Ye Olde Rocket Forum

Go Back   Ye Olde Rocket Forum > BARCLONE > Hardware
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 06-20-2023, 02:41 PM
Winston2021's Avatar
Winston2021 Winston2021 is offline
Master Modeler
 
Join Date: May 2021
Posts: 929
Default NARCON 2021: Design, Evolution, & Prod. of Long burning Rocket Motors

It's also a nice overview of the history of composite motor evolution in hobby rocketry.

At around 35:45 he says, "I learned about the use of three vs four fins to reduce or eliminate coning" and then doesn't specify WHAT he learned. I found the answer in the paper linked below and suspected the correct answer before finding it since sounding rockets with few exceptions have four.

NARCON 2021: Design, Evolution, & Prod. of Long burning Rocket Motors by Gary Rosenfield

https://www.youtube.com/watch?v=7iCoICrGXUA

Sounding Rocket Fin Design to Mitigate Roll Lock-In

http://rsandt.com/media/Sounding%20...l%20Lock-In.pdf

Abstract - Roll lock-in is a persistent high angle of attack, nonlinear coning motion sometimes observed in the flight of reentry vehicles and sounding rockets. For example, it has occurred during Aerobee sounding rocket and Sidewinder missile flights prior to the introduction of rollerons. This paper focuses on how fin design effects the probability of lock-in. The high angle of attack response is driven by misalignment and/or offset thrust and drag forces, amplified by during pitch-roll resonance. High angles of attack engender nonlinear roll moments which cause the roll rate to follow the pitch natural frequency. It is well known that such roll moments can arise when the center of mass is offset from the vehicle symmetry axis. However, this paper explores another source of nonlinear high angle of attack roll moments, interaction between vorticity shed from a fore body and tail fins. Both kinds of roll moment have similar magnitudes. However, lock-in due to center of mass offset is, apart from static margin, not affected by fin design.

VII. IMPLICATIONS FOR FIN DESIGN

[big snip]

By far the most important fin parameter for mitigating lockin is the number of fin panels, N. Most sounding rockets have flown with 4 fins with a small minority using only 3 fins, and almost none with 5 or more. Our model shows that there is very little difference between 3 and 4 fins when attempting implementation of the first part of our strategy. Small tweaks in taper ratio or exposed fin span can bring about very similar performance in these two cases. But, increasing the number of fins to 5 or more leads to dramatic improvements. Our model shows that with 6 fins major improvement is relatively easy, and it becomes trivially easy with 8. Note that mortar bombs are commonly flown with 8 fin panels.
__________________
The other day I sat next to a woman who has a profound fear of flying. I wanted to comfort her, so I said, "Don't worry, we're not gonna' crash. Statistically, we got a better chance of being bitten by a shark." Then I showed her the scar on my elbow from a shark attack. I said, "I got this when my plane went down off of Florida." - Dennis Regan
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 08:35 AM.


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