Lightest Mini Magg possible

[CoachSteve]

So, I wanted to try to build a Magg that would comply with level zero regulations.
1500G or less total weight
125g or less of propellant
Average thrust per motor less than 80N
Total thrust less than 320N
The plan is a twin 29mm Magg sporting 2 G53FJs.
G53 has 60 grams of propellant and 53N of average thrust
so -
3.3lb rocket
120 grams of propellant (in 2 separate motors)
106N average thrust (in 2 separate motors)

So to kick this off I needed to see what I was starting with. kit out of the bag, with all hardware, less glue and paint comes in at 1498G

Time to start shaving weight.

 

[CoachSteve]

the original motor mount was 38MM with 1/4 ply centering rings

this came in at 143g
the no motor tube 2X29 design with cut outs and balsa inserts came in at 67g - down 76g so far

 

[CoachSteve]

Motor retention , rail button and shock cord hardware came in at 80G
Going with alloy hardware and carbon fiber dowels for shock cord retention I got this down to 25g plus some epoxy and fiber cloth I will need to affix the lower shock cord mount to the side of the body tube.

The top shock cord will be mounted in the nose cone bulkhead (also balsa lighted ply).

Installed in nose cone with Balsa retainer ring

 

[samb]

1500 grams is the flight-ready weight threshold, right ? Motors and recovery device installed.

 

[dhbarr]

Just my idle speculation, never peeled a LOC.

When I skeletonized a Big Daddy I was amazed to find the glassine was something like 10-15% of the overall mass.

Obviously your percentage would be a lot smaller, but I'd be surprised if you couldn't pull 30-60g out.

Minwax Wood Hardener plus sanding brought my smooth surface back. YMMV.

 

[Theory]

Really like the idea behind this. Looking forward to following

 

[CoachSteve]

Yeah - 1500 on the pad, ready to fly may prove to be quite the challenge

 

[mbeels]

Very nice work with the cutouts! Did you do that by hand, or with some type of milling machine? Looks impressive!

 

[Andrew_ASC]

Soooo you gonna make this into a stumpy rocket??? If cutting the BT in half doesn’t shed enough mass you could always start making it look like a cheese grater too.

 

[CoachSteve]

I did all the cut outs by hand on a scroll saw clamped upside down in a vice - super high tech, I know .
The Rocket is a standard LOC Mini Magg so shortening the body tube is not an option as the stability is already marginal on the minis.
The Swiss cheese idea may have to come into play - we will see how the actual real world weights come out.
Here is the Fin work I have been working on the last few days.
They started out at 341g

then the high tech upside down scroll saw in action

then balsa fill

end result - with tabs comes in at 213g

 

[CoachSteve]

Little mock up to see how its all coming along

 

[mbeels]

That's a pretty significant weight reduction, fully 1/3 of the mass removed. Well done! And it looks great to boot.

 

[kuririn]

Looking good.
I was going to suggest ply core with cutouts and balsa outer skins like the eRockets SBB, MDRM, and upscale Goblin fin sets.
But yours look much cleaner and sturdier.

 

[Theory]

Looking great!!!

 

[CoachSteve]

so - here is how the "fin can", if you can call it that, looks

 

[CoachSteve]

Here is the battle I am fighting against

that's a lot of weight to try to shave

 

[CoachSteve]

so - when I throw it all on the scale, parts, laundry, motors (no glue, no paint):

Houston, we have a problem

 

[dhbarr]

Scallop the aft edge of the cone shoulder ?

 

[NateB]

With the reduction in weight, will it fly on 1 29mm motor?

 

[boatgeek]

Did you already cut out the nose cone back bulkhead? That might save 30-50g.

 

[mbeels]

How much does just the body tube weigh? Or just the nose cone?

 

[CoachSteve]

Nose cone came in at 357g

after my plate 347g - and moved the CG forward just a bit

 

[CoachSteve]

I could remove the plate altogether and attach the shock cord with a rod through the top of the nose cone (would shave some there) but then I would need to find a clever weightless way to keep the laundry from blasting into the cone and staying there on the way down

 

[Jozef]

Your nose cone plate is pretty far forward the way it is. Should not be any less of an issue if you eliminate the plate. Hook the chute lower on the harness. The velocity of the nose cone coming off the ejection charge should do the job. Very nice build.!

 

[CoachSteve]

I will most likely remove the plate and go for a hollow carbon fiber pin through the nose (carbon arrow shaft is what i am using, super light and crazy strong). this however will only save me maybe 30g as the current plate is quite light.
I need more

 

[crossfire]

Would kevlar over nylon strap save much? Also is a DMS motor less weight than a reloadable?

 

[mbeels]

Have you looked around for a lighter weight nose cone? A vacuum formed part would be much lighter, or perhaps there is a low power nose cone the right size.

Also, since you're staying below high power motors, perhaps a low power (thin wall) body tube would be sufficiently strong.

 

[CoachSteve]

5.5" stuff is quite limited - and this is the Mini Magg kit that I am trying to see if i can make it.
The Mini actually has the lighter of the 2 LOC 5.5 cones (this kit comes with the shorter one)
I removed the plate in the nose and dowel pinned the shock cord through the tip.
Nose cone now weighs 314g - saved another 30g

 

[kuririn]

Try to find a way to shave weight off the aft end. Remember, you still haven't accounted for the weight of epoxy, and that is all going to the rear half of the rocket. Last thing you want to do is have to add nose weight back to make the rocket stable.

 

[dhbarr]

Why would anyone use epoxy on this one, or really fillets of any substantial kind? Just enough wood glue for the bondline, methinks.