Mach 2 clone with HED

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Legendontour
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Mach 2 clone with HED

Postby Legendontour » Mon Mar 22, 2021 9:39 am

My latest build is 95% scratch built with the exception of the nose cone.

With Blake struggling to get supplies from overseas with current shipping issues, I took a punt in the Nov Black Friday sales and purchased some 54mm and 38mm Filamenent wound fibreglass nosecones from Madcow. They eventually arrived mid February.

I had initially planned to build a 54mm Darkstar/Katana clone, but despite careful calculations based on previous tube rolling, I wound up with a 1.2mm wall thickness rather than 1.6. Therefore I paired it with the thin wall cone I had and decided on the Mach 2 style build.

Given the 5000ft standing waiver at Cedar Grove and a general lack of 54mm motors in stock at Ausrocketry, I also decided to make it a 38mm motor mount. I figure if I really want to go nuts, I can make another booster section to pair with the AV bay.

Booster section is fairly standard. 54mm tube rolled on a phenolic mandrel with 7 wraps of 165oz twill. I’m using a fastest cure laminating epoxy and probably needed to break up the amounts a bit more as it got fairly thick towards the end and didn’t soak in as well in the last few layers. 180gm cloth and 165g of epoxy worked out at 42% epoxy by weight. outside of the tube looked a little dry, but it sanded smooth ok on my homemade lathe

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The 38mm aero pack retainer I purchased was sized for a 1.65mm tube. I made a motor tube with 8 wraps of 165gsm cloth with no peel ply. Initially seemed a bit big, but after a quick sand it was a perfect fit.

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I elected to cut some ply centering rings as it’s easier and quicker for me than glass ones.

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Fins templates were printed out from open rocket and then cut out of 2.4mm G10 sheet and sanded to shape on my bench sander.

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More to follow...


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Legendontour
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Re: Mach 2 clone with HED

Postby Legendontour » Mon Mar 22, 2021 12:04 pm

Construction of booster was similar to my last couple of HPR fibreglass builds and follows CJ’s build thread on TFR.

I measured and cut the slots with a dremel. Meanwhile I measured up the motor mount and glued the top and middle centering rings with epoxy.

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After some careful filing to ensure the slots were fairly tight I epoxied on the rear centering ring to create a fluid tight compartment for injecting the internal fillets once the fins were tacked in.

I’ve been 3D printing specific fin guides for all my rockets lately and it’s made the process of exact alignment stupid easy.

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After scoring all the relevant edges including where the external fillets would be, I tacked the fins in with 15min BSI, then injected with West System and some chopped carbon fibre. I’m not really sure what difference, if any, the CF makes, but it darkens the clear epoxy at least which allows me to easily see that it’s spreading easily.

After allowing a few days for the West’s to completely cure, I taped up the tube and fins and disc external fillets with Epi glue.

That’s pretty much where I’m at with the booster. When it finally stops raining, I’ll sand the fillets and paint it. But given the current weather forecasts on the East Coast, I may need to start on an Arc in the next few days.


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Legendontour
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Re: Mach 2 clone with HED

Postby Legendontour » Mon Mar 22, 2021 12:14 pm

Meanwhile the nose cone took a bit of lateral thinking.

The madcow nosecones don’t have a removable metal tip like the Wildman ones do, rather it appears they epoxy a solid tip onto the tip less filament wound cone. So the TRF method of screwing an eye bolt into the metal tip wasn’t going to work.


I pondered it for a week or so and then the solution came to me while I was out running. With a pretty bodged up drill extension and a head torch I drilled 4.5 mm hole into the epoxy in the tip.

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I then made a holder for a 5mm forged eye bolt and screwed it in tight, agin with my head torch illuminating proceedings.

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After scoring up the area as best I could with 40grit, I placed the nose cone point down in my vice and using a syringe and extension tubing (about the only rocketry related benefit of my job) and injected enough epoxy to cover the base of the eye bolt.

Threaded some 1500lb Kevlar through the bolt and hopefully it stays put!! Will obviously do some deployment testing before I launch for real, but it’s stayed put with my son and hauling on it so far.

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Legendontour
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Re: Mach 2 clone with HED

Postby Legendontour » Mon Mar 22, 2021 1:25 pm

The AV bay has been the bit that I’m most excited about with this build. I had an Eggtimer TRS that was in another rocket that didn’t really justify it. I replaced it with a quantum and put a nose bay in it to share an Eggtimer TX.

The OR file I used from Wildman called for a 5 inch AV bay and fortuitously that was what Blake had as his stock size. I think for my future Darkstar clone I’ll get a longer length to give me more wiggle room as this was a tight build.

My plan was to 3D print a sled designed in Fusion 360 incorporating Brass Heat Insert nuts for secure altimeter retention and also cutouts and secure battery retention on the other side. I also wanted to have a screw switch to arm/disarm the pyro channel on the TRS.

Fusion 360 tells me it took 20 prototypes to get the sled perfect ie all the cabling where it needed to be, the switch in exactly the right place and room for the TRS aerial to be mounted externally via an adapter.

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The sled is printed in PETG that I’ve been playing with for a couple of months and have dialed in fairly well.

The end caps are a new material to me, Prusa PC Blend. I needed to build an enclosure first and having done that I was keen to try it. They are noticeably stiffer than the PETG versions and should have more heat resistance along with the included charge wells

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I’ve sewn a 24 inch poly conical chute out of 40D kite fabric, but may redo it in 30D that I have on order. It fits comfortably as is and according to OR, on the biggest 38mm I can fit, should come down at no more than 7.5m/sec.

It’s basically fly ready apart from the paint and shock cord that I’ll get from Blake if we launch this coming weekend.


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markf74
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Re: Mach 2 clone with HED

Postby markf74 » Mon Mar 22, 2021 9:53 pm

Looking good Legend, can't wait to see it go , maybe we will need to build a water based launch rail.... :)



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