TCC NAR Competition Primer: USMRSC Rule 22, Precision Altitude Competition (PRA, RDA, STA)
This primer presents, in one place, all the information you need to succeed in NAR model rocket competition in this event.
TCC has provided a link to the official rules whenever we discuss a rule.
Your entry must:
* Be a model rocket as described by the United States Model Rocket Sporting Code. USMRSC 3.1-3.9
* 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
Your having a grasp of the bigger picture can increase your enjoyment of NAR competition. You can read the Pink Book Lite to see only the rules for competitors, not for Contest Directors or other contest officials. Read the full USMRSC (Pink Book) to see all the rules.
* Pink Book Lite: http://ojames3.tripod.com/tccnarcontesttips/USMRSCLight.html
* Full USMRSC: http://www.nar.org/pinkbook/
General Competition Tips:
Contest Etiquette by Kevin Paul Wickart, NAR 59720, cr 1998, the author
Beginning Competition -- The RSVP Principle by Kevin Paul Wickart, NAR 59720, cr 1998, the author
Guide to NAR Contest Rocketry Information for Beginners by Jeff Vincent, NAR 27910, Northeast Regional Contest Chair
Which are the Main USMRSC Rules for This Event?
What is the Goal?
* The goal of Precision Altitude Competition (ALT) is to accurately predict the altitude that a model will attain. USMRSC 22.1
Are There Any Special Considerations?
* Precision Altitude Competition is divided into three event classes: USMRSC 22.2
Predicted Altitude (PRA) – You will state your target altitude before you launch. The minimum altitude is 100 meters (328.084 feet). USMRSC 22.2.1
Random Altitude (RDA) – The Contest Director will randomly select the target altitude just prior to when the event is flown, by draw, dice, or other random device. The target altitude shall be a multiple of 5 meters between 100 and 300 meters. USMRSC 22.2.3
Set Altitude (STA) - The Contest Director shall set the target altitude when the meet is sanctioned. This value shall appear in the sanction form and all appropriate contest information. The target altitude shall be a multiple of 5 meters between 100 and 300 meters. USMRSC 22.2.2
* Your entry can be single stage, multi-stage, or clustered as USMRSC 22 does not specify single stage.
* You MUST make your Predicted Altitude flight BEFORE you attempt any other altitude event in the contest. USMRSC 22.3
* NAR altitude flights are tracked to apogee or to ejection. You must be prepared for either method by knowing the altitude your model is likely to achieve at both apogee and ejection. USMRSC 14.3 Best practice is to ask the Contest Director which method they will use.
Do I Have to Return My Entry?
* NO. However, the Contest Director can require that you return your entry. USMRSC 9.10
How Many Flights Can I Make?
* You can only make one official flight. USMRSC 22.4
* In the case of a track not closed or a track lost, any flight allowed under USMRSC 14.9 shall be made by the same model, and no changes in configuration, motor type, or prediction shall be allowed. USMRSC 22.4
How is the Competition Scored?
* Short answer: The contestant whose entry comes closest to the target altitude is the winner.
* Long answer: The altitude your entry actually achieves will be divided by the target altitude, and the result multiplied by 100. This figure shall then be rounded to the nearest 0.1%. If the result is greater than or equal to 100, subtract 100 from it; otherwise, subtract it from 100. The contestant whose score comes closest to zero shall be declared the winner. USMRSC 22.6
What Will Disqualify My Entry?
* Your entry will be disqualified if it spins or loops under power. USMRSC 9.3
* Your entry may be disqualified if, in the opinion of the contest officials, it does not comply with the competition rules or is unsafe in operation. USMRSC 11.1, 11.2
How About Some Suggestions for New Competitors?
Almost any kit and contest approved motor will work. Your only limits are listed in USMRSC 9.1.
Powered by a single motor containing no more than 62.5 grams of propellant.
Powered by a combination of motors not exceeding 125 grams of propellant in total.
The combined Total Impulse of all motors, in accordance with the Model Rocket Safety Code, shall not exceed 320 Newton-Seconds.
Use computer simulations to determine altitude for various rocket and motor combinations. Free altitude simulations:
wRASP - http://www.wrasp.com/
Make multiple flights with various models and motors using NAR competition type theodolites ( USMRSC 14 Altitude Data ) to determine the altitude your model achieves. Add weight, such as tracking powder, and/or use a different motor to reach the altitude you want. Make practice flights using theodolites to measure altitude and/or computer simulation to find how much weight to add and/or which motor to use.
* Delay Selection:
Check with the contest officials to see if trackers will follow your entry to apogee of to ejection. If they are tracking to apogee, select a delay time such that ejection occurs after apogee. If they are tracking to ejection, select a delay time such that ejection occurs as close to apogee as possible; before or after apogee. Use a computer simulation (wRASP http://www.wrasp.com/ or wRASP32 http://tccnar.tripod.com/sims/082_wRASP32_221.zip) to help you select the best delay time.
* Motor Selection:
Select a motor that fits the event class. A impulse for A ALT, B motor for B ALT, etc. Generally, a lower average thrust (the number after the motor letter) will achieve a higher altitude and be easier to track. Use the minimum body tube diameter for the motor you want to use. Use a computer simulation (wRASP http://www.wrasp.com/ or wRASP32 http://tccnar.tripod.com/sims/082_wRASP32_221.zip) to help you select the best motor.
* 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. 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.
* Electronic Altimeter: Follow the manufacturer’s instructions and USMRSC 14.10. Check with your HPR buddies or others who use electronic altimeters for suggestions.
What Else & What Next?
What Type of Fins Shape is Best by Tim Van Milligan:
Design, Construction, and Flying Strategies for Achieving Maximum Altitudes by Tim Van Milligan
Simple Tower: by Bob Supak, NAR 65523
Take 3 1/4" aluminum rods, each about 24" long. Depending on what size model you want to launch, take an 18" piece of same body tube and put a few wraps of tape at each end. Place the 3 rods in a triangle around the body tube and secure with rubber bands, leaving 6" of the ends of the rods exposed. Now place the rods into a coffee can full of wet cement or plaster and let set. Voila - launch tower
Piston Launchers Explained – Apogee Components:
Floating Head Piston Launcher – The Odd Couple Team T-085, Jeff Vincent NAR 27910 and Chuck Weiss NAR 35775:
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 - http://www.wrasp.com/
* Free sink rate simulation:
US Spacemodeling (International Competition Tips):
US Spacemodeling Home Page (International Competition):
Aerospace Specialty Products Streamer and Parachute Tips:
George Gassaway’s Competition Tips – Take No Prisoners!
rmr Frequently Asked Questions – Part 9: Competition and Records: