#11
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I don't think I've ever had an "estes-style" triflold mount fail. I've had the shock cord break off (due to age and heat) at the mount, but never the mount fail. So I'm a little curious about some of these options. I can understand the Kevlar past the body tube (to eliminate the break-off I just described), but the other options just seem to solve a problem that I've never had...
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#12
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Quote:
Here's the instructions to the LOC shock cord mount "SCM" that Stefan referenced in his post to better visualize what he described. It's a tried and true method. Not putting the Kevlar past the edge of the body tube will prevent the Kevlar from slicing through the tube and causing a nasty zipper. .
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#13
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Shock Cord Mount
All these ideas r good I'm sure but, extremely messy. I stumbled upon the article in "Sport Rocketry," the "Anti-Zipper " shock cord attachment. My first attempt was in a dual egglofter, using 1500 lb "tubular nylon." Never came close to breaking or pulling out. Today I took my "tail/fin" section, and rebuilt the body. Found another terrific idea, using a "jig" to smooth out center Plate. I'll take some photos and drawings and post here tomorrow. Basically, just like last guy said, Fins separate from body "rearward".
The build: Made a center plate using the jig to fit a BT-80. Once I had the fit, ran a piece of 200lb kevlar thru hole in middle about 3 ft long. Then plugged hole with "wall anchor" and glued with CA and wood glue. Tied rear end to fin assembly. There's a "baffle system" in fin assembly, with an "eye bolt" sticking out to attach parachute and kevlar. Plate was made from 1/8" fiber board. Other end of kevlar gets tied to nose cone. In my case, this "payload" section going to carry lights and battery, so it will b seen @ night @ Naram 51. There u have it! I swear by this system. Baffle works great and pulls parachute rearward, without wadding. I did use a small piece of elastic from kevlar to tail/fin assembly but, can always be replaced, unlike other shock cord mounts. |
#14
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Yes, that's it exactly. And you're right, you have to do it diring assembly of the engine mount. Jeff
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#15
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Baffle System & Shock Cord Mount
Heres a description of attached Photos. 1) regular "cloned BB 0." 3) "Goony" Bluebird. 4) "Baffle system," w/eye bolt attachment; 5) Baffle, main body, & blast plate. Note, the kevlar passes right on thru it, but plugged and glued; 6) whole rocket in separate pieces attached w/kevlar shock cord; 7/8) side by side BB and BB0.
Forgot to take pictures of "center plate" jig. Will do that next. Glenn NAR 89197 |
#16
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Choosing the wrong delay will cause a nasty zipper. That's almost always the cuplrit...not the kevlar hanging out the end. The kevlar may help facilitate the zippering phenomenon quicker than say, elastic alone, but it's not the main cause. I allow the kevlar anchor on all my rockets to hang past the end of the tube using the method Jeffyjeep described and have never had a zipper (I have many and fly often ). Am I lucky? I'd like to think it's because I've made smart motor choices.
I know some people use a piece of tape(or something along those lines) stuck to the kevlar line where it intersects the end of the tube. This is used as a means to buffer or cushion the line against tube and acts as an "anti zipper device", but I don't do that either. None of what I'm saying really pertains to your original question, and to that I'd say try the LOC method. I'm not implying that any of the previous suggestions about anti-zippering aren't good advice...they absolutely are! But just be careful with your motor and delay choices and you'll be golden. |
#17
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Replacement Shock Cord Mount
Referring back to your original post.......
If you don't want to use the tri-fold paper mounting system (which, by the way, has never failed for me either), you can use the mounting system used by FSI. Basically, stiff paper or card stock, about 3/4 to an inch wide and about an inch and half long, maybe two inches. Three holes equally spaced centered on the long axis. Check this link for a description of how to mount it. http://plans.rocketshoppe.com/fsi/f...FSI_Voyager.pdf
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Don NAR 53455 "Carpe Diem" |
#18
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I used this method in my Orbital Transport clone after forgetting to attach the kevlar before the motor mount was installed, and it worked very well. I sort of combined it with the LOC method, still using kevlar(knotted at the anchor end) as the anchor line and using epoxy as the adhesive. The tri-fold works just fine, I just prefer the other methods, mainly because think they are a little less obtrusive. |
#19
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I think the idea is that when the shock cord breaks it is much easier to replace with these other methods. The reason being that the shock cord is not integrated into the mount; it's tied to a more durable cord which is integrated into the mount. Now, all that said, you could just put some kevlar in a trifold mount and tie the shock cord to the kevlar and get much the same benefit. When the shock cord breaks, tie a new one to the durable kevlar. However, to some extent it is a solution for a non-problem. As I recall from way back when, I could usually dig an old trifold mount out with a #11 Xacto blade and a lot of patience. And even if you can't dig the old mount out, you can always just glue in a new one part way around the tube from the old one. I think it's kind of fun to use these other mounting methods and I get to play with kevlar and wire fishing leaders. Still, about half the time, I have the engine mount assembled before I remember than I meant to integrate a cord mount into it...even when the last thing I think before starting assembly is, "Don't forget the cord mount, this time." |
#20
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My problem with the tri-fold isn't that it fails, its that it creates a obstruction in the path of the parachute. There's enough problems with a getting a parachute to deploy properly, I don't need to add another.
Like Micromeister I us stainless steel fishing leads and beading wire mounted to the top centering ring.
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