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Old 03-16-2017, 09:44 PM
jeffyjeep's Avatar
jeffyjeep jeffyjeep is offline
Old Submariner
Join Date: Jan 2009
Location: Home of Wayne & Garth
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Default PNC: how tight is too tight?

I'm at the finishing stages on a DynaStar Lexxjet.

First of all, I want to thank Shrox for his beautiful and elegant design!

Now for the question: the PNC initially fit very loosely in the main BT so I had to wrap several layers of tape around the PNC's shoulder for a better fit. The fit is good when the model is in launch position, but when the model is in display--or horizontal--position the heavily weighted PNC sags in the BT and creates quite a gap at the top.

Obviously, I can fix this by wrapping more tape around the shoulder of the PNC, but at what point is the fit too tight for a reliable "laundry" deployment at ejection?

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-Just in case you ever wondered, Yoda’s last name was LayHeeHoo.

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Old 03-17-2017, 09:42 AM
neil_w's Avatar
neil_w neil_w is offline
Mr. Cut-by-hand
Join Date: Nov 2015
Location: Northern New Jersey
Posts: 343

It seems like the more appropriate solution is to do something temporary to improve the display. Can you not just wrap something non-adhesive around the shoulder to tighten it up a bit? Then remove it for launch.

Personally I'd be rather nervous about even asking the question "how tight is too tight" when the motivation is just to improve how it looks on display.
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Old 03-17-2017, 10:00 AM
jdbectec jdbectec is online now
the middle-aged rocketeer
Join Date: Sep 2006
Location: Urbana, Illinois.....the birthplace of HAL
Posts: 433

I seem to remember reading that you should be able to pick the model up by the nose cone but, be able to shake it loose. Back in the old days we used to blow into the engine mount and see if it would pop the nose cone off.
Jeffrey Deem
CIA section 527
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Old 03-17-2017, 02:26 PM
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ghrocketman ghrocketman is offline
Join Date: Jul 2005
Location: Michigan
Posts: 9,565

+1 to what Jeffrey just said above.
Be able to shake it off by holding the cone.
Blowing in the engine mount is a valid test too.
If EITHER of those fails, it is TOO tight.
When in doubt, WHACK the GAS and DITCH the brake !!!
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Old 03-17-2017, 05:52 PM
Jerry Irvine's Avatar
Jerry Irvine Jerry Irvine is offline
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The rule of thumb for low subsonic (<500 mph) is 5 pounds force. No more than 10.

The nose cone has lower drag than the rear body with the fins, despite the frontal area drag. Lovelace effect.

Supersonic rockets use break bolts.

Exemptions not regulations ACHIEVED. U.S. Rockets instaship. Model rocketry is as safe as safe can be defined in human existence. Bow and pray: GH Stine, Orville, Vern, Lee, Lonnie, Carl, etc. No, really. U.S. Rockets released first moonburner Toy Rockets G30, TRA first certified motor: H, invented LMR, HPR, Firestarter, reloadables 1-90, and now . . . ACHIEVED. LDRS first pre-HPR motor 38mm I200!!
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