Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > The Doctor is In! > Ask the Doctor
User Name
Password
Auctions Register FAQ Members List Calendar Today's Posts Search Mark Forums Read


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 03-16-2017, 08:44 PM
jeffyjeep's Avatar
jeffyjeep jeffyjeep is offline
Old Submariner
 
Join Date: Jan 2009
Location: Home of Wayne & Garth
Posts: 5,426
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?

Thanks!
Attached Thumbnails
Click image for larger version

Name:  IMG_0154.JPG
Views: 21
Size:  82.6 KB  Click image for larger version

Name:  IMG_0155.JPG
Views: 13
Size:  66.7 KB  Click image for larger version

Name:  IMG_0157.JPG
Views: 17
Size:  49.2 KB  Click image for larger version

Name:  IMG_0156.JPG
Views: 22
Size:  38.7 KB  
__________________
One should refrain from complimenting a woman on her mustache--regardless of how EPIC it is.

NAR# 94042
SAM# 0078
Reply With Quote
  #2  
Old 03-17-2017, 08:42 AM
neil_w's Avatar
neil_w neil_w is offline
Good at some things
 
Join Date: Nov 2015
Location: Northern New Jersey
Posts: 125
Default

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.
Reply With Quote
  #3  
Old 03-17-2017, 09:00 AM
jdbectec jdbectec is offline
the middle-aged rocketeer
 
Join Date: Sep 2006
Location: Urbana, Illinois.....the birthplace of HAL
Posts: 360
Default

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
NAR16741
CIA section 527
Reply With Quote
  #4  
Old 03-17-2017, 01:26 PM
ghrocketman's Avatar
ghrocketman ghrocketman is offline
President, MAYHEM AGITATORS, Inc.
 
Join Date: Jul 2005
Location: Michigan
Posts: 7,995
Default

+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 NEVER touch the brake !!!
No Harm=NO Foul advocate
BE a MENACE; CREATE the HAVOC, CHAOS, and MAYHEM
Yes, there is such a thing as NORMAL
, if you have to ask, you probably aren't
!
Reply With Quote
  #5  
Old 03-17-2017, 04:52 PM
Jerry Irvine's Avatar
Jerry Irvine Jerry Irvine is offline
Freeform rocketry advocate.
 
Join Date: Jan 2008
Location: Claremont, CA "The intellectual capitol of the world."-WSJ
Posts: 3,181
Default

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.

cite:

http://v-serv.com/usr/dd.htm
__________________
Exemptions not regulations. Please support DOT treating slow burning solids as not subject to HMR. 2015 NAR President declines!
U.S. Rockets instaship. http://bit.ly/1aca7mA Please buy some rockets.
The O administration believed in tax, spend, borrow, fine, mandate, monologue. D voters will soon be very happy with the election outcome!
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.
Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump



All times are GMT -5. The time now is 06:33 AM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe 1998-2017