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This is also the source for information on the Rocketeers Of Central Indiana (ROCI), Section #625 of The National Association of Rocketry (NAR). Feel free to check here for information about ROCIs launch events. The launch events are conducted throughout the warmer months at the Academy of Model Aeronautics' Headquarters and Aeromodeling Center in Muncie, Indiana. This facility is the finest flying field in the state and ROCI is proud to be the exclusive host of the rocketry events held there. ROCI is not currently conducting meetings as we have lost our meeting place.

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New NAR Thrust / Weight Estimations 3 months 1 week ago #3142

From the Electronic Rocketeer:

Safety First - Low-Thrust Motors
Rockets using long burning low thrust motors require additional scrutiny during safety check in. As an example, using the rule of thumb of dividing the average thrust in Newtons by 30 to estimate the maximum rocket liftoff weight in pounds that will achieve a safe 5 "g" acceleration at launch suggests a maximum launch weight of approximately seven ounces for an Aerotech H13, which is the loaded weight of this motor just by itself. Examining the motor’s thrust curve closely, however, it has an initial thrust of almost 32 Newtons, so using the rule of thumb with the initial thrust instead may be a better approach for low-thrust motors; this suggests a maximum launch weight of 16 ounces for this particular motor.


Very low thrust to weight ratios during the sustainer portion of the motor burn may cause rocket velocity to decrease even during powered flight as the negative 1 G of gravity and the effects of aerodynamic drag combine (as they always do!) to slow the rocket down. Unless the rocket lifts off at a high enough speed or has some sort of active control system it is possible that it may slow to the extent that it weathercocks into an unsafe trajectory while still under thrust.


Flyers and range personnel should consider the thrust curve for long burn rocket motors and base calculations for safe launch velocity on the initial motor thrust. Scales to verify model weights at check in are encouraged. Range personnel should ask for simulation data that shows an adequate end of rod/rail velocity (approximately 50 feet per second for most designs) and that shows that the rocket will maintain at least this velocity through burnout so that it will remain headed straight up. Rockets powered by long burn/low thrust motors are sensitive to high drag and high winds, so model diameter should generally not be significantly larger than motor diameter and such models should not be flown on windy days.

Safe rocket flying is no accident!
Stephen Lubliner,
Safety Committee Chairman


I usually err on the high side with rockets I think are "iffy" like Mini-Magg (base drag stab) to ensure engagement of fins and in the case of the magg, base drag. Probably a good thing to add to the RSO table.

Cheers / Robert
Cheers / Robert

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