Loc IV is now a dual deploy kit, and I have questions

Ok, so this is a little annoying. I applaud Loc for making the Loc IV more versatile, but it is frustrating for me since all instructional material a had reviewed were for their original configuration, and it was this abundance of this information why I selected the Loc IV, and it no longer applies to the new kit. For those unaware Loc has changed the kit to include payload bay for dual deployment, which aside from reading bits about here and there is still a very alien for me. My intention for my level 1 cert on single deployment.

John Cocker’s video was the only reason I didn’t go with an Apogee Zephyr, that and everyone I talked in club to told me to get the Loc IV. The changes went into effect in May, so the instructional material and suggestions are outdated. I am having some buyers remorse, but I am hoping to get informed enough to get over it.

So, to be clear, I am not blaming Loc, or anyone else, but it has left me with some obstacles I wasn’t prepared for.

How far apart do rail buttons need to be? The motor mount tube in the original kit is substantially longer than the new kit. If I use Cockers method with 1/4 plywood backing on launch lugs, my rail buttons will be a whole lot closer to one another. He states it should be mounted just outside of the forward centering ring. This appears to be roughly half the distance on the new kit. If I move them apart further should I be concerned about the plywood rail button backing interfering with or hanging on the parachute on release?

I know that dual deploy typically uses shear pins or screws between airframe and coupler, so do I use shear pins (that I don’t have) to hold upper assembly to coupler? Or do I epoxy it permanently in place? (Effectively making one very long nose cone for single deployment.)

Do I attach my chute lines to the eye bolt on coupler? Or do I need a leader?

The kit does now come with what looks like a nylon shock cord, instead of elastic, even though I bought a Kevlar one for giggles I guess. A nice upgrade I wish I knew about earlier.

Thank you for your time and help.

Hi Rawcat, first I did both L1 and L2 certs with LOC paper and wood kit. They ARE great. I fly several of my DD kit with no payload bay at all. Just need to make sure it is stable. OR and Rocksim are great for that. As far as the buttons go, I like my lower one as far down as possible. With the ply CR you can install it in that, although I put a ply backer and blind nut on the inside, even on glass kits. The upper one, a lot of people use the "rule of thumb" and put it at the CG. Myself I just kind of "eyeball" it between that and what would give good stability on the rail. There is nothing that says you cannot have 3 buttons. All of my rockets use the third loop for chute or streamer attachment. That is, you have loops at both ends, one for the booster to hook to and the other for the AV Bay. About a foot , or so , down from the AV Bay I put a third loop for drouge attachment. This keeps anything from getting tangled on the bulkhead, wing nuts, charge wells, terminal blocks. Then on upper section, again 3 loops, with the third near the NC to attach the main to. I usr kevlar on everything, I have had nylon break, never use elastic as it will cause a rebound and slam parts together. On the backers for the buttons I always bevel the edges on the ply backers, cover the blind nut with 5 minute, so it does not back out over time, and most of the time with them on the boost section, they are well below the drouge anyway. I would not epoxy the coupler in place, you may want it out to service it at some point. I will use nylon screws as shear pins, and steel ones on the section that is to stay together. Again I put ply backers with blind nuts at each location. Easier to get the broken shear pins out IMHO.
On your cert flight, keep it low and slow, you could see the entire flight on both of mine, small H motors are great for this.

Rawcat, My first HPR kit was a 3" LCO Caliber ISP, a single deployment rocket. After attending a number of launches and getting tired of the long retreive, I decided to modify it into a dual deployment rocket. I bought the LOC electronics bay. Any mods I made I checked in OpenRocket first to see what would happen, especially to the center of pressure. I've flown it a number of times now to 2500' and it has worked flawlessly. LOC has a RockSim file for the IV which you can open in OR to see how it will perform.

You don't have to fly it DD. But if you do you will need a harness in the booster (below the coupler) and another in the payload bay (above the coupler). I usually do a kevlar leader, as you call it, at any connection that has an ejection charge. So in DD I'll have a kevlar leader, about 2' long, on each end of the coupler, with nylon attached to that.

Leave your coupler loose though, so you can step up to DD later. Just pin, screw, or rivet the coupler in place and leave the nose cone loose. Or have it break at the coupler, in which case secure the coupler to the booster, and secure nose cone to payload bay.

If you never intend to go DD however then glue that sucker in place and leave the nose cone loose.

Put one rail button near the rear centering ring and the other about 10" up. No reason to over complicate it. You can glue blocks in your airframe and/ or use T-nuts, blind nuts, well nuts, etc. Dozens and dozens of ways to do it. My L2 has threaded inserts simply run into the body tube, 10 lbs and has flown on a K600, works fine. Works better with a block of wood for the insert to thread into though. I use #8 because it is the smallest of that type I could find and I use them for everything. A bag from McMaster lasts a good while.

Sheer pins can be tricky on paper/wood models but are doing. Just have something to reinforce the holes. Again, lots of ways to do this too.

Thanks guys, I kind of panicked when this kit came in so different than what I had planned for. The preparation and parts collecting I did for this to make it identical in construction to instructions I saw were basically for nothing and it frustrated me. I slept on it and revisited it this morning more optimistic, I have built far more complex mid and low power rockets, surely I can do this and not let high power intimidate me.

Let me run my new plan by you and see what you think.

I am going to glue the 4” coupler with bulkhead into the foreword air frame permanently. The cone is already super tight, like excessively tight, but I may add just a tiny amount of masking tape to friction fit it in place if need be.

The plywood backing I intended on using for the forward rail button is out, I don’t want my parachute, chute protector, cute release, or nylon shock cord hanging on it and I don’t know if I can bevel the plywood and smooth it out enough to give me the confidence it won’t create a problem. Instead I am going to apply a Fix-It epoxy over it on the inside in a small amount, just enough to increase surface area and make a nice very thin rounded and smooth surface. This way I can install the foreword rail button in front of CG without worry I will obstruct deployment in any way.

On the eye hook that attaches to bulkhead, I will attack both my nylon shock cord and my parachute lines.

The fin and motor mount assembly will be installed in the exact same way described in the instructional video I saw by John Cocker.

I do want to build a dual deployment some day, but I don’t want to do it on a paper kit.

Please review my plan and let me know if there are any issues that jump out at you.

I used a LOC IV for my first L1 attempt. Great rocket, not so great fins (I broke a fin on my L1 attempt flight )

If you want you can build the IV exactly like you saw in the video (I did) but...you would build the payload bay like LOC shows you in the addendum. This would get you an IV with a payload bay, not DD, but it's easy to build and fly for your L1. I used the Apogee rail buttons which had a metal T nut instead of using the wood backer, and those have worked great for me.

I would recommend flying it a few times on larger Gs to get an idea of how it's going to work for you before flying on the high powered motor. I flew mine on a G76 before an H128. This gave me a chance to double check my SIMs to be sure they're in the ballpark for the L1 flight.

Good luck!!

My LOC Caliber ISP has a cardboard tube and I've flown it a dozen times & it is still flight worthy. I like dual deployment as my rocket doesn't drift so far away now as when it was just a single large chute at apogee. I'd make it dual deployment. You can still flying it single deployment if you want.

Two quick notes...

Body tube(s): if you want to build the new IV just like the old IV, just use the coupler and glue the top and bottom tubes together. Omit the bulkplate and you no longer have a payload section! Only difference between old and new is the seam...which can be easily filled/sanded!

Fins: as Dave said...the combo of the current 1/8" fin stock and the fins that overhang the aft edge of the airframe are downfall of the IV design. They strike the ground first upon landing and are prone to breaking. If at all possible, reinforce the fins with fiberglass on both sides before assembly. A little effort here on the front end will save you much frustration and heartbreak in the future.

Rawcat said:

Ok, so this is a little annoying.

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It's good that LOC keeps updating their kits, but I'm sorry the advice you got was out of date.

Rawcat said:

How far apart do rail buttons need to be?

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The rule of thumb I always go with, from Scott Bartell, is as far aft as possible and then halfway between the aft and the C.G. I generally do put the forward rail button just forward of the forward centering ring (in the recovery space), which makes it easier to install. (See this discussion for more opinions.)

Rawcat said:

I know that dual deploy typically uses shear pins or screws between airframe and coupler, so do I use shear pins (that I don’t have) to hold upper assembly to coupler? Or do I epoxy it permanently in place? (Effectively making one very long nose cone for single deployment.)

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Shear pins are a disposable item, so it doesn't surprise me they are not included in the kit. I wouldn't rely too much on pins with a paper airframe so if you want it to be single-deployment, I'd epoxy the parts.

Rawcat said:

Do I attach my chute lines to the eye bolt on coupler? Or do I need a leader?

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You definitely want a bridle between the attachment point and the parachute (where the shroud lines come together). Rule of thumb I use is about 5x the length of the rocket in bridle.

Rawcat said:

The kit does now come with what looks like a nylon shock cord, instead of elastic, even though I bought a Kevlar one for giggles I guess.

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There is an endless argument of "Nylon" vs "Kevlar" on this forum. (Nylon has give, but doesn't handle heat well.)

JohnCoker said:

There is an endless argument of "Nylon" vs "Kevlar" on this forum. (Nylon has give, but doesn't handle heat well.)

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One bit of advice on the Kevlar / Nylon options. I would definitely go with Nylon first. Kevlar is great but typically it's not as wide as Nylon and therefore has a greater tendency to cut cardboard. There are ways to mitigate the risk of Kevlar zippering your airframe but it gets a bit more complicated. You can CA the tube so it's hardened. You can use some device like a ping pong ball to increase the surface area where the Kevlar meets the end of the tube. You can use Kevlar inside the tube and join it to Nylon using a quick-link. (I usually do this last option).

With the 4" tube you can usually replace the Nylon later wit Kevlar if you want, provided you plan for this and use a quick-link onto the eye bolt attached to the forward centering ring (I think the LOC instructions indicate to do this).

Thank you all.

I started putting it together last night. I will be using the forward section as a payload bay. I have yet to run a Rocksim on it, but my belief is using a payload bay will allow me to use smaller G motors perhaps for test flights by removing it. I already have the aeropack adapter. (I put a lot of thought into this as I was buying parts)

Running the variables through my head, I thought since the MMT is so much shorter on the new kit the deployment charge might push the nose cone off with less authority with a greater volume inside airframe. Perhaps not, I am certainly no expert. My theory was with a payload bay with bulkhead the area inside would be easier to pressurize. I don’t have the thing in front of me, but if I recall the new MMT is around 11” so it can accommodate the payload/dual deploy feature. It appears based on instructions the old MMT was 18”. That isn’t a tremendous difference, but just looking inside of a 4” airframe is pretty daunting for someone who has done mostly low power and only the occasional mid power.

JohnCoker said:

It's good that LOC keeps updating their kits, but I'm sorry the advice you got was out of date.

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I agree, it was just a little frustrating because as many times as I watched your video I thought this thing was going to go together with very little thought. Your video is what influenced my decision, that and people at the club had suggested the Loc IV. I love your videos BTW, keep them up.

Rawcat said:

I agree, it was just a little frustrating because as many times as I watched your video I thought this thing was going to go together with very little thought. Your video is what influenced my decision, that and people at the club had suggested the Loc IV. I love your videos BTW, keep them up.

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I added a comment on the video that LOC had updated the kit. Feel free to post any additional suggestions as well and thanks for the kind words.

JohnCoker said:

I added a comment on the video that LOC had updated the kit. Feel free to post any additional suggestions as well and thanks for the kind words.

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So, if I can pick your brain one last time, and get your view before I proceed. I got the t-nut and cut a small 1/4” plywood square, roughly 1x1”

I smoothed edges down, and very slightly beveled the bottom surface to better conform to airframe radius. I put a very small amount of aeroepoxy on the t-nut to ensure it will never move. Then I applied a small amount of Fix-It epoxy around the lip of the t-nut transition. (I have had a little glue residue interfere with chute release on low power, so I might have gotten excessive making sure this thing was nearly river stone smooth)

My CG is roughly 3” past the centering ring on the interior of my already assembled Loc-IV. I had to use coins in a bag to simulate the propellant weight, roughly 14 oz for a fully loaded P-38 2G casing. (Perhaps just a tad on the heavy side.)

That swivel is what I was considering using as the “bridal.” I planned on attaching the swivel to my Kevlar or Nylon shockcord with a knot, roughly 1/3rd of the way from eye hook in payload bay. On the other loop I would directly attach my shroudlines. (Assuming my picture worked, it has been a decade since I posted much on forums of any kind)

I greatly appreciate your time.

Rawcat said:

That swivel is what I was considering using as the “bridal.”

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The line itself (Kevlar, Nylon, thread, etc) is called the "bridle" (as in horses). The whole thing (bridle and connections) is also called a "harness" (again from horses).

Rawcat said:

I planned on attaching the swivel to my Kevlar or Nylon shockcord with a knot, roughly 1/3rd of the way from eye hook in payload bay. On the other loop I would directly attach my shroudlines.

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I don't often use swivels, but they are placed between the bridle and the parachute shroud lines. For attaching hardware to the end of a line, use a bowline knot.

Rawcat said:

Assuming my picture worked

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Nice job on the rail button mount. Rounding the corners is a good idea to avoid snagging during recovery.

JohnCoker said:

Nice job on the rail button mount. Rounding the corners is a good idea to avoid snagging during recovery.

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This is probably a dumb question, but rail buttons are supposed to spin a little right? So I could use blue loctite on the screw but not tighten it all the way to allow rail button to rotate, yes?

Rawcat said:

This is probably a dumb question, but rail buttons are supposed to spin a little right? So I could use blue loctite on the screw but not tighten it all the way to allow rail button to rotate, yes?

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You could do it that way but rail buttons need replacement at some point, and the small size of the screw might strip the head out if Loctite'd in when trying to remove it.

Rawcat said:

Rail buttons are supposed to spin a little right? So I could use blue loctite on the screw but not tighten it all the way to allow rail button to rotate, yes?

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I always mount my rail buttons so they don't spin. Much more important is to clean the rail before flying with ScotchBrite pads and WD-40 and make sure the rocket slides smoothly. (These supplies should be in the pad area for use when loading rockets, but bringing your own isn't a bad idea as a backup.)

Rawcat said:

Running the variables through my head, I thought since the MMT is so much shorter on the new kit the deployment charge might push the nose cone off with less authority with a greater volume inside airframe. Perhaps not, I am certainly no expert. My theory was with a payload bay with bulkhead the area inside would be easier to pressurize. I don’t have the thing in front of me, but if I recall the new MMT is around 11” so it can accommodate the payload/dual deploy feature. It appears based on instructions the old MMT was 18”. That isn’t a tremendous difference, but just looking inside of a 4” airframe is pretty daunting for someone who has done mostly low power and only the occasional mid power.

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Use a blackpowder calculator like this one: https://www.rockethead.net/black_powder_calculator.htm

Multiply the pressure by the surface area of your nosecone base, and you have the resulting ejection force.

If you touch the head of the screw with a soldering iron for a few seconds, the heat will soften the loctite.

can you buy a 'G" Motor prior to your Level 1 Cert?

rickster75 said:

can you buy a 'G" Motor prior to your Level 1 Cert?

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Most G motors do not require a Level 1 cert to buy. You can buy 1 H motor from a vendor before your certification flight as well, but they shouldn't sell you multiple H or above motors.

rickster75 said:

can you buy a 'G" Motor prior to your Level 1 Cert?

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Yes, so long as the average thrust (the number after the letter ‘G’) is 80 or lower.

And as long as it isn't a sparky motor(I think???)

Lukun7 said:

And as long as it isn't a sparky motor(I think???)

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Yes. That, too.

Must be 18 to purchase G motors

And also all hybrids are defined as high power. Valid mostly in the US.