Semroc Hydra VII CG/CP

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Well-Known Member
Jun 30, 2010
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Does anyone know where the CG and CP should be on this rocket from the tip of the Nosecone please?
The augmenter ring makes it hard to determine the CP exactly. Our best guess for the CP is between 26.8" through 27.2" from the tip of the nose cone.

The CG varies widely with the engine selection, but should be less than 25.2" from the tip of the nose cone for 1 caliber stability. Seven C6-7's are about the worst case combination for CG location.
Well we'll see today , it's going up on 6 C6-0's/ 1 C6-7 :p

I split the difference on the 26.8 and the 27.2 as possible CP locations, and gave it a 27 as the source to measure from. I loaded my repaired Hydra VII with (7) C6-7's and balanced the rocket using the original payload section. The rocket balanced (CG) a marginal 1.5" from the CP, which is less then the 1 caliber needed. Since the BT dia. is 1.6" roughly this is where the instability came in to play.

Fix: (2) one ounce lead fishing weights attached to the eye hook in the payload section will fix the problem. This will just clear the 1 bodytube caliber needed for straight flight of the Hydra VII. For a little security, I will add 1 more one ounce lead weight.

Next flight will be July 10th...

Thanks for the info Carl.