation and satisfaction from doing just what you (seemingly) deride. To understand the why's not just the how-to's, and yes to surpass rules of thumb with comprehension.
    I live and work in Rocket City, my club is composed of engineering students, retired missile folks, and rocket scientists (as well as others from 'normal' backgrounds that somehow found a way to put up with us :rolleyes:). We enjoy this hobby as not only personal recreation, but also as a way to grow ourselves and teach those around us (especially the younger generation we desperately need to prepare to fill the country's technical workforce). That includes encouraging folks to see this hobby as more than just getting out to literally burn money and "Make Tube Fly With Fire!".

    There's nothing wrong with the casual hobbyist trusting to rules of thumb and working from what's worked before. But when it fails, they'll have more work to do figuring out what went wrong and how to prevent it. And when the casual hobbyist with enough disposable income to buy/build/fly the big'uns without certain technical knowledge has a failure, the results can be a bit scarier. That may be along the lines of the OP's quandary, when 'overbuilding' is turned to to make up for a lack of detail.

    I've said it before and I'll say it again; there are tons of ways and methods to enjoy this hobby. Heck, Low and slow lends itself to better recovery east of the mississippi in rocket-eating-tree country!

    Anyhow, I'm just a guy on the internet riding a dinosaur. That's my opinion to add to the stew:cool:
     
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  30. Feb 27, 2019 #120

    lakeroadster

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    Life is short.. be happy. There's room here for everybody.. Kit builders, Scratch builders, Designers and Rocket Scientists.

    One thread talks about being inclusive, the next not so much.
     

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