Cluster Duck

Discussions on mid/high powered model rockets using F powered motors and above.

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Aquaman33
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Re: Cluster Duck

Postby Aquaman33 » Mon Mar 15, 2021 5:26 pm

SammiMD wrote:Have you decided on a name for it?


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Good question.

My L2 rocket is called the Angry Bee, so I am thinking this might be the Angry Duck.

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Re: Cluster Duck

Postby Aquaman33 » Mon Mar 15, 2021 8:01 pm

I wanted to give this rocket a small amount of nose weight, and I don't trust plastic loops on nose cones.

First job was to chop off the base of the nose cone on a miter saw.
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Rough up the inside of the tip of the nose cone with some 80 grit taped to a rod.
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Drill a hole through the tip and insert a brass rod.
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Find an eye bolt and some threaded bar in a drawer.
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Fill the tip with epoxy and lower the eye bolt in.
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After the epoxy cures cut off the excess brass and its ready for sanding.
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The brass rod locks the epoxy (and eye bolt) in place so it can't pull out.

Thanks to John Coker for the idea:

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Re: Cluster Duck

Postby Aquaman33 » Sun Mar 21, 2021 10:05 am

Fin can installed, fins installed, nose cone (the beak) painted.

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After installing the back end I weighed it and checked the CG. The numbers weren't quite where I wanted them to be. According to Openrocket it will have a stability caliber of about 0.7x with D12 motors or 0.8x with C11 motors.

I think it falls into the short stubby rocket category because the length to diameter ratio is approx 8. So I am hoping I can get away with stability below 1.

I noticed that when to nomex cloth and chute are pushed down to the fin can it moves the CG quite a lot, so I decided to install a frame to keep them up in the hollow nose cone.

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Kevlar lines are more than sufficient to stop the laundry sliding back down the rocket.

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Installed in the body tube just below the bottom of the nose cone shoulder.

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Not sure how the 3d print will cope with the ejection charge, but I can add a little wadding below the frame.

Next step fin fillets.

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OverTheTop
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Re: Cluster Duck

Postby OverTheTop » Sun Mar 21, 2021 11:21 am

3D print will be fine, as long as it can withstand the mechanical point loads from the string, although I am unsure of its lifespan if it is printed in PLA or PETG. My experience is mostly with ABS.

FYI, for next time consider using larger radii where the mounting points meet the outer hoop. The small radius can cause stress raisers, resulting in part failure at lower loads. Stress concentration effect is inversely proportional to the radius.
https://en.wikipedia.org/wiki/Stress_concentration
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Aquaman33
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Re: Cluster Duck

Postby Aquaman33 » Sun Mar 21, 2021 5:49 pm

OverTheTop wrote:3D print will be fine, as long as it can withstand the mechanical point loads from the string, although I am unsure of its lifespan if it is printed in PLA or PETG. My experience is mostly with ABS.

FYI, for next time consider using larger radii where the mounting points meet the outer hoop. The small radius can cause stress raisers, resulting in part failure at lower loads. Stress concentration effect is inversely proportional to the radius.
https://en.wikipedia.org/wiki/Stress_concentration


Thanks OTT.

I did add a radius in those corners, but I should have made them bigger. Hopefully it will hold.

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Re: Cluster Duck

Postby Aquaman33 » Sun Mar 21, 2021 5:50 pm

Simple motor retention.

Image

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OverTheTop
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Re: Cluster Duck

Postby OverTheTop » Sun Mar 21, 2021 6:02 pm

Looks good!
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Kryten
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Re: Cluster Duck

Postby Kryten » Wed Mar 24, 2021 10:19 pm

You could try a swing test for stability
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Aquaman33
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Re: Cluster Duck

Postby Aquaman33 » Thu Mar 25, 2021 5:31 pm

Kryten wrote:You could try a swing test for stability


Yes. Good suggestion.

After too many hours in OpenRocket its time to get out the good old piece of string. :D

.....just need to wait for it to stop raining!

Not enough room to swing a rocket (or a cat) in my house.

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Re: Cluster Duck

Postby air.command » Fri Mar 26, 2021 9:15 am

Now I want to tie a string to a cat and swing it around. I guess it should be stable with feet always pointing aft. :D
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Aquaman33
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Re: Cluster Duck

Postby Aquaman33 » Sun Mar 28, 2021 8:26 pm

It finally stopped raining long enough for me to slap on some paint.

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Final OpenRocket sims say:
3 x C11-5 = Apogee 247 feet.
3 x D12-5 = Apogee 683 feet.
3 x E30-7 = Apogee 1,545 feet.

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OverTheTop
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Re: Cluster Duck

Postby OverTheTop » Mon Mar 29, 2021 12:27 pm

Looking good. Nice outcome.
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