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  #1  
Old 06-04-2019, 11:05 PM
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timorley timorley is offline
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Default Pershing II Rebuild

About 10 Years ago I built a Pershing II based on the Estes BT-80 body tube. An employee of mine was stationed with the Pershing II for a short period. Knowing I build model rockets he challenged me to build one.

I launched the Pershing II on a D12-3 for the first time. It was a bittersweet launch. Perfect launch and it went up straight as an arrow. Chute deployed fine, but the wind picked up about then and carried it over to the ball field. It slammed pretty hard into the chain link backstop wedging the nose cone in it. Knocked a fin off which is an easy fix, but it shattered the styrene wrap on the nose. It proved out to be a great flyer, but from there is sat damaged for 10 years on a shelf.
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"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

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  #2  
Old 06-04-2019, 11:07 PM
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I had a hard time finding data on it too. But I did finally find the Pershing II Technical Manual online.

Page 116 of the PDF of the Pershing II Technical Manual has some useful missile data. Itís section 5-1 Table 5-1.

First Stage
Length = 144.74 Inches
Max Diameter = 40 Inches

Second Stage
Length = 97.3 Inches
Max Diameter = 40 Inches

Guidance and Control/Adapter Section
Length = 61.51 Inches
Max Diameter = 40 Inches
Min Diameter = 27.75 Inches

Warhead Section
Length = 64.25 Inches
Max Diameter = 27.7 Inches
Min Diameter = 20 Inches

Radar Section
Length = 49.75 Inches
Max Diameter = 20 Inches
Min Diameter = 0 Inches

Missile
Length = 417.55 Inches
Max Diameter = 40 Inches
Min Diameter = 0 Inches

Unfortunately, it combines the Guidance and Contol (upper fins mount to this) measurements with the Adapter (first reduction in body diameter). My best guess from studying images at the measurements for these individually are:

Adapter Section (Estimates)
Length = 17.51 Inches
Max Diameter = 40 Inches
Min Diameter = 33.1 Inches

Guidance and Control (Estimates)
Length = 44 Inches
Max Diameter = 33.1 Inches
Min Diameter = 27.75 Inches

There was no data for the fins, so I originally used photos and came up with my best guess. Pretty sure in hindsight the upper fins are larger than my original build, but I think the lower fins are close.
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Tim

"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
NAR 98303 Southwestern Ohio Rocketry Association (SWORA) #624
https://www.rocketryohio.com
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  #3  
Old 06-04-2019, 11:17 PM
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Now 10 years later arrives 3D printing. Time to make a new nose cone! Iíve added in some new details for the upper fins, and I made them larger. Printed in PETG. I'll make an STL available after I get a chance to flight test it and I may tweak it a little.
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Tim

"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
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  #4  
Old 06-05-2019, 10:29 AM
jetlag jetlag is offline
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Quote:
Originally Posted by timorley
Now 10 years later arrives 3D printing. Time to make a new nose cone! Iíve added in some new details for the upper fins, and I made them larger. Printed in PETG. I'll make an STL available after I get a chance to flight test it and I may tweak it a little.


Awesome, Tim!
I'll buy one!

Allen
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Old 06-05-2019, 10:39 AM
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Out of curiosity, what's the weight difference between the old and new NC? Are you going to have to move up to a composite motor from the D12?
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Old 06-05-2019, 08:46 PM
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Old cone weighs 77 grams. New 3D cones weighs 50 grams so far. Keep in mind there is currently no bulkhead for the new cone, it's hollow from the base to the tip, and I don't know if I'll need to add nose weight or not. I've changed the size of the fins a little on the nose (bigger) and they are a wedge shape now. I think the old cone has some small amount of nose weight, if I remember correctly that was more of an assurance than a necessity though.
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"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
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  #7  
Old 06-05-2019, 10:27 PM
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Quote:
Originally Posted by timorley
Old cone weighs 77 grams. New 3D cones weighs 50 grams so far. Keep in mind there is currently no bulkhead for the new cone, it's hollow from the base to the tip, and I don't know if I'll need to add nose weight or not. I've changed the size of the fins a little on the nose (bigger) and they are a wedge shape now. I think the old cone has some small amount of nose weight, if I remember correctly that was more of an assurance than a necessity though.


Cool. Let us know how it ends up. It's nice to be able to compare it with other construction materials and methods.


.
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  #8  
Old 06-06-2019, 01:01 AM
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For my Pershing 1A 3D build, it's interesting that the TLP paper cone (111 grams) and 3D printed nose cone (113 grams) are virtually identical in weight so far. Keep in mind I did modify the TPL cone to separate at the body like the Estes cone instead of the top balsa cone as the TLP instructions would have you do, so there is the added weight of the coupler. Neither has additonal nose weight added yet.
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Tim

"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
NAR 98303 Southwestern Ohio Rocketry Association (SWORA) #624
https://www.rocketryohio.com
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  #9  
Old 06-06-2019, 11:59 AM
astronwolf astronwolf is offline
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Quote:
Originally Posted by timorley
For my Pershing 1A 3D build, it's interesting that the TLP paper cone (111 grams) and 3D printed nose cone (113 grams) are virtually identical in weight so far.

Those 3D prints look pretty rough. Will you be filling and smoothing out the roughness of the 3D prints? If you do, that might add a lot of weight.
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  #10  
Old 06-06-2019, 01:43 PM
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The top part is actually incredibly smooth. The bottom part I'm working out some issues with how it printed, it's a draft version, I tried an experiment printing it upside down without support and I got some weird sagging, part of why I'm not sharing the STL yet. And I'm using PETG for strength and heat resistance, it won't print details and be as smooth as printing in PLA. It's all tradeoffs for what you want. The Pershing 1A parts are really smooth, a shot of primer and a light sanding and you see nothing. I've noticed photos of course show every little bobble, nook and cranny with the glossy plastic finish before painting.
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Tim

"You know, it, uh, won't fly unless somebody pushes the button." From the movie October Sky.

I am SAM # 0167
NAR 98303 Southwestern Ohio Rocketry Association (SWORA) #624
https://www.rocketryohio.com
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