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pcotcher

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I am working on building my first bigger high power rockets and have a few basic questions - probably a million opinions to come - but that's what I'm after - just need some thoughts on how to improve upon the basics that come in the kits that I am working on.

Largely, these are for LOC kits - which to me seem to cheap-out in the recovery department, the epoxy/nylon thread recovery harness just doesn't seem like it'll be all that strong for continued successful flights.

I’ve been reading through Mark Canepa’s book, and one thing that it’s impressed upon me is the need for bullet-proof recovery systems. But then in talking to some of the locals, they say that for the lower end of high power, you don't have to go all that over the top on your recovery gear.

Both of my current projects will easily handle both L1 and L2 motors, so I'd like to be able to fly them with both - therefore it would make sense to build them stronger.

* Good source for bulk Kevlar thread? What sizes to buy, etc. So far the smaller kits have a short length included, but the LOC kits only have the elastic shock cord, and so far as I can tell for mid and high power, that stuff is bound to fail at some point. I can find it, but it's typically through a rocketry supplier, and I would think that there would be somewhere to buy the right size in bulk where there's more than enough for several projects.

* Good source for bulk tubular nylon? Again sizes, etc. I found that LOC sells the stuff in 25’ lengths - but again, seems like this is something that could be bought in a roll much less expensively.

* At what point should you cross over to the tubular nylon vs. Kevlar thread?

* Nomex sleeves & blankets? Are these worth the extra weight, or should I just stick with dog barf? Since I’m trying to build my anchors from the top CR, should I always use a sleeve due to the close proximity to the ejection charge?

* Are the closed/forged eye bolts really necessary? (Based on what I've read here, I think I already know the answer). I can find the open style pretty easily at Home Depot and similar stores, but I’ve yet to find any of the closed variety. And the U-bolts – while great for the big stuff, really don’t work in the BT80 / 54mm and smaller tubes. If the open eye bolts are so prone to failure - why is it that all these kits come with those parts?

* More advanced / looking forward question – is it okay to build in an electronics bay and then not use it? For example, on the Bruiser – it comes apart at the center, and while this is great for L1 and L2 certs on smaller motors, at some point, I’m going to want to “get it up there” and put in a bigger 54mm motor. So if I build in the separate altimeter bay for dual deploy later on, that will still be okay with standard apogee deployment right?

* And for an aftermarket avionics bay (I'm starting simple with a pre-made LOC bay) - they set those up with the open eye bolts as well - if I convert those to U-bolts - what do I need to do to fill the left over hole from the eyebolt? Does anyone make better avionics bays that are setup with better hardware?

Sorry for the basic questions, I just want to get some discussion started on this front - as I am admittedly suffering from a bit of analysis paralysis on my current projects - I don't want to end up past a point in the build where I can't include some necessary upgrade....

Thanks for your input!

Paul
 

Handeman

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I guess I'll weigh in on some of your questions. As you said, you'll get a million opinions.

As for Kevlar thread vs tubular nylon, why not tubular Kevlar. You can get it in various sizes. Search McMaster-Carr for Kevlar. Thread and tubing

The Nomex blankets work pretty well, but keep them away from direct flame. I have several with holes from ejection charges.

As for the eye bolts, it depends on how heavy your rocket is. If it's light and you use long shock cords, the eye bolts will work just fine. It's when you have a heavy rocket or high speed deployments that the forged bolts are really needed. If you can't find the forged ones, stop by a welding shop with the eye bolts, slip the guy a $20 and I'm sure he'll tack weld a half dozen eye bolts closed for you.

As for the electronics bay, I would build one, just because all the rockets I've built for L1 & L2 all had bays. I like using the altimeters. You don't have to worry about long or short motor delays. I think you get gentler and more dependable deployment with altimeters.

Hope that helps. I'm sure you'll get the opposite advice on some of this too. Hope you like making decisions.
 

pcotcher

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Thanks for the suggestion on that site - wish I had found that before I ordered my supplies (Commonwealth.net) - as it appears they have a better choice on the shock cords.

Another question - I purchased tubular kevlar in bulk, instead of with pre-sewn loops. What's a good method for making REALLY strong loops for that stuff? I have nice strong attachment points for my rocket, and have 25 feet of shock cord for my 7.5' rocket - but need to have a method for attaching the raw tubular kevlar to quick connects.

I've seen epoxy used, what other binder should be combined? Or does anyone want to buy my raw kevlar, so that I can weenie out and buy pre-looped stuff...

Thanks!

Paul
 

pcotcher

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Yep - it was suggested in the post before my last - wish I had purchased from them before I got what I did from Commonwealth. I'll still make it work, just need some suggestions on looping/building connections for the raw tubular kevlar...
 

MarkM

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Yep - it was suggested in the post before my last - wish I had purchased from them before I got what I did from Commonwealth. I'll still make it work, just need some suggestions on looping/building connections for the raw tubular kevlar...
I use THIS knot to make loops in the ends of my tubular kevelar as well as a loop to connect the parachute to.

For connections of the TK to anchor points like nosecones and ebays, I use quicklinks of 3/16" (I like the triagular style) for 3"-4" diameter rockets weighing at least 15lbs. I use oval quicklinks of the same diameter to connect the parachute to the TK harness.
 

MarkM

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I have nice strong attachment points for my rocket, and have 25 feet of shock cord for my 7.5' rocket
IMO, this is too short! I use 30-40 for a drogue harness and 20-30ft for my main; depends on the rocket.
What size TK? I wouldn't use smaller than 1/4" TK. You could go larger, but probably don't need it for the rockets you're currently building. Besides, the thicker 1/2" TK gets to be pretty heavy.
 
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cjl

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IMO, this is too short! I use 30-40 for a drogue harness and 20-30ft for my main; depends on the rocket.
What size TK? I wouldn't use smaller than 1/4" TK. You could go larger, but probably don't need it for the rockets you're currently building. Besides, the thicker 1/2" TK gets to be pretty heavy.
25 feet will work fine. I would normally go longer, yes, but 25 feet is still enough length to avoid damage. I've used 25 feet on my Deuce for years, and it has worked flawlessly.
 

SpartaChris

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* Good source for bulk tubular nylon? Again sizes, etc. I found that LOC sells the stuff in 25’ lengths - but again, seems like this is something that could be bought in a roll much less expensively.
Any climbing supply place should be able to help. Also check our vendors. What's Up Hobbies carries quite a bit for a good price.

* Nomex sleeves & blankets? Are these worth the extra weight, or should I just stick with dog barf? Since I’m trying to build my anchors from the top CR, should I always use a sleeve due to the close proximity to the ejection charge?
I like the nomex sleeves I've used, but it's not a huge deal if you don't. I always use nomex blankets or even deployment bags for recovery. Top Flite makes nomex sleeves and blankets and quickbust has deployment bags.

* Are the closed/forged eye bolts really necessary? (Based on what I've read here, I think I already know the answer). I can find the open style pretty easily at Home Depot and similar stores, but I’ve yet to find any of the closed variety. And the U-bolts – while great for the big stuff, really don’t work in the BT80 / 54mm and smaller tubes. If the open eye bolts are so prone to failure - why is it that all these kits come with those parts?
I usually use a u-bolt for most everything, though much of that depends on the size and weight of the rocket. For a light weight 3 or 4" rocket, normal eyebolts are fine. Anything bigger and I'd start looking at U-bolts or forged eyebolts.

* More advanced / looking forward question – is it okay to build in an electronics bay and then not use it? For example, on the Bruiser – it comes apart at the center, and while this is great for L1 and L2 certs on smaller motors, at some point, I’m going to want to “get it up there” and put in a bigger 54mm motor. So if I build in the separate altimeter bay for dual deploy later on, that will still be okay with standard apogee deployment right?
Yes.

* And for an aftermarket avionics bay (I'm starting simple with a pre-made LOC bay) - they set those up with the open eye bolts as well - if I convert those to U-bolts - what do I need to do to fill the left over hole from the eyebolt? Does anyone make better avionics bays that are setup with better hardware?
Put some tape on the back end and then fill with epoxy or epoxy mixed with a filler. It really makes no difference which you use as both will seal the hole right up.

Sorry for the basic questions, I just want to get some discussion started on this front - as I am admittedly suffering from a bit of analysis paralysis on my current projects - I don't want to end up past a point in the build where I can't include some necessary upgrade....

Thanks for your input!

Paul
There's no substitute for experience, and Canepa's book is a good one. Just remember, there's a million ways to do things, and it's your rocket so do what you think is necessary to help you sleep at night.

Have fun and be sure to send pics!
 
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pcotcher

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Thanks for the input - that actually is very helpful. I am still learning, and experience will definitely help, I'm just trying to avoid dumb mistakes on the first few rounds here.

So that leads to my next question -

I got my commonwealth order last night, and have some bulk 200lb test TK in hand.

The rocket I'm building is a LOC 81" Black Brandt X (I think they call it Tweed-B). It weighs in around 3.5 pounds - so it's not heavy. It's based on a 3" tube.

What are the threasholds that folks use to upgrade from one level of TK to another?

What types of attachment would you use at this weight/size? Seems like I can just tie this stuff off to the u-bolt that I've mounted to the upper MMT - it's thin enough that I can tie it, as it's not actually "strap" like.

25' is a little more than 3x the length of the rocket, so based on the guidelines that I've read it should be enough - especially for this size.

Just trying to make sure I'm in the ball park...

Thanks!

Paul
 

m85476585

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You can reuse recovery harnesses between rockets. Just put an eye bolt/u-bolt in the centering ring and altimeter bay or nose cone, and connect the shock cord with quick links. I have one tubular Kevlar shock cord that I use for a drogue or for single-deploy rockets, and one tubular nylon shock cord I use for the main in dual-deploy rockets. I use these two cords in my three largest HPR rockets, so I don't have to buy more. The smaller rockets have lighter shock cord and no quick links to save weight.

I use a Kevlar parachute protector when I remember (I forgot it last time), and again I only have one that I use in all my 3-4" rockets. I also use dog barf with them just in case, but I can use less dog barf.

REI is a great place to get TN. It's like $.10/foot.

I always make my own e-bays. I use a full-length coupler cut to whatever length I want, then a slightly shorter piece of the same coupler with a slot cut all the way down so it fits inside the first coupler. I buy coupler centering rings that fit in the outer coupler and rest against the inner coupler. The coupler centering rings are attached to eachother with threaded rod all the way through the e-bay, then I use forged (closed) eye bolts from McMaster-carr to attach the shock cord. The altimeter sits on a piece of G10 mounted somewhere inside the e-bay to minimize the chance that it will be damaged if the rocket crashes.
 

MarkM

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You can reuse recovery harnesses between rockets.
True. I have shock cords for my 4" rockets and re-use those between my various 4" rockets. For my 3", I have one extra smaller diameter shockcord for the main and for the drogue use one of the shockcords I use in my 4". My L3 rocket has a completely different set since I use much thicker harnesses for that 40 lb-er.


I always make my own e-bays. I use a full-length coupler cut to whatever length I want, then a slightly shorter piece of the same coupler with a slot cut all the way down so it fits inside the first coupler. I buy coupler centering rings that fit in the outer coupler and rest against the inner coupler. The coupler centering rings are attached to eachother with threaded rod all the way through the e-bay, then I use forged (closed) eye bolts from McMaster-carr to attach the shock cord. The altimeter sits on a piece of G10 mounted somewhere inside the e-bay to minimize the chance that it will be damaged if the rocket crashes.
Me, too. I use very similar construction methodology. But, I think you made an error in terminology. You probably use coupler bulkheads - not centering rings - as endcaps of the ebay.
 

als57

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So that leads to my next question -

I got my commonwealth order last night, and have some bulk 200lb test TK in hand.

The rocket I'm building is a LOC 81" Black Brandt X (I think they call it Tweed-B). It weighs in around 3.5 pounds - so it's not heavy. It's based on a 3" tube.

What are the threasholds that folks use to upgrade from one level of TK to another?

What types of attachment would you use at this weight/size? Seems like I can just tie this stuff off to the u-bolt that I've mounted to the upper MMT - it's thin enough that I can tie it, as it's not actually "strap" like.

25' is a little more than 3x the length of the rocket, so based on the guidelines that I've read it should be enough - especially for this size.

Just trying to make sure I'm in the ball park...

Thanks!

Paul

In smaller rockets (dia) I usually use 1/4" tubular kevlar long enough to get out of the booster section by 6 to 12". Then switch to 9/16" tubular nylon for the upper section. Quick links to connect the lines. And a fire resistant blanket to protect the TN/chute. Note you use a 4" protector in a 3" tube to give some extra coverage. Good thought if your cord is long.

At this weight you can get away with an eye bolt ; but I prefer a u-bolt if you have the space.



Al
 

m85476585

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Me, too. I use very similar construction methodology. But, I think you made an error in terminology. You probably use coupler bulkheads - not centering rings - as endcaps of the ebay.
That's what I meant.
 

Rocketcrab

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In regards to the standard LOC recovery system mounting [the epoxy/braided nylon loop], I have never had a problem with it flying in the higher end of the model rocketry range, ie, F and G motors. Some of my LOC models are 20 years old and that shock cord mounting is fine. I can't speak for the HPR range though.
 

als57

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In regards to the standard LOC recovery system mounting [the epoxy/braided nylon loop], I have never had a problem with it flying in the higher end of the model rocketry range, ie, F and G motors. Some of my LOC models are 20 years old and that shock cord mounting is fine. I can't speak for the HPR range though.
Yeah I used the standard Loc loop attachment in my Hi Tech. And its worked OK for 6+ years and 40+ flights. Mostly G's and H's.

On the Mini Magg I'm just completing swapped the eye bolt out for a U-bolt. And the shock cord is going to 1/2" TK (3') and 9/16" TN (12'). Adding a bit of weight to the cone to balance it for a 38/600 motor.:cool:

Al
 

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