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98mm subminimum diameter

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tfish

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This is going to be a 2 forum thread. The research motor portion will be over in the Research forum.... and the actual rocket build will be here. More then likely some of the posts will overlap. This first post is identical in each of the threads.

This is not going to be a fast passed build thread!

A year or more ago Gary and Karl gave me a spent O5040X https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/o5280x_rcs_assembly.pdf that had been static tested out at Black Rock. My intentions are to refurbish the motor and turn it into a subminimum diameter rocket.

I have played around with using spent DMS motors in the past. I built a subminimum dia 54 for Hamster Dance at Balls 2019 The rocket sort of worked great, motor worked ('trade mark' term Mark Clark), the fins stayed on but my shock cord parted at apogee. so the concept worked.
hamster.jpg


I've done a few long motors (not crazy Mike Fisher long) Bottom is AT 98/15360 (36" propellant), middle DMS 98mm O5040 (51" propellant), Top Dr Rockets 98/25600 (60" propellant)
98mm cases.jpg



This is what the 98mm DMS motors look like inside. ( I cut a spent motor case in half length wise and made the grains out of salt for a demo motor for STEM stuff) https://d11fdyfhxcs9cr.cloudfront.net/templates/170652/myimages/m1340w-ps_rcs_assembly.pdf
98mm demo.jpg


Tony
 

MClark

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motor worked ('trade mark' term Mark Clark),
Tony's Hamster Dance motors worked great.
I made a P motor for another’s airframe at BALLS, did a giant death spiral across the sky. At motor burnout I turned around and said "Motor worked." And walked back to the flight line.
Not my fault on stability, my problem to find it.

M


1000 pounds of thrust for 14 seconds.
 

Ethan

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How long do you think this one will be misplaced for Tony?

*Ducks*
 

tfish

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Ethan,,,hopefully only an

hour or 2. I'm too old to wait another 7 or 8 years.

I scrounged up (some 1950's posts from my front porch remodel) some mostly clear Redwood to make a sub 98mm nose cone...which will be the plug for a mold..
20201101_111611.jpg

20201101_111620.jpg

remind me to throw away that saw blade..

I like the pinnacle nose cone shapes and upscaled their 54mm nose cone..
20201102_142718.jpg

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20201102_101336.jpg


Tony
 

Idunno

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For us uneducated folks can you explain what a subminimum diameter rocket is? Is the rocket motor is also the airframe?
 

Nytrunner

Pop lugs, not drugs
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For us uneducated folks can you explain what a subminimum diameter rocket is? Is the rocket motor is also the airframe?
Minimum Diameter (MD) is what folks call a rocket whose airframe diameter is just large enough to fit the motor. No motor mount, no centering rings, no extra weight/drag.

Subminimum is as you describe. the motor case is the external diameter, and it requires clever engineering and custom parts to match that diameter
 

tfish

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The nose cone plug is almost done. A couple more coats of primer and some fine sanding and a few coats of wax.

20201111_110516.jpg
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The "parting board" is ready too.
20201111_110755.jpg
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This now frees up my lathe and I can make the parts for the 'coupler'.

Tony
 

DeeRoc29

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Nice work, T. Hey how fast are you going on this one? I remember seeing some wooden cones failing on high speed flights back in the 90s.
Edit: ok I see the wood is just a mold.
 

rocketkyle

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Tony, I would love one of those cones if youre interested in making more than one.
 

ECayemberg

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Great work, Tony! Awesome project and beautiful cone!!!
 

tfish

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My mocked up prototype bolt on coupler is ready to be welded together..Then the OD will be turned down to fit a short section of...motor case.

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The idea is.....as I understand it, the 98 and 75mm DMS motors require the buyer/flyer to assemble them...and that the noz is already glued in place. (?) So, this coupler will be added shortly after the FC is glued in place, With the aid of the motor case, a section of body tube, some angle iron and some electrical/duct tape these 2 sections will held 'straight' until the epoxy sets.

Tony
 

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tfish

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I was able to layup a nose cone last night and I just popped it out of the mold..Came out easy and looks pretty good.

20210203_183514.jpg



20210203_183421.jpg


The epoxy I used is really thick Loctite EA 9396 AERO it's 35 Poise when mixed. I bought and used a cool little roller to help work the epoxy in..and the 120 min pot life helps too.
20210203_184249.jpg


Tony
 

Nytrunner

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Geez! Is the motor CG already in front of the CP? lol

Have you ever gotten one of those back?
 

BABAR

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Sub minimum diameter 18 mm rockets. Note the fiberglass motor cases. (these are 7" propellant giving a F17.) Upper bodies are rolled from paper tape and nose cones are modified Apogee. Fins are 1/32" plywood.
View attachment 449305
Wow!

it does seem as if you are going to that much work you would go with a tower rather than lugs?
 

DeeRoc29

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Tony, what weight cloth are you using for the molded nose cone? Looks good!
 

Rocketjunkie

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Got 1 of 12 back. They carry a 1.5" x 12" ribbon streamer.
 

Rocketjunkie

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Wow. How much altitude are you expecting?
Estimate 3-4K feet with F motors. These are not optimized but a 10 sec delay works well.
Wow!

it does seem as if you are going to that much work you would go with a tower rather than lugs?
Just still dialing in delay, etc. Fire and forget so no electronics. Eventually when we have launches again I'll see if the recovery rate improves. I can also make smaller ones down to a C10. If I go for altitude I will need to polish the upper tube and nose cone. I do have a couple of 15 N-s D15.s for other rockets. These are 18 x 70 mm.
 

boatgeek

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