Colton Acosta
New Member
Hi Everyone,
I am currently working toward an L1 certification using the Zephyr kit from Apogee. I am basically done with construction, but when I started looking at the OpenRocket model to determine my delay for motor ejection I noticed a really disconcerting discrepancy between the OpenRocket and Rocksim models. Using the .rkt file provided directly from Apogee and recommended motors (ex. H100, I140) OpenRocket gives me static stability margins ranging between 0.45-0.6 (marginal), whereas Rocksim gives me values above 1.0 (stable) due to the CP being calculated ~2" further back than in OpenRocket. Changing the Rocksim CP calculation method to the classical Barrowman equations gives the same results as OpenRocket. I tried changing the fins in OpenRocket from Freeform to trapezoidal as I read that RockSim is better with more complex fin geometries, but I didn't see a significant change in CP. I am under the impression that the Zephyr should be a very stable and a safe L1 cert rocket, so I am unsure what to trust here. I've read that for shorter, stubby rockets marginal stability can be acceptable but I have no experience here or intuition for the numbers. Every rocket I've seen fly has had a static margin of at least 1.5. Has anyone else run into this before? Am I missing something?
Colton
I am currently working toward an L1 certification using the Zephyr kit from Apogee. I am basically done with construction, but when I started looking at the OpenRocket model to determine my delay for motor ejection I noticed a really disconcerting discrepancy between the OpenRocket and Rocksim models. Using the .rkt file provided directly from Apogee and recommended motors (ex. H100, I140) OpenRocket gives me static stability margins ranging between 0.45-0.6 (marginal), whereas Rocksim gives me values above 1.0 (stable) due to the CP being calculated ~2" further back than in OpenRocket. Changing the Rocksim CP calculation method to the classical Barrowman equations gives the same results as OpenRocket. I tried changing the fins in OpenRocket from Freeform to trapezoidal as I read that RockSim is better with more complex fin geometries, but I didn't see a significant change in CP. I am under the impression that the Zephyr should be a very stable and a safe L1 cert rocket, so I am unsure what to trust here. I've read that for shorter, stubby rockets marginal stability can be acceptable but I have no experience here or intuition for the numbers. Every rocket I've seen fly has had a static margin of at least 1.5. Has anyone else run into this before? Am I missing something?
Colton