Loc Magnum Build

Though not the largest, smallest, fastest, or most extreme, I can honestly I haven’t been this excited for a build in a long time!

Why the Magnum?

1) Loc rocks and the Magnum is a classic. It just so happens that my discovery of High Power Rocketry (HPR) was with the Nov/Dec 1992 issue of High Power Rocketry magazine with Wayne Anthony’s flamed Magnum on the cover. This is the issue of HPR that got me hooked, and that photo is the initial image that sticks in my mind.


2) Not sure why, but I really like 75-3G motors…I guess its just a nice size for me. I also picked up 75-2G AMW hardware and an L700 load last year. Well, the 2G and 3G 75 loads from AMW are largely progressive, meaning they have a gentle start up and therefore don’t have tremendous kick off the pad. I wanted a rocket that could achieve a minimum 5:1 thrust-to-weight ratio with only 500 Newtons of average initial thrust (ie L666 thrust curve: https://www.thrustcurve.org/simfilesearch.jsp?id=606). That ends up being a 22 lb on the pad weight. 22 lbs minus an 8 lb L666 Skid leaves only 14lbs for airframe, electronics, and recovery. I have two 4” kits with 3” holes on hand, so let’s throw them on the scale. Without recovery, electronics, epoxy, or otherwise, dry weights of the Extreme Darkstar and Air-X Delamar both were around 13 lbs…no chance in heck I’d keep it under 14lbs constructed without doing surgery on the kits…no thanks. However, I’m very confident I can build a lightweight Magnum!

3) Again, Loc rocks! I have more Loc rockets than any other brand; I love them for their simplicity and efficiency. Furthermore, I spent a bit of time with Barry and Mark from Loc at Midwest Power a few months ago. You see, I appreciate having quality rocket manufacturers/suppliers on the field at launches I attend. For instance, among others, I saw Loc, Loki, CTI, Stickershock, and Wildman present (but not necessarily vending) at MWP; each received an order following Midwest Power.

Getting back to the excitement of the build; I have longed to have a Magnum and have been on a nostalgia kick of late. After building a Dynacom Tarantula https://www.rocketryforum.com/showthread.php?t=26622 clone that blazes the skies and topped 20K on its first flight, I’m excited to build a lightweight classic that can majestically soar on lighter thrusting longer burning motors! So here we go!

First up: Magnum arrives nicely boxed from the fine folks at Loc:


-Eric-

Subscribed op:

Wow, someone building a large HPR rocket that is not all fiberglass. How quaint.


There is a story floating around these parts that a guy built a Magnum and used only the original paper & wood components for the construction. No glass, no epoxy, and successfully flew it on a small M.

I did my L3 on a Magnum3-E (Glass fins) - It is one of the cleanest designs out there and a real classic.

Looking forward to watching this one develop.

ECayemberg said:

3) Again, Loc rocks! I have more Loc rockets than any other brand; I love them for their simplicity and efficiency. Furthermore, I spent a bit of time with Barry and Mark from Loc at Midwest Power a few months ago. You see, I appreciate having quality rocket manufacturers/suppliers on the field at launches I attend. For instance, among others, I saw Loc, Loki, CTI, Stickershock, and Wildman present (but not necessarily vending) at MWP; each received an order following Midwest Power.

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I agree. Barry and Mark came by my tent at MWP. Actually they came by looking for Hope-N-Pray (a highly customized LOC Bruiser EXP) which I didn't have with me. But that time/attention has led to three orders for LOC from me since November.

This thread has already grabbed my attention, for a few reasons:

1. I used to fly monthly with Wayne Anthony with the CTRA-NARCONN club in Eastern NY. Great guy, great LCO.

2. I have owned two Magnum's in my rocketry life. The first was built stock, apart from a stretched payload tube and extended 29mm tubes. I never did fly it with a cluster or air-starts. That was my first big rocket. The second was a scratch build using carpet tubing that had alternating foil layers. It was exactly the same OD as LOC tubing, and I was able to peel layers out to make the cone fit. This one had a 76mm Motor Mount and flew on several 54mm AT loads and EX 76-3500 loads. Probably had 15 flights between the two of them.

3. I want to build another! I'm close to flying my first 2 stage rocket, and I would love to follow that up with my first cluster/air-start rocket. The Magnum would be a perfect candidate for that, flying on a 54-1400 to 2x 29-250 combo to 6,000' or so. Building the rocket in this fashion will also allow me to do it in my apartment without the need for any composite reinforcement.

That being said, the kit price of $179 ($214 w/ electronics bay) is slightly off-putting. I know that LOC kits are quality, but that seems steep in my opinion for "what it is." Much to H Rocket's point, I could easily just purchase a Competitor 4 for $200, which has more robust materials. The end result is not the same, but it's these really difficult decisions that I face every day...

I am looking forward to the build. Should be a trip down memory lane, and if you do a good enough job you may convince me to re-purchase my own Magnum and give air-starts a crack.

I used a LOC Magnum for my Tripoli certification back in 1988.

I flew it with an AeroTech single-use I140 motor.

Good kit. I built it stock with epoxy adhesive.

Magnum = a classic. Perfect looking rocket, the proportions are spot on imho. The price, plus the price of big level 2 motors, keeps me away from big kits for now. But I think $250 is reasonable for a rocket this big if the fins are FG. Even if the airframe is just paper.

All good comments...thanks! We've become spoiled with high quality 'glass rockets at very affordable rockets thanks to Perf. rocketry, Wildman, etc...but I feel the cardboard rockets still have their place! Loc really helped pioneer the hobby under Ron and Deb, and Barry has done a great job preserving the classics and advancing the line into today's hobby. This Saturday, if the winds are low...I'll be flying two Loc rockets on long burn motors. EZI-65 on an I65...and a Caliber ISP with a Kosdon I130 C-slot. EZI weighs under 2.5 lbs WITH dual deploy setup! Caliber ISP weighs 2.25lbs minus motor. These low weights allow the low thrusting long burning motors in relatively large rockets...something that isn't easy attainable in glass rockets.

ECayemberg said:

All good comments...thanks! We've become spoiled with high quality 'glass rockets at very affordable rockets thanks to Perf. rocketry, Wildman, etc...but I feel the cardboard rockets still have their place! Loc really helped pioneer the hobby under Ron and Deb, and Barry has done a great job preserving the classics and advancing the line into today's hobby. This Saturday, if the winds are low...I'll be flying two Loc rockets on long burn motors. EZI-65 on an I65...and a Caliber ISP with a Kosdon I130 C-slot. EZI weighs under 2.5 lbs WITH dual deploy setup! Caliber ISP weighs 2.25lbs minus motor. These low weights allow the low thrusting long burning motors in relatively large rockets...something that isn't easy attainable in glass rockets.

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It appears that your interests are right there with mine...creepy.

I had considered purchasing an EZI-65 as well to fly on long burn motors. I was intending to try to mix my own moon-burn motors for these rockets and get some nice long burns in minimalist airframes.

There must be something with the nostalgia of it that attracts me to these types of flights. I was in the hobby long enough ago that I saw many a J90W and J180T while even catching a couple of H45W and I65W flights. While these flights aren't necessarily incredible, I like the gentle flight path and the sound of a motor continuing to burn as it is out of sight.

I would love to somehow get my hands on an I65 and fly one as it was intended! I'd also love to see pictures and possibly a video of your flights this weekend.

As the box indicates, I ordered a Magnum 3E...necessary to accomodate the 75mm casings.

Step one: open box and admire components. Yep, this came from Loc; well packaged, precise lightweight components that fit well, and look and smell great! What’s this, even a few surprises thrown in that I didn’t anticipate…thanks Loc! Holy decal sheets, Batman

Parts 'N Pieces!


Step two: Modify modern day stock PK-90 (3E) airframe to be stock PK-84 of yesteryear.

When Magnums were first produced in the mid-to-late 80’s, they came with shorter Minie Magg style nosecones (Bob, was your NC plastic, wood, foam?). I like the looks of the version when the PNC-5.54L long cones became available in the early 90’s…this is the version I’m attempting to recreate. This same era seemed to be the hayday for Magnums... they were the standard for large rockets...the basis for the relatively new avionics that began appearing on the scene, and as many of you mention, a great planform for airstarting! I wanted one then, I'm finally building one now.

Back to (de)construction: stock length of the Magnum from the 90's was 83"....45" main airframe, 17" payload, 21" exposed nose. Modern day PK-84 Magnum is 80" whereas PK-90 3E is 90". So...7" will be cut from the main airframe to give the same overall length as the ol' 84.

Besides shortening the extended 3E version back to original length, the fins also need to be trimmed to match the old planform. Somewhere along the lines, Barry increased the dimensions of the Magnum fins, thereby increasing fin area and stability of the rocket...logical reasoning, but I prefer the original shape for aesthetic reasons.

Using a pattern from long long ago in a time less known, we can see the difference between new fin shape and old fin shape. Hello jigsaw!


To be continued...

patelldp said:

catching a couple of H45W and I65W flights. While these flights aren't necessarily incredible, I like the gentle flight path and the sound of a motor continuing to burn as it is out of sight.

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Graduator on a G25...
Hitech H 45 on an H45...
EZ I65 on an I65...

Rocketry perfection.

Typical tail tacking:

Fins were cut to size using a jigsaw and a semi-steady hand. Edges sanded straight using a block and some course-ish sandpaper. Edges were rounded to take off the edge.

The glassine coating on the thick wall paper motor tube was removed where the fins and centering rings were to contact the tube. Lines were drawn every 120 degrees to align fins. A wrap of tape marks the leading edge of the fin roots. Ends of motor mount tube were coated in thin Zap CA to prevent peeling, swelling, or otherwise.

Fins were tacked in place using 15 minute Bob Smith and a cardboard alignment guide or two (one shown; think I used two while epoxy set.


Before filleting, a quick test fit in the airframe to ensure all the pieces of the puzzle fit. If not, it's easy to break a "tack"...not so much after filleting. It fits!

Shifting gears to the main airframe. The provided payload length is 27"; provided main airframe length is 42". I wanted the extra length of the payload section for standard dual deploy setup, and didn't need the length of the main airframe since 75-3G is the largest I intend to fly in this bird (I have plenty of other rockets to accomodate the longer cases...it's not that the Mag couldn't handle it...it's just not my intent for this one). Also, we have a "traveling" rocket that needed a few inches of non-zippered 5.5" airframe...this will work!

Sin #1: I honestly intended to build this thing with no glass...but I just couldn't do it. Therefore, I'm incorporating glass into the two areas where I've experienced the highest frequency of "needs repairs" over the years: front of lower airframe and fin fillets. I could make the lower airframe "zipperless", but I'd rather just wrap a few layers of glass around the airframe. So we start by peeling the glassine in the area-to-be-glassed so the epoxy soaks in a wee bit better.


Then 2 wraps of 4" wide heavy (10oz?) plain weave E glass is wrapped over what will be the joint to be cut; 2" on each side. Covered over all that with one wrap of ~6oz plain weave E.

Using the same epoxy, a one wrap veil of 0.6oz E was applied to eliminate the "pinholes".

Once dry, the airframe trimmed and cut 7" down from one end. As mentioned earlier, the 7" piece goes to another rocket that suffered a zipper. The cut has begun:


I reckon that's about it for now. More to follow...

-Eric-

Nice. The fins look beveled. What is your method for beveling?

Eric, for a guy that doesn't use Rocksim (or other) you are taking quite a few liberties with the length and arse end of that thing!

Eric
The Magnum was my L-2 rocket. I did my L-2 before there was a AT J-350. I even got LEUP permit so I would be legal to purchase and fly my L-2 Magnum on the AT 54mm J-275. It still suprises me when I see the small rockets flyers are useing today for there L-2. No way would one try a flight with a 2-3" rocket it was just unheard of.
Gary

dixontj93060 said:

Eric, for a guy that doesn't use Rocksim (or other) you are taking quite a few liberties the length and arse end of that thing!

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Well, if there has ever been a proven design, this is it. He is recreating the old design and I am sure he will have plenty of weight up front with the altimeter bay and main chute.

Or you're being sarcastic. Either is fine.

ECayemberg said:

Yep, this came from Loc; well packaged, precise lightweight components that fit well, and look and smell great!

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You nailed one of my favorite parts about LOC kits: the smell. It's weird, it brings back good memories of my childhood

I love your builds, Eric. Keep us posted!

What are the chances I'll get to see it fly at Thunderstruck?

dixontj93060 said:

Eric, for a guy that doesn't use Rocksim (or other) you are taking quite a few liberties with the length and arse end of that thing!

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That's an easy problem to figure out. And if you don't have Rocksim, OpenRocket converts RS files rather nicely to verify CP location which you can get from that site.

DAllen said:

That's an easy problem to figure out. And if you don't have Rocksim, OpenRocket converts RS files rather nicely to verify CP location which you can get from that site.

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patelldp said:

Well, if there has ever been a proven design, this is it. He is recreating the old design and I am sure he will have plenty of weight up front with the altimeter bay and main chute.

Or you're being sarcastic. Either is fine.

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Dan, Dave, chill I was just giving Eric a playful jab.

Dave though, BTW, the CP shown on Rocketreviews.com at 69.44" is the CP for the PK-84 (newer) version. I don't know, by chance it may happen to match the PK-16, but seems unlikely.

dixontj93060 said:

Dan, Dave, chill I was just giving Eric a playful jab.

Dave though, BTW, the CP shown on Rocketreviews.com at 69.44" is the CP for the PK-84 (newer) version. I don't know, by chance it may happen to match the PK-16, but seems unlikely.

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Hence my sarcasm quote. Emoticons!

dixontj93060 said:

Eric, for a guy that doesn't use Rocksim (or other) you are taking quite a few liberties with the length and arse end of that thing!

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Not true Tim!:y: Quite the opposite actually...although I do not use Rocksim; I'd venture a guess that I spend more time than most on the design/calculation side of things than most out there (maybe that just makes me more ineffficient). You see, I've been at 'puters with CAD since I started in HPR and before RockSim took over the world. So rockets get drawn up in CAD and CP calculated using the Barrowman equations...used to do it by hand, now I use an Excel spreadsheet. I've worked with RockSim through the demo version, as well as with SLI/TARC/R4S teams. After a fair comparison, I still prefer my method of madness.

I should mention this soapbox stance isn't aimed at Tim, it's just an explanation of my preferences. I've said it before and I'll say it again; RockSim is a wonderful tool! That said, it has it's limitations. Alas, I can't count on my fingers or toes the times I've heard "it was stable in Rocksim" after a rocket goes tumbling down range.

I really don't mind dodging rockets, but a few years back a short stubby unweighted-nose-cone rocket took off at a large launch and turned towards the registration/food tent(s), where my pregnant wife was at the time. Impacted nearby. She wasn't shaken by it, but I was. We knew the associated risks with attending a launch, but it didn't excuse the instability of the rocket!

I'm an extreme believer in knowledge of CP!:gavel: I'm off the soapbox now!

-Eric-

Buckeye said:

Nice. The fins look beveled. What is your method for beveling?

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Thanks!!! If it's G10/Carbon laminate, I'm lazy and send them off to a friend to bevel them. In this case, it was the good ol' elbow grease method. 3M sanding pad (not sponge)...sand until equal distances of ply layers show aroudn the edges (bevel), then round off the edges that remain. Used 80 grit...rough surface is fine as they were eventually covered in glass (sin #2 post forthcoming). Edges aren't perfect, but they're close enough!

crossfire said:

Eric
The Magnum was my L-2 rocket. I did my L-2 before there was a AT J-350. I even got LEUP permit so I would be legal to purchase and fly my L-2 Magnum on the AT 54mm J-275. It still suprises me when I see the small rockets flyers are useing today for there L-2. No way would one try a flight with a 2-3" rocket it was just unheard of.
Gary

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Gary, how times have changed, huh! Do you still have that Magnum? Thinking back to my first HPR launch...Bong in '93 or '94. Biggest flight of the day was a Magnum on a J275 or J415. Setup was from in Lot E?...directly across from the R/C flyers. Magnum landed in the drainage pond alongside the road. I also remember Gary Buck was there with a Rocket R&D (of course) Big Brutus...don't think it flew however.

Hope to see you at "The Bong" on Saturday!

-Eric-

daveyfire said:

You nailed one of my favorite parts about LOC kits: the smell. It's weird, it brings back good memories of my childhood

I love your builds, Eric. Keep us posted!

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Thanks Dave! Exactly...first rocket larger than Estes was a Lil Nuke. Smells great and flies well too!

Mad Bomber F/X said:

What are the chances I'll get to see it fly at Thunderstruck?

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Steve-O,

It just so happens that the first flight of the Magnum is scheduled for Thunderstruck. Motor choices include: AMW: L666SK or L700BB; Sconnie L900 White; L500 Sparky. Can't wait to test out the Tripoli Indiana range!

-Eric-

Eric,

Any chance you would be coming to LDRS XXXI - perhaps a Magnum race might be in order?

As an event planner I figure I will get in one or two flights all week. This is one I would definitely reserve time for.

A

H_Rocket said:

Eric,

Any chance you would be coming to LDRS XXXI - perhaps a Magnum race might be in order?

As an event planner I figure I will get in one or two flights all week. This is one I would definitely reserve time for.

A

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Al; I had high hopes of attending LDRS in the fingerlakes! Unfortunately, July ends up being the busiest month of the year for my family, so adding another travel-required event is unlikely. If I can fit it in; I'd love to attend and I'll be sure to let you know! It'd be great to see another mass Magnum drag race!

-Eric-

I also had a Magnum from Loc.
I flew it a few times then built a clone with a few mods:
6-29mm outboards and larger fins.

I later sold the stock Magnum, then crashed the clone and was left with no Magnum.

It's a great kit!


JD