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Rocket Stability

On this page, you'll find links to other sites that have additional information about model rocket stability.


Rocket Stability (Information Links)

What is an overstable rocket? You've designed a rocket using the RockSim software, and it indicates the rocket is "overstable." What does that mean to the flight of the rocket? Read this article to find the information you need.

Why do Rockets go Unstable? RockSim says the model was stable. But when you launched it, the model went crazy. What happened? Read to find out over 20 reasons why rockets that should be stable go crazy when launched.

Why Does the Swing Test Fail? - For decades, other modelers have recommended doing a swing test to see if the rocket design is stable. Here are some factors to consider as to why the swing test can give wrong answers.

What is the Normal Force Coefficient? This two part article explains what the number is, and what it is used for in determining the stability of the rocket. Part 1 (600K pdf),
Part 2 (500K pdf).

Does fin thickness affect the rocket's CP location? - Read this article to find out if it does or doesn't. The answer will surprise you. (276K pdf)

Does the CP location change when you upscale a rocket? - YES! Read what you'll have to consider when you upscale your favorite old kit. (784 pdf)

Stability of Short, Stubby Rockets - What to look for when you are designing short/fat rockets. (1.2 MB pdf)

Designing Rockets with Asymmetrical fins - An asymmetrical rocket is one where the fins are not evenly spaced around the perimeter of the tube. Read this article to learn how to design models like this using the features in RockSim. (620K pdf)

What is "Static Margin?" - The static margin is the distance between the CG and the CP; divided by the body tube diameter. But this number can be misleading. You could end up designing a rocket that goes unstable when you launch it. Read this article that explains the number, and how it should be used to design rockets. (756K pdf).

Barrowman's Original NARAM R&D Report All the other documents that state the Barrowman equations reference this important document. However, they are all missing one important piece of information that this report contains.

For articles on rocket stability check out the Peak of Flight index. This is a list, by topic, of all of the great articles the Peak of Flight put out over the years.

Apogee Components' Technical Publication #17 "Numeric Methods in Model Rocket Design" (P/N 36017) This report covers the methods of calculating the CG and CP of odd rocket configurations; which are used by the RockSim software.

Understanding Rocket Simulations From the RockSim Software A report that covers the cardboard cut-out method, and computer simulations.

Exploring the Cardboard Cut-out Method. An article that explains how the cardboard cut-out method works, and how it differs from the Barrowman Method of calculating stability.

http://www.apogeerockets.com/software/narcon99.zip This is an R&D report in PDF format. Written by Ed LaBudde, it explains how to extend the Barrowman Equations to high

Wind Caused Instability A report by Bob Dahlquist on how wind affects the stability of rockets, and gives a procedure for calculating the rod length or rocket speed necessary for a
stable flight.

"Comparison of Barrowman Stability Analysis with Wind Tunnel Data" By Tom McAtee. Does the Barrowman CP method stack up to real NASA wind tunnel data? This report answers that question.

"A Design Procedure for Maximizing Altitude Performance." An R&D report written by Ed LaBudde that gives some good information on Dynamic Stability procedures. (College level) 324K Download.

http://www.ninfinger.org/~sven/rockets/gcsfaq.html Guidance and Control FAQ's from RMR.

http://www.webcom.com:80/sknkwrks/guidance.htm An explanation of rocket guidance written by a high school student.

http://modelrockets.8m.com/guide/designing.html Simple design suggestions, with a brief explanation of rocket stability.


Check the Links below using the Wayback Machine!
Wayback Machine If you find any dead links, don't give up. Try using the Wayback Machine! It will allow you to read the text of old web sites that may not be active any longer. http://www.archive.org

To use the WayBack Machine, you may need to cut and past the URL into the web site. Please be patient, as the Wayback Machine can be slow...

If you find more links that are needing to be moved here, please let us know!

www.nar.org/pdf/shipping_rocket_motors.pdf - Regulations regarding the shipment of rocket motors.

http://www.execpc.com/~culp/rockets/Barrowman.html The classic Barrowman Equations for determining the CP of a model rocket.

http://www.dars.org/jimz/manuals/tir-30.pdf The old Centuri publication of Jim Barrowman's equations. PDF file.

http://www.cmass.org/uploads/Robert.Galejs/sentinel39-galejs.pdf Extension to Barrowman Equations to account for body lift. Written by Robert Galejs (PDF format 144K).

www.rockets4schools.org/launch2k3/ Basic_Rocket_Stability.pdf Explanation of stability on the elementary school level.

http://members.aol.com/ricnakk/fins.html Explanation of why fins are necessary on a rocket.

http://naca.larc.nasa.gov/reports/1929/naca-report-285/index.cgi?page10.gif Finding the CP/CG relationship of fins, and adding balance weights for improved performance.

http://naca.larc.nasa.gov/reports/1957/naca-report-1307/naca-report-1307.pdf "Lift and center of pressure of wing-body-tail combinations at subsonic, transonic, and supersonic speeds"by William C. Pitts, Jack N. Nielsen, George E. Kaattari. NACA Report 1307, Jan 1957. A method is presented for calculating the lift and centers of pressure of wing-body and wing-body-tail combinations at subsonic, transonic, and supersonic speeds. This was the report that was used by Jim Barrowman to come up with the classic method of determining the stability of rockets (University Level). An Adobe Acrobat (PDF) file of the entire report (4090257 bytes).


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