Madcow lists in the directions where the CG *should* be. Mark that on the airframe. Put the parachute and shock cord into the body of the rocket, install the NC, and see where the CG actually is.
Once you have the rocket balanced bare, take a ziploc baggie, and fill it half full of BBs or lead shot or whatever you have. Seal it and place it just forward of the NC/BT joint on the nosecone. If the balance point is now at the desired CG, congratulations, you're done. If the rocket is tail-heavy, add more weight, if it is nose heavy, take some out. I suggest you include about 4 short drywall screws, as you'll need them to secure the weight and epoxy into the tip of the nosecone.
Once you have the weight you need, follow these directions:
- Screw the drywall screws into the nosecone about 2" down from the tip
- Suspend the tip of the nosecone in a small pail of ice water.
- Pour the weight into the nose cone.
- Mix up a batch of epoxy and pour it into the nosecone
If you want to avoid the whole drywall screw and epoxy issue, try this:
- Suspend the tip of the nosecone in a small pail of ice water.
- Pour the weight into the nose cone.
- Mix up a batch of 2-part expanding foam and pour it into the nose cone.
- Once the foaming has stopped, clean off the nose cone
Once either method has completely set, re-install the NC and recovery gear into the airframe and check your CG, which should balance at or forward of the marked CG. If it didn't balance in the right place, you could install a forged eye bolt into the center hole of the NC which should add enough weight to fix a minor error.
You could try to do this in RockSIM or OpenRocket, but that would require
exact weights and measurements.
Hope this helps!
G.D.
