CG question for Level 1 Build

Greetings! I am working on a level 1 build for NARAM 54. It's a Madcow Phoenix. I need to make sure my CG is 24" from the tip of the nose. I have a Monster Motors 38/360 reload case for Aerotech motors. How much weight should I account for in the motor before establishing my CG?

You can determine motor specs by searching in www.thrustcurve.org. All certified motors are there. Search for a 38/360 specific motor and look at the propellant weight, loaded motor weight, etc. to figure out what you need to know.

BTW, I would think that if this kit needs nose weight that the amount should be specified in the manufacturer's instructions.

--Lance.

loaded weight with an I161W 385 g (187.5 g of propellent). Always measure the CG in a fully loaded launch ready condition.

Thanks for all the info! It's greatly appreciated. I've just about got all the weight I need added to the nose. I didn't have a motor on hand since I'm not certified yet. Instead I used a large bolt and some washers that totaled 385g and placed them exactly where the motor went to check CG. They say to secure the epoxied lead in place by putting screws through the nose and grinding off the heads to get a smooth finish. I'm worried about the strength of the screws with no head as well as marring up the surface of my nose cone. I was thinking about keeping the epoxied balast from breaking loose by filling the inside of the nose with expanding foam. Has anyone else tried this? Is it a safe substitute?

I find that Gorilla Glue works best for me for attaching nose weight (its sticky as can be). If there is a hefty amount of weight to be used, I use two part expanding foam to keep it in place.

Thanks! That was really helpful. I'm going to go with the foam instead of the screws through the nose that the instructions called for. Just need to add the foam and finish the painting and I'll be ready for my cert flight

Load it all up with motor & parachute & make sure CG is at least 4" in front of
your center of pressure. All will be good then. Does kit tell you C/P?

No they don't list the CP in the kit instructions. They just list the CG as 24" from the nose tip. I did find an Open Rocket file for a Madcow Phoenix. It listed the CP as 27.2" from the nose tip.

Ok great just to be safe make your CG 23" or less from tip of nose cone.
More forward CG means a more stable rocket. Skywriting is cool but not for rockets!
To cement your Level 1 cert mark your center of pressure on the outside of body tube. The
traditional symbol for center of pressure is a circle with a dot in the middle of it.

tstone said:

Ok great just to be safe make your CG 23" or less from tip of nose cone.
More forward CG means a more stable rocket. Skywriting is cool but not for rockets!
To cement your Level 1 cert mark your center of pressure on the outside of body tube. The
traditional symbol for center of pressure is a circle with a dot in the middle of it.

Click to expand...

You've probably already read this, but for NAR certification attempts it is a requirement to have the CG/CP clearly marked on the outside of the rocket.

Tripoli too.

chadrog said:

You've probably already read this, but for NAR certification attempts it is a requirement to have the CG/CP clearly marked on the outside of the rocket.

Click to expand...

CarVac said:

Tripoli too.

Click to expand...

No I was not aware of that. Thanks for telling me. I thought you needed proof of the CG and CP locations, but I didn't know they had to be marked on the body. Would removable stickers suffice? I'd rather not have the markings permanent.

013Rocketry said:

No I was not aware of that. Thanks for telling me. I thought you needed proof of the CG and CP locations, but I didn't know they had to be marked on the body. Would removable stickers suffice? I'd rather not have the markings permanent.

Click to expand...

Sure, as long as they're accurately placed.

chadrog said:

You've probably already read this, but for NAR certification attempts it is a requirement to have the CG/CP clearly marked on the outside of the rocket.

Click to expand...

A good idea but Cg/Cp marking is not required. From https://www.nar.org/hpcert/l1certreq.html "During the safety inspection the modeler will be expected to provide oral answers to technical questions related to the safety and construction of his model. The questions may include (but not limited to) identification of the model's center of gravity and center of pressure, methods used to determine model stability, and interpretation of the rocket motor's designation."

Bob

Hmmm, not sure why I thought it was, but ok.