Magg-nificent two-stage HPR build thread

[jhill9693]

I like the LOC Mini-Magg. Maybe it's the fact that it looks a bit like the Genie missile. I dunno. What if we stack two on top of each other, sort of?

This was the inspiration for my first two-stage HPR attempt. (Give a guy his L2 and he gets visions of grandeur!)

I'm building it for the occasion of my youngest brother's safe return from his first deployment with the Navy. I plan to test it at the SEARS launch in Samson, AL this weekend, and with any luck he'll get to watch it fly in his honor at the ROSCO launch on 5/20. Maybe I can even persuade Chuck to let Sam Hill (yes, that's really his name) push the launch button.



This is an appropriate one to build for him 'cause it's short and squat, er I mean stout, like Sam

Here is the design, in Navy colors of course:




You'll notice a few differences from the stock design. First, I lengthened it by 10". I agonized over this, but it's the right thing to do and cuts down on the amount of nose weight needed. Second, it's two-stage with a 54mm booster and a 38mm sustainer.

Several things came together recently to make this project happen. I already had the nose which I bought off Ken with Performance Hobbies at a ROSCO launch last fall.

Then, I came into a case of OOP 5.38x42" tubes via eBay. I refuse to pay the retail price for these from LOC. Perfect, since I'm not following the exact Mini-Magg proportions anyway.

Lastly, I drove to Colorado Springs to visit my MIL and other family members. While there I hit up Jesse Ulibarri (ModelRocketGuy.com) and Apogee for the MMTs, CRs, and honking J760 and J94 motors to put in this puppy.



Jesse is great. Work with him anytime you can! It was nice supporting him and saving shipping all at the same time.

Up next: build pix!

 

[3stoogesrocketry]

I built one very similar in the mid 90's. On my version , I took the stubby cone and cut it into a tail cone and the booster had a central 98mm . Then I used a long cone ( magnum ) on the sustainer with a 3 inch main chute tube in the cone . The booster was powered 2 times by a cluster of 4 G80s and 3 G125s staging to a J275 then on the second flight a J135. I will be following this

 

[jhill9693]

After cutting all tubes and couplers to the proper length on a table saw, I marked the fin slots using a LOC slotted CR as a guide, and cut the slots using a Dremel wheel cutter and x-acto knife.



My first thought was to use the PayloadBay.com fin alignment tool to print out a template to mark the tube, but this method proved to be much more accurate.

 

[jhill9693]

I built one very similar in the mid 90's. On my version , I took the stubby cone and cut it into a tail cone and the booster had a central 98mm . Then I used a long cone ( magnum ) on the sustainer with a 3 inch main chute tube in the cone . The booster was powered 2 times by a cluster of 4 G80s and 3 G125s staging to a J275 then on the second flight a J135. I will be following this

Sweet! Pix please

 

[jhill9693]

I glued the aft CR with Devcon 5-minute epoxy which I just squirted onto each triad and mixed up in place with a stick.

The CR kept wanting to slide down, so I used a coupler as a backstop temporarily. As soon as the epoxy began to set, I removed the coupler.



A similar process was used to attach the forward CR to the booster MMT. I used a coupler and the booster tube as a prop while the epoxy set up to keep everything square.

 

[3stoogesrocketry]

Sweet! Pix please

As I said it was in the mid 90's maybe 96'. I did not even have a camera back then. If you want I can recreate it in OR

 

[jhill9693]

Using a set of laser-cut Minie-Magg fins, I traced and cut out the sustainer fins from 1/4 lite ply. Then I added a gentle airfoil using 120 and 220 grit sandpaper. A table jigsaw, belt sander, and pad sander made short work of it.

Note the forward placement of the fin tab, to allow for the interstage coupler to fit under the aft part of the sustainer fins.

 

[jhill9693]

Almost forgot to add the shock cord attachment hard point to the forward centering ring! Used a u-bolt with a backer plate that I had lying around.



That's not going anywhere.

 

[jhill9693]

Scrounged up some extra hardware: rail buttons, Aeropack 54mm and 38mm retainers, quick link...

 

[jhill9693]

Not shown: attached the rail buttons BEFORE inserting the MMT and forward CR from the front of the airframe, and tacking it into place with a bit of thick CA to keep it from sliding out while the fins get attached.

Shown: the fun part, tacking in the fins with a generous amount of thick CA to the root of each fin! I pretty much eyeballed each one, and shocked myself at how perfect they ended up.



That's a looong way down... how on earth do you guys get the epoxy down there for all the internal fillets? That's the next step, please help me out here.

 

[jhill9693]

First look at the sustainer silhouette! Not bad for a day's work. More to come!

 

[tsmith1315]

I wish I could make it to SEARS to see that one fly!

That's a looong way down... how on earth do you guys get the epoxy down there for all the internal fillets?

I'd drizzle it by eye from a small paper cup with a creased lip. Or...

You can also run it down a dowel, or metal rod and let it drip off the end (mechanic's tip getting fluids into tough to reach places)

Tape a syringe to a dowel and tape the plunger to another dowel to extend reach.

Use a long drinking straw (pink) with a paper cone (white) as a funnel taped to it:

 

[teepot]

To get epoxy down there it would depend on the epoxy. If it is pourable I would do what @tsmith1315 suggests. I pour JB Clear Weld down the side of the motor tube covering the fin tab and creating an epoxy dam on the CR.

 

[jhill9693]

I knew I would forget something. I meant to cut the side access panel and insert a backer coupler and an electronics mounting board inside BEFORE installing the forward CR and MMT.

Oh well, I can probably work what I need to inside if the access cutout is large enough.

 

[jhill9693]

First time using West Systems Six Ten epoxy from my local West Marine. I must say I’m impressed. It has the consistency of Vaseline. I got so excited I forgot to mask off and had to touch up a bit with rubbing alcohol. Not as perfect as I’d like, but my technique will improve with practice, and man was it ever nice to be able to lay down all the fillets in one go!

 

[jhill9693]

I mixed up a cup of BSI 30 minute epoxy an dribbled it down each fin root. Seemed to work okay.



I very carefully marked and cut an access panel with a new x-acto knife. For a moment I thought I would do it with the Dremel like the fin slots but… that proved impossible to do accurately enough.



I had this old sled from a LOC e-bay that a guy printed mounts for an Eggtimer TRS and Quantum. So that’s what I’ll be using.

I had to trim it down some to get it to slip into the access hole.

 

[jhill9693]

This morning I glued in pieces of a coupler and reinforced them with wood. This forms the rim of the opening and provides something to screw the panel down to.



Titebond II is the obvious choice for wood-on-cardboard.

 

[jhill9693]

More sled trimming was required to allow it to fit into the access opening. A thick piece was glued in with 5 minute epoxy to provide a hard point to attach the sled to.



The LOC allthread brackets on the back of the sled serve to center the sled on the MMT and provide a bit of stability.

 

[jhill9693]

Reinforced the access panel and added a lip with a bit of coupler, with a strip of ply for a screw to catch.

 

[jhill9693]

I like upcycling spent 18mm motor casings into charge wells. Here’s one that has been cut to about 7/8” and then cleaned up with a Dremel reaming tool.




Had to use a hand drill since I forgot to pre-drill through the forward bulkhead before gluing it in.



Glued the charge well onto the forward bulkhead with BSI thick CA, and used the back end of a small drill bit to align the holes.

 

[jhill9693]

Using the same CA (love the stuff), attached an Aeropack 38mm retainer. It’s used, like so many other things in this build.

 

[jhill9693]

Added a stainless 5/16 eye bolt to the base of the nose cone and removed all flashing. A cutout in the base allowed me to add a washer and nut and will allow me to add weight as needed for stability.

 

[jhill9693]

Final step: screw-mounting the sled and access panel. Used a hand drill for pilot holes.

 

[jhill9693]

And with that, sustainer assembly is complete!

 

[OzHybrid]

Don't forget that by putting the AV bay on the side, you have a weight that is off-centre from the line of thrust of the motor. Depending on how much weight is in the electronics and additional components for the AV bay, you may have to counterbalance it on the other side with an equivalent weight to avoid the rocket arcing over.
Norm

 

[jhill9693]

Don't forget that by putting the AV bay on the side, you have a weight that is off-centre from the line of thrust of the motor. Depending on how much weight is in the electronics and additional components for the AV bay, you may have to counterbalance it on the other side with an equivalent weight to avoid the rocket arcing over.
Norm

I’m curious if anyone has actually experienced this? Seems that if the stability margin and airspeed are good it wouldn’t be an issue.

 

[OzHybrid]

Unless you have perfect alignment of your fins, there will be some rocket rotation about the thrust axis. This will mitigate any off-center action of your side mount AV bay. Also if it's windy there will always be a degree of windcocking.
Off-center mass is going to be more of an issue on a short-fat rocket as the caliber of stability is likely to be low and the possibility of a larger off-center distance becomes possible. So if it's going to be an issue, it's much more likely in this scenario.
So what caused the squawking and the magnitude of the squawking is dependent on the chicken or the egg..... But the math says it will happen.
Good luck with the flight and let us know how it goes.

 

[cerving]

Put the battery on the opposite side and that should take care of the off-center mass issues.

 

[Hobie1dog]

This is a fun thread to follow.

 

[BDB]

How did this project turn out? I love the idea of a squat 2-stager.