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Model Forum / General / Rockets / August 2004Fin Breakage questions
When have you experience fin breakage? 1) going up 2) at deployment 3) the sudden stop at the bottom 4) Less than kind treatment away from the launch site. 5) Never, not an issue, not even after a lawn dart 5) other _________ What sort of breakage has occurred? 1) fin snapped clean off bodytube. 2) fin snapped at fillet. 3) portion of fin snapped not effecting fillet 4) nailgun inadvertently split balsa 5) fin ripped away 6) fin sheared 7) other __________ Including type of material, adhisive, fillet type and attachment (TTW, TMM, surface, ..) would help too. Joel. phx (snapped is considered to result from a force perpendicular to the fin, ripped considered a force in the same plane but away from the rocket body, and sheared in the same plane, but along the bodytube 'fin line') I had the fins on a Estes Maniac simply tear off. When I flew it on a F101. ;-) RDH8 > When have you experience fin breakage? > 1) going up [quoted text clipped - 21 lines] > ripped considered a force in the same plane but away from the rocket body, > and sheared in the same plane, but along the bodytube 'fin line') << When have you experience fin breakage? 1) going up>> Rarely. Once it happens, I know to use a sturdier fin (or less powerful motor) the next time. << 2) at deployment>> Never << 3) the sudden stop at the bottom>> This is where I've had the most breakage problems. Since I fly in the desert, often in very rugged areas, it usually occurs when the rocket lands on a rock. Sure, this can be alleviated somewhat by using bigger chutes, but then there's a greater risk of losing the rocket due to excessive drift. I prefer a relatively fast descent. I build my tail assemblies tough so that even when a rocket lawn darts, I can usually just replace the forward airframe. Of course, some lawn darts are energetic enough to damage or destroy the fins anyway. << 4) Less than kind treatment away from the launch site.>> Not yet, though my rockets do get pretty scraped up bouncing around in the back of my Trooper when i'm off-road. > When have you experience fin breakage? > 1) going up -ONE TIME surface mounted fins ripped off when nose cone came off and rocket went unstable at about 500 mph > 2) at deployment -ONE DENTED FIN estes dent, balsa fin > 3) the sudden stop at the bottom -MANY TIMES hinged fins, broken fins, dislodged fins. TTW, surface mount, FinLock (tm) > 4) Less than kind treatment away from the launch site -YES > 5) Never, not an issue, not even after a lawn dart [quoted text clipped - 17 lines] > ripped considered a force in the same plane but away from the rocket body, > and sheared in the same plane, but along the bodytube 'fin line') > When have you experience fin breakage? > 3) the sudden stop at the bottom > What sort of breakage has occurred? > 2) fin snapped at fillet. > Including type of material, 1/4" ply adhisive, wood glue fillet type ? attachment, TTW Doc  SignatureDrake "Doc" Damerau www.rocketmaterials.com NEPRA President NAR Section 614 NAR 79986 L3 www.nepra.com Remove "My Shorts" to reply Not sure if you only want answers from the HPR club. I'm still doing low-power, but my answers are below: >When have you experience fin breakage? >1) going up [quoted text clipped - 3 lines] >5) Never, not an issue, not even after a lawn dart >5) other _________ 3 & 4. Granted, #3 has usually been caused by the recovery device failing to open properly, or having the shock cord separate. But, I *have* had a couple of rockets that were fine when I loaded up end up damaged when I pulled them out of the case. >What sort of breakage has occurred? >1) fin snapped clean off bodytube. [quoted text clipped - 4 lines] >6) fin sheared >7) other __________ 1 & 2. I've had a few of both. I've also had a plastic fin break on my SnapShot. No fillet involved.<g> >Including type of material, adhisive, fillet type and attachment (TTW, TMM, >surface, ..) would help too. White or yellow glue, surface mounted fins. I've had a fin on a Fat Boy(through the tube) break loose, but it could have just been a bad joint to start with. Eldred Signaturehttp://www.umich.edu/~epickett Screamers League IICC League GPLRank -6.0 MoGPL rank +267.80 Ch.Rank +52.58 MoC +741.71 Hist. +82.34 MoH:na N2k3 rank:in progress Slayer Spektera lvl 79 assassin Slayer Spectral_K lvl 44 Necro US East >When have you experience fin breakage? >1) going up [quoted text clipped - 3 lines] >5) Never, not an issue, not even after a lawn dart >5) other _________ 1, 3, 4, 6 >What sort of breakage has occurred? >1) fin snapped clean off bodytube. [quoted text clipped - 4 lines] >6) fin sheared >7) other __________ 1, 2, 3, 5, 6, 7 >Including type of material, adhisive, fillet type and attachment (TTW, TMM, >surface, ..) would help too. What is adhisive? Some sort of glue made from cat after nailgun procedure? >Joel. phx The underscore was intended as fill in the blank. Where else have you experienced damage and what sort? I'm planning on a TRF poll which should gather more data because it doesn't require 'de-lurking'. Thanks, Joel. phx Adhesive. Why didn't spell check catch that? At least you didn't comment about 2 # 5s :) > >When have you experience fin breakage? > >1) going up [quoted text clipped - 24 lines] > > >Joel. phx >The underscore was intended as fill in the blank. Where else have you >experienced damage and what sort? I'm planning on a TRF poll which should >gather more data because it doesn't require 'de-lurking'. I'm not sure, maybe #4 covers all 5_ (6 whatever). Some "others" include fins sheared off penetrating a tree or other obstacle, fins damaged on recovery "lateral" impact with wall or fence. Heavy tool box crushing a Saturn V model (including fins) in a minor car accident. BTW, I have a few years experience on missile loads. I was not working on the saturday when a crated missile was dropped from a fork lift. It was OK. But in life all manner of things happens, even sitting on a model rocket. Not that you would want to design or build for all eventualities. Alan >Thanks, >Joel. phx > >Adhesive. Why didn't spell check catch that? At least you didn't comment >about 2 # 5s :) I thought so, but between test at the far left of an old cheap monitor and my tired old eyes, I gave it a pass. >> >When have you experience fin breakage? >> >1) going up [quoted text clipped - 25 lines] >> >> >Joel. phx > BTW, I have a few years experience on missile loads. I was not > working on the saturday when a crated missile was dropped from a fork > lift. It was OK. But in life all manner of things happens, even > sitting on a model rocket. Not that you would want to design or build > for all eventualities. Oh man, you would love the funnier than snot story about missile testing at some army base when a fueling accident starts a fire and a grunt goes a running "for his life". He thought the nuke would go off! Wish I saved the link, but I was searching on Nike missile bases at the time. Joel. phx > Alan <response in-line> > When have you experience fin breakage? > 1) going up Most shreds were balsa fins and resulted in jagged breaks along the fillet or pieces of the fin breaking off. > 2) at deployment From shockcord snap-back. > 3) the sudden stop at the bottom Majority of breakage. Balsa and basswood usually snaps off along fillets, splits along the grain, or a combination. Many dings and dents as well. Plywood fins seem to break at glue joints, usually by a thin surface wood delamination at the joint. Laminated fins (paper, fiberglass, etc) tend to break the substrate (in weird ways) but hang together from the laminate. > 4) Less than kind treatment away from the launch site. > 5) Never, not an issue, not even after a lawn dart > 5) other _________ Have had surface mount fin booster shreds at staging when the booster started tumbling at high speeds. IIRC these were the only times the body tube delaminated and an intact fin-fillet separated from the airframe. > What sort of breakage has occurred? > 1) fin snapped clean off bodytube. [quoted text clipped - 13 lines] > ripped considered a force in the same plane but away from the rocket body, > and sheared in the same plane, but along the bodytube 'fin line') Breaking fins on landings is a pet peeve of mine. I try to use fin planforms that don't entend aft so that a vertical (never really happens) landing hits on the reinforced tail section instead of a fin tip. These are experiences with MR and LMR, not HPR. I use yellow glue for standard builds and epoxy (30 min and finishing) for the glassed models. I fillet yellow glue by applying many thin layers and smoothing over with FnF. Epoxy fillets are all epoxy. I only surface mount fins on min diameter rockets and I glass those. If there's any room at all, I use some through-wall mount. I don't have any kit rockets, except my NARTREK BBII scale model. All my rockets are scratch built to address things like fin breakage. In general, I find the adhesives to be the strongest parts of my models and rarely, if ever, see an actual bond failure. Balsa and basswood fins tend to break and paper tubes delaminate before glue joints fail. TTW mounts with reinforced balsa and basswood, plywood, etc,, are strong enough to transfer energy (and damage) to other airframe components so models with strong fins have correspondingly strengthened CR's, motor mount tubes, airframes, etc. SignatureGary Bolles summum jus, summa injuria est To contact me; bollesg at comcast dot net http://home.comcast.net/~bollesg/rockets/rockets.html |
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