Stock as possible LOC Magnum: "Price of Admission"

I'm building a 5.5" LOC Magnum. Obligatory parts shot.

Ari.

A couple of questions are coming up as I'm looking at the parts.

1. The stock 18" drogue looks strangely small to me. Open Rocket predicts 85 fps descent with a 4-grain 54mm casing. LOC 5.5" kits seem to come with 18"/78" combinations whereas similar-mass 7.5" kits come with 50"/78" combos.
2. 3 of the centering rings look about 1/8" oversize. The 4th ring--according to instructions its purpose is to be the attachment point for booster eye bolt--fits like a glove. I wonder if LOC is giving me bonus plywood that I need to trim (seems like a lot to trim) or if there's another purpose to the oversize rings.

Ari.

iter said:

A couple of questions are coming up as I'm looking at the parts.

1. The stock 18" drogue looks strangely small to me. Open Rocket predicts 85 fps descent with a 4-grain 54mm casing. LOC 5.5" kits seem to come with 18"/78" combinations whereas similar-mass 7.5" kits come with 50"/78" combos.

Ari.

Click to expand...

Drogues should be that much smaller. The body of the rocket generates much more drag at higher speeds, so you only need a little one to make sure it doesn't go stable and point straight down

Are you saying that OR's prediction of 85 fps is imprecise, or that 85 fps is a safe descent velocity to open a 78" main? At that speed, OR predicts an 18G main deployment.

Ari.

iter said:

Are you saying that OR's prediction of 85 fps is imprecise, or that 85 fps is a safe descent velocity to open a 78" main? At that speed, OR predicts an 18G main deployment.

Ari.

Click to expand...

Personally, I think 85 is okay...what's the point in dual-deploy if it doesn't descend a good deal faster on drogue? I don't know what kind of parachutes LOC kits come with, but my preferred Spherachutes would probably be able to handle that just fine.

I must be lame or lazy, not sure which. I don't even use a drogue on my 5.5 inch LDRS 28 commemorative rocket (and smaller) as long as I'm certain it won't do the ballistic thing.
But honestly, the drogue is just supposed to prevent the rocket from coming in too hot for the main chute
Besides, I'm willing to bet Barry (the doc of Loc) wouldn't give you a drogue that wouldn't work with the main...

The 18 inch should be fine, I doubt from experience it will fall that fast. You want to get it down fast. I have heavy fiberglass rockets that fall on drouge that fast. Those are fine on deployment, use a u bolt, lifting eye or welded eye bolt, it is very important at that velocity. I had a stock eye bolt start to open and replaced it with a u bolt.

Not sure why the other CR's are that much bigger, they should slide right it like the other one.
As you see below in the Big Nuke, outside view, (which is the same view as the Magnum) he uses a separate ring for the eye bolt. I, too, use s.s. u-bolts(from Lowes or home depot). I see no reason to use a separate one CR, just drill the last cr for the motor mount, it will be attached to the rocket with more strength anyway. I think he uses one style CR for the eyebolt so all he has to change is your choice of MM tube and associated rings.

https://www.locprecision.com/uploads/IS-82_Big_Nuke.pdf

Again, I am puzzled why the 3 rings are bigger, could be honest mistake of Loc, call Barry and see if he will send you the right ones.

cbrarick said:

But honestly, the drogue is just supposed to prevent the rocket from coming in too hot for the main chute

Click to expand...

And to keep the two halves from colliding on the way down,
and keep the upper section above the fin can at main deploy so the fin can can't foul the main,
and allow the use of shorter shock cords to reduce shock on the system during main deployment,
and to keep the fin can from getting in a slight fin down mode and flying off pulling the upper with it.

Shorter shock cords do not neccessarily reduce shock to the sections. It is not uncommon to see 30' and 50' cords on large projects just for that reason.
You want longer cords so the energy can be dissipated by the time it snags back. Make the difference in the cord lengths large enough so the sections are far apart so they do not bang against each other on the way down.
You can take the long cords and fan-fold them and wrap with a rubber band. Keeps them from tangling during the packing process and when they eject. That even helps slow down the sections during ejection, too. Do not worry if you wrap the bands tight, they WILL break at ejection.
See below a sample of my L2 Flight Profile, which was a Magnum OBTW.

What motor mount is it? 54mm or 3"? Guessing 3". A 'stock' Magnum from back in the day was 54mm with twin 29mm for cluster / air starts. Thinking a stock 3" MM would not include outboards.

Dave A said:

Shorter shock cords do not neccessarily reduce shock to the sections. It is not uncommon to see 30' and 50' cords on large projects just for that reason.
You want longer cords so the energy can be dissipated by the time it snags back. Make the difference in the cord lengths large enough so the sections are far apart so they do not bang against each other on the way down.
You can take the long cords and fan-fold them and wrap with a rubber band. Keeps them from tangling during the packing process and when they eject. That even helps slow down the sections during ejection, too. Do not worry if you wrap the bands tight, they WILL break at ejection.
See below a sample of my L2 Flight Profile, which was a Magnum OBTW.
View attachment 120732

Click to expand...

There shouldn't be so much energy that it needs to be dissipated. A short shock cord is better if you use the "just more than enough" mentality rather than the "blow it out or blow it up" mentality with ejection charges.

CarVac said:

There shouldn't be so much energy that it needs to be dissipated. A short shock cord is better if you use the "just more than enough" mentality rather than the "blow it out or blow it up" mentality with ejection charges.

Click to expand...

But long is better if you have trees at your launch site(s).

CarVac said:

There shouldn't be so much energy that it needs to be dissipated. A short shock cord is better if you use the "just more than enough" mentality rather than the "blow it out or blow it up" mentality with ejection charges.

Click to expand...

If you go to great lengths with "just enough charge" you risk not having quite enough based on tightness of the sections plus the shear pins. A little extra cord and charge is cheaper than another LOC Magnum kit. (Sorry Barry)
Never saw one blow up except on a reality show.

Dave A said:

If you go to great lengths with "just enough charge" you risk not having quite enough based on tightness of the sections plus the shear pins. A little extra cord and charge is cheaper than another LOC Magnum kit. (Sorry Barry)
Never saw one blow up except on a reality show.

Click to expand...

But I have seen a main open and the fin can continue falling the length of that long cord and never stopping when it got to the end. The momentum just tore the anchors out like they weren't there.

Handeman said:

But I have seen a main open and the fin can continue falling the length of that long cord and never stopping when it got to the end. The momentum just tore the anchors out like they weren't there.

Click to expand...

That also can happen when you do not connect the top two cr's with allthread or use a cheap eyebolt that is not forged.

With the exception of putting an altimeter bay in the coupler and a TN shock cord, I had a Magnum built completely stock. It flew on everything from an I357 to a Kosdon L850 and Aerotech K250 and K1100 (with outboards). I used no drogue at all and it fell at about 70 fps. It died by cato after 15 flights.

This is the 3" MMT, Magnum 3E. The 3" hole leave little room for outboards, and I'm planning on flying it on a single motor.

The CR size mystery finds its resolution when I call LOC this morning. Apparently, this is what happens when you use a 1/4" bit instead of 1/2". They are sending me a new set of CRs. While I'm waiting for replacement CRs, I'm starting on the A/V bay.

Another question that comes up is nose cone retention. The plastic NC has this little tab in the middle. The instructions have me slide the TN belt through the tab and into a Quick Link. This tab looks like something that would break under the NC's own weight, much less survive a BP ejection. I wonder what people use to attach shock cords to these larger LOC NCs.

Ari.

I cut a hole in the side of the shoulder and put an eye bolt in the bottom. Fixing the hole is optional.

Do not use the plastic loops. They worked for elastic, not TN or Kevlar.

I'm starting the build with the A/V bay, and I'm starting that with the sled. I choose to use U-bolts rather than eye-bolts, but I like to keep the holes in A/V bay bulkheads. This means I'm using a single all-thread to hold the bulkheads together.

I use 2-56 t-nuts to mount electronics.

Clockwise from left: ArduPilot for GPS telemetry and flight recording, Adept DDC22 backup altimeter, PerfectFlite MAWD primary altimeter, GPS unit.

ArduPilot has a "second story" board that plugs into the one in previous photo; zip-ties hold down AP's RF transceiver, antenna and GPS receiver.

3 separate 9-volt battery holders (independent power to each A/V unit) and a 5/16 lug for all-thread go on the back of the sled. I use Gorilla glue to attach plastic to wood.

Ari.

Stainless steel 1/4" U-bolts from the hardware store are almost the right size for the hole pattern. I use a round file to extend the holes by 3/32" of 1/8". I attach the U-bolts with locknuts and washers.

My previous builds use bolt-in terminals for initiators. When I go to Radio Shack to pick up some for this build, I notice speaker terminals on the shelf next to them. I pick up a pair and decide to use them. They have spring contacts which means one fewer tools for prepping the rocket (other terminal block requires a flat-head screwdriver) and as a bonus, the new terminals' wiring comes out under them rather than on the side, so no wire holes to seal. I drill 8 holes in the bulkhead and glue them down. When the glue sets tomorrow, I'm going to solder altimeter wiring to the terminal tabs that protrude on the inside of my bulkheads.

Ari.

cavecentral said:

I cut a hole in the side of the shoulder and put an eye bolt in the bottom. Fixing the hole is optional.

Do not use the plastic loops. They worked for elastic, not TN or Kevlar.

Click to expand...

Ah, the elastic legacy makes sense.

On previous (smaller) rockets that use LOC nosecones, I drill 1/2" holes in bottom of the nosecone closer to the edges and thread a few loops of para cord though them. I then use a quick link to attach shock cord to the para cord lops. Something like this: https://www.rocketryforumarchive.com/showthread.php?p=513332#post513332. I keep expecting the plastic to break, but it keeps holding together.

Smaller LOC NCs have a hole for an eyebolt in the center. This one has only a square loop (left-most in the photo). I wonder if that affects its strength as far as installing an eye-bolt.

Regarding the ArduPilot, can you use this device to track your rocket as well?

Are you planning on using this for admission to L3, after which you're going to make some crazyass L3 glider?


Later!

--Coop

DRAGON64 said:

Regarding the ArduPilot, can you use this device to track your rocket as well?

Click to expand...

Arupilot's primary function in this installation is GPS flight tracking.

Ari.

Coop--the level of stress and drama one has in one's life is a choice. I can dial it up if I'm bored or down if I'm stressed out. I'm dialing it way down.

Ari.

Dig that.


Later!

--Coop

iter said:

Another question that comes up is nose cone retention. The plastic NC has this little tab in the middle. The instructions have me slide the TN belt through the tab and into a Quick Link. This tab looks like something that would break under the NC's own weight, much less survive a BP ejection. I wonder what people use to attach shock cords to these larger LOC NCs.

Ari.

Click to expand...

Never use the plastic tabs! What I do with most of my builds, is epoxy a bulkhead in the forward body tube to take up some of the space. I use a u-bolt in the bulkhead for recovery attachment. The nose cone is held in with three #6 sheet metal screws.

https://www.rocketryforum.com/showt...uild-upscale-Estes-Shadow&p=410615#post410615

Thank you for the link Jim. I guess this means you eject the nosecone together with the nosecone, rather than eject the nosecone and leave the payload tube on the A/V bay. This is another datapoint for my other thread.

A little progress from last night. The lighter connector wiring is complete, as is the wiring for arming switches. In previous builds, people ask me for wiring photos. This may or may not be clear enough. I'm running the ground connection through the normally-closed contacts on a 1/4" phono jack. This particular one is stereo and has two sets of contacts. I wire both of them in parallel, so that either one completes the circuit--on the off-chance that one might bounce during a high-G maneuver. Both my altimeters have large capacitors though, and can take power disruptions of a couple of seconds.

Ari.

Wiring is complete on the A/V bay. The whole affair is surprisingly painless. Everything rings through, everything beeps, altimeters detect continuity and everything. I have DDC22 deploying main at 1,200' and MAWD at 1,100'. Their configuration is a bit cryptic for my taste (my background is in cognitive science) so I put a legend next to each of them. Now I can adjust their settings without referring to a manual. I'm waiting for adhesive to dry on the phono plugs where I'm gluing them into the switchband. Once that's dry, I have a complete A/V bay.

Replacement rings show up in the mail today--faster than my expectation, thank you LOC! I'm very happy that I can continue building through the weekend. The new rings are smaller and fit nicely inside the body tube and around MMT.

I cut 4, 1.5" strips of coupler and 1" strips of stiffy to serve as a sort of fillet between CR and body tube. A table saw with a jig and a fence make quick work of this.

Ari.