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TCC NAR Competition Primer: USMRSC Rule 23, Cluster Altitude (CA)


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All Entries

Your entry must:

* Comply with the NAR Model Rocket Safety Code: USMRSC 2.2

* Be a model rocket as described by the United States Model Rocket Sporting Code. USMRSC 3.1-3.9

* Use NAR Contest Approved motors: USMRSC 4.1, 4.4

* NOT eject its motor casing(s) without a recovery system. USMRSC 9.2

* Have your NAR number or your name on the outside, large and clear enough that the contest officials can easily read it. Teams must use the Team number or name. USMRSC 9.4

* Have been constructed by yourself or by one or more members of your Team. You may not enter Ready-To-Fly rockets (no construction required) in NAR sanctioned competition. USMRSC 9.9


Know the rules

Pink Book Lite:



Which are the Main USMRSC Rules for This Event?

* The main rules are 9, 14 and 23.


What is the Goal?

The goal of Cluster Altitude Competition (CA) is to achieve the highest flight of a single stage model rocket using a cluster of more than one motor, with all motors igniting at lift off. USMRSC 23.1, USMRSC 23.6


Are There Any Special Considerations?

* CA is divided into classes based on the quantity and total impulse of the motors you must use. USMRSC 23.5

* Each CA class uses a certain number of the same impulse motor:

            1/8A uses 2 motors

            1/4A uses 2 motors

            1/2A uses 3 motors

            A uses 4 motors

            B uses 5 motors

            C uses 6 motors


Do I Have to Return My Entry?

* After the flight, you must present the model to the contest officials so they can verify that no motor casings were ejected from your entry. USMRSC 23.3

* Rule 10.4 does not apply.


How Many Flights Can I Make?

* You can make up to two official flights. USMRSC 10.1

* If the altitude trackers do not accurately track your entry’s altitude (TRACK LOST or TRACK NOT CLOSED), that flight is not disqualified, but is unofficial and you can choose to make antother flight. USMRSC 14.9

* You can use more than one model. USMRSC 9.7


How is the Competition Scored?

* Your official score is the highest single altitude achieved by your entry on up to two official flights. USMRSC 23.1


What Will Disqualify My Entry?

Your entry will be disqualified if:

* You cannot return the model. USMRSC 23.3

* If it is unsafe in operation USMRSC 11.1, 11.2


How About Some Suggestions for New Competitors?

Optionally, you can use a tower launcher for better performance. The launch lug adds a lot of drag and reduces altitude.


The Estes Model Rocketry Technical Manual, page 13, discusses clustering and igniting clustered motors.


You’ll probably not find any suitable kits at your local hobby store. Start with three fins and a nosecone, using a streamer for recovery. Your entry will drift less than with a parachute and be easier to return.


However, you could kitbash (build a rocket using parts from more than one kit) several Estes or Quests kits. Stability will be an issue because, by using multiple motors, you are moving the rocket’s center of gravity toward the rear of the rocket. For kitbashing, start with a long model as the basis or central tube.


Your entry will be more reliable if the motor arrangement (cluster) is symmetrical. Here are some examples of clusters for Cluster Altitude Competition:


Here are some important design considerations:

* Your motor mount tubes must be carefully aligned so that all of the motors in the cluster are thrusting in the same direction or vector.

* You have to seal your motor mount assembly so that ejection gasses cannot escape except by deploying the recovery system.

* You are using more motors than usual. This moves the rocket’s center of gravity toward the rear. You’ll need larger/more fins and/or nose weight. See the Estes Model Rocketry Technical Manual, pages 7 and 8, for a discussion of stability.

* Optically tracked:  The trackers/officials MUST be able to see your entry to track its altitude. This is easier for the lower powered events. For higher powered events or if trackers are having difficulty spotting the rockets, you should consider using “tracking powder”. Tracking powder is colored powdered chalk or dry Tempra paint that you pack in your rocket so that it is ejected with the recovery system. You can buy chalk for a carpenter’s chalk line at almost any hardware store. Chose a color that contrasts with the cloud/sky conditions you expect to encounter. Red works well in most conditions. Don’t use blue unless white clouds cover the sky. When you pack your recovery system, leave some space at the top for the powder. Tracking powder is messy. You can simply pour the powder in or wrap the powder in a small piece of recovery wadding to minimize the mess. Powder adds weight. Experiment before the contest to determine the minimum amount you can use and still get a noticeable cloud of powder at ejection. For example, for B ALT (about 1000 feet), using a ¾ inch body tube, use enough powder to fill the tube for ¾ inch (one caliber). This will be about 0.1 ounce of carpenter’s chalk.

More info on using tracking powder:

* Electronic Altimeter:  Follow the manufacturer’s instructions and USMRSC 14.10. Check with your HPR buddies or others who use electronic altimeters for suggestions.


TCC Competition Vendor List for Kits and Parts


What Else & What Next?

Online Cluster Altitude Competition Plans

(If you find any, please contact me at Thanks)


Piston Launchers:

QCR Piston Launchers -


TCC NAR Competition Bibliography


Yahoo group for discussing model rocket competition:


Use computer simulations to determine altitude and sink rate for various rocket/motor/parachute combinations.

* Free altitude simulations: 


wRASP 32 -

* Free sink rate simulation:


George Gassaway’s General Competition Tips (note: Some links on George’s page are inactive):


George Gassaway’s Egg Lofting Altitude Competition Tips


US Spacemodeling (International Competition Tips):


US Spacemodeling Home Page (International Competition):


rmr Frequently Asked Questions – Part 9: Competition and Records:



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