Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > Work Bench > RockSim Asylum
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 01-13-2013, 06:37 PM
Les Les is offline
BAR 13790
 
Join Date: May 2008
Location: Johnson City, NY
Posts: 523
Default Conical rocket

I am trying to build a rocket that will be conical based on a plastic piggy bank.

I went to the Apogee site and in their newsletter 162 found a method on simulating a pyramid style rocket by creating a massless transition at the rear. I tried this and it states the rocket is over-stable, but when I simulated a launch it flips around and crashes. Can someone let me know what I am doing wrong?

I attached the RockSim file. It is not 100% complete (like I have some centering rings missing), but it should have been good enough for the simulation.

Thanks
Les
Attached Files
File Type: rkt Number 2.rkt (15.8 KB, 71 views)
Reply With Quote
  #2  
Old 01-13-2013, 08:44 PM
bernomatic's Avatar
bernomatic bernomatic is offline
Master Modeler
 
Join Date: Jun 2011
Location: Cleveland, Ohio
Posts: 1,174
Default

The difference between static stability and dynamic stability probably. In other words, sitting on the launch pad it is stable. when interacting with the real world it becomes unstable. Without studying the file or getting into real deep, because I'm not on this forum anymore the usual suspect is the wind (tip off upon leaving the launch rod) or causing a shift in the CG CP relationship .
__________________
Bernard J. Herman Ohio RLS

Starport Sagitta Rockets
email bherman@sagittarockets.com

NAR # 97971 SR

What's your idea on the best way to change Washington D.C.?
Let us know at the Cantina
Sagitta Cantina

We're looking for a few good Catos, please tell us about any you may have had. Survey of Anecdotal Malfunctioning Engines or S.A.M.E.
Reply With Quote
  #3  
Old 01-14-2013, 07:05 PM
Ironnerd's Avatar
Ironnerd Ironnerd is offline
Bona-Fide Space Hero
 
Join Date: Apr 2009
Location: ATL
Posts: 718
Default

I don't think the software can correctly simulate a flight with cones or other short/fat rockets. I am limited to OpenRocket, and it cannot accurately sim dynamic stability - RockSim may have similar limitations.

The swing tests I have done seem to confirm the "Massless Cone" method of finding the in-flight stability of a squat rocket.

What I normally do is:

1: input the massless cone and find the dynamic (in flight) stability.
2: Remove the cone, and reduce the mass of the rocket to "0"
3: Make a mass item the same weight of the total rocket weight, and position it so the CG/CP relationship is the same as was with the massless cone attached.

Have fun.
__________________
John Adams
"There is a lot of rocketry under 20ns"
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 01:05 PM.


Powered by: vBulletin Version 3.0.7
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Ye Olde Rocket Shoppe © 1998-2024